Transmission jerk on downshift 3nd to 2nd low Speed no pedal gas

[alexdmc1]

Hi,
I have done about 1200 miles after the total rebuild of the gearbox, I am enjoying this splendid car with my family. During testing I find only one problem: the transmission jerks when hot when I leave the accelerator pedal at low speed in 3rd gear. it should shift to 2nd gear but it doesn't, I don't know what to do. the Governor was also replaced for safety. can you help me? Thank you

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[alexdmc1]

Hi,
I have done about 1200 miles after the total rebuild of the gearbox, I am enjoying this splendid car with my family. During testing I find only one problem: the transmission jerks when hot when I leave the accelerator pedal at low speed in 3rd gear. it should shift to 2nd gear but it doesn't, I don't know what to do. the Governor was also replaced for safety. can you help me? Thank you

Inviato dal mio Redmi Note 8T utilizzando TapatalkP.s.

When coasting to a stop in 3rd gear, there is a very noticeable jerking sensation like something in the transmission is grabbing then letting go repeatedly. It doesn't do this if I manually shift it into 2nd gear or neutral.

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[Michael]

Have you adjusted the governor cable and set it to the proper clearance?

If so then you probably need to build a set of test lights and see what the computer is telling the solenoids to do. After reading again, it sounds like your solenoids are really acting up (mine acted similarly when my second computer failed). It wasn't jerking, the computer was telling the car to shift like 5 times a second which made it feel like it was jerking.

Just because you replaced the computer, don't dismiss it. I went through like 3 brand new rebuilt computers before I got one that held up. The first two lasted about 2-400 miles each.

[alexdmc1]

Hi Michael.
Very nice to hear you.

yes, I adjusted the Governor cable so that the RPMs were higher. but I remember even adjusting the cable correctly (see manual) the problem was still there... the Governor was replaced about 1200 miles, 8 months ago. could he be the flaw? I see that with a cold engine it behaves much better.....



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[David T]

If you notice the shift computer, aka governor, shifting differently when it is hot, it is typically bad solder joints inside the shift computer. When you take it apart you may also find 2 of the large capacitors have exploded, they should be replaced.

[alexdmc1]

Thanks for your advice.

I'm sorry to have to dismantle the Governor purchased a few months ago. it's a long job.

Is it possible for a newly built device to have these defects? I take this opportunity to ask you if the level of the ATF overfill liquid can create this lack of hot climbing? Can excess oil lead to overheating? overheating can lead to gearbox control errors. Why? manually (with lever 2-1) the gearbox shifts fabulously.....

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[David T]

Overfilling can lead to all kinds of unusual problems so it is important to check the level as explained in the Service Manual. Don't forget you should also check the level in the final drive too. When checking the automatic transmission you should do ALL of the in car checks including the shift linkage, control cable to the shift computer, line pressure, check the transmission mounts, fluid levels, etc. Make sure all of the wiring is secured away from the hot exhaust pipes and the vacuum line to the vacuum modulator is not leaking.

[Michael]

In my case, it wasn't the capacitors that failed, there were two diodes in the governor that failed.

Like I said earlier, build yourself a light kit and go for a drive. It will not take long for you to either rule out a governor, or identify it as the culprit....even if it was just replaced last month.

My governor actually worked when cold....very cold. After a few miles, it reared it's ugly head.

Once you have your test lights built, (I ran long wires and affixed mine to the sunvisor) you will know with a high degree of certainty, where the problem lies.


Edit: which governor did you use? Ed's? DMCH? (They are the same) or Marty's?

I'm not knocking Marty's builds. We are keeping a 40+ year old car with Lucas electronics on the road here. I'm not going to call anyone out who is actively trying to find answers to problems. It's just the nature of the beast.

[alexdmc1]

In my case, it wasn't the capacitors that failed, there were two diodes in the governor that failed.

Like I said earlier, build yourself a light kit and go for a drive. It will not take long for you to either rule out a governor, or identify it as the culprit....even if it was just replaced last month.

My governor actually worked when cold....very cold. After a few miles, it reared it's ugly head.

Once you have your test lights built, (I ran long wires and affixed mine to the sunvisor) you will know with a high degree of certainty, where the problem lies.


Edit: which governor did you use? Ed's? DMCH? (They are the same) or Marty's?

I'm not knocking Marty's builds. We are keeping a 40+ year old car with Lucas electronics on the road here. I'm not going to call anyone out who is actively trying to find answers to problems. It's just the nature of the beast.Hi,
Ed's Governor.

I confirm that during the first kilometers I have no problems. I will first install the test lights. I will update my post soon. thank you all

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[alexdmc1]

Hi,
Ed's Governor.

I confirm that during the first kilometers I have no problems. I will first install the test lights. I will update my post soon. thank you all

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[alexdmc1]

Overfilling can lead to all kinds of unusual problems so it is important to check the level as explained in the Service Manual. Don't forget you should also check the level in the final drive too. When checking the automatic transmission you should do ALL of the in car checks including the shift linkage, control cable to the shift computer, line pressure, check the transmission mounts, fluid levels, etc. Make sure all of the wiring is secured away from the hot exhaust pipes and the vacuum line to the vacuum modulator is not leaking.I found this video on YouTube, it seems to have the same problem as me. read among the comments, we're talking about vacuum Advance issuse.... what does it mean?

https://youtu.be/uRa4djWjs6Y?feature=shared

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[Jonathan]

Might not be a bad idea to double check that none of the shift computer wiring cables got melted lying too close or on top of the exhaust. 1,200 miles is plenty of time to melt those cables if they weren't zip tied up out of the way of the exhaust crossover pipe.

[AugustneverEnds]

Have you checked fuse 13? If you pull the fuse the transmission defaults to 3rd gear, maybe the terminals are getting loose and causing your trouble.

[alexdmc1]

Might not be a bad idea to double check that none of the shift computer wiring cables got melted lying too close or on top of the exhaust. 1,200 miles is plenty of time to melt those cables if they weren't zip tied up out of the way of the exhaust crossover pipe.HI. I checked the cables. they are blocked away from the drain lines

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[alexdmc1]

I did another test drive yesterday. For the first thirty minutes the car performed perfectly without any problems. after a while it started to create problems for me when braking, not only that, when the transmission is hot even the gear changes are a little rougher. when cold the car behaves perfectly, when hot it doesn't.

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[alexdmc1]

Hi everyone. I have some updates: according to the latest tests during the problem the computer remains in third gear. I checked the line pressure and it corresponds to 8 bar at 2500 without intervention of the vacuum valve. in the meantime I found other videos on YouTube tube. when cold I have no problems.

in manual no problem. no slippage problems when cold and hot.

Thanks



https://youtu.be/OKvnnzqu31s?feature=shared

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[JBaker4981]

The Youtube videos that you posted caught my attention as I already battled these issues, lost, and replaced the whole Hydraulic Unit.

Look more into this guy's videos on the issue: https://youtu.be/m2qCU-eHVO0?si=B_x2CdqKOZFYm_nK

This guy led us to find the same issue on my car - my C2 Clutch had a fracture in it and could not hold the pressure needed to provide full acceleration in Third Gear. This caused the driving symptoms to appear that I was slipping in third between 45-60mph however this could be bypassed by accelerating through this 45-60mph threshold in Second Gear THEN let it shift into Third Gear providing near constant pressure when driving.

I replaced 75% of my entire Renault 4141 and she has never driven better.


Your last Youtube link is ME!

[JBaker4981]

when cold I have no problems.
When cold, the fluid is thicker... when hot, the fluid is thinner and will slip through any cracks or fractures in your Drum(s) causing loss in pressure.

[alexdmc1]

Pleased to meet you. I looked for you all over the web!!!! wow!!! Thanks for your answer.

the viscosity of the hot fluid certainly influences the behavior of automatic transmissions. in my case, I don't have any slippage in 3rd gear; The car moves on full power up to 85/100 miles effortlessly...that's pretty fast. my problem, like yours was only when I drop the accelerator pedal.....I need your help! [emoji24]

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[alexdmc1]

Attached. Acceleration 2-3 upshift. Full Power.http://cloud.tapatalk.com/s/664f55523884d/VID-20231224-WA0022.mp4

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[JBaker4981]

Attached. Acceleration 2-3 upshift. Full Power.http://cloud.tapatalk.com/s/664f55523884d/VID-20231224-WA0022.mp4

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I would not drive the car as briskly as that while diagnosing this - The car downshifted 3-2 for most of your video and then 2-3 at the very end.

I would be interested to see how she accelerates in 3rd without hitting WOT (Wide Open Throttle) and making it down shift. I have a feeling that you are going to be slipping in 3rd at lower speeds or other behaviors may appear.

[alexdmc1]

I would not drive the car as briskly as that while diagnosing this - The car downshifted 3-2 for most of your video and then 2-3 at the very end.

I would be interested to see how she accelerates in 3rd without hitting WOT (Wide Open Throttle) and making it down shift. I have a feeling that you are going to be slipping in 3rd at lower speeds or other behaviors may appear.Hi JBaker. I just returned from a long tour. when cold it drives well, when hot the problems begin.....if I drove at full throttle in third gear no problems, no slipping. I also replaced the ATF dexron 3 oil to be safe but the problem was not resolved. I notice that when I release the accelerator, in third gear the revs (rpm) are low? it's like it doesn't have enough pressure to tighten the clutches....I don't know. what do you say?http://cloud.tapatalk.com/s/6651f52bc3bb1/VID-20240525-WA0022.mp4

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[Ron]

Maybe I'm not following all this correctly but:


I notice that when I release the accelerator, in third gear the revs (rpm) are low?Are you sure that isn't where you are in 2nd gear (accelerating) and when you let off it shifts up to 3rd (which would drop the RPM, i.e., normal)?


it's like it doesn't have enough pressure to tighten the clutches...
If the clutches aren't tight the engine would rev up a lot.

[alexdmc1]

Maybe I'm not following all this correctly but:

Are you sure that isn't where you are in 2nd gear (accelerating) and when you let off it shifts up to 3rd (which would drop the RPM, i.e., normal)?


If the clutches aren't tight the engine would rev up a lot.Hi Ron. How are you. you're right: during acceleration the car shifts from second to third and obviously the engine rpm drops. like every other car does. the problem is when I'm in third gear at low speed without accelerating (foot raised) instead of downshifting you hear jerking..... but when cold for the first 20 km everything works perfectly.

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[Ron]

Hi Ron. How are you. you're right: during acceleration the car shifts from second to third and obviously the engine rpm drops. like every other car does. the problem is when I'm in third gear at low speed without accelerating (foot raised) instead of downshifting you hear jerking..... but when cold for the first 20 km everything works perfectly.

Inviato dal mio Redmi Note 8T utilizzando TapatalkI see... My first guess would be the GC, new or not considering your other tests results. Put test lights on it if you haven't yet...

[alexdmc1]

I see... My first guess would be the GC, new or not considering your other tests results. Put test lights on it if you haven't yet...Hi Ron. I just did the test with the lights. At first everything works perfectly. the lights come on and the automatic transmission shifts correctly. when it warms up and in third gear at low speed I don't press the accelerator pedal, the car remains in third gear, the lamps are both off and the problems begin..... thanks for your help

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[Bitsyncmaster]

Hi Ron. I just did the test with the lights. At first everything works perfectly. the lights come on and the automatic transmission shifts correctly. when it warms up and in third gear at low speed I don't press the accelerator pedal, the car remains in third gear, the lamps are both off and the problems begin..... thanks for your help

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This does really sound like the electronics are failing in high temps. It's to consistent to be a marginal connection.

[David T]

Hi Ron. I just did the test with the lights. At first everything works perfectly. the lights come on and the automatic transmission shifts correctly. when it warms up and in third gear at low speed I don't press the accelerator pedal, the car remains in third gear, the lamps are both off and the problems begin..... thanks for your help

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Go back to my post #5. You have bad solder joints on the circuit board. You just have to open it up to get to the circuit board and reflow some solder on each joint. Between the vibration and the temperature a cold solder joint can cause this, very typical. It is possible to do this without taking the whole thing off. You remove the cover, pull the circuit board out enough to get to the backside and with a soldering iron (a small pencil iron, you don't need a big gun) you reheat each joint and add a SMALL amount of fresh solder. Be careful not to add too much solder or make any solder "bridges" to other circuits on the board. On some of the shift computers you do have to remove the coating, use a small steel brush.

[Michael]

Go back to my post #5. You have bad solder joints on the circuit board. You just have to open it up to get to the circuit board and reflow some solder on each joint. Between the vibration and the temperature a cold solder joint can cause this, very typical. It is possible to do this without taking the whole thing off. You remove the cover, pull the circuit board out enough to get to the backside and with a soldering iron (a small pencil iron, you don't need a big gun) you reheat each joint and add a SMALL amount of fresh solder. Be careful not to add too much solder or make any solder "bridges" to other circuits on the board. On some of the shift computers you do have to remove the coating, use a small steel brush.

He is using Ed's governor which I believe is a new solid state design like DMCH sells.

70638

[alexdmc1]

He is using Ed's governor which I believe is a new solid state design like DMCH sells.

70638This Is my replacement unit. 70639

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[David T]

This Is my replacement unit. 70639

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Well, it is malfunctioning. Maybe send it back for repair or replacement? Maybe there is some kind of warranty?

[alexdmc1]

I should have a guarantee. I wanted to remind you that when you move the lever to second gear manually it works perfectly. shifting from: 1-2 and 2-3 works perfectly. the downshift from 2-1 also works both cold and hot... if it were a computer problem it shouldn't always do it... in my case only the 3-2 shift without accelerating stops working.... the problem arises when I don't use the pedal. the downshift from 3-2 by pressing the pedal works perfectly.....

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[Ron]

Hi Ron. I just did the test with the lights. At first everything works perfectly. the lights come on and the automatic transmission shifts correctly. when it warms up and in third gear at low speed I don't press the accelerator pedal, the car remains in third gear, the lamps are both off and the problems begin..... thanks for your help

Inviato dal mio Redmi Note 8T utilizzando TapatalkI'm assuming that, after "the lamps are both off and the problems begin", the lights remain OFF while it coasts along for a bit of time acting up?? If so, I would try repeating the test and pulling fuse #13 when it starts the problems....If it does not settle down then and stay in third (assuming you still have high speed), I'd suspect something else since the solenoids should be disabled then (no shifting) and pulling the fuse should accomplish that....

(I guess you know driving at low speeds w/o fuse#13 is hard on the lower gear clutch packs.)

[alexdmc1]

I'm assuming that, after "the lamps are both off and the problems begin", the lights remain OFF while it coasts along for a bit of time acting up?? If so, I would try repeating the test and pulling fuse #13 when it starts the problems....If it does not settle down then and stay in third (assuming you still have high speed), I'd suspect something else since the solenoids should be disabled then (no shifting) and pulling the fuse should accomplish that....

(I guess you know driving at low speeds w/o fuse#13 is hard on the lower gear clutch packs.)HI. I wasn't able to take the test you asked for. I find it very difficult to do this. I'm afraid of ruining the newly installed clutches. the problem only comes out when the car is warm, during the first kilometres, the car works perfectly, it seems strange to me that it is an electronic problem. because the gearbox works perfectly when you go from first to second and from second to third.... it makes me think that maybe it's a design problem. I hope other people with automatic transmissions are reading these posts too.....

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[Bitsyncmaster]

HI. I wasn't able to take the test you asked for. I find it very difficult to do this. I'm afraid of ruining the newly installed clutches. the problem only comes out when the car is warm, during the first kilometres, the car works perfectly, it seems strange to me that it is an electronic problem. because the gearbox works perfectly when you go from first to second and from second to third.... it makes me think that maybe it's a design problem. I hope other people with automatic transmissions are reading these posts too.....

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Not saying it is electronics but, yes an IC or transistor can work fine cold and completely fail hot. Let it cool off and it will repeat the same.

[Ron]

HI. I wasn't able to take the test you asked for. I find it very difficult to do this. I'm afraid of ruining the newly installed clutches.
...
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Remove the fuse and run two wires with male spade connectors to the fuse box. Connect them with a switch to make it easier.
The test shouldn't bother the clutches since you would be performing the test at a medium to high MPH, no load (3rd gear). Just make sure you turn the switch back on before you try to pull off from a standstill (low MPH, load).
Note that the GC calls for 3rd gear by turning off both solenoids -- Pulling Fuse #13 does the same thing. If there is no power, nothing else (such as a bad part, short, etc.) can turn the solenoid(s) on.

[alexdmc1]

Hello all. after a few months of driving my DeLorean or some updates on the automatic transmission problem. I did a pressure test on the move I would like your opinion:

Test 0: pressure line when hot temperature:

113/108 psi to 2500 no vacuum advance/ third gear

Test 1: pressure when cold

Parking: 58 psi
Neutral: 50 psi
Retro: 50 psi
Driver: 50 psi

Test 2: pressure when hot

Parking: 21 psi
Neutral: 21 psi
Retro: 21 psi
Driver: 29 psi

Test 3: cold temperature when changing Gear low gas:

From 1 to 2: 159 psi to 87 psi
From 2 to 3: 87 psi to 84 psi

No pedal gas - 30 mph - 1000 rpm - 43 psi

Test 4: hot temperature when changing Gear low gas:

From 1 to 2: 130 psi to 94 psi
From 2 to 3: 94 psi to 43 psi

No pedal gas - 30 mph - 1000 rpm - 29 psi

Test 5: vert hot temperature when changing Gear low gas:

From 1 to 2: 100 psi to 72 psi
From 2 to 3: 72 psi to 58 psi

Test 5: Medium acceleration when hot temperature:

From 1 to 2: 203 psi to 87 psi
From 2 to 3: 87 psi to 58 psi

the problem that occurs is a jolt when the car is hot and I release the accelerator at low speed:

https://youtu.be/uRa4djWjs6Y?feature=shared

thank you all




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[axh174]

I wanted to remind you that when you move the lever to second gear manually it works perfectly. shifting from: 1-2 and 2-3 works perfectly. the downshift from 2-1 also works both cold and hot...



Maybe I'm misinterpreting what you're saying, but with the lever in second gear manually, you shouldn't be shifting from 2 into 3 at all. You would go from 1 to 2 and no higher. In this gear, one of your solenoids should still be powered (if using the breakout lamp box, one light should be lit and the other should be off). So it's quite possible the issue affecting your transmission is related to the connections (such as the solder joints) for the remaining solenoid. Reflowing the solder joints, as David T suggests, could prove beneficial.

[alexdmc1]

Maybe I'm misinterpreting what you're saying, but with the lever in second gear manually, you shouldn't be shifting from 2 into 3 at all. You would go from 1 to 2 and no higher. In this gear, one of your solenoids should still be powered (if using the breakout lamp box, one light should be lit and the other should be off). So it's quite possible the issue affecting your transmission is related to the connections (such as the solder joints) for the remaining solenoid. Reflowing the solder joints, as David T suggests, could prove beneficial.you're right. i explained myself badly. forgive me.

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[axh174]

you're right. i explained myself badly. forgive me.

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So, to summarize:

1) When the transmission is cold, the transmission upshifts from 1st to 2nd to 3rd gear without any issues and at the correct times. It also downshifts from 3rd to 2nd to 1st with no issues and at the correct times.

2) When the transmission is hot, the transmission upshifts from 1st to 2nd to 3rd gear without any issues and at the correct times *every time*. But the transmission will not downshift from 3rd gear to 2nd gear when your foot is off the gas pedal and the car is naturally slowing down. The transmission gets stuck in 3rd gear and the car starts to shudder. The same thing happens if you are applying a little pressure to the gas pedal, but not enough to prevent the car from slowing down and reaching the 3rd-to-2nd gear shift point.

3) When the transmission is hot and the car is slowing down and it won't downshift from 3rd into 2nd gear, you can move the automatic transmission gear selector into 2nd and the car WILL then downshift into 2nd gear.

Is this a correct summary? (Sorry for repeating all this, I want to make sure I clearly understand the situation).


Assuming all of the above is correct, have you noticed any issues while the transmission is hot, in 3rd gear, and you are maintaining a 50mph cruising speed? For example, does the transmission ever slip?

Do you experience any other type of strange shifting behavior? Does the transmission ever suddenly shift from 3rd gear down into 2nd gear when you are doing 60mph? Does the transmission ever try to upshift from 2nd into 3rd when you are doing only 35mph?

[alexdmc1]

Hi everyone,
I respond to your summary.

1) correct

2) correct

3) correct

The transmission never slips. never. does not suddenly shift from third gear to second at 60 mph.
The transmission changes gears at about 2000 rpm with light accelerator pedal.
I noticed that when the transmission heats up I lose engine braking....

[Bitsyncmaster]

Hi everyone,
I respond to your summary.

1) correct

2) correct

3) correct

The transmission never slips. never. does not suddenly shift from third gear to second at 60 mph.
The transmission changes gears at about 2000 rpm with light accelerator pedal.
I noticed that when the transmission heats up I lose engine braking....

Maybe it's a torque converter problem. I've never heard of them failing though. Maybe a pump lets the converter loose fluid.

[alexdmc1]

Maybe it's a torque converter problem. I've never heard of them failing though. Maybe a pump lets the converter loose fluid.thanks for the reply. the pump was replaced because the previous one broke. I bought the spare part from Ed, in Europe. The converter was bought new from Ed in Europe, for safety it was also overhauled by a specialized company.

could it be the wrong oil? I used a synthetic Dexron 3 oil

710317103271033

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[axh174]

I just did the test with the lights. At first everything works perfectly. the lights come on and the automatic transmission shifts correctly. when it warms up and in third gear at low speed I don't press the accelerator pedal, the car remains in third gear, the lamps are both off and the problems begin...

Based on this and your kind reply to my summary post (thanks!), I think it is reasonable to say the automatic transmission computer governor is not telling the transmission to shift from 3rd gear into 2nd gear when it should, if at all.

The question now becomes, why is the computer governor not telling the transmission to downshift? Is it because there's something flawed within the computer governor itself or is it because of something else on the transmission sending a bad signal to the computer governor? If you had the original dual-Op-Amp governor design, I could offer some suggestions (bad reference voltage Zener diode, faulty solder joint to one of the Op-Amps). But I am not at all familiar with how the new solid-state governor works.

It is definitely a heat-related issue. So, something you could try to further isolate the problem is to let the car completely cool down (maybe let it sit over night), then get the computer governor nice and hot using a heat gun just before driving the car. If you then have the down-shifting issue right away before the transmission itself has a chance to heat up, that would pretty much conclude the issue is in the computer governor.

In the mean time, I'll try to refresh myself on how the entire shifting system works.

[alexdmc1]

I appreciate your comment. I take this opportunity to share this very temporary solution: by connecting the negative of the kick down to the ground I will constantly ask the Governor to downshift; therefore it will do so before it should but always accompanied by some jolts. When cold everything works regularly.

What do you think about the low pressures when the oil heats up?
Could the jolt be prevented by the torque converter engaging and disengaging?
Could the culprit be a loss of pressure that affects the converter?

Thanks

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[David T]

There are 3 ways the transmission can downshift. By the shift computer, by the valve body, and by the gearshift lever. Recheck that the cable from the throttle to the governor is properly adjusted and check the adjustment for the gearshift on the chance it is not exactly correct. Because you notice the problem when it gets warmed up, it would appear to be temperature dependent. Make sure the filter in the transmission is clean. Disassemble it and clean it or just replace it. If the fluid is nice and red, is not dirty, and has no burnt smell it should be OK. Go through the procedure to check the fluid level as per the Workshop Manual. You must be on level ground and the transmission warmed up. Do the line pressure adjustment too. If you still have the problem it is probably the valve body (a spool valve is sticking). The shift computer controls the valve body and the valve body controls the clutches. On my car I have "hard" shifts hot and cold but that is because I used stiffer springs in my clutches so I get firm shifts. I did that so the clutches don't slip as much during shifting so the clutches will last longer. Soft shifts mean the clutches are slipping during shifting, letting it be in 2 gears at once so the shift is less noticeable. That is why the vacuum line is connected to the line pressure regulator. It reduces the line pressure during shifting to soften the shifts. That is another thing to check, make sure the vacuum line to the line pressure regulator is hooked up and not leaking.

[axh174]

There are 3 ways the transmission can downshift. By the shift computer, by the valve body, and by the gearshift lever.

Hi David,

Can you elaborate a little more on how the valve body portion of the system can cause the transmission to downshift? I haven't recalled yet how this portion of the system works (i.e.., whether it is independent of, or in conjunction with, the computer governor).

With regard to the gearshift lever, if memory serves, the gearshift lever activates two different micro switches on the computer governor wiring harness, which then provide a fixed path to ground for one or both of the solenoids (depending on the selector position), energizing the solenoids and causing the car to downshift. The kickdown switch is an alternate path to ground for the 3rd gear solenoid (the latter of the two solenoids), forcing it to be energized and downshifting the car from 3rd into 2nd. If I recall correctly, the wiring of these switches interfaces with the governor computer at the output end of the entire circuit. From this perspective, the downshifting of the transmission is still electronically controlled via wiring on the computer governor circuit board, albeit by bypassing the computer governor commands (it sounds like this portion of the circuit is still functioning correctly).

[David T]

Hi David,

Can you elaborate a little more on how the valve body portion of the system can cause the transmission to downshift? I haven't recalled yet how this portion of the system works (i.e.., whether it is independent of, or in conjunction with, the computer governor).

With regard to the gearshift lever, if memory serves, the gearshift lever activates two different micro switches on the computer governor wiring harness, which then provide a fixed path to ground for one or both of the solenoids (depending on the selector position), energizing the solenoids and causing the car to downshift. The kickdown switch is an alternate path to ground for the 3rd gear solenoid (the latter of the two solenoids), forcing it to be energized and downshifting the car from 3rd into 2nd. If I recall correctly, the wiring of these switches interfaces with the governor computer at the output end of the entire circuit. From this perspective, the downshifting of the transmission is still electronically controlled via wiring on the computer governor circuit board, albeit by bypassing the computer governor commands (it sounds like this portion of the circuit is still functioning correctly).

As I explained in my previous post, the "governor" aka shift computer, controls the valve body, the valve body controls the clutch packs. The valve body has it's own "logic" so the shift computer can't do anything that could damage the transmission like shifting to 1st at 60 MPH. There are spool valves inside the valve body and they can get "sticky" if the transmission fluid was burnt or very dirty. On one Delorean that had trouble shifting there was a blob of silicone blocking one of the solenoids on the valve body. The shift computer opens and closes the solenoids and those solenoid valves tell the valve body when to shift and what gear is being commanded. The valve body can override those commands if it thinks it has to with it's mechanical logic of valves and springs. If you do take the valve body out there is no documentation on it except that if you suspect it to be faulty it is to be replaced. It CAN be disassembled and cleaned but CAREFULLY note and document EVERY spring, valve, ball check, bolt, washer, and clip so you can put it back together correctly.

[axh174]

The valve body has it's own "logic" so the shift computer can't do anything that could damage the transmission like shifting to 1st at 60 MPH.

I was unaware of this, but in retrospect it makes perfect sense. Thanks for the explanation!

[Michael]

This is still going on?

Post number 2 of this thread and pretty much every post after pegged the governor as suspect.

Did the light test actually work because I couldn't tell jack from that video or the explanation.

So if the trans is shifting weird and the lights are synching up with the weirdness, then the governor is the problem. In other words, if the trans wants to stay on third and you don't see any lights on, you know with a high degree of certainty is the governor. If the car doesn't want to shift into second, and it's not getting the signal to do so, it's the governor. Keeping in mind that governor you are using has a high failure rate, it seems clear.

Replace that governor already! It takes what an hour, hour and a half and most likely you will have not only fixed the car but saved yourself all this mess.


I would reach out to Rob at PJ Grady and see if you can get a rebuilt OE board. Hopefully you still have your old one.

[David T]

Maybe try your old board and see if you still have the same problem? If you don't have harsh downshifts with the old board, then you have confirmed there is a problem with the new shift computer. In a picture on I think it was post #9 you had the old governor alongside the new one. It would not be unusual for the electronics (or a solder joint) to be sensitive to temperature. You can also contact Ed and ask if he has seen this problem before and what to do about it.

[Michael]

Sully mode on : Can we all get real now?


We all have $50k+ cars. Spend 3 or 4 hundred bucks, replace the governor and put this BS behind us.

[axh174]

The more I think on this, the more I agree with Michael and David. The most likely culprit is the governor; your transmission wants to downshift but the governor is not sending the signal to do so. Using the gear select lever or forcing the kickdown switch to activate both provide an alternate means of informing the transmission to downshift, and they both work. So, it's likely not anything mechanical with your transmission that is causing the problem.

Given the heat-related nature of the problem, it's likely a bad solder joint. You could try reflowing the solder joints, as David suggested, or you can reach out to someone to see if they can fix/replace the current or old boards, as Michael suggests.

If you are still unsure of the diagnosis, you can also try to further isolate the cause. For example, try heating up the governor yourself while the car is cold and then driving it. Or you can drive the car until the shifting problem happens, park it, and somehow cool the governor down (wrap with dry ice?) and try driving again.

Let us know what you find out/choose to do. We'd love to hear the conclusion to the story!

[Michael]

Yeah just to clarify, I'm not saying the governor is 100% your problem, but I am saying it probably is. My logic is more than that though, if you do have an internal problem, then the trans most likely has to come out and apart to even diagnose, let alone rectify. A governor is 400 bucks sans fluid and gasket and 1.5 hours of your time. Even if I was only 50% sure replacing the computer would fix it, I would roll those dice vs. the alternative.

There are a few things that would be worth checking while your pan is off such as the wiring to the plug and solenoids, debris in the valve body (maybe pull the filter and check for any red flags in the element), and make sure the electrical plug connections are clean and making good contact.

[axh174]

Slightly off topic: is there a knowledge base somewhere for how the digital governor circuit works or what it's capable of doing?

If it has programmable shift points, maybe it was incorrectly programmed for when to downshift?

[David T]

Slightly off topic: is there a knowledge base somewhere for how the digital governor circuit works or what it's capable of doing?

If it has programmable shift points, maybe it was incorrectly programmed for when to downshift?

Not on the digital one. For the OEM one we have the schematic and procedures on how to resolder the joints and replace the capacitors that typically blow. To change the shift points you would have to change the resistors and capacitors to different values. For minor changes you can play with the adjustments to the shift cable. We call it a "shift computer" but it really is not doing any "computing" and is not programmable. The digital one may be programmable but you would have to get in touch with Ed. This is the point at which you need to have a conversation with your vendor as to how to proceed. Maybe he can exchange or repair your governor or at least test it to make sure it is functioning properly. Or, as I suggested in my last post, put the old one back in and see what happens.

[Ron]

Slightly off topic: is there a knowledge base somewhere for how the digital governor circuit works or what it's capable of doing?

If it has programmable shift points, maybe it was incorrectly programmed for when to downshift????
I'm confused -- You posed in this thread. /dmctalk.org/showthread.php-Automatic-Transmission-Governor (https://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor)

Anyhoo, at this point, I agree with just changing out the GC.

[axh174]

???
I'm confused -- You posed in this thread. /dmctalk.org/showthread.php-Automatic-Transmission-Governor (https://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor)

Anyhoo, at this point, I agree with just changing out the GC.

Hi Ron,

That thread discusses the design and function of the original OEM governor after we as a community back-engineered it. I was inquiring if there was a thread that discussed the design and function of the newer, updated Ed/DMCH governor.

In the past, I've heard rumors the shift points are programmable on the newer design. But I never really looked into it to see if that is true. I've also been really curious about the type of controller chip it uses and how it drives the shifting solenoids. But I'm guessing that information might not be generally available.

I've been half tempted over the years to buy one and back-engineer it like we did with the OEM.

[Bitsyncmaster]

I've been half tempted over the years to buy one and back-engineer it like we did with the OEM.

You would probably find (by bench testing) the new one does what the OEM one does. The micro would just input voltages and use those values to turn the solenoids off or on with those switch points hard coded in the software. The micro just drives transistors which in turn drive the solenoids.

It's more work to un-assemble the software than to write your own new software.

[Ron]

Hi Ron,

That thread discusses the design and function of the original OEM governor after we as a community back-engineered it. I was inquiring if there was a thread that discussed the design and function of the newer, updated Ed/DMCH governor.

In the past, I've heard rumors the shift points are programmable on the newer design. But I never really looked into it to see if that is true. I've also been really curious about the type of controller chip it uses and how it drives the shifting solenoids. But I'm guessing that information might not be generally available.

I've been half tempted over the years to buy one and back-engineer it like we did with the OEM.


Aaah...the new one...had a brain fart.
{Those were the days}