Auto transmission slipping i 3rd gear

[martiq]

Hi

I need some help with my auto transmission.
It's slipping in 3rd gear when warm. (i have not experienced the fault on cold transmission)

Prior to this day the car han been brought back to life after 20 years of stand still.

Summary for the transmission is:
New filter
New oil: Dexron II
Old oil didn't smell burnt and still red in colour
No debris in old filter other than it was dirty.
Kickdown cable and full trottle switch is adjusted according to specs in repair manual.

I have made a video of the problem. You will see diodes monitoring the govenor (seems to be working fine) and a pressure gauge monitoring the oil pressure in the transmission.

You will find video here. https://www.youtube.com/watch?v=Fb5bTF3E1LY
Annotations are in the video.

Help and pointers to what the problem is is much appriciated

regards
Martin

[Jonathan]

Sounds like a shift computer governor problem to me.

Your lights say the computer is trying to keep it in third, but the transmission itself has other ideas. One way to find out is to pull fuse #13 while driving at highway speeds and see if the car stays in third gear. Fuse #13 is the shift computer and if you yank the fuse, it will default to third gear. Be prepared to put it back in after your test, as driving around in 3rd gear, especially from a stand still is not good for the transmission. If the car stays in 3rd gear without the fuse, I believe that tells you the transmission hydraulics are fine and says it is the computer that's the problem. Maybe someone else can chime in as I forget exactly how that logic works, but that's the jist of it.

Also, I wouldn't drive the car a great deal until you get this sorted out. Revving the crap out of the engine at highway speeds like that is tough on the drivetrain.

EDIT: some more info here: http://support.delorean.com/kb/a69/automatic-transmission-shifting.aspx

[AugustneverEnds]

I agree that the governor is probably the reason for your problem and I would recommend you have your favorite vendor repair it. It is possible to do yourself. Removal instructions can be found here: http://dmctalk.org/showthread.php?7648-How-To-Remove-the-Automatic-Transmission-Governor-Computer&highlight=governor+removal

It seems all of us with automatics have to have the governor repaired sooner or later. Good luck resolving your problem!

[martiq]

Okay. But (correct me if I'm wrong) I thougth the behavior of the lights told me that the govenor is working correctly, controlling solenoid A and solenoid B.

Someone else suggested that I should check the vacuum line to the vacuum modulator.

How should the lights be in "P" & "R" ? - Mine er both "on" in P and R

[OverlandMan]

I would check the vacuum lines just to be sure. Its a tapered line coming off the driver-side of the intake going down to the gearbox. Another thing to check would be the governor gearbox cable that comes off the throttle spool. If those are both OK, then I would agree with Jonathan's analysis.

[Dangermouse]

FYI, if it is the governor, forum member Elvis from Germany reportedly does a good job repairing them. (May be convenient for you)

[martiq]

I would check the vacuum lines just to be sure. Its a tapered line coming off the driver-side of the intake going down to the gearbox. Another thing to check would be the governor gearbox cable that comes off the throttle spool. If those are both OK, then I would agree with Jonathan's analysis.

Yes I will check the vacuum just to be sure. Cable is perfectly adjusted as mentioned in my first post.

[martiq]

FYI, if it is the governor, forum member Elvis from Germany reportedly does a good job repairing them. (May be convenient for you)

Thanks.

[Jonathan]

Okay. But (correct me if I'm wrong) I thougth the behavior of the lights told me that the govenor is working correctly, controlling solenoid A and solenoid B.

Someone else suggested that I should check the vacuum line to the vacuum modulator.

How should the lights be in "P" & "R" ? - Mine er both "on" in P and R

You may have already seen this, but there is a TON of info in this thread:

http://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor

I thought it would be easy to find the answer to your question about what the lights should be doing in PARK and NEUTRAL, but I did not see it. It may be in there somewhere though if you go through it all.

I don't claim to know the circuit as well as Jeff or Ron or others, but what you may be experiencing is the difference between what the shift computer governor is telling the solenoids to do and what they ACTUALLY are doing. Could very well be that something went bad on one or more of your solenoids, internally, or the connections/wires leading to them.

DCS 2016 is just getting underway, so some of the more experienced voices that could lend a hand on this might be away until after the weekend to chime in.

[David T]

If the lights are off the shift computer is commanding the transmission into 3rd gear and it slips so the trouble is NOT the shift computer and although it may have other problems, it is not causing the slipping. Slipping is deadly to the clutches so don't drive it a lot till it is fixed. There are two possibilities for the clutches slipping. One is worn clutches but you say there was little to no debris in the pan so we can rule that out. The other cause is low pressure. That can be caused by too little oil, too much oil, or a blocked oil filter. On one car it was found that a blob of sealant had gotten into one of the solenoid valves and blocked it so that is a remote possibility too. What I recommend you do now is remove the oil filter and see if it still slips. Make doubly sure the level is correct as per the procedure G:04:02. Are you sure you used Dex II? You say it didn't slip before you did the service so anything you did is now suspect. As long as you are underneath check that the wiring harness is not damaged from contact with the hot exhaust pipes and the vacuum hoses and pipe to the line pressure regulator is not missing or leaking. You can screw the pressure up a little too. It will give you firmer, harder shifts but it is better for the clutches since there will be less slippage during shifts. As the transmission shifts it is in 2 gears at the same time for a short time but the clutches slip so it works to make smoother shifts. Also the line pressure regulator lowers the line pressure during lift foot shifts and light loads to make the shifts smoother letting the clutches slip (that is what the vacuum line is for).

[martiq]

What I'm dealing with as far as i see it is a pressure loss or bad clutches. But there was no sign in old filter or old oil that would point to burnt clutchplates.

The fault is only occurring on warm transmission, and the gear is engaged. It's just slipping under load. I have forward momentum on light cruisingpower.

I still dont see how it could be the govenor. I mean: If the govenor was faulty then the control of the solenoids would be wrong, and not engaging the gear at all. Right?? And why then no problems when cold.

Another owner suggested a crack in the clutch drum (known design fault). When warm or hot, the crack would result i pressure loss and slipping.

Anyway. I will try pulling fuse 13 while driwing to see if the slipping still occurs.

Regards/

[martiq]

but what you may be experiencing is the difference between what the shift computer governor is telling the solenoids to do and what they ACTUALLY are doing. Could very well be that something went bad on one or more of your solenoids, internally, or the connections/wires leading to them.



That could also be the case.

[martiq]

If the lights are off the shift computer is commanding the transmission into 3rd gear and it slips so the trouble is NOT the shift computer and although it may have other problems, it is not causing the slipping. Slipping is deadly to the clutches so don't drive it a lot till it is fixed. There are two possibilities for the clutches slipping. One is worn clutches but you say there was little to no debris in the pan so we can rule that out. The other cause is low pressure. That can be caused by too little oil, too much oil, or a blocked oil filter. On one car it was found that a blob of sealant had gotten into one of the solenoid valves and blocked it so that is a remote possibility too. What I recommend you do now is remove the oil filter and see if it still slips. Make doubly sure the level is correct as per the procedure G:04:02. Are you sure you used Dex II? You say it didn't slip before you did the service so anything you did is now suspect. As long as you are underneath check that the wiring harness is not damaged from contact with the hot exhaust pipes and the vacuum hoses and pipe to the line pressure regulator is not missing or leaking. You can screw the pressure up a little too. It will give you firmer, harder shifts but it is better for the clutches since there will be less slippage during shifts. As the transmission shifts it is in 2 gears at the same time for a short time but the clutches slip so it works to make smoother shifts. Also the line pressure regulator lowers the line pressure during lift foot shifts and light loads to make the shifts smoother letting the clutches slip (that is what the vacuum line is for).

Thanks David. Exactly my point regarding the shift computer/gevenor

[Jonathan]

David made a good point. I should have thought of my own experience like this last season, but didn't remember. When my auto trans filter was dirty (before replacing it), I saw the car do something similar to yours in that I lost forward power and it revved up like yours does. I was in town at the time and coasted into a parking lot. What I found was that if I shut the car off and then turned it back on, this debris that had gotten sucked up into the filter fell down again and took another little bit to get sucked back up into it again. Once home, I took the pan off, replaced the filter and was good to go.

As David also mentioned, your previous work is suspect now. You'll need another volume of ATF to do this, but you may need to drop the pan again, look over the filter, see if anything might be getting caught in it or whether it was installed incorrectly.

One piece of advice I got on the replacement ATF filters (assuming you got yours from the same source) was that some shipments got pushed down slightly around the inlet opening (bottomside). When this happens, it constricts the fluid flow into and through the filter. It won't need to be pried up much, but have a closer look and make sure the opening is good around the complete circumference.

Check also whether somehow the gap at the bottom of the filter between it and the surface of the inside of the pan looks to be ok. Again, if something got thicker or pushed out more than it should (cork gasketing material used between filter and bottom of trans perhaps) it could be limiting that suction space and causing your starving fluid problem.

I'll switch my vote to it being fluid related and not shift computer as well at this point.

[martiq]

I'm quite sure the new filter is installed ok. The problems started while the old filter was in the car. and it didn't even look that dirty or dammaged. Even the old fluid looked to be ok.

Installing new filter and new fluid was my first attempt to fix the problem.

Byt yes I'm also sure it's fluid related, but I'm affraid I have to dig deeper in (so to speak).

[axh174]

Okay. But (correct me if I'm wrong) I thougth the behavior of the lights told me that the govenor is working correctly, controlling solenoid A and solenoid B.

Someone else suggested that I should check the vacuum line to the vacuum modulator.

How should the lights be in "P" & "R" ? - Mine er both "on" in P and R


At the moment, I'm going to throw my hat into the "not a governor problem" ring along with the others, at least insofar as your slipping in 3rd is concerned.

The lights on your break-out box are functioning correctly: both on for "P" and "R" and 1st, one on for 2nd, and neither on for 3rd. They find their path to ground through the power transistors soldered on the governor circuit boards (if you're interested, you can see the circuit diagram in the thread Jonathan posted). What this means is that your governor is correctly attempting to drive the solenoids that cause the transmission to shift.

Now, what your solenoids are actually doing is another matter. As others have mentioned, it's possible there's a problem in one of the solenoids itself (clogged?). Although it this case that would mean it's having trouble staying in a de-energized state, which I'm having trouble wrapping my head around.

Much more likely scenarios are what David and Jonathan mentioned: checking the vacuum hosing + metal pipe on the modulator and a problem with the filter.

A question for those more knowledgeable about the pressure in the transmission: I noticed the pressure gauge tends to drop when the transmission starts slipping, but is that due to no longer maintaining the same RPM or because of a potential loss of pressure? Would it tank further if there were a clogged filter?

[martiq]

Thank you axh174 for clarifying the light readout vs. the governors "intentions". That means I have understood it correct. I also thought about a problem with what the solenoids actually are doing then - as you mention.

I have checked det vacuum line for leaks this evening and found nothing wrong. I have just been on another test drive checking the "pull fuse #13" Resust is: It's also slipping when fuse is pulled i.e. govenor disengaged.

The thing you mention about the pressure loss vs. slipping I noticed myself. But actually I think it's me easing off the trottle right after I have provoked and feeling the slipping.

The car is grounded for now, and next thing I will try to check the solenoids functionality, wiring etc.

I will keep you all posted, but is probably going to take a break from the project for some days.

Keep the inputs coming they are much appreciated .Thanks :D


PS: Let me refresh: The problem only occurs on hot transmission. I can not make it slip when cold. And before you ask: Yes Oil level is within the marks both hot and cold ;-)

[DMCMW Dave]

Try running it with no filter at all. You might be surprised, won't hurt anything in the short term (damage is probably done). Start saving for a replacement/rebuild.

[Elvis]

The slipping definiteld is NOT the governor !!!!!

The governor only say 1, 2 or 3, but not neutral !

Good luck finding it, I'm curious what it is.


The getting stuck in 2nd or 3rd most likely IS the Governor.
Your tranny seems to have several problems.



BTW - I've seen / driven automatics that went into a "neutral" when doing a kickdown to first gear.
Anybody has some facts what it is ? (also definitely NOT the governor!)

[axh174]

Going to throw out some thoughts here for discussion.

The way the governor works is it keeps the solenoids that do the actual shifting energized in low gears. The path to ground for these solenoids are the power transistors on the governor circuit boards (it's the same path for the breakout box as well). The transmission shifts from a lower gear to a higher gear by successively turning off the power transistors, which breaks the path to ground and causes the solenoids to de-energize. That means when you are in 3rd gear, both solenoids are de-energized.

I found myself wondering if perhaps the slipping we were seeing might actually be a solenoid energizing against the governor's wishes and causing a downshift. This would suggest a problem in the wiring harness. However, with fuse 13 pulled there is no path at all for power to get to the solenoids. So I think the fuse 13 pull test demonstrates that the problem doesn't exist in the governor or the wiring harness at all.

Martiq, when the transmission slipped, did it feel like you had some traction like an unintended downshift to 2nd, or did it feel like you entered neutral?


Also, +1 on Elvis' comment about getting stuck in a higher gear probably being a governor problem (bad capacitors causing noisy transmission signal?) Does getting stuck also only happen when the transmission is warm?

[martiq]

Martiq, when the transmission slipped, did it feel like you had some traction like an unintended downshift to 2nd, or did it feel like you entered neutral?


Also, +1 on Elvis' comment about getting stuck in a higher gear probably being a governor problem (bad capacitors causing noisy transmission signal?) Does getting stuck also only happen when the transmission is warm?

The slipping definitely don't feel like a unintended downshift but i see your point, and had the thought myself to begin with, and thats why I started to check the govenor with test ligtht in the first place. It's "just" a slip in 3rd gear, and easing the trottle on and off still makes the transmission pull the car, and clearly let you feel that you are still in 3rd gear.

Agreed that the "getting stuck" or hesitation to downshift might be a secondary problem related to the gevenor...But to answer the guestion - Yes it also only happens when warm

Regards
Martin

[hmcelraft]

After setting for so long, the sealing in the clutches has probably been lost because of scoring, rust, etc. If it was started dry the seals may have broken. There is a possibility that the sealing could recover, if not broken, but more than likely the slipping will get worse and eventually no 3rd gear. It very unlikely also that the governor has anything to do with your 3rd gear issue. After all, you pulled the fuse and had the same issue.

A rebuild is the best option it would appear to me. The rebuilding is pretty straight forward. The measurements and clearance adjustments are the things where I hear of the most struggle. I had a guy in NJ rebuild a trans for me. Worked great for about 40,000 miles then it started slipping. Symptoms very similar to yours. I just replaced the trans the second time. Rob Grady had a new trans available to mount to my final drive. Nice after that!

[martiq]

The car drove flawless the last months and under the few test drives over the past year while I was bringing the car back to life. The fault occured within the last 3 weeks.

I have made up my mind - after checking the solenoids (I'll do that first) - the transmission is coming off and taken apart for further investigation and rebuild.

I'm pretty confident in taking it apart and do a rebuild, and yes I also have my attention to measurements and clearance adjustments as being the most difficult.

I've already bought an old Renault 4141 repair-manual as extra reference

I did get a comment from another owner on Facebook. He had the EXACT same problem a few years ago (I was like he was describing my problem). He had a crack in the clutch drum which caused pressure loss and slippage. He linked me to a picture (attached) Makes awful lot of sence, as the crack likely would expand and open up when the transmission is warm. A failure like that will ofcourse be "worst case". I might also be anoter seal or what have we, that could be affected by temperature in degree of leaking. Anyway I'm going in..

[David T]

If you decide to do your own rebuild there are a few things to consider. You need to buy, rent, or borrow the special tools. You need to buy the seals, clutch plates and steels. If one of the clutch housings is broken you will need to obtain one. You will discover parts are difficult to find. The clutch housing for C-1 is prone to breakage but it doesn't split, the spot welds tear and you won't get any drive at all when that happens. On 1 rebuild I did a spit ring cracked on assembly causing the transmission to slip because of low pressure so maybe that is what happened to you but if the transmission hasn't been taken apart recently I doubt it but who knows? Bottom line, one of the clutch packs is slipping either because of low pressure or worn friction plates. Before you take it out try driving without the filter.

[martiq]

On which pins do I connect power (positive and negative) to properly test the solenoids - Just to be sure not frying anything. I suppose I would hear them click?

I measure 25,6 - 25,7 Ohms across the wires to each solenoid

Are they supposed to be open or closed when energized, and do they work differently, hence the one with clear wires is supposed to sit in the outer position in the valvebody and must not interchanged?

44894448954489644897

[martiq]

On which pins do I connect power (positive and negative) to properly test the solenoids - Just to be sure not frying anything. I suppose I would hear them click?

I measure 25,6 - 25,7 Ohms across the wires to each solenoid

Are they supposed to be open or closed when energized, and do they work differently, hence the one with clear wires is supposed to sit in the outer position in the valvebody and must not interchanged?

44894448954489644897

NEVER MIND ;-) I figured it out :-) The solenoids are tatally quiet when operating, so you need to pressure test them to check. Watch my video. They both operate fine :-)

https://youtu.be/Ov4acHXbCCI

[David T]

I didn't think it was the solenoids causing the slipping. If you weren't getting into one of the gears then they could have been a problem. When you put them back in, put the pan on WITHOUT the filter and see if it still slips. If it does, it is a mechanical problem inside the transmission. When you put the solenoids back make sure you do not mix them up. Refer to G:06:02 Notice in 1st column 1/2 way down.

[martiq]

I checked them just to be 100% sure. I'm aware of the correct place for each solenoid ;-)

I' have noticed the suggestion about trying without the filter installed. Just for me to understand: What exactly will that prove that has not already been proven with the connected pressure gauge. I measured 8 bar at 2500 rpm in 3rd gear and hot transmission.

regards

[Elvis]

...
Also, +1 on Elvis' comment about getting stuck in a higher gear probably being a governor problem (bad capacitors causing noisy transmission signal?) Does getting stuck also only happen when the transmission is warm?


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number one problem especially with heat - are the bad solder joints, they break due to heat and vibrations

[David T]

I checked them just to be 100% sure. I'm aware of the correct place for each solenoid ;-)

I' have noticed the suggestion about trying without the filter installed. Just for me to understand: What exactly will that prove that has not already been proven with the connected pressure gauge. I measured 8 bar at 2500 rpm in 3rd gear and hot transmission.

regards

The pressure gauge may not react fast enough for you to see a quick dip in pressure. The filter may be blocked or if you don't have enough fluid you might be getting air. If it doesn't slip when you try it without the filter at least you aren't slipping any more and I would then cut the filter open to see what is inside. There is no way to see if the filter is dirty unless you cut it open.

[martiq]

The filter is brand new! And the slipping only occurs on hot transmission, so fluid leve and air suction doesn't make scense. If that was the case it would be far worse on cold transmission with lover fluid level - and it's not. Btw my fluid-level is absolutely correct.

[DMCVegas]

The filter is brand new! And the slipping only occurs on hot transmission, so fluid leve and air suction doesn't make scense. If that was the case it would be far worse on cold transmission with lover fluid level - and it's not. Btw my fluid-level is absolutely correct.

Yeah, but the OEM filters are not the best. Under heavy suction, some I believe can partially collapse and restrict fluid flow. So testing without a filter can help a great deal.

[David T]

Yeah, but the OEM filters are not the best. Under heavy suction, some I believe can partially collapse and restrict fluid flow. So testing without a filter can help a great deal.

The filters are fine BUT. There was a batch of filters long ago that were made incorrectly. There is a small chance you may have gotten one of them. The best way to check is to either open it up or try driving without it. Your only other option is to take the transmission out. Trying without the filter is much easier. Your choice. If not corrected quickly you will be taking the transmission out soon. The clutch packs can't handle a lot of slippage without being destroyed. You asked for advice and here it is. If it isn't the filter the transmission needs to come out and be rebuilt. Make sure you are checking the level as per G:04:02 and don't forget to check the final drive level also. Recheck the type of fluid you are using, it has to say Dextron II or equivalent. The wrong fluid can also cause the transmission to slip.

[martiq]

Took the transmission apart. The C2-clutch drum is cracked.
Case closed!!!

[Michael]

Yeah, but the OEM filters are not the best. Under heavy suction, some I believe can partially collapse and restrict fluid flow. So testing without a filter can help a great deal.

Just so we are clear, the remaned filters I made are better than OE because of this. We opened up the restrictive mesh just a little to allow for better fluid flow which was an issue with the old OE filters (and maybe one of the many reasons the Auto Transmission was so prone to pre mature failure)

[David T]

Just so we are clear, the remaned filters I made are better than OE because of this. We opened up the restrictive mesh just a little to allow for better fluid flow which was an issue with the old OE filters (and maybe one of the many reasons the Auto Transmission was so prone to pre mature failure)

Hard to tell from the picture any cracks. If the case of the clutch pack is cracked it is often due to a bad shift computer. Usually happens to C1. The main reason for mechanical failures of the automatic transmissions IS the shift computer. The defective filters affected only a small # of cars. Keep inspecting the clutch packs. Was there much debris in the pan and on the magnet?

[martiq]

Pretty easy to see. It's cracked almost half way round. It looks very similar to the drum from another owner that I posted earlier in this thread.

And I talked to DeLorean Europe. Its the large C2 clutch drum that always break not the C1 drum

Michael: I'm running your filter. :-)

But enough talk about the filter ;-)

I found the cause of the pressure loss and slipping, which was the entire purpose of this thread.

[David T]

Pretty easy to see. It's cracked almost half way round. It looks very similar to the drum from another owner that I posted earlier in this thread.

And I talked to DeLorean Europe. Its the large C2 clutch drum that always break not the C1 drum

Michael: I'm running your filter. :-)

But enough talk about the filter ;-)

I found the cause of the pressure loss and slipping, which was the entire purpose of this thread.

Perhaps it can be welded up? Getting "hard" internal automatic transmission parts for this transmission is not easy. Maybe in Europe where they were more popular, parts are more plentiful? While you are in there you should replace the steels and frictions, seals too and check your running clearances.

[martiq]

I already have the choice of a new or a used drum on hand.
All steels, frictions and seals will be replaced wit new ones, and assembly will be done by the book when time comes.
Currently I'm manufacturing some of the special tools on my own.

[David T]

Even with the "special" tool kit you have to rework some of them to actually work anyway. Someday someone should make up a set of prints so anyone can have them made. Make sure to check, and if necessary, adjust with shims, the running clearances. Very important. Also note there are some problems with the Workshop Manual. First one, the cut-away view on G:01:01 has the differential wrong, if you put it back that way you will get 3 speeds in reverse. G:05:02 #4 Governor cable adjustment has the wrong clearance. G:07:07 the example has errors. Some pages may be missing in your manual, check the page numbers. Use transmission assembly lube on the seals. Have the torque convertor rebuilt and replace the plastic (nolotron) thrust washer with a bronze one. Be careful installing the clutch packs, the reaction rings can break easily and you won't get enough pressure to shift.