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/a...-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?76...vernor+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?35...ssion-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).