An odd slipping phenomenon of the automatic transmission

[SBL]

My automatic transmission on my 1982 is slipping. It seems to be most prevalent from 1st to 2nd gear. Usually soon afterwards it goes into 3rd and stays, which is the limp mode. HERE IS THE INTERESTING THING I FOUND: while I am rolling in neutral after falling into limp mode/3rd gear, if I turn the ignition off for 1 sec and then back on, and then place it in Drive, I hear engagement of a lower gear (I have felt 1st and 2nd engage), and it drives fine for a little while until it’s time to upshift.

It is like the computer gets reset, but I have never heard of such. I want to think that the computer does not know the engine speed, and gets confused but is somehow temporarily fixed by ignition on/off. It does not work simply because RPM is down or that I am in neutral. BTW, this only works for a few shifts, then back to limp.

So far I have:

1. Checked for proper fluid level and it is exactly correct
2. Read 14 v at fuse 13 on the transmission side and watched it as the system slips. It remains present, goes off when I turn the ignition off, and then is back on when ignition is on and the downshift occurs
3. Checked the throttle cable. When at idle the rheostat is fully where it should be, at ½ throttle it is ½ way through its course, and at full throttle is fully turned.
4. Connections to the computer and transmission are very nice and tight. NOTE: this is a new DMC “advanced” auto trans computer installed by DMCFL about a year ago, so while I suspect the computer or a solenoid, I am looking elsewhere first.
5. Disconnected the full throttle microswitch for now so that is out of the equation.

I have found less information on the wiring for the auto trans compared to manual car, and in fact my big wiring diagram does not even show a fuse #13. I have seen the treads that show the board and some other components, but I could n=have missed something of course.

So here are a few questions:

What is the wire up at the firewall engine connector harness that provides the +12 v and ground for the computer? Looks like there is one 6 wire and one 3 wire L-shaped connector up there. I could check that to be sure it is getting what it needs. Or even jump it to a known good voltage source to eliminate that issue.

I read that manifold vacuum also helps to teach the computer the engine speed/load. Where is that connection? I would like to check it.

I can check the logic voltages as well, but I was planning on doing that later. I will also check the filter (messy job, so I am saving that too, after I check what I can that is easier to access).

Any suggestions? Has anyone experienced the “reset thing”.

steve

[Michael]

When's the last time you replaced the filter?

[SBL]

I need to check to see if DMCFL did it when they put in the computer. I have not had it very long so if they did it then it has been about a year. If not, then I don't know. On the list.

[Ron]

What is the wire up at the firewall engine connector harness that provides the +12 v and ground for the computer? Looks like there is one 6 wire and one 3 wire L-shaped connector up there. I could check that to be sure it is getting what it needs. Or even jump it to a known good voltage source to eliminate that issue.

Power to the GC is on the (G)reen wires. Ground is on the (B)lack wires. Check at the red bulkhead connector too .
GCPlugs.jpg

I read that manifold vacuum also helps to teach the computer the engine speed/load. Where is that connection? I would like to check it.

Fwiw, the GC is dumb, it can't learn anything.
ModulatorLocation.jpg

I can check the logic voltages as well, but I was planning on doing that later.
Any suggestions?

You can tell a lot about what it is doing if you check the logic now...
A chart is in post 1 and a easy way to make lights are in post 6 HERE.

Check the harness closely where it gets close to the exhaust (common problem).

[Jonathan]

Sounds like the filter is plugged to me.

I would not trust what you think or hear or feel in regards to what gear the car is in without making up one of those diagnostic light contraptions to tell you for sure.

[dmcnc]

When you say limp mode, do you mean it slips into neutral? If you've had consistent slipping, a lot of that friction material has likely made it to the filter, which will make things worse.

[David T]

The vacuum modulator is there to reduce the line pressure in the transmission to soften the shifts. It also adjusts the line pressure. To troubleshoot the slipping problem you should check the line pressure and make a light box to watch what happens and when the shifts are commanded by the shift computer. Could be the shift computer, could be the transmission. Hard to say. If the line pressure is low the filter is probably plugged up. If you are slipping you can quickly load the filter up with friction materiel from the clutch discs. That further lowers the line pressure leading to more slipping. You can see where this is going. It is impossible to see how much stuff is inside the filter without cutting it open. Dark, gritty fluid is a warning sign of a lot of friction materiel circulating around. DO NOT drive on a slipping transmission. Because the clutch packs are so small you can burn them out very quickly. Once you burn all of the friction materiel off the friction discs the only fix is to rebuild the transmission.

[DARCOM]

My trans felt like was slipping back in 2013. Changed the filter and all was good again. I believe for me it was cause by the trans starting out in second all the time because the trans computer was going out. It built up a lot of clutch material it the filter. Fixed all that and it a champ now. But get to it quick or you will need a rebuild.

[Michael]

IMO the filter is a lousy design. The OE mesh is too restrictive and the feed/rest cavity is too shallow. It doesn't take much material at all to plug up a OE filter.

The filters I made a few years ago have a filtration element that is not as dense as the OE mesh was. I think this improved the throttle response as the clutches were (again IMO) somewhat starved at idle while in gear.

[SBL]

Sorry about the delay. Work got in the way.

Well I changed the filter, and, it shifts perfectly. I think the lesson here is to do a quick visual check, of course, but filter filter filter. The fluid was clean and no metal on the magnets.

Now I am faced, though with a leak in the seal that I never had before. I noticed that the PO had used the DPI silicon gasket, but I had the cork one from DMCH, so I figured what the heck. There was no warping of the pan, and the screws were not over torqued when I took off the pan, or when I reinstalled it. Unfortunately, we are talking about a drop every 2 seconds. So, must do something. I was thinking about loosening all the bolts and shifting things around (although there isn't much wiggle room, and tighten them down again.

The leak is passenger side, front corner. The rest of the bolts/seal interfaces are bone dry. I did not use any chemical sealant, because of some of my readings about it ending up in the transmission. Any suggestions?