Is this typical AT governor failure mode?

[Dangermouse]

..or something more..?

Regular readers of our home at the time, dmchelp, may remember my transmission failure back in June. After a few month hiatus, and egged on by nullset, I finally got out last night to find out what was going on. I made up the suggested LED test rig and observed the following:

The test rig had two LEDs, one connected to each solenoid. Solenoid energized = LED lit. In first both lights were expected to stay lit. In 2nd, one would go out and in 3rd both would go out.

Started off cold (well, ambient 65F). Both lights were lit in all positions - PRND21 (I was expecting only one light in 2 ?)

While cold, car drove normally, lights showing shifting between gears both up and down. I was just driving around the neighbor hood, lest I get stranded

When warm (after about 3 minutes of light driving), I noticed slipping in second (one LED lit) . Stopped car. Box dropped down to 1st (both LEDs now lit). Slippage there also as car accelerated slowly and eventually into second.

Stopped again. (Both lights on- box still in D) Major slippage in 1st. Car would not move. Put box in R, (both lights still on) and car would not move.

Put box in P, turned engine off, and then on again. Put back into D (both lights on) and car moved off normally. Stopped and put it in R (both lights on) and car reversed normally. Back into D and drove about 300yds and slippage started again. Stopped and tried to drive off again. Minimal motion, just slippage. Put box in P, turned engine off and on, put box back in D and car would move again.

So, long story short:

while cold, everything OK.
When warm, slippage occurs in all gears
When hot, cannot move in D. However, turn engine off and on, and now will move, albeit for a few hundred yards

Checked fluid level when hot and found it to be a little low (at the end of the WARM text) Added fluid, but no discernable difference. Fluid smells burnt and is no longer red. (obviously will be changed)

So, is the above simply classic symptoms of a failed AT governor, or is there something more at play.

[DMCMW Dave]

That does not sound like governor failure. More like you are losing the hydraulics (pump?) Have you had the pan off and cleaned or removed the screen? This could be clogged.

The governor is really pretty simple: as the car goes faster it drops one and then the other solenoid. It has no impact in reverse. If both your lights are on it should be in first.

The only other thing it could be is a bad solenoid, but that's pretty rare, and would still not impact reverse.

[Dangermouse]

Probably about a year ago I replaced one of the cooling hoses, which necessitated dropping the pan, cleaning the filter screen and replacing the fluid.

Or do you mean there is a screen on the pump?

[David T]

Definitely sounds like the shift computer (aka governor) is functioning as it should and from your description of the mechanicals it does sound as though the clutch plates inside are "toast". The only things left to try is to clean or replace the filter and make sure you have full line pressure. If that doesn't fix it (and it probably won't) your choices are to get a rebuilt or NOS transmission or have yours rebuilt. The fact your fluid smells burnt is a BIG hint that the clutch packs are done. That and the slipping.
David Teitelbaum

[DMCMW Dave]

.... cleaning the filter screen and replacing the fluid.

Or do you mean there is a screen on the pump?

Sounds like you got it already. That's the only filter screen. If you changed the fluid a year ago and it's dark/burnt already, as DT said that's not a good sign.

It is pretty strange to lose reverse.

[Dangermouse]

Bugger !!!

Out of curiosity, what cause clutch packs to fail?

[DMCMW Dave]

Driving with a bad Computer Governor is the #1 cause - especially if the failure is that you start out in second or third gear all the time. That puts tremendous stress on the clutches leading to overheating which what is really killing the parts.

This would be similar to driving a manual car in third gear only - the clutch wouldn't last long there either.

Other causes are waiting, say, 30 years between fluid changes, drag racing, other general abusive driving, etc.

[David T]

There is another cause, there was a run of defective, improperly made auto trans filters a long time ago. They would not flow right and prevented full line pressure. Low line pressure would allow the clutch packs to slip since they are not tightly compressed. Whatever the cause, it now sounds like too much friction materiel has come off but if your line pressure is low and there is still enough materiel on the friction disks you may just get it going if you can get the line pressure up to where is should be (if it is low). Since you say when it warms up you lose reverse you are probably way past where improving low line pressure will help.
David Teitelbaum

[Dangermouse]

Are there any other tests I can perform that might confirm these diagnosis?


Driving with a bad Computer Governor is the #1 cause - especially if the failure is that you start out in second or third gear all the time. That puts tremendous stress on the clutches leading to overheating which what is really killing the parts.

This would be similar to driving a manual car in third gear only - the clutch wouldn't last long there either.

Other causes are waiting, say, 30 years between fluid changes, drag racing, other general abusive driving, etc.

Not that i can do anything about it now, but it would be good for me to ID the cause so the replacement, if that's what it takes, is not toasted too.

I think the governor is OK, based on what i saw last night. Does that sound right?

The fluid was changed in 2001 at around 32k (may well have been the first change - no way of knowing). I bought it in 08 at 35k, and changed the fluid in '10 at 36k.

I certainly didn't drag race or abuse it (can't comment on the PO). Now that I am thinking about it, the car was always slow but not having driven another D, I just assumed that they were all like that.


There is another cause, there was a run of defective, improperly made auto trans filters a long time ago. They would not flow right and prevented full line pressure. Low line pressure would allow the clutch packs to slip since they are not tightly compressed. m Possible, but there was no record of a new filter being installed back in '01.

Am I potentially looking at a full box ( 100105) or just the MECH ASSY, PUMP/CLUTCH 100106 ?

[DMCMW Dave]

Are there any other tests I can perform that might confirm these diagnosis?

Nothing else I can think of, although you could put a pressure gauge on it and see if the line pressure ie exceptionally low.



I think the governor is OK, based on what i saw last night. Does that sound right?
IIRC your description sounded normal


I just assumed that they were all like that.
If you felt both shifts then it was normal. I'm always amazed when I get a car in here that's been missing first gear and the owner didn't realize it. Then we replace the governor and suddenly the car seems quick. The really wierd one was an owner who was missing third and didn't realize it, but complained about bad gas mileage on the highway!


Am I potentially looking at a full box (100105) or just the MECH ASSY, PUMP/CLUTCH 100106 ?

You should really only need the pump/clutch assy 100106, but I'm not sure it's available, and you should ask if it includes the converter (if not you need to add that or get yours rebuilt).

I honestly have never sold one so I don't know offhand. All I have in stock here are complete transmission assemblies (100105). It's common practice on any automatic transmission to rebuild/replace the converter when the clutches have failed, because it's difficult-to-impossible to adequately clean the inside of it by simply flushing with ATF.

[David T]

There is no half measure to this. If the clutch packs are done you rebuild/replace the whole "slush box" including the torque converter, and flush the cooler lines and hoses. Once you wipe out the friction discs the friction materiel gets everywhere and it must be cleaned out to prevent damaging the new box. This is one reason why it is so important to check the line pressure. It is a big indicator of the health of the internals of the transmission. Driving on low line pressure (for whatever reason it is low) causes increased wear. Once the transmission fluid gets contaminated with friction materiel it is like sandblasting the internals because it also cools and lubricates all of the internal parts. It becomes a vicious cycle, the more the fluid gets contaminated the more wear and so on. Cut the filter open when you take the transmission apart. That is one thing to examine to determine why it failed. Do the line pressure check first though.
David Teitelbaum

[Ron]

Started off cold (well, ambient 65F). Both lights were lit in all positions - PRND21 (I was expecting only one light in 2 ?
Just to be sure-
It was not moving (at least not fast enough for it to ever shift) during this part, right?


I'm with Dave S on the reverse being odd...But the filter David T mentioned could very well be the cause, especially if it is now stopping up with clutch material (and settling when you shut it off). Unfortunately, from the fluid description, I have to agree that it sounds like T time in any event.

[Dangermouse]

Just to be sure-
It was not moving (at least not fast enough for it to ever shift) during this part, right?

Correct.

I was just moving the shifter to educate myself on what the lights did in each position.

Why did both lights stay on when I was in 2nd? If you select 2nd does it start in 2nd; or start in 1st, then go to second but not beyond?



I'm with Dave S on the reverse being odd...But the filter David T mentioned could very well be the cause, especially if it is now stopping up with clutch material (and settling when you shut it off). Unfortunately, from the fluid description, I have to agree that it sounds like T time in any event.

Next question,

how doable is this without a lift?

[David T]

Pulling the transaxle is VERY doable without a lift. You will need a floor jack and jackstands that can hold the car up high though so you have room to get the whole thing out from under the car. Drop it out with the floor jack and roll it out. You need a flat, smooth, level floor and a helper. Use some blocks of wood to hold the front of the motor up and as you slide the transmission back make sure the torque converter stays in the bell housing.
David Teitelbaum

[Ron]

Why did both lights stay on when I was in 2nd? If you select 2nd does it start in 2nd; or start in 1st, then go to second but not beyond?
Next question,
how doable is this without a lift?
The lights stayed on because they were connected straight to the solenoids' ground sides. And the governor uses the ground sides to control (energize) the solenoids. So you don't see a change in the lights until the governor actually changes one of the grounds -- They show what gear you are in, not what you gear you request.

If you select 2nd it starts in 1st, then goes to 2nd but not beyond.
Now if you are in 3rd and select 2nd it will immediately go to 2nd, hold/drag a while, and then settle into 1st.
3rd to 1st does the same but goes to 1st as soon as it is 'safe'.
(One of the switches the selector controls can directly ground one of the solenoids making it perfectly happy to let you blow the engine in 2nd accelerating or the differential decelerating.)

I agree with David T, it's not bad as it goes. Just have to be careful!

(I'm pushing 29 hours, so I reserve the right to revise and extend my remarks ;-)