85 Eldorado / HT4100 / Harsh Down Shift / Error Code 39 Torque Convertor

[Whit Otis, 1188]

Last fall I took two days to drive my 85 Eldorado with HT4100 up to Hickory Corners.  I had an intermittent issue that perhaps someone might know something about.

On the second day of the trip, as I was approaching Chicago, I went to pull off the interstate for gas.  As I coasted up the ramp to a stop sign, when my speed was down to around 25 mph, the car acted like the accelerator was stuck at that speed.  As I stepped on the brakes and the speed dropped down to where transmission downshifting would occur, it was if I had one foot on the gas and the other on the brakes.  This resulted in some extremely hard downshifting until I came to a stop.  When I moved off again again, the car moved off in first gear, but then stumbled all over itself and then ignored second and went to third or fourth (OD?), not sure which.  At the next stop sign, it started to do this again, so I threw the car in neutral to avoid the harsh down shifting and the car idled down to a normal idle and because it was in neutral there was no harsh downshifting.  When I moved off again, I had the same upshift problem mentioned above.  When I got to the gas station, I hit the buttons for the code readouts and I had a "Code 39" which the shop manual says is a torque convertor clutch engagement problem.  Oddly enough after a couple more of these incidents, it never did it again on the whole trip which was a total of about 2200 miles.

Thoughts:  If the idle speed controller was not working, I would presume I would have gotten some type of error code for that, but nothing, just the code 39.  Is this what some of you were referring to on the General Discussion Forum when it was stated that the GM transmissions through the 80's had a tendency to remain in lock up mode?  If mine remained in lock up mode would this cause this harsh downshift issue?

Anyone have any ideas on this one?
Thanks
Whit, 1188

[JerRita]

I had a similar issue with my 85 Seville The lock out solenoid would act up when hot I had it replaced and serviced the tranny and have no issues since cost about 300 at a reputable tranny shop  JeRita

[936CD69]

The torque converter lockup solenoid was a know issue in several GM transmissions of that era. As Jerita said, have the solenoid replaced and the problem should be solved.

[TJ Hopland]

What does the shop manual say for diagnostics for that code?   I would think the code would be indicating an electrical issue with the solenoid circuit which may or may not be related to or effecting its operation.

Seems like Bruce Roe said he had seen a lot of what was it accumulator springs? broken in one of these transmissions?   I don't remember what the symptom was or if it was the 325 (non OD) or the 325 4L (overdrive which is the case here). 

It would probably be worth a look at the TV cable.   Its one of the 3 cables that is part of the throttle arm on the throttle body.  One goes to the gas pedal,  one to the cruise, and the 3rd is the TV down to the transmission.  On this trans its not just a kickdown signal, its one of the primary inputs to the trans so if its sticking the trans won't shift right.

[James Landi]

I've owned three Eldorados 83,84,85... My super high mileage (3Xs around the clock!) would sometimes have a transmission acting up-- helping it through rough shifts by "manually shifting" as you have, would often yield lengthy periods without issues...You may wish to look into getting that auto idler control working again.  Mine would "lock up" because the original grease hardened into a rocklike substance... open up-clean-up and grease up, and engine speed will better coordinate with shift points...

[Whit Otis, 1188]

Hey James,  By "auto idler" do you mean the idle speed controller located on the throttle body??
Thanks
Whit
1188

[James Landi]

That's it Whit.,, just be careful with handling it at you take it apart... it's a motorized worm gear...has a copper contactor at the base...once cleaned and greased, you watch that idler plunger constantly adjusting based on the engine management coming for the ECM.   

[Whit Otis, 1188]

Before jumping into the Torque Convertor Clutch lock up issue, I decided to replace the idle sped controller (ISC) on my ’85 Eldo since I have no idea if the one on the car is an original or if it had been replaced at some point.  When I bought he car, it had 69000 miles on it and was in great shape, but who knows.  I bought a new ISC rather than take the old one apart.

I put the new ISC on and then went through the complete factory set up specified in the shop manual (I also checked all my “Serviceman Bulletins” in case there were any procedural changes).  Without repeating what’s in the manual, I brought the engine up to operating temp, then increased the throttle speed while pushing in on the ISC plunger and at the same time disconnecting the plug.  When this is done, the throttle linkage is against the mechanical stop and the ISC is out of the picture operationally and the engine idles very slowly.  Checked engine rpm on the diagnostics and it was within spec. I went through all the other diagnostic checks and found that the Throttle Positioning Sensor (TPS) was off, showing -1 on the read out.  Set that up to get the proper reading of zero.  Finished up adjusting the TPS and then set the ISC to .060 clearance to the mechanical linkage (Note, I had to screw the ISC plunger in approx. ¼” to achieve this setting).  Everything was fine, car ran fine, idle speed was compensated for depending on conditions (AC on or off, etc., etc).

Everything was great until I went out the next day and flipped on the ignition switch (cold engine) and there was a loud clicking sound taking place about two times per second.  Opened the hood and looked and the ISC plunger is pulsating in and out approx. 1/8” as if it couldn’t find its place.  Started the car and it ran OK but idle was somewhat erratic.  Finally went through the whole ISC set up procedure again figuring I left something out, but same thing happened.  Next day, cold engine, I decided to simply screw the ISC plunger back out.  After the first 1/8” or so, the plunger pulsation became less and less until it finally went completely away, so that is where I left.  When cold, no more ISC plunger pulsations, car runs fine and also idles fine.

Anyone ever have this happen when installing a new ISC?

Thanks
Whit
1188