Hello,
I have a 91 Bonneville, it has 150k on the car. I just had the engine rebuilt because of a front end traffic accident i had with it..However, i think due to the accident, the transmission suffered some problems. The car still drives, i drive it at 65mph. but im noticing that sometimes the tranny seems like it doesnt know what gear to stay in, the car will shake slightly, and it feels like the car isnt driving. I also notice sometimes when accerates from a red light. it will hesitate to go, and when u gove it more gas, the engine like roars to a high rpm, then it goes back down, It'* very weird. I assume the whole transmission has to be rebuilt or replaced, i mean 150k is a pretty good life for a transmission i would think. Does anyone know if what i am describing sounds like the tranny needs rebuilding, or could it be the torque converter? also, is there any web sites that sell rebuilt trans for reasonable prices. I have a 96' Bonne that i just bought and i want to keep it in the garage in the winter..so i want this one to work right...Thanks again...

I don't know that much about diagnosing bad transmissions but for as long as I have driven my car (over a year now) I have had this nagging problem with the car. When I get to about 35-45 and up Mph, the rpms drop to about 1500 or 1100 and don't want to get any higher no matter how much i push on the pedal, but then when I push the accelerator enough it downshifts into a lower gear and goes fine from there for a few seconds until i let up on the pedal some or it goes fast enough to upshift on its own again (as it should) but once again it goes down to the 1500 or 1100 rpm syndrome. I got fed up with this issue and was lucky enough to find another fellow at the bonnevilleattitude forums who was explaining this exact same problem. (see it at BA'* forum in the 92-99 mechanical section under the thread: "Misses at low RPM in Overdrive" (dont worry overdrive has nothing to do with it). Basically, in the end, someone mentioned his car had a kind of similar issue where it was diagnosed to be the Torque Converter. He claimed that to test it, you have to get to when the problem happens then tap the foot on the break and if the problem goes away during the application of the break, its the Torque Converter. Subsequently my car seems to act as if it were the Torque Conv. i have yet to take it to a trans shop to officially get it diagnosed.

Maybe you coudl try holding your foot just enough on the break so that the brake lights are active and the car knows its breaking and then try accelerating off the line and seeing if the problem goes away.. that should prove the torque converter as at least one of the problems... anyone else have any ideas?

Mike Diaz.

What you are seeing is normal operation of the Torque Converter Clutch or TCC aka "lockup" though I have not heard of it happening below 45 mph before (have seen the code for 3rd gear lockup around 37 mph in the ECM, just never had it happen other than in 4th in my cars)

If the engine is in closed loop operation (must be warmed up), and the speed is over a set amount (around 48 mph on our 90 SE & +/- 3 mph on others), and the TPS (how much the gas pedal is depressed) is low or in cruise. The transmission will :lockup the torque converter. When this happens the rpm will drop about 500 rpm and the engine will be locked to the drive so rpm will track speed exactly and not jump when you push on the gas. In other words it acts like a manual transmission.

Push the gas far enough and it will unlock sometimes accompanied by a down shift. Take your foot all the way off the gas and it will disengage also. This is as it was designed and will help the mpg and lower the trans temperature.

If you are militant about not liking it, you can just unplug the TCC solenoid line to the trans.

Is it safe to drive with the Torque Converter Clutch solenoid disengaged? If so, will i get an SES light showing? And, where is the TCC solenoid so that I can disconnect it?

I still get the feeling that this can't be the normal operation (at least not what'* goign on in my car). I realize now that the Torque Conv. is supposed to lock up and i have read about it before but I don't think it should lock up this much and require that much gas to get it to de-lock.. it'* almost as if (for me) it wants to lock up too quick (35mph!!) and when i break it loose with enough gas it downshift for about a second and then goes back into lock mode!!

Mike Diaz

a) my first Fiero had a failed TCC (did not lock) and we drove it for about 5 years/40,000 miles that way including some road trips. No problem but MPG was not real good.

b) my comment was about MikeD'* (what year is yours ?) description not Kevdogg'*. The pausing and reving between gears he is seeing is not normal.

c) The TCC is controlled by the ECM and its PROM settings, the lowest I've seen one engage is 1300 rpm/45 mph (digital readout) though I have seen code that would lockup in 3rd (D) at 37 mph as well as in 4th (o/d) at 45 mph. In other words I'd need to look at a PROM dump to see what it is being told to do.

TPS has a definate effect on TCC but basically it will lock on TPS > 4% (about .6v - why it unlocks if you take your foot off the gas) and unlock for TPS >50% (about 2.2-2.5v) so a grosely malajusted TPS could confuse things (idle should be in the .35-.42v range and WOT >4.2v). Note: the ECM will calcualte the range based on the idle position so exact value is not critical but needs to be close.

From what you describe though the TCC is doing what it is being told to. The question is why is it being told to do that ?

If you really want to get into this, you need a scan tool so you can read the values the ECM is seeing and the PROM code (four digit number). I have quite a few 5B (3800 "C" ) dumps but nowhere near all of them.

Oh, my home is in Orlando. Right now my employment has me travelling a lot.

Thanks for your advice...so, it sounds that your saying that the transmission itself is fine, and the torque convertor needs work? If it is the torque convertor causing this, would that be expensive to fix? I still might think the tranny is dying because i can hear it making a funny like clicking noice or something when im idling..When you give the car alot of gas on takeoffs, it sometimes will accerate fine and drive how it used to, but now, it seems like its hesiting to drive, and when it does, the engine winds up. I have also noticed that every time i come to a stop. just before the car stops, the car like makes a noise and stops it abrubtly...i dont know what this is related too....It seems like a waste to just junk it, because i just had the engine rebuilt....Thanks again...

We were really talking about MikeD'* issue, Kev it does sound like you need a new trans. To me there are only two choices - a low milage one from a yard (even so I'd pull the pan first to see if anything is lying on the bottom like white plastic). Prefer one totaled from the rear or side- often nice looking ones were junked because the trans died.

The other alternative is a rebuilt "crate" from GM. These are considerably more expensive (like $1200) but when GM rebuilds one it is usually better than new because any TSB that came out will be in the rebuild (and 4T60s had a lot of TSBs).

Know the 440T4/4T60 was used through 90 and the 4T60E in 92 but do not know which was used in 91s.

Our Bonne is a '90 SE we bought with 300 miles on it. Now has 120k on the chassis and 70k on the engine. Prolly should put something in the intro area. As to overheat, it run the entire drivetrain cooler than stock: 180 t'stat, revised fan maps, and improved airflow. Temp gauge sits below the first mark idle or drive (but enough to stay in closed loop).

Will have to be home to do pics, never got around to it. Is 90 SE - dark red monotone with grey interior, 16x7 crosslaces with Michelin X-Ones in 225x60x16 (just had to replace all of the plastic center caps which were deteriorating). Paid $50 extra NOT to have grey lower body. Has steering wheel controls (want to find a factory CD - see other post) & auto a/c. Garaged entire life but considering a repaint

i'm not seeing any real revving between gears. my only real problem is that my TCC kicks in at about 35-40mph *(way too early)* and takes too much gas to get out of. I once thought it might have been the TPS and its still a possibility.
I have a 1987 bonnie and you're right whoever said the thing about the trans cooling lines being on the driver'* side of the radiator. That'* how mine are, however i'm lucky enough to be at 153k miles and the trans has been a-ok witth the exception of needing a new vacuum modulator once at about 147k miles (we've had the car for about 5 years since circa 90k miles and it has given me little greef.. except that the ac compressor went out and i never got it fixed... and the mysterious oil leak which might now be solved.. and the paint job getting kinda nasty...and the windows closing really slow. .. and now this trans problem we're discussing here.. but even with all those things its still the #1 car in the world for me! ) anyways back to the TPS. My chilton'* has a way of testing its voltage output but I couldn't get any feedback from my multi-meter hooked up to it. I'll go at it again tomorrow but if someone can give me some basic directions on how to measure the voltage output would be appreciated (the chiltons has all the ranges etc so i dont need those). Oh and how do i go about adjusting my TPS? And last but not least anyone got a part # for my TPS?