RPM drops while accelerating

[mounddog]

Hells Bells, Jed Rule - you seem to have something there! I tried out the idea of tapping on the brake with left foot while i noticed a drop in RPM - and sure enough the RPM will spike for a moment right when i do that. For example if im going 30 or 40 or 50mph (seems to have some range) and i notice the rpm drom from 2000rpm to 1500rpm - if i tap on the brake at the same time as i have the gas pedal down (while the car has kind of plateued in its acceleration) i will notice it spike back upto 2000rpm. So it appears that the TCC is very much involved. I have no knowledge of this device - does it mean its having a problem? You seem to have an idea as to the problem - pray tell. Im a pretty good shady tree mechanic - have fixed alot of things myself though in no way an expert - is this something i should be able to fix? I have access to a lift and a million tools (my buddies place). Mike

[Jed Rule]

The Torque Converter Clutch is applied by fluid pressure which is controled by a solenoid located inside the transaxle.The solenoid is energized by completing a circuit through a series of switches and sensors.

There are a number of things to check that affect the trans operation.

TPS - provides throttle position data for determining when to shift or engage the TCC.

Vacuum modulator system - senses changes in engine load. Check for more than 17 in vacuum at the modulator with hot engine running in drive.

VSS - Vehicle speed sensor provides speed data to PCM for determining when to shift or engage TCC

TCC brake switch completes TCC engage circuit when pedal is released

Transaxle temp switch determines shift patterns during high temp operation. TCC will not apply until engine temp reaches 140F

To test the TCC solenoids ( and the A and B shift solenoids) without a scan tool you can read the resistance at the trans axle connector. I can give you more info if this is the route you wish to take.

You will need a scan tool to check for transaxle codes or properly evaluate the sensor readings.
You may also want to test the trans line pressure to verify the internal condition of the unit.

If a shudder occurs while TCC is applying the problem is within the transaxle or torque converter. Something is not allowing the clutch to become fully engaged or is trying to apply and release the clutch at the same time.

If a shudder occurs AFTER the TCC has applied most of the time it has nothing to do with the transaxle. Unnoticed engine problems become noticeable due to the lock-up between the engine and trans. Check the usual suspects with regard to engine missfire, to avoid unnecessary transmission repairs.

I hope this helps. I worked 27 years as a service advisor for GM and am familar with the operation all vehicle components. I would feel comfortable performing these tests but I wouldn't attempt to take a transmission apart. Leave that to the pros.

[Opps123]

yes that is what i feel i figured it was the torque converter locking up but what can be done to fix this?>

[mtheis]

The torque converter locking up is normal for your car and doesn't need to be fixed. It's functioning just like it's supposed to.... mine does the exact same thing like you described. The tcc will lock only in your highest gear and when the transmission fluid pressure is correct. Yes, it can be annoying having the sluggish engine feeling. Just give it about half throttle and it should unlock. If it's really bothersome, you can wire a toggle switch to the tcc. Just make sure you engage it when you're driving at highway speeds or you'll overheat your transmission.

[kappal]

I had the same problem with RPM dropping going up a hill on my 97 buick lesabre. I read the posts above and decided to just flush my auto transmission fluid and see what happens. paid $140 for complete flush of transmission fluid, replace filter and gasket, lube guard. The problem went away and I don;t hear the shudder anymore... happy ending in my case

[deadring]

mine does that sometimes too.. depends ont the situation ( 92 PA SC) but from what i saw, if you happen to step on it while the torque conveter is locking up it will not unlock the millisecond you step on it.. it will first lock and stay there unless you let go the gas and then step back on it.

i think this is normal .. and surely enough the torque will around 50 MPH. i find it annoying that the torque locks so low and then the rpms drop to 1400... geez.. when i drive around town i put in in D .. not OD... so i dont get that annoying thing happening too much.

btw,

i found out that a chip in the ECM will cure this problem by putting the lock up at 55- 60 instead.. and remove the speed limiter at the same time.

zooom zooom

i might buy this heheheheh i'll keep you posted


Deadring