Trans 'bucks' in overdrive?

[blacksnake]

Don't know how best to describe it. I was on a 3 hour run down the interstate just cruising at between 72 and 82 in overdrive. For no apparent reason I feel the trans 'buck'. That's not a very good description but it felt as if it tried very quickly to either upshift or downshift. At that speed I was no where near a shift point. Just a split second but you definitely felt it. Each time I was not really accelerating or decelerating, just cruising along with the traffic flow. It happened 10 or 12 times during the trip usually every 15 to 20 minutes. I couldn't see a drop in rpm or anything else significant when it would happen. I could not find one common rpm point or speed at which it would happen other than the speed range I mentioned. I also could not make it happen by duplicating the speed/rpm from the previous time. It definitely did not feel healthy although some of the incidents were fairly soft but a couple were pretty hard. I have 6,000 miles on the car. My first thought is that it is a computer thing rather than a mechanical thing. Anybody experience anything similar? Any answers or speculation would be appreciated!

[martyo]

Could this be the torque converter locking/unlocking?

[carfixer]

I was thinking you may be feeling the A/C clutch cycling on and off, which is normal. Try it with the a/c system on vent or off.

[Thomas C Potter]

I was thinking TCC also. Did you tap the brake during these events?? But you should have seen the RPM's change with TCC unlock/lock. In therory, our brake pedals have a switch that both activates the brake lights and unlocks the TCC. Mine does not seem to unlock the TCC however.

TP 03 300B

[blacksnake]

That sounds reasonable. What would make the torque converter lock and unlock like that? BTW several days before this I accidently let the battery run completely down (zero function) and had to recharge it. Would this affect the situation? Thanks for your help.

[blacksnake]

I didn't touch the brakes. I only feathered the throttle slightly to maintain cruising speed. What triggers the torque converter to lock/unlock? Obviously I am not a gearhead. Thanks for your help!

[woaface]

My car has done that once or twice at that speed. I've heard it called "searching gears" as the car's computer is trying to find something comfortable.

But the torque converter locking/unlocking theory sounds about right.

Try again with the cruise control on.

[BillyGman]

Do you have the stock converter, or an after market one? Some after market ones lock-up very hard and you can feel it locking-up quite often.

[mtnh]

I didn't touch the brakes. I only feathered the throttle slightly to maintain cruising speed. What triggers the torque converter to lock/unlock? Obviously I am not a gearhead. Thanks for your help!

This could also be the mal-adjusted transmission shift cable linkage scenario. Or, it could be the beginning of a chafed harness, by the wiper assembly cover, above the brake master cylinder. The car should not be chugging at that speed, period. I have never felt the a/c compressor make a noticable drag on the engine, either, at highway cruising speed.

Mike

[BillyGman]

I have never felt the a/c compressor make a noticable drag on the engine, either, at highway cruising speed.

Mike



Ditto.....me either. but if you have the Stallion Torque converter, you will feel it locking up and unlocking at various speeds since it locks-up so hard.(harder than the stock unit) That's what it's supposed to do.

[cyclone03]

Well I've noticed the AC clutch cycle and the trans go to a FREEWHEEL type feeling too.

The harness and shift cable adjustment are good places to look too...