4r55 rebuilt... question on TC operation

[budwich]

Just got my 96 back from a transmission rebuild. Of course, things are better as it lost its clutch plates (I had no movement). Anyways, I have a question about the torque converter lock up.... seems to be different than before the trans failure. Basically, going down the highway at "normal speed"... 80-90 km/hr (50mphish). No acceleration, steady speed, the TC is locked and everything is good. If I release pressure on the throttle a bit, no noticable drop in rpms, then apply pressure on the throttle again to maintain speed... basically like a "semi coast"... kind of like you are getting to close to someone type of thing.... the TC lockup drops out and then again during the reapply of pressure, rpms "flare" a bit and then the TC locks back up. I don't seem to think it was working like that before the failure. The question is this correct operation???? I know it is supposed to drop if the brake is applied but I didn't think it should drop so quickly with a throttle pedal "reduction".

When I first got the truck back, there was a problem whereby lockup wouldn't hold as I was going down the road, its would "hunt"... they replaced a solenoid and that problem has disappeared.

Thanks for any comments.

 

[BrooklynBay]

It might be one of several things. The valve body might have leaking end plugs causing a small amount of hydraulic leakage. It will try to engage gears or even lock, but there might be a small amount of seepage causing the EPC to hunt, and fluctuate to maintain the proper amount of pressure. Have the shop connect a scanner to test the gears in all of the ranges, and connect a pressure gauge to the EPC port to monitor if there is any fluctuation (high, then low pressure, then high again) in each gear range. Another possibility could be that they replaced the torque converter with another one with a different stall speed. The other possibility could be that they rebuilt the transmission, but didn't do much to the valve body as far as a leak test, shift kit or replace the solenoids. You said that they replaced a solenoid after the rebuild, and it helped for a while. They wouldn't have had to replace a solenoid after the rebuild if they would have replaced it during the rebuild.

 

[budwich]

thanks.... the replaced solenoid... they said was the wrong one.... but I can't say if they actually replaced all units.... but the "work list" doesn't specifically identify much outside of "clutches" and "work bench".... I suspect your right though about the solenoids.... :-(