: Transmission Noise



Trailmug
12-04-05, 02:57 AM
My 4T80-E has had a transmission pump noise since I picked it up.. I did not notice the noise during the test drive, because the car has to be fully warmed up for some time befoer it starts to appear. The nosie is a "scratch-scratch-scratch" sound (somewhere a bit less than four times per second at 700RPM idle), with sort of a rolling quality. The noise is coming from the side cover area of the tranny. I took the car to a trans shop, who quoted $1200 for a "tear down and rebuild," although the noise is very obviously coming from the transmission side cover. The nosie happens both moving and still, in all gear selector positions, when warm.

When I got the car home, I decided to check the trans fluid level (again) for giggles. I noticed that the level was above the top full operating range, so I turkey bastered some fluid out. After about a dozen turkey baster attempts, the fluid was still at the same level. I decided to start a siphon with the engine running and monitor the level. I pulled nearly a gallon (three quarts and some change) of extra fluid out of the transmission before the level dropped to an acceptable level. Normal trans add-to-full only takes a quart, so I realize this is an absurd amount of extra fluid. I underestimated what "sligtly overfull" on the dipstick could really mean when I first checked out the car. I've monitored the level since then, and it's been spot-on.

The 4T80-E has a dry-sump system (the fluid is stored in the side cover, not the pan, during operation), and a scavenge pump is responsible for emptying the sump, and keeping the side cover full. I understand why I was able to remove loads of fluid without appreciably affecting the dipstick level -- the sump wasn't dry, and the scavenge pump refilled the side cover as I was emptying it. My question is -- is it reasonable to assume that the scavenge pump was damaged due to overstressing (turning a solid stream of fluid from the pan all the time instead of the "burbles" that it is designed for), and might be the cause for the noise? I imagine a full column of fluid place a gar greater load on the pump than small gulps returning from the pan would. I've searched everywhere, and can't seem to find any information on the effects of overfilling a dry dump transmission on the pump system.

Any information is greatly appreciated -- also, if this should be in a different forum, please let me know!

Thanks

Trailmug
12-04-05, 03:07 AM
Correction: I meant to say a pint typically goes add-to-full.