Okay had my 700r4 rebuilt with a corvette servo and boost valve..its clunking from 3-2 when in drive...Ive read a lot of threads about the corvette servo being a possible culprit but nothing definite and no talk of how to repair or modify it that I could find any info about this problem and a possible solution would be greatly appreciated..thanks.

 

I built mine from the ground up and used the sonnax super hold servo witch is alot stouter that the vette one even and a vette 3-4 servo and mine kinda does it a little too. Nothing bad enough to really bother me or anything, just subscribing to see what anyone says. I work at a tranny shop, if you really need to know im sure my boss knows and i can ask him.

 

Well I drove it today in O/D and it doesnt seem to do it...only in drive. Ive heard of probuilt making a modified corv servo to stop this exact problem, so Im tryin to find out if I can do something to mine to stop this from happening in D.

 

and you are talking about lettting off the gas and coasting down and it shifting fro 3 to 2 correct?

 

yep. when Im coming up to a light or stop sign and it shifts from 3rd to 2nd.

 

alright, well just to take a guess, i wanna say its not the servo. My last tranny that was all stock aside from a gear bangin bandm shift kit..did the same thing.

 

anyone know what could be causing this?

 

It is a timing issue within the transmission. The 2-3 & 3-2 shifts are the only ones in a 700R4 that can have this issue. The trans ends up in 2 grears at the same time (for an instant) and locks up.

For the 3-2 shift this causes the driveline to twist up tight. Which when released on 3rd dis-engaing causes a clunk.

As an example for the 1-2 shift the 2/4 band is applied and overruns 1st. Since 1st doesn't needs to be dis-engaged there is no possible binding. The trans just moves from 1 to 2nd as quicky as 2nd can be applied.

On the 3-2 shift, this is not the case. The 3/4 clutch pack is dis-engaging at the same time the 2/4 band is engaging. If the timing isn't dead-on, then the driveline binds up.

This issue can also manifest itself on the 2-3 shift. If the 3/4 clutch pack doesn't engage soon enough there is a flair. If the 3/4 clutch pack engages too soon, there is a clunk.

This timing can be adjusted via the feed & release feed sizes, servo size, accumulator springs, check *****, and so on.

RBob.