Okay guys, I have searched the forum to death & posted this question a couple of times over the last couple of years with no real answer that satisfied me. So here goes again. (I'm sure someone here can help.)

I have a '96 CE LT4 with the ZF6. I’m sure (I think I’m sure; I hope I'm not losing my mind) that when I bought the car with 52k on the clock the transmission shifted as smooth as silk between all gears regardless of driving circumstances. But for last 7K miles or so it has felt notchy to me (64K on clock now). But only when jerking quickly from gear to gear, as if it resists being pulled into any gear quickly.

Any of you with a ZF6, please try this for me: Start your Vette and sit still with the clutch pushed in fully. Shift as quickly as possible from 1st to 2nd, 2nd to 3rd, etc. Does it go as smoothly as silk? Mine does!

Now, start the car rolling; 5mph will do. Shift the same way again. Is it still just as smooth? Mine is not! It is notchy. But, if I shift slowly (normally) from gear to gear it seems to shift okay.

Is this normal functionality for a ZF6? My local dealer says so, but the tech did not seem sure & I'm not sure I trust his judgment. Plus, I could have sworn mine did not behave this way when I first got it, but I do not have a ZF6 Vette nearby to test drive myself to see. I really need to know if a new tranny will fix this, or if I'm imagining a problem that is not there.

I have replaced the following since first seeing this problem: Clutch, fork, throw-out bearing, pressure plate, clutch master cylinder (twice), clutch slave cylinder (twice), and ZF fluid (several times with GM part#).

I'm putting this in General & in Tech/Perf so that I might find a few members to try my little experiment on their cars & give feedback.

Thanks in advance guys!
David

 

Ttt

 

What fluid are you using? How long since it's been changed?

Mine is a little notchy when hot, shifts great when racing or slamming gears, but not so smooth when putzing around.

 

I wonder if the clutch fluid is low.

 

Sounds normal to me. Be sure to perform regular maintenance, like changing the tranny fluid and checking or flushing the clutch fluid.

 

My ZF fluid is new (the specified GM part from dealer). Have changed it a couple of times. Made no difference.

 

I would say rebleed the system using the method Bill @ zfdoc reccomends. check his site out. He says most trannies he sees for repair are all because of faulty hydraulic systems. I know that you have changed almost all the parts, but just maybe there is air in there that needs to get out. good luck!

 

Clutch fluid is not low. Have replaced both slave & master cylinders (for different reasons) and clutch disengages way before gettinf to the floor. I feel certain that, if there is a problem, it is not clutch or fluid.

Any other ideas? I need to understand if other peaoples behave the same way. (????)


David

 

Hey DieL,

When I spoke with Bill on the phone while troubleshooting this problems a couple of years ago, he said the same. I bled the system as he recommends (used the recommended Mighty-Vac to push the fluid up from bottom). I even used teflon tape (per his suggestion) on the threads of the bleeder screw to be sure air wasn't being sucked in.

My clutch (which is pretty new) begins to disengage near the top of the pedal stroke, and I have absolutely no tropuble at all going into 1st or reverse, so I do not believe clutch and/or fluid level is the problem.

Any othe ideas. How, specifically, does yours behave?


David

 

bump

 

Just got an email from zfdoc on ZR1NET & he said it has been discovered that for about 2 years now napa & oem slaves were made wrong with a seal reversed causing very fast failure. That explain something to a lot of us?

 

I also have a 96' CE LT4 with 55k on it. It does have a Hurst shifter in it so it is not as smooth as a stock shifter. It shifts smooth when just sitting there and when rolling @ 5mph it is a little notchy. I drag race mine and at WOT it is smooth as silk(powershifting). Sometimes it hangs up going into 5th when driving around town.

 

I have a 90 zf6 but I'm a C4 rookie, 12/04 I got mine. My observation with mine is it is a bit notchy at low speeds, like around town driving. If I lean on it the smoother the shifting feels. My car has 16,900 on it so I don't know if that has anything to do with what I'm observing??

As a side note I'm having hydrulic trouble now. I'm a member of the "I got sold deffective slaves & masters" Club. Funny thing is that before the new hydraulic parts go south the trans still shifts the same as it did before I had hydrulic trouble...more rpms, the smoother the feel.

Tom

 

David we must be working from the same play book. I changed my slave twice, my master once, my clutch twice, the throwout and pilot bearings, the ball stud and the throwout fork. I was battling a stiff clutch pedal and difficultly shifting into first and third. The fork and ball stud seemed to help. However my clutch master seems to be hanging up on the outer rubber seal. Does anyone know if there is any reason why I couldn't widen the hole in the rubber seal so the push rod doesn't catch on it or should I just replace the master. I think it's an off brand unit.

Jim