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Old 06-17-2017, 02:35 PM   #1
haxxx
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Default ZF shifting woes

96 LT4

I didn't want to write this thread as I though I solved this last year by replacing the clutch master and slave with Dorman CM39763/CS360017 respectively. Originally did it because 1st and 3rd shifts weren't great. Felt like I had to force it in and I would have have to let off the clutch and try again. I have installed the new parts and reverse bled the system. I didn't drive it much last year. Now I've noticed nothing has really changed and I have reverse bled twice to ensure no air is in the system. Driving this spring I've put less than 1,000 miles on it. The bottom of the new master cylinder reservoir is black. Doesn't seem right, but I'm not sure where to go from here and I don't want ruin this transmission.
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Old 06-17-2017, 04:47 PM   #2
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The bottom of the new master cylinder reservoir is black. Doesn't seem right
It's not right. In my experience, that is deteriorating seals in the master and/or slave.

I'd replace them both with a different brand.

If the clutch isn't coming off, it will cause all kinds of weirdness. It can even scratch in a gear or two and you'd swear it was synchros, but fix the clutch and the problem disappears.

Always fix any issue with the clutch before diagnosing the trans. It has to come all the way off.
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Old 06-18-2017, 12:18 AM   #3
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Check your Pivot ball and fork...
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Old 06-18-2017, 10:46 AM   #4
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It's not right. In my experience, that is deteriorating seals in the master and/or slave.

I'd replace them both with a different brand.
or try DOT 5 silicon based brake fluid in the clutch system
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Old 06-18-2017, 01:54 PM   #5
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It's not right. In my experience, that is deteriorating seals in the master and/or slave.

I'd replace them both with a different brand.

If the clutch isn't coming off, it will cause all kinds of weirdness. It can even scratch in a gear or two and you'd swear it was synchros, but fix the clutch and the problem disappears.

Always fix any issue with the clutch before diagnosing the trans. It has to come all the way off.
I didn't think it was right on brand new parts. The Dorman parts seem to be the concensus replacement parts. Any recommendations on another brand? I'd like to try to confirm that they are defective because they are brand new. This is why I'm hesitant to throw more parts at it.

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Check your Pivot ball and fork...
Any instructions on how to do so?

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or try DOT 5 silicon based brake fluid in the clutch system
I'm using the Valvoline synthetic. IIRC it's not supposed to degrade the seals.
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Old 06-18-2017, 07:48 PM   #6
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He's right. It could be the fluid also.

I would call anything that generated debris like that "bad" You shouldn't have that kind of degradation so quickly. It's a closed system and quite small, so what you're seeing must be the seals in the master or slave, or both, coming apart.

I guess heat could be a contributing factor also. Depending on your exhaust it might be something worth looking at.

I've used the dorman stuff also and it worked fine for me. But, something is obviously coming apart in there. Bad part? Bad batch of fluid? Excessive heat? That debris came from somewhere and now it isn't wanting to pressurize, so...

Last edited by confab; 06-18-2017 at 07:49 PM.
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Old 06-18-2017, 10:50 PM   #7
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or try DOT 5 silicon based brake fluid in the clutch system
GM recommends DOT 3 brake fluid, now that the old hydraulic fluid is no longer available.
That said, I flushed, bled, and refilled the clutch system with Valvoline Synpower brake fluid several years ago in mine and haven't experienced any problems.

Last edited by rocco16; 06-18-2017 at 10:54 PM.
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Old 06-19-2017, 07:26 AM   #8
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You have to pull the trans, trust me there is a good chance its the issue. I had the same issue and it would be really bad one day and no so bad the next. I had one of my Zs on the lift so I paid my friend to change the clutch after swapping multiple lines, slaves, etc. I had bought I new ball and fork and asked him to check it. picked up the car and same issue, he said ball and fork were fine and he didn't change it

One year later pulled it after having the same problems....pivot and fork were worn out and grooved; it doesn't take much

swapped them and no more issues
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Old 06-19-2017, 08:48 AM   #9
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You have to pull the trans, trust me there is a good chance its the issue. I had the same issue and it would be really bad one day and no so bad the next. I had one of my Zs on the lift so I paid my friend to change the clutch after swapping multiple lines, slaves, etc. I had bought I new ball and fork and asked him to check it. picked up the car and same issue, he said ball and fork were fine and he didn't change it

One year later pulled it after having the same problems....pivot and fork were worn out and grooved; it doesn't take much

swapped them and no more issues
Thanks for the reply. I suspected the trans would have to be pulled. I'm planning on doing the clutch/flywheel soon anyway because the dual mass flywheel sounds like it's on it's way out. I figure what's a pivot ball and fork on top of the clutch and flywheel. Can you point me to where you purchased your pivot ball and fork?
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Old 06-19-2017, 10:23 AM   #10
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Old 06-19-2017, 11:47 AM   #11
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You mentioned the bottom of the new master cylinder is black...

A couple years ago, I had my OEM clutch cylinders refurbished by Jim Jandik at power torque, did a great job. Put them back on and filled/bled with Valvoline synthetic DOT4 brake fluid which is what many experts recommend for these systems. After about 1 year I noticed some dark color at the bottom of the master reservoir. It wasn't too bad but enough to notice the fluid is no longer clear, and thought it was strange to see this with a completely rebuilt hydraulic system. Bled everything, brand new fluid (same type), and now everything is staying perfectly clear over a year later. So I'm thinking the initial discoloration of the fluid was just a bit of wearing-in of the new seals on the reconditioned cylinders. Hope this helps you. I drive the car about 5000 miles per year and the clutch gets bled with fresh fluid every 2 years.

EDIT: last time I talked with Jim Jandik, he indicated he has refurbished OEM cylinders lying on his shelf waiting for a new home. I'm not sure of his prices but if you are looking to replace your Dorman units, I'd suggest giving Jim a call.

Last edited by DGXR; 06-19-2017 at 11:55 AM.
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Old 06-19-2017, 12:09 PM   #12
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Believe it or not that's clutch dust that enters the system....if you look up a guy named Ranger...known for C6 drag racing he covers it in his write up and website
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Old 06-19-2017, 01:03 PM   #13
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I'm getting a 'page not found' error on that link.
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Old 06-19-2017, 01:10 PM   #14
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I'm getting a 'page not found' error on that link.
Try calling Jim at (641) 342-7446.
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Old 06-20-2017, 02:45 PM   #15
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Jim's website is down/no longer in use, he'll respond to phone but as of ~2 months ago he didn't have any cylinders.

I think the black at the bottom is normal, at least according to Jim and some online reading. Does your clutch lose pressure if you sit and keep it depressed? If so there's the issue, either master or slave.

If not then I would start to worry about the fork
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Old 06-20-2017, 03:07 PM   #16
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Jim's website is down/no longer in use, he'll respond to phone but as of ~2 months ago he didn't have any cylinders.

I think the black at the bottom is normal, at least according to Jim and some online reading. Does your clutch lose pressure if you sit and keep it depressed? If so there's the issue, either master or slave.

If not then I would start to worry about the fork
Clutch feels very good. I'm feeling confident that it's a fork issue the more I research. I know I have to go in there soon for what I believe is the dual mass flywheel issue. If I drive it for a long period of time in hot weather the transmission starts to sound like a dryer with rocks in it. That problem started before the shifting issue. I probably can't kick the can down the road any longer.

Time to bite the bullet and start getting all the parts together. Thanks everyone for the help. I will post an update once the transmission is out. Probably won't be for a while because I'm getting married in less than two weeks
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Old 06-20-2017, 03:10 PM   #17
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Congrats on getting married! Come back and update the thread with whatever you find, I'm curious
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Old 06-20-2017, 04:27 PM   #18
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Believe it or not that's clutch dust that enters the system....if you look up a guy named Ranger...known for C6 drag racing he covers it in his write up and website
Clutch dust is going out of the bellhousing, through the seals on the slave cylinder, through all the tubing, through the master cylinder, and into the reservoir?

I don't buy it.
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Old 06-23-2017, 04:24 PM   #19
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I pulled the slave out and felt the fork to do the best I could to make sure it wasn't a couple miles away from leaving me stranded. Ended up finding this on the clutch hose:



Moving the slave cylinder was the final straw and it started leaking. Not sure if this was my problem all along. I'm thinking it would either work, or blow and be catastrophic failure but who knows.

These aren't easy to find and they don't give them away. Corvette central had like 7-10 days to process. Called zip and they had one they could send out Friday. Unfortunately overnight shipping still only gets it here Monday but it's the best I can do. They were great over the phone. We want it fixed for next Friday so we can use it to do some wedding pictures. Should be fun, going to be a long week
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Old 06-23-2017, 04:37 PM   #20
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well at least it was a simple solution, not an easy fix but definitely could be worse lol
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