1990 L98 Vert ZF6 165k miles

I've been having a tough time shifting lately. The trans will often not want to go into gear and when it does, it is very rough. When sitting at a light (pedal pressed) and shifting into first, the car will roll forward as it engages the gear. If the car is slowly rolling backwards and I shift into gear (pedal pressed) the car will buck a little

To me, this sounds like a hydraulic problem. Any other ideas?

If that diagnosis makes sense, where can I find a new/rebuilt slave? The masters seem to be easy to find but none of the local parts guys can order the slave.

Thanks for the help!

Is the clutch pedal soft and grabbing low? If so , the slave master cylinder is up on the firewall. Is it empty? Usually caused by slave leaks. I went with a 91 version of the slave because there are no 90's to be found. The bleeder is in a different position. That's about it. I had mine done at the dealer becase I'm not to good at twisting into tight spots. They replaced the slave, master cylinder and hydraulic line. Cost me $$$. I'm just a layman so take what i say with a grain of salt.

Sounds like it could be. Check out this for some more info:

http://zfdoc.com/faq.htm

CentralCoaster will chime in, he knows a lot about the ZF.

Matthew

With the car on a flat surface, put it in first. If the car moves, yes, it's either the slave or master.
You should be able to sit still with the clutch in, normally you check this by holding the clutch in for about 30 seconds, no movement?, the hydraulics are working.

CC knows a boatload about the slave cyls. There are a bunch of posts here.

Quote:

Clutch engagement feels about right, yet. If it is lower , it is not by much.

I checked the fluid level at the MC and it is a little low but not out yet. The fluid also looks terrible - very black probably OE. I should have flushed that out some time ago I guess.

I thought the 91+ changed the hyd. line too and they wouldn't work. If they do work than I should be able to find one of those w/o to much difficulty.

Matatk:
Funny, I looked over that FAQ a few days ago and completely missed Q 4 which pretty much describes my problem - except I do not have clutch shudder.

Quote:

I was in a parking lot waiting for traffic to clear. I had the clutch engaged and tranny in neutral for a bit and when the traffic cleared I put her in first and the car jerked forward with the pedal still to the floor.

For the record, this transmission has never shifted particularly smoothly. I've always had somewhat notchy shifts and a little difficulty with 3rd gear (it feels "funny" too).

I wonder if the clutch is right for the car.

Sounds like the hydraulics can't do the job.

FYI: The current clutch/PP/TOB have about 50k on 'em. I bought the kit from Carolina Clutch I think. Standard Luk OE replacement. AFAIK nothing is different than stock.

The increased notchy-ness is new as is the jerking trying to get it into gear.

You definitely have a clutch issue. If you've drive it like that long enough, you'll have a trans issue too.

If the clutch doesn't fully disengage, the synchros wear much faster. They're trying to slow the gears down, but the clutch is still putting some power to them. As the synchros thin out, you have to shift more carefully to get it into gear. You'll know what harm you did after you get the hydraulics up to snuff.

I believe the 89-90 slave cylinder is discontinued. A 91-96 cylinder should work though, and fit your stock clutch hose. Basically just the bleeder changed locations. The factory making them was assembling all of them wrong, and I guess at some point they shut them down and fixed the issue, but the 89-90 slave hasn't been available since.

Also, the last one I purchased was a Raybestos (AC-Delco) unit, which is the DOM steel unit. It had an aluminum piston. This is bad, because if moisture gets in there, the aluminum piston will corroded the hell out of the steel wall. Mine was pitted so badly from corrosion after 1 year, that it wouldn't hold any pressure at all after about halfway through the pedal.

There's also a Chinese unit that is cast iron with a steel piston. I'm using this now, and so far so good. It's labelled as a PBR unit, but PBR only makes the box. I don't know if there's any other sources for a cast unit.

Regardless of what you buy, I'd suggest disassembling it and inspecting it. I opened a new raybestos clutch master that had a 1/4" long steel sliver stuck across the rubber seal.

A leaky master will usually weep fluid into the footwell, pull the carpet back and look for damp carpet insulation at the very top.


A working system should have about 5/8" of travel at the clutch slave pushrod. Tolerances in the ZF clutch setup are tight, so you can't afford to have any air in the system. Plus it's kind of a bitch to bleed properly.

I sent my last slave cylinder to Bill B. at ZFDoc, and he took it apart and blessed, maybe he still does this. It was the second one in 18 months, the first was assembled wrong.
You don't want to drive the car untill this is fixed, make sure you use the GM fluid in the master and it would not be a bad idea to change the trans fluid as well.

Good luck,

Randy

Thanks for all the advice everybody!!

Next question, are there other brands that use the cast piece? Locally I have BrakeBest (Wagner?) and Perfection (AdvanceAuto). I noticed thepartslady on ebay supposedly has the cast version for $70 but I was hoping to get someone local if possible.

Thanks!

And, I'll crawl under the dash in the AM to check if the MC is leaking.

Mine is a Napa brand. Cast one piece body

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That's the one!

Sweet! Thanks!

I ordered a master and slave from the local Napa. Unfortunately they are coming from Texas so they probably won't be in until early next week.

I can't tell if the MC is leaking but with the mileage and the terrible looking fluid I'm guessing it's in my best interest to replace them both now rather than having to do this again in a year.

Ordinarily, not a bad idea But in this case, the QC just gets worse and worst as time goes on.

If any of those older cylinders still check out, you'll probably get more life out of them then a replacement. You can pull them apart and inspect internally.

When mine acts like that the clutch disk is worn out.

Do make note that the housing mounting surface is thicker. I had to roll the nuts out to compensate for that. Before you attempt to attach the slave, work on the nuts, get them loose without buggering them up.

I forget what I did for that. Either the nuts fit, or I removed the studs and put bolts in.

Quote: Crap, did I say nuts ? Its the bolts in the tranny that need loosening, man I'm going nuts.

You mean bellhousing studs?

Quote:
YES That's it !! Thanks.

Well, I got the new parts in from Napa. The slave was the cast piece so all is well in that department. When i pulled off the slave, there was a nice little puddle of brake fluid in the boot - I guess that solves that mystery

New problem...
While I was trying to remove the line from the slave, the fitting twisted off. I hate corrosion.

There is still plenty of good hard line to splice into but does anyone know the fitting specs? I've tried AutoZone and O'reilly today and they do not have any brake line with the right fittings.

I'll try to hit Napa and Bumper/Bumper tomorrow but if anyone has any bright ideas, I could sure use 'em

Thanks!

The bleeder has M12-1.0 thread. (12mm)

I would expect the line uses the same threads. I'm not sure what the flared end would be called though. It just has to match whatever angle the port is cut at.

No luck. Napa, Bumper2Bumper and the local dealer were all stumped.

GM has been using these kinds of fittings (metric ISO/bubble flare) since the early 80's and no one carries the friggin fittings or lines. This pisses me off. I went thru the same hassle when I lost a brake line on my 86 Firebird.

Unless anyone has a better (cheaper) idea, it looks like I'll have to order the whole line for $100 instead of $10 worth of parts.

Thanks all!

I might be able to reuse the existing fittings and get some tubing and couplers from McMaster-Carr for ~$20. Hmm...

My only concern is that when you start cutting off tubing to replace the fitting you might not be able to match it up to the slave. It is always best to replace the line with the slave (I know expense is probably a factor). It will sure make the job a whole easier. I would also add, it was so much easier to rethread the line onto the slave with it mounted, it took me two tries to get it started, opposed to 45 minutes and giving up with the slave hanging semi-freely.

check Russel or Earls hoses.

I bought a braided clutch line from corvettesalvage. I've heard that the zr1 lines were braided and the base model were rubber, but I really don't know.

I'd also be surprised if a local hose shop couldn't fix it for you.

I lookes the hose or tubing up in my Corvette America cat., Gawd $110 to $140 - ridiculous.

One way you can go is to get a pre assembled clutch line.
Example: a 3ft, teflon, steel braided , hi press hose with 2, 3AN fittings costs $20.00. $27 for 4 AN.

Two adapter fittings will run $20 to $40 depending on what's in the slave.

$40 to $60 for the setup with a braided steel line.

Maybe some fitting ID here: http://www.fedhillusa.com/?page=tech2

Preassembled lines: www.pegasusautoracing.com