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'93 Vette ZF Transmission removal and Replacement/Rebuild
Hi all, I have a '93 vette that was having some problems going into gear. I am new to working on this car and have ran into some problems. When I bought the car about a year ago it has always had issues shifting into specifically first gear. Then as i drove it more recently it seemed to become worse. In an effort to fix this issue I replaced the clutch hydraulics with OEM ones (I know many people do not have luck with these) but to my demise those didn't seem to fix the issue. So then the next step was to remove the transmission to see if either the clutch or the transmission itself was the issue. So last weekend I spent my time tearing apart the car and managed to get the transmission out as well as the clutch. I bought a replacement clutch kit (LuK 04-113) off of summit racing. From what I could tell the old clutch was still in decent shape, while it still needed replaced. Either way I believe the transmission needed a rebuild. I believe the issue is the synchronizers inside the transmission are the issue because first gear is really hard to get into and will sometimes grind. The whole transmission seems as though it is extremely notchy.
My question to you guys is
1. What is the best way to rebuild a zf s6-40 transmission and roughly how much will it cost and will that fix the notchy shifting issue (I have about $1500 for this project)
2. Is there another, less expensive manual transmission that I can swap it out with that will work for street driving
3. What exact solid flywheel should i get, or should i attempt to get my original dual mass flywheel resurfaced (i know this is normally impossible)
I am new to all of this and am having a really hard time finding parts and would greatly appreciate any helpful knowledge from you wizards.
93vetteWes - First off - Welcome to the Forum !!!
Second - give yourself a pat on the back for tackling a trans removal as one of your first Corvette C4 Projects - it's NOT an easy job and the ZF Box is heavy.
So - let's get down to business.... If you do a little searching on the Forum - you're going to find out that the ZF is a tough gearbox. Unfortunately - it's not all that common,and it's not easy to rebuild. The place to talk to is ZFDoc, but a full rebuild is going to cost you a LOT more than you have budgeted (like $4K for the rebuild +++). People have swapped in other gearboxes, but it's far from a Bolt in.
Now - as for the clutch replacement. As far as your flywheel goes - you "MAY" be able to salvage your OEM Dual Mass flywheel. I've had pretty good luck running a Scotch Brite "Roll Loc" disc on a right angle die grinder on the surfaces of the flywheel. If you don't see cracks, and the flywheel is not in bad shape - that may be a realistic option.
If the flywheel is in bad shape - New Dual Mass Flywheels are no longer available, so some people will buy a LT1 Camaro flywheel, and have a shop machine it to match the dimensional specs of the OEM Dual Mass flywheel (I forget how much needs to be taken off the face - I think it's like 0.070" - but please don't go by that). You could buy an aluminum flywheel - but they are not great for street use.
BUT ... You didn't say how many miles were on your C4 - but it's not all that common for the ZF gearbox to need a rebuild unless the previous owner abused it, Before you spend money on that (gearbox rebuild) - I'd do two things:
1) Give Bill @ ZF Doc a call and talk to him about how your trans was behaving.
2) Drain the trans fluid and look for signs that there is metal (synchro ring particles) in the lube.... If the lube looks like it's been there for a while - and you don't see evidence of metal - It may still be the hydraulics. (Your conversation with Bill will probably involve a discussion about the hydraulics...)
I know you say that you bought a Clutch kit - and that normally includes a new disc, a new pressure plate and a new throwout bearing. Consider re-using your OEM pressure plate. If you do some searching on the forum, you're gonna hear that pretty most all replacement clutch parts are made in China. Some people have had problems with the new pressure plates. If your pressure plate is in good shape - at least consider reusing it..... *You can clean it up the same way I suggested for the Dual Mass Flywheel).
Holy cow to be honest I did not expect a response so quickly thank you! My vette has 94k miles and it sat for 7 years before I had gotten my hands on it. I realize now that changing the trans fluid should have been the first thing that i did. I drained the fluid before I removed the trans and hadn't noticed any metal pieces so that's good. (I stripped the drain plug when i first did it). Here is my plan, ill contact Bill like you said and see what he has to say. I tried to attach some pictures of the flywheel and old clutch system but it wouldnt work for some reason. As far as the new clutch kit goes, would you recommend using the old pressure plate with the new disk? I'm not even sure if that would work, but I'm not experienced in that area. As far as Bill goes, ill call tomorrow if he is available. I agree that it could still be the hydraulics I had a really hard time bleeding them, the new Clutch Master Cylinder(upper) (Chinese made) one had a thicker base that attached to the firewall, so i stuck in some spacers in the bolts to move the plunger out to let fluid down the lines. That's a different story, but nonetheless, I experienced the same issues with the old hydraulics the same with the new one. My thought process originally was that the clutch was not fully disengaging which in turn would make changing gears extremely difficult, similar to what I am experiencing.
I figured that if i give everyone more information on my build then the issue can be narrowed down more specifically
Also given that I will have this car for a lot longer I absolutely am going to utilize this forum more....this is great!
Something that I noticed in these pictures, is it normal for there to have these marks on the flywheel and pressure plate surfaces, it looks almost as if it is discolored due to heat, or some oil got in Disk (old) Pressure Plate (old( Flywheel (old)
I agree with everything Purple92 said up there. He's got you on the right track. You may think the clutch hydraulics are disengaging completely, but if there's any air at all in the system it will degrade the performance of the hydraulics. The clutch won't be completely disengaging if that's the case.
Your flywheel is probably still good if its got 94K miles on it. But the rotational play between the friction surface and the larger flywheel base piece should be measured. Total rotational movement (both directions) between the two pieces is supposed to be less than 1 5/8" or something like that - someone here knows the GM spec better than I do.
Your clutch pressure plate basket (the casting that surrounds the springs and pressure plate) will have a stamped logo on it. If yours says "Valeo" on it, then it's an original OEM part and it will be better quality than any new replacement LuK 04-113 kit made in recent years. Now those are all made in China and they have a casting number of "C70043" molded into the casting. Many of those have real quality issues as mentioned above; uneven machining in the pedestal feet (where the bolts go) and porous metal with air pockets, you name it. They can cause issues even when brand new.
Okay, while i have everything out of the car I will bleed the system again and make sure there is no air in the lines. It is entirely possible this is the case, but i wont get my hopes up yet. Still though, I would like to put in a new clutch regardless, just to know it is fresh. Purple92 mentioned using a scotchbrite Roll loc, wouldn't that create sandpaper marks on the flywheel? Not only that, but wouldn't some surfaces be raised more than the other if they are sanded down all evenly? Maybe I'm looking at the wrong product, but to me they look like sandpaper. Also when looking at the flywheel there is a notch were the edge of the disc sat from wear. When putting in a new disk don't you want the whole flywheel to be flat and isn't that the purpose of resurfacing?
-Many thanks
So you mentioned first grinds or is tough to get into. For the other gears does the clutch disengage right when you push the pedal in? I have a 92 and this clutch disengages right as you push the clutch pedal in. On all my other cars the clutch usually disengages a little deeper into pushing the pedal. I have a 93 Jeep that used disengage right about the middle of the pedal. The hydraulics went bad and I replaced them. Now no matter what I do and how many times I have replaced them it disengages at the last bit of pushing the pedal all the way in. It is tough getting into first in my Jeep. Where your clutch disengages in the pedal should tell you if it is the hydraulics or the transmission itself. My clutch cylinder in my vette also went bad. I replaced it and have the exact same pedal feel. disengages right as you push the pedal in.
I was reading on zf doc's site the other day, about clutch hydraulics bleeding. He said to put Teflon tape on the threads of the slave bleeder. Has anyone had to do that? Hoping it'll help out OP if the issue is air in the system.
I love my C4's, but the lack of support on the zf6 is worrisome.
Also, I might be having to do the same as you in the future. I've heard good things about the RAM clutch kit.
Holy cow to be honest I did not expect a response so quickly thank you! My vette has 94k miles and it sat for 7 years before I had gotten my hands on it. I realize now that changing the trans fluid should have been the first thing that i did. I drained the fluid before I removed the trans and hadn't noticed any metal pieces so that's good. (I stripped the drain plug when i first did it). Here is my plan, ill contact Bill like you said and see what he has to say. I tried to attach some pictures of the flywheel and old clutch system but it wouldnt work for some reason. As far as the new clutch kit goes, would you recommend using the old pressure plate with the new disk? I'm not even sure if that would work, but I'm not experienced in that area. As far as Bill goes, ill call tomorrow if he is available. I agree that it could still be the hydraulics I had a really hard time bleeding them, the new Clutch Master Cylinder(upper) (Chinese made) one had a thicker base that attached to the firewall, so i stuck in some spacers in the bolts to move the plunger out to let fluid down the lines. That's a different story, but nonetheless, I experienced the same issues with the old hydraulics the same with the new one. My thought process originally was that the clutch was not fully disengaging which in turn would make changing gears extremely difficult, similar to what I am experiencing.
I figured that if i give everyone more information on my build then the issue can be narrowed down more specifically
Also given that I will have this car for a lot longer I absolutely am going to utilize this forum more....this is great!
Something that I noticed in these pictures, is it normal for there to have these marks on the flywheel and pressure plate surfaces, it looks almost as if it is discolored due to heat, or some oil got in Disk (old) Pressure Plate (old( Flywheel (old)
Your flywheel and pressure plate surfaces look pretty decent looking at the pictures. You should check the flywheel movement per the shop manual. If it is good I would just clean up the surfaces a bit and run a new disk.
If you have to convert to a single mass flywheel then leave it all and go with the RAM conversion kit, it turns out to be slightly cheaper and you leave that hydraulic slave in the trash where it belongs. It also converts the clutch from a Pull type clutch to a normal Push type clutch.
I have done both jobs and the RAM has bee working for me.
Talk to Bill about your transmission issues first, also install his shim to make the transmission quieter if you do go to the single mass flywheel. It will keep the noise down in the transmission if you give up the dual mass flywheel.
Good luck ?
OP - it's a shame you didn't come here 1st before the removal. With your mileage and assuming the fluid hadn't ever or maybe seldom had been replaced maybe your issue is essentially the lubricant used. You don't mention a change, have you? Most everyone will agree that the lubricant specified in the ZF-Doc presentation isn't the most desirable. I agree that after a measure of the DM a disc with a scuff/clean of the P/plate and DM might be a viable and prefered approach.
I realize the shim from ZF-Doc gets much conversation but I always thought it was intentioned for the US builds and not actually required for 'original builds'.
Okay, while i have everything out of the car I will bleed the system again and make sure there is no air in the lines. It is entirely possible this is the case, but i wont get my hopes up yet. Still though, I would like to put in a new clutch regardless, just to know it is fresh. Purple92 mentioned using a scotchbrite Roll loc, wouldn't that create sandpaper marks on the flywheel? Not only that, but wouldn't some surfaces be raised more than the other if they are sanded down all evenly? Maybe I'm looking at the wrong product, but to me they look like sandpaper. Also when looking at the flywheel there is a notch were the edge of the disc sat from wear. When putting in a new disk don't you want the whole flywheel to be flat and isn't that the purpose of resurfacing?
-Many thanks
If you’re going to use the new pressure plate I would send it to the ZFDoc to check it. He can machine it to make it true if it needs it. Most China made ones do.
I hope I can try to answer everyone's questions from earlier.
Topfuel67- From what I can remember the clutch definitely did not disengage at the top of the pedal. It felt identical to what you are describing, as though the clutch disengages at the very bottom of the pedal. From my knowledge that would be a hydraulic issue, but i bled the system a million times and still didn't fix it. From there I continued to think it was wear on the clutch disk itself, as I did not know how many miles were on the clutch. And that takes us to today
1993C4LT1- I bled the system this morning, again. Just to be absolutely positive there is no air, and let me tell you it was much easier to do with the exhaust off. (don't take the exhaust off just to blead the system its not worth it, but it was just convenient for me because it was already apart). Anyways the slave cylinder has no air, but i will need to double check the master cylinder. Air often times gets stuck in the forward corner of it and needs to be shaken loose. Should I run into the bleeder valve or the hose leaking I will try and do the Teflon tape method. Once I eventually get the clutch back together I will reattach the slave cylinder and check for movement.
WVZR-1 - Yes that is correct from my ownership there has not been a change in the transmission fluid. And yes I wish I had gone to this forum before taking it apart as well, but that's in the past.
I contacted Bill and left a message at ZFDOC, and hope to hear from him soon. While I have the LuK clutch disk, I believe my next step over this next week is to clean up the old pressure plate and flywheel, throw in the LuK DISK and see how that helps with the shifting. I will watch this forum very carefully in case I am doing anything wrong. Aside from that I will absolutely try and give detail descriptions for 1993C4LT1 just in case you, or anyone, run into having to replace the clutch and remove the trans.
As far as the trans fluid goes I am going to try and get the recommended BMW fluid (BMW SAE 10W-60) for the ZF transmission, as well as a new drain plug for ZF. I think cleaning off the pressure plate and fly wheel and such will work well with break cleaner and a dish cleaning sponge (abrasive side). That will help any grease get removed from those items.
I also should mention that I do not have a c4 corvette 1993 Shop Manual, but will absolutely look into getting one if anyone has any they don't use. I found that the Hanes Manual for corvettes just doesn't go into as much detail as needed for these projects
As far as the trans fluid goes I am going to try and get the recommended BMW fluid (BMW SAE 10W-60) for the ZF transmission, as well as a new drain plug for ZF. I think cleaning off the pressure plate and fly wheel and such will work well with break cleaner and a dish cleaning sponge (abrasive side). That will help any grease get removed from those items.
I also should mention that I do not have a c4 corvette 1993 Shop Manual, but will absolutely look into getting one if anyone has any they don't use. I found that the Hanes Manual for corvettes just doesn't go into as much detail as needed for these projects
Thanks
NO to this fluid!!! The fill/drain plug is a very inexpensive buy from a VW dealer. Buy new!
I would bet your issue is in the hydraulics. Many of these replacement parts aren't good. That's the issue I have with my Jeep. The transmission is in perfect condition. I never had a problem with any gear. Hydraulics went bad and I have replaced the slave 2x and the master 3x. On the jeep you have to pull the trans to replace the slave. Anyways, on the vette I think your pedal should be like mine where it is at the top. Try different brands on the master and slave cyl.
Your flywheel and pressure plate surfaces look pretty decent looking at the pictures. You should check the flywheel movement per the shop manual. If it is good I would just clean up the surfaces a bit and run a new disk.
If you have to convert to a single mass flywheel then leave it all and go with the RAM conversion kit, it turns out to be slightly cheaper and you leave that hydraulic slave in the trash where it belongs. It also converts the clutch from a Pull type clutch to a normal Push type clutch.
I have done both jobs and the RAM has bee working for me.
Talk to Bill about your transmission issues first, also install his shim to make the transmission quieter if you do go to the single mass flywheel. It will keep the noise down in the transmission if you give up the dual mass flywheel.
Good luck ?
How is the clutch pedal effort with the RAM kit compared to stock?
Yes I would tend to lean towards your idea topfuel67, but im not going to dismiss anything yet until the issue is fully resolved. Later this week ill start piecing everything back together. I ordered a drain plug from a VW dealer and should be here on feb. 11th. Does anyone have a diagram of the wiring for the trans?? IE the ground wires and the brackets attaching to the trans.
Does the Maintenance manual go over that?
Also, I broke some studs for the exhaust, and they need replaced. How do i go about doing that and how can i find replacements. I went to a Chevy dealer for a diagram, but they were not able to help me fully.
Is there anything wrong with using the old pressure plate with a new disk?
I've never understood what is wrong with that. Sure, it's a gamble, especially "since you're in there"...but when parts are hard to get...and the old one was working fine.
IDK. In my whole career I've never understood if or why reusing FW and clutch on a good working clutch with a worn disk is "unacceptable". Less than idea? Sure. But like I said, when decent parts are hard to come by.....I'd consider it, for sure.
'93 should use 6 X M10 studs. NAPA or any local auto parts store should help. 14057005 would have been original number I believe. Those would be manifolds to converter but you likely destroyed some hanger hardware for the converters also. A stud used there for a single location maybe?
There's not a VW or maybe Audi dealer closer than 8 days? You're located where?
Honestly for some reason it didn't occur to me that I could have gone to a VW dealer. Nonetheless I don't plan on having the car back together super fast so didn't mind some shipping. I'm in western Pennsylvania.
02-04-2022, 05:57 PM
'93 Vette ZF Transmission removal and Replacement/Rebuild
