1990 clutch replacement
09-22-2016, 11:42 PM
#1
1990 clutch replacement
My clutch is slipping on my 90 6 speed, so it will have to be replaced. I am wondering what all needs to be/should be done while doing this job. Can the stock flywheel just be resurfaced? or will i need a new one? Is there a Pilot bearing or bushing that should be replaced? Throwout bearing? any info is appreciated, Thanks.
09-23-2016, 12:55 AM
#2
Race Director
Going off a 5yr old memory....
89-90 had a different style slave than later years. Even if they are made again (after initially being discontinued), the later style is better for conversion. It requires the connecting hose and slave to be replaced. To do so probably means the clutch master too. (If you want to do it when the trans is pulled and you have more space.)
89-90 DMFW also have a seal that is considered less reliable. When you get in there, you'll probably be able to tell if it's leaking. Does it "rattle/clunk" at idle? If so, how bad?
The problem is the DMFs were discontinued which means finding a good used (preferably) 1991-1996 if possible. Or, convert to a SMFW.
LuK originally made the DMFs and clutch kits so consider that as a replacement. Those kits come with a TO bearing and pilot tool. At the very least, you could just do that and put it back together. At the worst, you may have a slipping clutch due to leaking -- which will dictate what to replace.
The ZF6 weighs more than a typical manual so you might want a helper on hand.
If you haven't taken the shifter **** off your car yet, you'll find that to be total joy too!
Once the C-beam/driveshaft are out, the transmission will come out with the shifter still attached.
Give serious consideration to a short-throw shifter -- if you are going to keep the car. For a modest price, you'll find them your best bang-for-the-buck upgrade to a ZF6 car.
89-90 had a different style slave than later years. Even if they are made again (after initially being discontinued), the later style is better for conversion. It requires the connecting hose and slave to be replaced. To do so probably means the clutch master too. (If you want to do it when the trans is pulled and you have more space.)
89-90 DMFW also have a seal that is considered less reliable. When you get in there, you'll probably be able to tell if it's leaking. Does it "rattle/clunk" at idle? If so, how bad?
The problem is the DMFs were discontinued which means finding a good used (preferably) 1991-1996 if possible. Or, convert to a SMFW.
LuK originally made the DMFs and clutch kits so consider that as a replacement. Those kits come with a TO bearing and pilot tool. At the very least, you could just do that and put it back together. At the worst, you may have a slipping clutch due to leaking -- which will dictate what to replace.
The ZF6 weighs more than a typical manual so you might want a helper on hand.
If you haven't taken the shifter **** off your car yet, you'll find that to be total joy too!
Once the C-beam/driveshaft are out, the transmission will come out with the shifter still attached.
Give serious consideration to a short-throw shifter -- if you are going to keep the car. For a modest price, you'll find them your best bang-for-the-buck upgrade to a ZF6 car.
09-23-2016, 09:50 AM
#3
Le Mans Master
The stock dual mass flywheel is usually not recommended to be resurfaced. Because it is not a solid flywheel the machining can result in a bad surface and/or balance. However Jim at Powertorquesystems.com can resurface them if needed. He is the expert on C4 ZF clutches.
The original LUK dual mass flywheels and Valeo clutches, and INA throwout bearings are no longer made. Again, contact Jim since he used to have some old stock and has some replacements. He also rebuilds the slave cylinders.
There are a number of choices for the flywheel. The stock dual mass is heavy at about 40 lbs. There are aftermarket single mass flywheels made for the conversion to single mass and can be the same weight or about half, or some very light. The choice is up to you. The heavier flywheels will make it easier to launch the car but at the expense of not revving as quickly. If you get a single mass flywheel, the clutch is nearly the same clutch except that the disc needs springs while the one for the dual mass is solid.
The reason for the factory to have a dual mass flywheel is that the transmission is noisy especially at idle. That flywheel helped to minimize the noise. A single mass will make the transmission louder. To me this was not objectionable, but many people do not like it. There is also an improvement that can be made to the ZF transmission to help eliminate the noise. Contact ZFdoc.com about it. Basically he recommends a shimming that will eliminate most of the noise. It can be done fairly easily without taking the whole transmission apart.
I don't know what the best choice for throwout bearing is. Most of the currently available ones are made in China. My personal thought is that the design of the pull style clutch is poor. The throwout bearing is mounted in the clutch pressure plate fingers (turning whenever the motor is running) and also mounted in the clutch fork (stationary at all times). So the result is that the throwout bearing is moving internally whenever the motor is running so it is amazing to me that any survive at all let alone for 100k miles or more. My point in that thought is to suggest getting the best one you can. If any of the INA originals can be found they are worth it.
If you are getting aftermarket parts or mix and match, there were some changes during the years.
If getting an aftermarket flywheel make sure it is for a single mass conversion. The LT1 Camaro/Firebird flywheel is similar but about .090" wrong on depth. Early conversions before the Corvette conversion flywheels used the F body flywheel but had to do other steps to account for the difference.
If using a stock dual mass flywheel, they can be interchanged from 1989 through 1996. The balance and dimensions are the same whether L98/LT1/LT4.
The solid flywheels use an sprung hub clutch disc. This is the same part as the F-body disc. The sprung disc should also come in the Corvette single mass conversion clutch sets.
The dual mass flywheels use a solid clutch disc.
The pressure plate can be interchanged from 1989 through 1996. The balance and dimensions are the same.
The throwout bearing has two versions. The early version is a larger ID and fits the 1989 to 1993. The later version has a smaller ID (usually visible by a plastic insert) to fit the 1994 to 1996. The change was because the transmission input shaft guides have different diameters and you need the right throwout bearing to match.
There is a pilot bearing that should be replaced also. There are 3 types. one is a bronze sleeve bushing, another is the same bronze bushing with some grooves molded in, and the third is a real bearing. I mostly see the bronze with the grooves being recommended. The bronze bushing types are a powdered metal type that have some lubrication built into the material. They recommend that you do not oil or grease the bushing since that will clog the way it self lubricates and may cause failure. (In practice, I am not sure that it would cause a failure, but that is their suggestion and I did not oil mine.)
There are a lot of people post about engine vibration due to the clutch and flywheel. Many of them are talking about after replacing parts. The main key is that the flywheel is balanced to the L98/LT1/LT4 engines. It is not a zero balanced flywheel. While it is best to have the flywheel balanced to your engine rotating assembly, in practice the standard balance for these motors is fine for the flywheel. If you order the correct flywheel it should come close enough for most. The pressure plate and disc should be zero balanced from any vendor.
In my recent case, I have a '96 with a bad chatter and engine vibration at 3k rpm and up. Mine turned out to be a SPEC flywheel that was balanced incorrectly (about 20 grams off). Not sure on why the chatter, but I suspect the SPEC pressure plate although not sure if it was due to improper tightening causing damage or if the pressure plate was bad to begin with.
I replaced it with a 1990 stock LUK dual mass flywheel, stock Valeo clutch, stock INA throwout bearing. I got lucky and found virtually new parts. The clutch works like new and there is no vibration.
Although I had problems with the Spec flywheel, I had it balanced and plan to use it in another car and don't expect any issues.
Sorry about being long winded.
Good luck.
The original LUK dual mass flywheels and Valeo clutches, and INA throwout bearings are no longer made. Again, contact Jim since he used to have some old stock and has some replacements. He also rebuilds the slave cylinders.
There are a number of choices for the flywheel. The stock dual mass is heavy at about 40 lbs. There are aftermarket single mass flywheels made for the conversion to single mass and can be the same weight or about half, or some very light. The choice is up to you. The heavier flywheels will make it easier to launch the car but at the expense of not revving as quickly. If you get a single mass flywheel, the clutch is nearly the same clutch except that the disc needs springs while the one for the dual mass is solid.
The reason for the factory to have a dual mass flywheel is that the transmission is noisy especially at idle. That flywheel helped to minimize the noise. A single mass will make the transmission louder. To me this was not objectionable, but many people do not like it. There is also an improvement that can be made to the ZF transmission to help eliminate the noise. Contact ZFdoc.com about it. Basically he recommends a shimming that will eliminate most of the noise. It can be done fairly easily without taking the whole transmission apart.
I don't know what the best choice for throwout bearing is. Most of the currently available ones are made in China. My personal thought is that the design of the pull style clutch is poor. The throwout bearing is mounted in the clutch pressure plate fingers (turning whenever the motor is running) and also mounted in the clutch fork (stationary at all times). So the result is that the throwout bearing is moving internally whenever the motor is running so it is amazing to me that any survive at all let alone for 100k miles or more. My point in that thought is to suggest getting the best one you can. If any of the INA originals can be found they are worth it.
If you are getting aftermarket parts or mix and match, there were some changes during the years.
If getting an aftermarket flywheel make sure it is for a single mass conversion. The LT1 Camaro/Firebird flywheel is similar but about .090" wrong on depth. Early conversions before the Corvette conversion flywheels used the F body flywheel but had to do other steps to account for the difference.
If using a stock dual mass flywheel, they can be interchanged from 1989 through 1996. The balance and dimensions are the same whether L98/LT1/LT4.
The solid flywheels use an sprung hub clutch disc. This is the same part as the F-body disc. The sprung disc should also come in the Corvette single mass conversion clutch sets.
The dual mass flywheels use a solid clutch disc.
The pressure plate can be interchanged from 1989 through 1996. The balance and dimensions are the same.
The throwout bearing has two versions. The early version is a larger ID and fits the 1989 to 1993. The later version has a smaller ID (usually visible by a plastic insert) to fit the 1994 to 1996. The change was because the transmission input shaft guides have different diameters and you need the right throwout bearing to match.
There is a pilot bearing that should be replaced also. There are 3 types. one is a bronze sleeve bushing, another is the same bronze bushing with some grooves molded in, and the third is a real bearing. I mostly see the bronze with the grooves being recommended. The bronze bushing types are a powdered metal type that have some lubrication built into the material. They recommend that you do not oil or grease the bushing since that will clog the way it self lubricates and may cause failure. (In practice, I am not sure that it would cause a failure, but that is their suggestion and I did not oil mine.)
There are a lot of people post about engine vibration due to the clutch and flywheel. Many of them are talking about after replacing parts. The main key is that the flywheel is balanced to the L98/LT1/LT4 engines. It is not a zero balanced flywheel. While it is best to have the flywheel balanced to your engine rotating assembly, in practice the standard balance for these motors is fine for the flywheel. If you order the correct flywheel it should come close enough for most. The pressure plate and disc should be zero balanced from any vendor.
In my recent case, I have a '96 with a bad chatter and engine vibration at 3k rpm and up. Mine turned out to be a SPEC flywheel that was balanced incorrectly (about 20 grams off). Not sure on why the chatter, but I suspect the SPEC pressure plate although not sure if it was due to improper tightening causing damage or if the pressure plate was bad to begin with.
I replaced it with a 1990 stock LUK dual mass flywheel, stock Valeo clutch, stock INA throwout bearing. I got lucky and found virtually new parts. The clutch works like new and there is no vibration.
Although I had problems with the Spec flywheel, I had it balanced and plan to use it in another car and don't expect any issues.
Sorry about being long winded.
Good luck.
Last edited by QCVette; 09-23-2016 at 10:01 AM.
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wideopen85 (09-23-2016)
09-23-2016, 09:10 PM
#4
Two excellent responses from QCVette & GREGGPENN !!!
I've pulled more than one ZF6 tranny out - and it's not a whole lot of fun - but it's not that that horrible either. The tranny weighs about 120 Lb - so plant to use a trans jack, and since there isn't anything flat to put the jack under - it's normally a two man job to R&R the trans.
Pull the exhaust, then undo the driveshaft at the diff U-Joint and get the "C Beam out. I do that by putting a floor jack under the diff, and pulling the two bolts that hold the batwing to the chassis, which allows the whole rear suspension to be lowered - this gives you some room to get the "C" Beam unbolted and out. You'll want the rear suspension lowered to get a better angle to help clear the shifter as you pull the tranny back anyway.
The first time I did a C4 clutch - I ended up cutting the shifter **** off with a hacksaw as I couldn't figure out how to get the retainer "pin" out. After you remove the shift pattern indicator - you see the square pin sitting in the shifter handle. That pin has to come out by getting pulled straight up. Sometimes you can grab it with a small vice grip and tap the vice grip to pull the square pin up. Otherwise consider drilling and tapping that pin and threading in a machine screw & puling it out that way.
Two other "suggestions". 1) If the clutch is way worn, and after you get the trans out, and after ypu unbolt the bellhousing - you may find you can't get the bellhousing off - the problem is that the clutch arm is too far "in" and you're essentially fighting the throwout bearing. The way to solve that issue is to remove the pivot ball that the clutch actuator arm pivots on. This pivot ball is accessible from the back of the bellhousing once the trans is out. I believe it's a 12mm allen head recess on the back of the pivot ball, but since you're unscrewing it from the back - you have to make sure to turn the bolt the correct direction so it unscrews INTO the bellousing.
As others have pointed out - the Dual Mass Flywheels are no longer available. If yours appears to be in good shape - a quick going over with a Scotchbrite wheel driven by an 90 degree air powered die grinder can be used to clean up the surface of the DMF. I've done this a few times, and it's worked - but only if the DMF is in good shape.
Finally - putting the tranny back in is not exactly what most people do for fun. A couple of short pieces of threaded rod temporarily screwed into the bellhousing can help guide the trans into place, but the ZF tranny seems particularly susceptible to clutch disc misalignment. If you seem to be able to get the trans in part of the way home - but it just doesn't want to go that last inch or so - one thing you can try if all else fails is to have a helper push on the clutch pedal a bit while you and your helper continue trying to get the trans all the way "home". This relieves the pressure on the clutch disc and allows the disc to move just a touch to let the mainshaft move into the pilot bearing and lets the trans get to the fully seated position. I've had to do it on one occasion - and it did work....
Ty to get penetrating oil on the exhaust bolts and let it soak in as long as possible before you pull the trans.
I've pulled more than one ZF6 tranny out - and it's not a whole lot of fun - but it's not that that horrible either. The tranny weighs about 120 Lb - so plant to use a trans jack, and since there isn't anything flat to put the jack under - it's normally a two man job to R&R the trans.
Pull the exhaust, then undo the driveshaft at the diff U-Joint and get the "C Beam out. I do that by putting a floor jack under the diff, and pulling the two bolts that hold the batwing to the chassis, which allows the whole rear suspension to be lowered - this gives you some room to get the "C" Beam unbolted and out. You'll want the rear suspension lowered to get a better angle to help clear the shifter as you pull the tranny back anyway.
The first time I did a C4 clutch - I ended up cutting the shifter **** off with a hacksaw as I couldn't figure out how to get the retainer "pin" out. After you remove the shift pattern indicator - you see the square pin sitting in the shifter handle. That pin has to come out by getting pulled straight up. Sometimes you can grab it with a small vice grip and tap the vice grip to pull the square pin up. Otherwise consider drilling and tapping that pin and threading in a machine screw & puling it out that way.
Two other "suggestions". 1) If the clutch is way worn, and after you get the trans out, and after ypu unbolt the bellhousing - you may find you can't get the bellhousing off - the problem is that the clutch arm is too far "in" and you're essentially fighting the throwout bearing. The way to solve that issue is to remove the pivot ball that the clutch actuator arm pivots on. This pivot ball is accessible from the back of the bellhousing once the trans is out. I believe it's a 12mm allen head recess on the back of the pivot ball, but since you're unscrewing it from the back - you have to make sure to turn the bolt the correct direction so it unscrews INTO the bellousing.
As others have pointed out - the Dual Mass Flywheels are no longer available. If yours appears to be in good shape - a quick going over with a Scotchbrite wheel driven by an 90 degree air powered die grinder can be used to clean up the surface of the DMF. I've done this a few times, and it's worked - but only if the DMF is in good shape.
Finally - putting the tranny back in is not exactly what most people do for fun. A couple of short pieces of threaded rod temporarily screwed into the bellhousing can help guide the trans into place, but the ZF tranny seems particularly susceptible to clutch disc misalignment. If you seem to be able to get the trans in part of the way home - but it just doesn't want to go that last inch or so - one thing you can try if all else fails is to have a helper push on the clutch pedal a bit while you and your helper continue trying to get the trans all the way "home". This relieves the pressure on the clutch disc and allows the disc to move just a touch to let the mainshaft move into the pilot bearing and lets the trans get to the fully seated position. I've had to do it on one occasion - and it did work....
Ty to get penetrating oil on the exhaust bolts and let it soak in as long as possible before you pull the trans.
09-25-2016, 08:10 PM
#5
8th Gear
Member Since: Jul 2014
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1990 L98--I only have it for 2 years an less 2K miles of the current 90K miles. A few months ago I had just the clutch plate and throw out bearing replaced at a local transmission shop. My clutch just started to slip. The trans shop did his homework and we made the decision after he inspected the DM FLYWHEEL. His concern with the conversion kit was the risk of noise and chatter. The original flywheel had very little blue and he was able to clean and lightly buff/sand it. The plate was not yet down to the rivets but the car would not hold on a slope in 3rd and even worse in 4th. I am not an aggressive driver and not intending to take it on a track or race it. So for me, this repair fit how it use the car. It is working fine even if I push it occasionally to test the integrity of the repair. Cost ~$750.
Last edited by mcdelucia828@gmail.c; 09-28-2016 at 09:55 PM. Reason: Spelling correction