Hoping to learn from other's experience. I got my 96 lt4 with about 24k on it. I had to replace the clutch already. I know that it wasn't my doing, but that's niether here nor there. I had the work done at a GM dealership. My brother oversaw the work, and the technician is a top notch guy. I would trust both of them with my life. The only thing they did not do was machine the flywheel because GM says specifically not to. They did their best to smooth it out in house. The problem is that it makes noise when the clutch is engaged. This noise also produces a whine, especially in 1st -3rd.
My question is this, has anyone else had this experience? What was the trouble? How did you fix it or did you? Or, is this just a zf thing and I should learn to accept it for what it is?

 

I dont think the noise is normal......most people replace the EXPENSIVE dual mass flywheel when doing a clutch ...I'll be curious to others responses as well.

 

ZF's do make a little noise with the clutch engaged at low RPMs, but it's generally not that noticable with the factory flywheel. A lot of people don't even notice it at all. It's also more of a "rocks in a can" sound, not whining. It also goes away by about 1000-1500 RPM.

If yours is whining with the clutch engaged (foot off the pedal), I'd say the fork/throwout bearing may not be installed properly. It's a really tricky fit to get it on right and you also need to make sure the pivot ball is properly tightened and secured to ensure there is no preload on the bearing.

If it was whining with the pedal depressed, I'd say bad throwout bearing or bad pilot bushing (the bushing that goes into the end of the crankshaft that the trans input shaft slips in to.)

 

If you still have the dual mass, there shouldn't be very much noise at all. the only way you're going to be able to cpmpare is to drive and hear another car with similar mileage. Did he replace the flywheel with a single mass ? Also if there is whine present that wasn't there before its most likely due to an improperly centered c-beam. There are appropriate measurements to center it or there will be side load on the trans input shaft which in turn causes it to whine.

 

A gear whine isn't associated with the clutch.

The "Blue Tag" (L1993-1996) ZFs is quiter than the "Black Tag" (1989-E1993) in regards to gear whine.

The flywheel is an interesting peice. It is what is called a "dual mass" flywheel. It is just that, two masses of metal connected by springs. These springs act like the springs in a conventional sprung hub clutch friction disk. The unit cannot be machined because of a number of reasons, the springs don't like it much, the space issues are massive - take away that little bit, and the clutch won't line up correctly.

And another reality - the DM won't last forever. 120k miles is MAX on a DM. They simply wear out. Scuffing the DM is ok on a low mileage unit. That is acceptable and will take desposits off and will let the DM last a full life cycle. In acutality, the clutch assembly is a 100k mile unit in normal street usage. At this time, replacing the DM is advisable.

Another source for the whine could easily be the throw-out bearing. The latest units are JUNK!!! They are nasty, stamped pieces made in China. I wonder, tho, if the bearing casing could be spot welded, if it would improve it's strength/durability?

CentralCoaster had a helluva time with the throw out on his converted (from 4+3 to ZF) 1985 back over the summer. It cost him a week trying to replace the part.

 

Thanks for your replies. It did make this noise before the clutch replacement. We thought it might be the throw-out. This was replaced with the clutch. They did the whole thing, pressure plate and all. What I'm not sure about is if they replaced or checked the pilot bearing. The reason my brother believes was the cause of the clutch going out was the clutch fork bolt was backing out and almost all of the way. Anyway, it's not the noise that really bugs me, you can't hear it when gas pedal goes down. (If you know what I mean;-) I just don't want to replace the clutch often.

 

IIRC, the GM pilot bearing is actually a bushing. I doubt that would cause it.

My thinking is more akin to the natural whine of the ZF6.

Check out this site: www.zfdoc.com

 

The ZF has a normal rattle that most unfamiliar techs would diagnose as an input bearing failure in the trans. A bad pilot bearing can lead to input bearing failure also, but yours shouldn't have a bearing unless the tech pulled it out of his parts bin.

GM used a pilot BEARING on black tag ZFs and a pilot BUSHING on the blue tag ZFs.

I would never recommend using the bearing, and GM's switch seems to agree.

It sounds like your previous problem could have been the pivot stud backing out, a bend fork, or a bent flange on the throwout bearing. All these will take away from your clutch travel. Only the broken/bent throwout bearing would really require a clutch replacement, since it's usually only available by buying the whole clutch set. (Except for AC-Delco who sells it seperately). The throwout bearings are a very weak design. When they do break, you'll get stuck in gear, the clutch pedal will go to the floor and pumping it up will make it rock solid and do nothing.

 

I've got first hand experience with this.

The whine is normal for the ZF6 due to the fairly straight cut gears in 1st to 3rd. Although, it should not be too loud. If you notice a difference before and after the clutch change I'm 100% certain it is due to transmission alignment. The ZF6 is very sensitive to alignment.

When I changed my clutch, I let the car idle in neutral. You'll clearly hear a "whirl" sound in the transmission. Then I loosened off the bolts between the transmission and clutch housing. Using a jack I gently moved the transmission up and down until the noise was as quiet as I could get it. Thousands of an inch make a difference here. Then I tightened the bolts following the recommended torque pattern. This made a huge difference.

There is also a GM Tech Bulletin out on ZF6 alignment issues as well. I can't remember the number off the top of my head but Google should find it.

Also, one thing ZF Doc told me (and I agree), if the mechanic who re-installed the transmission used the transmission bolts to pull the transmission in against the clutch housing it is possible they distorted the clutch housing. Don't under estimate how sensitive the ZF6 is to alignment. The next time I have my transmission out I'll be using a dial indicator to verify my clutch housing is perfectly aligned.