Connerdsny

I'm about to swap a zf6 into an 85 auto car, and I was interested in getting someone's thoughts on what flywheel/clutch I should use. has anyone used a single mass flywheel with the unsprung clutch? will it damage the transmission or just be uncomfortable? I'm using the blue tag zf6 if that makes a difference.

I would like to keep the pull clutch if possible to keep it as original as possible. is the bolt pattern between the lt1 and 85 350 close enough that I could drill/machine the dual mass to fit?

thanks for any help!

mtwoolford

89(?) through 91 were L98 ZF six speed combo's

Kevova

OEM dual mass flywheel will not fit 85 and earlier crankshaft, the flange is entirely different. Using a solid flywheel you may notice more gear rattling in neutral. Depending on intention there a variety of different weights to choose from.

WVZR-1

OP - aside from this being your first 'logged in' post it seems you are likely very 'new' to the C4 so I'd suggest if you actually want an M6 you do what's required and sell the '85 A4 and just buy.

Experienced people through the years have struggled with the change to the M6-ZF and some/most of those already were 4+3 cars with the D44 rear and pedals in place. They were done generally 10+ years ago when an M6 car would have been very expensive.

Maybe you've most of the required parts but your post hints NOT. It seems there's more than the 'solid disc' (which would be foolish) and lack of knowledge of 2-piece vs 1-piece crankshaft flanges for flywheel swaps.

There's some very interesting threads by many who did the ZF swap to '85 2-piece rear.

Search posts by LD85 and then use various threads and links to get a better grip on the 'degree of difficulty'. I doubt that anyone who has done it earlier would say they'd do it again. LD85 posted his experiences on a couple different forums and anything he mentions deserves serious consideration.

Maybe he'll stop in for a visit and comment. Others might also.

Connerdsny

I appreciate the concern. Unfortunately, I won't be talked out of punishing myself
this isn't my first swap from auto to manual, but it is my first swap on a corvette. I've owned this car for about a year, and I've been lurking here... but i haven't done anything significant enough for an introduction. I figured I would start a thread once I had some good pics from the swap.
I got a great deal on a transmission and all the parts from the same car, but I left the flywheel and clutch since the flange was clearly different. I tried to do the best research I could, and I think I'll stick with the 4+3 flywheel and late model clutch combo. I understand there will be gear noise, and it removes any damping in the clutch- I just wanted to be sure it wouldnt cause premature damage to anything. I specifically wanted to hear from someone who has tried the combination if they saw this.

thanks!

WVZR-1

This would be a 'suggested' GOOGLE search and then read, read, read -

https://www.google.com/search?q=ZF6%20by%20LD85

Do you intend on leaving the D36? Do you have the spacer for the master?

Connerdsny

Thank you, a search of LD85's posts and that link were super helpful. I actually already have a dana 44 in the car, which is what partly drew me to this swap. I think I did grab the spacer for the master.

Looking through the info you shared, it looks like I need a longer clutch fork pivot ball to use the 4+3 flywheel. Is the zr1 pivot longer?

WVZR-1

Just READ and then READ again and then maybe a couple more times.

What year is your ZF (last 3 digits off the tag would ID it) and the pedals were removed from what year? Brake pedal ratio changed I believe in '92. That might present it's own challenge. I mentioned might.

I've never done a ZF swap. A local fellow I helped with parts etc for a ZF to an early Monte Carlo G body. It was a very long time ago maybe '03 or '04. I remember very little to nothing. I made no notes.

You want a conversation with someone who has used the same 'pile of parts' you have accumulated.

bumperkar kid

if you want ALL the right answers, contact bill boudreau at ...zfdoc.com he is the guru of ALL the 6-speed transmissions. some say he knows more than the people in germany that made the transmissions.

mtwoolford

If your engine uses a two piece rear seal then you'll have to use a flywheel designed for that mounting flange; 1985 / 1986 seems to be the years that the change over to one piece rear seal cranks began. If you want to retain the ZF style pull clutch, that presents difficulties with a crank designed for a two piece rear seal and may require a custom flywheel.

With a ZF clutch it ain't just the flywheel to crank bolt pattern that's the issue. The ZF flywheel height (thickness) is different. Before aftermarket flywheels became available for ZF transmissions and clutch, a common practice for replacing the dual mass oem flywheel was to take a flywheel from an F body (Camaro / firebird) which used a T56 trans and (more ordinary style) clutch and machine 0.090 - 0.095 inch from the flywheel face and use it with the ZF style clutch.

This could probably be done with a flywheel designed for a two piece rear seal.

Another solution would be to use an aftermarket clutch with a hydraulic throwout bearing, but those are pricey.

mtwoolford

On my 96, when I changed out the clutch, instead of reusing the oem spacer, I cut a series of plates in the shape of the spacer and installed them in the place of the one piece oem spacer, which allowed me to vary the thickness of the spacer / distance of the clutch master cylinder to the firewall (and ultimately the travel of the piston in the master cylinder bore and by actually measuring the travel of the throwout bearing I found that a stack approximately one half the thickness of the oem spacer yielded the throwout bearing travel closest to what Bill Bourdreux aka ZF Doc recommended.

Connerdsny

Thank for all the help! I'll start a real swap thread and put a link to it here once I start.

one more question, would the pilot bushing that went on the late c4s with the zf work in my 2 piece rear main engine? I can ask a parts guy to pull a couple and compare them later today, but if someone happens to know that would be great.

WVZR-1

Crankshaft inserts are all very similar. It's argued from time to time wether you want a 'fluted' insert, solid bronze or a bearing. Use your favorite.

Connerdsny

Heres the actual swap thread

https://www.corvetteforum.com/forums...post1597021231

MatthewMiller

In addition to all that's been written above...
...don't use a solid/unsprung disk with a single-mass flywheel! It will substantially increase the noise that you're already going to experience from the ZF with a single-mass flywheel. I can't think of a good reason to even try this.

Given all the above (hassles making a ZF flywheel fit a two-piece-main crank), I wonder if the best option isn't just to ditch the pull-type clutch setup and convert to a push-type with hydraulic throwout bearing? There is no good-quality option for a new pull-type pressure plate and bearing these days (all made in China, all are crap, regardless of brand). If you're kind of starting to create a clutch setup from scratch anyway, I don't know that it makes sense to hamstring yourself with pull-type setup.

Connerdsny

I just got the car done and I wanted to post this here for people reading this in the future. The zf6 with the factory 4+3 flywheel and pull clutch is definitely very noisy. I dont mind the noise, but if you want a perfect build follow some of the other suggestions. I think in the future I'm going to try to swap in a 1 piece rear main block to eliminate any ambiguity in the clutch

this worked great for me, thank you