That I should lookout for when test driving a 1996 with the ZF6?

 

When idling in neutral with clutch engaged some whirring from the zf is normal. Clattering or “rocks in a can” noise is indicative of a failed dual mass flywheel or after market single mass.

There’s the obvious stuff as well... does it shift smoothly, no grinding, etc.

 

The ZF S-640 (ZF6) is nearly bulletproof, but a notchy 3rd gear is common. My 3rd gear is notchy on upshift but super smooth on downshift. Just be sure it shifts into all gears, on upshifts and downshifts. It's common for the lubricant to be neglected as the manual says it does not need to be changed, but of course the level should be full. 1st gear is very short and 6th gear is very tall. The clutch system may be more important than anything, as a malfunctioning clutch can wreak havoc on any manual transmission. Most clutches push the throwout bearing against the pressure plate splines, but these cars have a pull-action clutch. It is odd but it works. Check for leaks from the master and slave cylinders (as well as the transmission, engine and differential). Also check the level and condition of the fluid in the master.

 

You speak the truth.

 

Excellent, you guys rock. Thanks

 

Driving my "new" '89 w/ ZF6 is night/day from driving my '88 w/A4, enjoy the experience.

 

Should shift nice and smooth if its in good shape.

 

Probably the more common failure in ZF6 cars is the clutch slave and master cylinder. Make sure that it goes into gear and shifts fairly smoothly (possibly excepting the upshift to 3rd, as previously mentioned). If it has trouble with these things then the hydraulics may not be fully releasing the clutch. That's fixable - not a deal breaker - but it's good to know what you're getting.

At 2.68:1, 1st gear in a ZF6 is actually relatively tall compared to the 1st-gear ratio in most production cars' manual transmissions.

 

Yep, it’s why we can get away with 4.XX ratios in the rear and still have streetable cars. The 0.5/1 of 6th balances out the other end as well.

 

Wicked info and tips everyone. Car has stock gearing in the diff. Which would be 3.45s? What should my rpm be at 70mph on the highway, in 6th gear? Stock tire sizes as well.

Also, was reading up not to give it lots of throttle in 6th gear.

 

Stock gearing should be 3.45's and rpm at 70 should be about 1700 rpm.

Why not give it throttle in 6th gear? I have done it fairly often with no damage. ZF's are pretty tough. However, don't expect that tall of a gear to perform very well. If you want it to run, downshift.

Like others have said, make sure the clutch engages and disengages well without a lot of chatter or slipping under load in higher gears. Make sure it shifts without unusual noise or feel. I had one that was a little "notchy" when going into second when cold. It just seemed to not fully synchronize and went into gear to easily but with a slight click. The ZF rattle varies between cars/transmissions quite a bit. My '96 has very little rattle even when I had a solid flywheel. Others were a little louder. I have never found mine to be objectionable for noise in 5 ZF's I have had. Although I confess that I listen to the exhaust that is probably too loud.

The real thing to watch out for when driving a '96 ZF car is to be careful not injuring yourself with too big of a grin.

 

Yes, stick rear gear is 3:45. You should see roughly 1700rpm at 70mph. Stock tires are either 255/45/17 front with 285/40/17 rear for the base setup, or 275/40/17 all around with the Z07 performance suspension option.

 

While it's fairly hard to get to - you might want to take a quick peek at the color of the fluid in the clutch slave cylinder. It's brake fluid - so it should be relatively clear - If it's black - it tells you the owner does not go completely nuts with fluid changing, and that if you buy the car - a clutch fluid change should be on your spring / summer "to do" list.

The ZF-6 should shift smoothly - both up and down, and the clutch should engage somewhere in the middle of the travel. Clutch Assemblies for the ZF 6 Speed C4's are not as available as they once were - and a replacement dual mass flywheel is simply not available...

 

Particularly in 2nd and 3rd, run the car up a little in rpm, and let off the gas while in gear... it shouldn't pop out or your synchros are warn out... Those 2 gears take the most abuse... though others can have the same issue... Good Luck.

 

Nice! I'll do that.

 

Almost 190,000 on mine, second clutch, changed the oil in the tranny at 100K, no complaints, great trans. I've never heard about full throttle 6th gear problems. There is really no point anyway, when you need a little acceleration at highway speed use 5th or 4th.

 

if it has the noise, and the owner can confirm he replaced it with a single mass:

shake his hand and buy it.

the dual mass (ie. ‘Useless mass’) flywheel is a heavy 38 lb boat anchor that is hurting rotational inertia.

the single mass comes in anywhere from 12 to 24 lb flavors - all of which providing a weight reduction benefit.

The rattle noise can be fixed correctly by proper shimming of the countershift vs. the factory GM’s band-aid fix of slapping an extra heavy , dampening flywheel on it.

putting a proper thicker shim on the zf countershaft will eliminate 95% of the rattles. Will a dual mass eliminate 100% ? Possibly but its a weight adder.

the modern sportscars dont run heavy flywheels like this anymore

 

My 96 ZF6-40 had 2nd gear synchro issues. $3200 later it is happy once again. Sadly my reverse lights are not working.
Does anyone have any suggestions on replacement clutches?
I have heard guys talk about replacing the dual mass flywheel. What is the consensus here?
Also, once these trannys are all dead, and no parts, what will be the replacement tranny?

 

MikieG1971 - As I said earlier - you really can't get a Dual Mass Flywheel any more. Maybe there are one or two hidden away somewhere - but for the most part they are simply unavailable. They are not rebuildable...

Your options are: 1) Re-Use your current DMF. You typically replace the clutch because of slipping. If it didn't get too bad before it was pulled - the flywheel may be re-usable. I've had very good luck with using the 2" "Rol Loc" disks on a high speed angle head die grinder to "clean up" the face of the flywheel.

2) Replace the DMF with a "Conventional" Flywheel. They make Aluminum Flywheels with steel faces for the LT1/LT4, or you can use the flywheel that Chevy Used on the Camaro with the LT1 - but you need to remove a fair amount of material for that to work.

If you read through this thread - and look at the numerous other threads on this forum about replacing the DMF with a conventional flywheel - you'll see that those who have done it report a "knocking" or "clunking" in neutral with the clutch engaged - it's worse when the trans is warm (read that as being with warm gear oil). Many say that you can reduce or eliminate this clunking with proper shimming of the trans input shaft - I can't say if that's true or not. I can say that no one has ever shown any harm comes from this "knocking" - but it's certainly noticeable inside the car.

As for the Clutch - it was made by Valeo - and supposedly the "issue" today is that all the replacements are made in China. So - there are replacement parts available but the quality is questionable. If your OE pressure plate is still in good shape - you might want to consider just changing the Clutch disc, and re-using the pressure plate.

 

i am using a spec stage 3+ clutch kit installed in 2012.

even though Jeremi at SPEC swears they make their own pressure plates - it appears as if its a chinese replacsment pressure plate.

I had it balanced to the flywheel. It was way off and required lots of drilling at different points around the circumference to make it match.

this was different than when i last did the clutch (in 02) with a valeo new old stock (made in usa) flywheel. The balance was pretty close.

All this said , my ‘SPEC’ pressure plate (which i suspect is chinese) is working fine.