My car has developed a slipping clutch under WOT in 3rd and 4th gear. I have a non-adjustable slave cylinder and the clutch seems to have the proper amount of free play so I dont think that is causing the problem.

If I drive it gently how likely am I to toast the flywheel? I would really like to delay changing it until this winter. Also, I can't find any stock style 240z replacement flywheels. Does anyone have any recomendations for one? Should I just spring for a 280 flywheel?

Thanks

It's impossible to accurately say how long you can let the clutch slip before damage happens. If the stock flywheel isn't too badly damaged by the time you pull it out, you can have it machined true again and put it back in. A 240 flywheel shouldn't be that hard to come by, just put a WTB ad on one of the forums and you should find one pretty easily.

Hi hogie:

Just some additional thoughts....

First I agree with Jon... and BTW - I don't think there is any difference in the flywheels on the L24/L26 or L28's. The only difference is that the 2+2's have larger diameter machined surface for a large clutch disc.

If you are shifting around 5500 -6000 RPM into 3rd and then 4th - and the clutch is slipping - then it is most likely slipping every time you start out in 1st as well.

If you shift into 3rd at much lower speeds/RPM's and then go to WOT.. and the clutch slips.. it may still be strong enough to hold during a soft launch from "0" in first. In which case you could take it easy and most likely not do any real hard for several weeks or even months.. depends on how much you drive.

Flywheel damage is "usually" caused by overheating - which causes hot spots {change in the temper of the metal" in places. If the clutch is worn, and it was the riveted type.. the metal rivets can cut deep groves in the metal... sometimes too deep to safely remove.

For sure you should plan on haveing the flywheel turned true {usually done on a brake lath}.. but then it should also be resurfaced properly. That way the new clutch will not result is a "shutter" when engaging the flywheel.

Best recommendation is to buy a good used flywheel {with good ring gear teeth}... and have it turned and resurfaced - that way you have it on hand when you change the clutch.. and you don't get held up for two or more days...

FWIW,

Carl B.

I haven't driven it too much as it has only been on the road for 3 months or so. I have mostly been driving to and from work which is only a couple of miles either way.

The symptoms of my slippage occur when I get hard on the gas in 3rd or 4th gear and around 3 or 4k. It will rev up extremely quick to around 5k and then my actual acceleration catches up a second to two later. This has only happened a few times, so I hope I haven't slipped it enough to have overheated anything.

I have not noticed any slippage at all under aggressive starting conditions. Luckily I have a daily driver, so any down time is just an inconvenience. With any luck I can just have my current flywheel machined and not have to purchase one.

The symptoms of my slippage occur when I get hard on the gas in 3rd or 4th gear and around 3 or 4k.

That makes perfect sense as the torque peek of the engine occurs around 4400 rpm.

If the flywheel was warped, you would feel a violent shimmy as you release the clutch. In any event it's good practice to have it resurfaced. If it's been resurfaced once before, you may need to replace it.

I am so used to driving trucks and their much lower red line that I don't usual remember to wind it out.

The awesome part is this was supposed to have a "new clutch" and good 5 speed before I bought it.

Could definitely be a worn out clutch, but......

Similar thing recently happened to me.

Noticed it would begin to happen after the car was running for a while on a longer trip, but got progressively worse. Thought the 'new' PO-supposedly installed clutch might not have been new or not installed.

Figured something was adjusted too far out that was interfering with the clutch's ability to 'grab'.

Started looking into the whole system.

New master (PO installed) and original adjustable slave, worn clevis pin and worn, elongated receiving hole in the pedal arm.

Figured the PO had to adjust the slave rod all the way out to accommodate the slop in the linkage.

So it was time to correct the obvious problem child/children.

Replaced the slave (many recommend to replace both if you have to replace either master or slave).

Purchased a new clevis to remove some of the slop. I'll eventually get to welding the elongated pedal hole and re-drilling.

Bled the system and now had the opposite problem. Grinding gears and couldn't get it into reverse.

OK, enough about my issue.

Did a search and (sorry, can't find the post) found somebody suggested to check the adjustment on the clutch master push rod (thank you whoever it was, never would have thought that). If the locking nut isn't tightened properly, it can eventually 'walk' its way out affecting the amount of stroke when you push the pedal. So between the new clevis, the master adjust, the new slave and the slave adjust, she engages 1/3 (?) of the way up instead of just off the floor (feels right) and pulls like a banshee and still has what seems to be the right amount of freeplay so I don't tax the throwout bearing.

Try adjusting the throw of the pedal by checking/adjusting the master push rod.

At the least, it might buy you enough time until your winter change-out.

At most it might show you don't need a clutch replacement at all.

Sorry, but I'm a little long winded tonight.

Hope this helps.

I don't know if that was me, but I do know that I've posted that bit of info before, as I incorrectly adjusted the rod to the clutch master too tight and had it slip progressively worse at the track as the clutch fluid heated up. That would be a pretty reliable symptom though. The more you drive, the worse it slips. If it still feels the same after driving for an hour in stop and go, the clutch adjustment isn't the problem.

As to when a clutch slips most, I think it is far more likely to slip in a higher gear than a lower gear, because you're not multiplying the torque via the transmission in the higher gear. In the same way that it's easier to spin the pedals in the lowest gear on a bike and harder to spin the pedals in a high gear, the clutch (and motor) get loaded a lot more in a high gear. I always test a clutch like this: find a steep hill, drive at a fairly low speed, say 35 mph. Put the trans in 4th, rev to 4000, drop the clutch. If the clutch is prone to slipping, it will slip on this test. You may not notice the problem taking off from a light in 1st, but you WILL notice on this test.

Edited September 22, 201014 yr by jmortensen

I double checked my pedal adjustment today and it was already quite close to the 72 fsm specs of 8.8 inches from the floor with .95-.97 inches of free travel. I actually have a bit over 1 inch of free play.

If I had to adjust the master cylinder I am not even sure it would be possible...someone has apparently pre-buggered this one. It looks like they used some hardcore bronze colored expoxy putty or something.

I will be driving the car to work in the morning. Hopefully I will have good news.

Edited September 22, 201014 yr by hogie

I came across this again recently and might help when it does come time to change the clutch http://www.biopatent.com/clutch.html. It might not be time for that but can't hurt to have the info to plan ahead. He swears by Centerforce product but I have no experience with that.

Hogie, been there, done that with my '75 at a much earlier age. I might have even driven a lot like you at the time!

Like you, I wanted to get to summer break before launching into the clutch. My 280 was my only car, and I needed it to commute about 30 mi to and from school. Fortunately the terrain was relatively flat -- no hills to climb, at least at higher speeds. I decided to stretch the clutch life as far as it would go (not causing damage to the FW, just like you.)

I did make it to summer break with "sensible" driving. I think it was about 6 months -- probably about 5000 mi of city driving. It was getting pretty slippy towards the end, particularly in 4th gear (4 sp transmission). There was no damage to the flywheel, perhaps because there was never a time it slipped that I didn't know it, so I could back off of the accelerator to stop the slippage.

Here's what I'd recommend:

1. Make sure you can hear your engine (i.e. keep the volume down), so that you'll know when the clutch is slipping.

2. Drive in lower gears when you can't avoid slippage in higher gears.

3. Engage your clutch as quickly as possible, without much gas.

4. Use your brakes more, and don't downshift into your stops.

With a bit of care and thought, I think you should make it to winter break.

Edited September 22, 201014 yr by FastWoman

Good deal, sounds like I can make it to the winter after all. I have a very short, very flat drive most of the time.

I took it out today after adjusting the pedal and this is the result. It is still slipping in 3rd and 4th, however it is only momentary. As you get on the gas it accelerates hard, then the engine revs up a little higher than it really should as it slips.....then the cluth will start grabbing and then bog the engine to where it really should be. I wonder if I the clutch got a little grease or oil on it and that is causing the slip.

I am not getting any clutch stink or noise out of it, so I am really unsure about it. I thought once they started slipping they wouldn't grab again until there wasnt any extra power being put in.

Just because it is slipping doesn't mean that there is grease or oil on it. The disk itself has a wear surface on it, and as it wears down it gets thinner like a brake pad. The thinner it gets the less pressure the pressure plate can put on it because the springs in the plate aren't compressed as much, so that can cause slippage.

You can also increase power levels until you get some slippage. My stock clutch held down the SU's just fine, but when I went to Mikunis I had to change to an ACT clutch because it couldn't hold the power anymore.

If you aren't making a lot of power, then the likely culprit is just wear on the disk, and as said before the biggest risks are putting a lot of heat into the flywheel and/or wearing the disk down to the rivets and having them chew up the flywheel.