Gents,

I have an ACT ZM2-XTSS clutch. It's got 19,000 miles and ~55 track days on it. Call it 110 track hours. It functions fine. No issues. When should I be contemplating replacing it?

Thanks,

 

When it starts to slip?

In all seriousness though, I don't think you'll get a good answer. Everyone drives completely differently which will change the wear on each individual clutch. I, for one, know that I am hard on clutches at the track when I really start to push, but can make a street car clutch last forever. Clutches don't seem to have standard maintenance intervals as the wear changes with conditions, similarly to brake pads.

 

I change transmissions more than I change clutches.

 

Would it make a difference if I said the trans was out of the car?

 

It would if you'd told us the thickness of the remaining friction material on the disc as compared to the thickness when new.

I mean, to a certain extent, you've just answered your own question. Unless you are legitimately broke, or really enjoy removing and installing the transmission in your car, this is like asking whether the water pump should be changed while you've already got the timing belt off.

 

Joe,
There has to be a breakeven point. If my transmission failed with a clutch that only had 5,000 miles and 10 track days, I wouldn't replace the clutch. I didn't do it at 15,000 and 43 track days. If I could get another year out of what I have, I'd be good with that. The car rests on jack stands in the garage from late Nov to mid-Feb. Plenty o'time to remove and replace nearly everything.

Honestly, it's really the opposite--I don't mind spending money on her. Sometimes, I have to stop myself. The best New Year's resolution I ever conjured was "Try to make do with what I already have".

 

Measure the thickness of the clutch material and compare it to the spec for a new one?

--Ian

 

Certainly the best answer, but I was looking for subjective opinions based on feelings, as I try to assimilate into the new normal...

 

Subjectively, so long as you are not abusing the clutch, they tend to live a long and happy life on track. For the most part, they are run fully engaged and are not suffering any wear. This requires you to avoid power shifts and do a good job with rev matching.

Third gear OTOH . . . .

 

hornetball,

That was seriously well done.

 

Well, if we're going on feelings, then how do you feel about replacing clutches?

• I'll do it in the paddock on the hottest day of the season with whatever tools I have on hand and I don't care how many nuts or bolts are left over.
  • Great! Throw the spare clutch in an unmarked box and hide it somewhere in your trailer. Finding it will be part of the joy of the repair.
• If I can't get the car off the trailer at the event, I'll just call it a day and head home, no worries.
  • Man, you're chill. Don't even order a replacement, just in case some new hot clutch comes out in the meantime.
• The clutch gives out on the second-to-last session of the weekend. You leap out of your car, on track, and throw your helmet at the (unmanned) flag station. The safety crew leaves you out there, ranting and raving about being screwed by the international clutch syndicate. You make your way back to the paddock and punch a clown.
  • Find a new damn hobby.
• I'll only do it in the comfort of my garage and replace every nut and bolt while I'm at it.
  • Replace it now.

But seriously, how pissed will you be when this fails? That should probably factor in. If a missed track day is going to hit you hard, do it now.

 

Yeah, road course duty is pretty gentle on clutches -- except when you're trying to load it onto the trailer. A winch will make the clutch last a LOT longer.

--Ian

 

I'm saddened this got me some negcats. I really was looking for some subjective opinions. Something like "I've been tracking Meyoters for almost 50 years and I always replace the clutch after about (fill in the blank) track hours 'cuz **** just starts to happen about then..." or somesuch. ACT says the clutch is 8mm thick new and is good down to 6mm. I measure the compressed disk at just shy of 7.5mm, so from an objective standpoint, she's good to go. I was actually hoping for anecdotes and war stories, but irregardfull, I don't plan to replace it now because of the objective data.

 

Miata clutch job takes 4 hours if you're drinking too much. Under 3 if you're motivated.

I'd just send anything that wasn't oil soaked or slipping.

 

but would you really take the subjective into account when deciding to change your clutch? I certainly wouldn’t, as they wouldn’t be relevant to your usage.
the only way to know, if it’s not slipping, is to measure it, which you’ve done. 0.5mm wear out of 2mm service life means you have 3 times as much to go. There’s your answer..

oh, for some subjective opinions, I can give you two.
A mate I know has gone through three clutches in as many years, on his std power track car. He flat changes and rides the clutch in the pits.
I on the other hand have had the same HD clutch in for over 10years now, over 110 track days, approx 35000km of track day/road use, with the last 10 track days and 5000km it has been rotrex’d.
so if you listen to my mate you should change it as often as possible, and in my case don’t bother at all…

 

Alrighty then... a follow-up post.

I grenaded another five-speed at VIR a couple of days ago. The ACT clutch I referenced in the original post from almost three years ago is still in the car. It's at least 75 track days older, so I believe I made the correct decision keeping it. That said, even though I haven't pulled the transmission yet, I'm ordering another clutch kit. Five plus years behind a supercharged motor is probably enough.

(I had already downshifted into Third going into Turn 3. I lifted a bit to let someone by going into Turn 4. I rolled in behind him, stabbed the throttle, and all hell broke loose. Fortunately, First, Second, and Reverse still worked. It's time for a six-speed.)

 

I had an engine failure on track at over 100mph and it shocked the drivetrain so much it cracked my clutch disc, didn't realize this until the next event with a new motor and didn't make it one lap. Any exciting driveline failures I always inspect the clutch but if it looks ok I will reuse, have raced for years and years on the same clutch in Spec Miata so low power but have grenaded quite a few transmissions with 106hp NAs and 130hp NBs.

 

I finally got a chance to remove the transmission, and I removed the clutch. The friction plate shows no more measurable wear than I had mentioned earlier in the thread, which I attribute to me trailering her now. Is this too much wear on the diaphragm spring fingers? There is a slight ridge.





Thanks,

 

That's pretty typical. If there isn't any issue with clutch disengagement or clamping force, you can continue to run it.

 

Curly,

Excellent. The next question is... new release bearing, or keep the one that has worn the diaphragm spring? I had no clutch issues. The one that's in there is marked NTN Japan, but I have a new ACT release bearing on hand. It's unbranded.

Thanks,

I just spent a few quality minutes with both release bearings. I can spin the NTN and it keeps turning. I hear the ball bearings buzz. I can't do that with the new ACT bearing. I believe I answered my own question.