Spec Clutch Issues

This clutch disk (part number SZ363 for a 1.6L Miata) has been used for about 1000 road-course miles in my track day car. Until a piece of the spring cage detached and prevented the clutch from being disengaged (which was determined after the transmission was removed), the car drove fine and exhibited no issues at all and engagement was as it should be. This disk was installed as a replacement for another that failed the same way.

The car on which this clutch is used produces 130bhp, is naturally aspirated, and has a clutch-type limited slip differential. There is no discernable side-to-side or thrust movement in the transmission input shaft. There is also no measurable flywheel runout and the pilot and throw-out bearings are in good order.

Any ideas what might be causing this? Note that the corrosion is due to the fact that we changed this clutch in the rain.

1.

2.

3.

1, 2, 3:

There is really little need for the springs in a race car. That being said, I have seen numerous Spec clutches break that way where other, even stock, discs hold up.

looks like the stamping process is creating a stress concentration at those locations. gotta say i love my "kung fu grip" spec clutches T-shirt, but I don't think i'd buy a third disc from them if the first two have failed the same way...

Spec sprung clutches are notorious for failing that way.

This was the way the OEM Clutch died in my '89 Probe GT...

Looks like their quality isn't up to Spec'.

At that HP level, why not just go with a stock disc?

z31maniac wrote: At that HP level, why not just go with a stock disc?

For constant track use, the stockers don't seem to last very long. This car sees no street use.

Agreed with the either go stock or go solid hub.

Opinion here, I really think 1k track miles is pushing the limit on a disc. I also believe that it could be possible that the pressure plate is losing clamping force and at a lower RPM is shocking the disc causing the failure.

I've also had bad experiences witih Spec. The local custom clutch builder and rebuilder in Lansing (Clutch Dynamics) after looking at the Spec disc that came out of my car explained to me why in his opinion some of the rivets and general construction techniques installed were backwards on the ceramic puck disc I had in a heavy boosted Audi...and he couldn't understand why anyone would've assembled in the manner they did (from a strength/stress/wear standpoint). That, and the premature failure of my own, has turned me away from Spec clutch products. YMMV

Ranger50 wrote: Opinion here, I really think 1k track miles is pushing the limit on a disc.

Based on what? That sounds very short.

1000 miles for most people is less than 10 track days. I've just not heard of people replacing their clutches 1-2 times per season. Even on high HP beasts like Mustangs.

The guy sitting next to me at work has been tracking his '97 M3 with 205k miles on it for the last 4 season and racing last year.......on the original disc not slipping.

z31maniac wrote: The guy sitting next to me at work has been tracking his '97 M3 with 205k miles on it for the last 4 season and racing last year.......on the original disc not slipping.

At stock power, that M3 disk is more than the car will ever need though.

I won't lie, I have a spec flywheel(its a bit nicer than the fidanza) in my '95 sho, but their clutches aren't that good.......which is why I chose south bend.

I had a friend running a spec in his Galant VR4 and it did the same thing. Not sure how prevalent this is but that seems more than coincidence.

I blame my clutch failures on the source- which would be the guy bangin the shifts.

z31maniac wrote:

Ranger50 wrote: Opinion here, I really think 1k track miles is pushing the limit on a disc.

Based on what? That sounds very short. 1000 miles for most people is less than 10 track days. I've just not heard of people replacing their clutches 1-2 times per season. Even on high HP beasts like Mustangs. The guy sitting next to me at work has been tracking his '97 M3 with 205k miles on it for the last 4 season and racing last year.......on the original disc not slipping.

No, short is having to replace clutches after very dragstrip pass.

Call it peace of mind, but waiting and waiting and waiting for it to just quit working is asinine. When does it fail? Just like how you describe, out in the rain and at the track. I would prefer to check that crap out inside a garage at home when I have the time to properly do everything. I'd rather be running then changing out broken E36 M3 when I could have prevented it.

Ranger50 wrote: No, short is having to replace clutches after very dragstrip pass. Call it peace of mind, but waiting and waiting and waiting for it to just quit working is asinine. When does it fail? Just like how you describe, out in the rain and at the track. I would prefer to check that crap out inside a garage at home when I have the time to properly do everything. I'd rather be running then changing out broken E36 M3 when I could have prevented it.

Except that the vast majority of the time a clutch gives very obvious signs that it's starting to weak. On something like the avg HPDE car, it's very unlikely the clutch is going to go from "working as it should" to exploding on the next shift.

The pickup point gets higher and higher, the pedal gets weaker, it starts not grabbing as hard on the occasional cruddy upshift. And even this happens on a scale of hundreds or thousands of miles.

So yeah, waiting for that point is much more reasonable than dropping the trans every 3 months to "inspect it"

z31maniac wrote: Except that the vast majority of the time a clutch gives very obvious signs that it's starting to weak. On something like the avg HPDE car, it's very unlikely the clutch is going to go from "working as it should" to exploding on the next shift.

My 95 sho was exactly that way, and I didn't even beat on it......spring pack came out of the disc, shredded, and got the pressure plate stuck in engauged. That 20 mile drive home sucked.....

yamaha wrote:

z31maniac wrote: Except that the vast majority of the time a clutch gives very obvious signs that it's starting to weak. On something like the avg HPDE car, it's very unlikely the clutch is going to go from "working as it should" to exploding on the next shift.

My 95 sho was exactly that way, and I didn't even beat on it......spring pack came out of the disc, shredded, and got the pressure plate stuck in engauged. That 20 mile drive home sucked.....

As I said, that is very rare. In 6 standard vehicles over tens of thousands of miles the last nearly 15 years.......I've never had that happen.

I overprepare and maintain my vehicles like crazy. But to think a basically stock HP engine is going to toast a clutch with track work in 1000 miles is perplexing to me.

Why are you running a puck clutch? There's no need for that. I avoid them whenever possible, I'm not a fan of their engagement.

I'd just go with a good clutch from another company, Spec seems to have proved their point here.

In reply to z31maniac:

It shouldn't......evidentally the spec ones are E36 M3ty, and the factory parts are even E36 M3tier in this case.....

AngryCorvair wrote: looks like the stamping process is creating a stress concentration at those locations. gotta say i love my "kung fu grip" spec clutches T-shirt, but I don't think i'd buy a third disc from them if the first two have failed the same way...

Yes, this, and I would be on the phone in a very POed way.

I thought it was pretty common internet knowledge that spec clutches fail regularly when they shouldn't. IMO the first thing to try is a different brand of disc.

Look at the failure.

It looks like the springs do not have enough material to keep them from being flung outward with centrifugal force. Do the spec clutches have a RPM life rating?

If it was being 'ham fisted/man handled' shifting, you'd probably see it at the coiled ends of the spring, not down the length of the outside. (Probably...?!? )