A Real Headscratcher

So, this fall, while at the Tail Of The Dragon, the transmission started acting up in my Miata. At first, I noticed that the clutch was slipping whenever I would hit 5000rpm in 2nd gear and up. Frustrating, because it had a new 250lb-ft rated ACT with 8000 miles on it. I parked it for the day, because the weather was 40 degrees and rainy and a 245whp Miata on near-bald Rival S 1.5Ss in those conditions is frightening. The next day was warmer and dry, so I decided to run the Miata but just keep engine speeds down. After one trip up the Dragon, it picked up a slight rattle that went away when I pushed the clutch in. My friends and I figured it was maybe a throw-out bearing going away, again, frustrating because it had 8000 miles on it. Parked the car, hopped in with a friend, and figured I would be okay for the long drive home because it's mostly bombing along in top gear. Go to take it back to the campsite, and the noise seems much louder, but figure I'm paranoid. Get a quarter way back to the camp and the trans pops out of gear and it starts making the worst noise I have ever heard a car make, like someone threw a fistful of gravel in the transmission. Park it, rent a U-Haul, tow it back to NY and let it think about what it's done for a few months.

Finally pushed the car in the garage the other night, bench press the transmission out of it, for like the 3rd time in 5 years, and what do I find?

Note the input shaft plate bolt that is completely MIA. These bolts are not blind, you can see the shaft bearings through the hole. This caused all the trans fluid to leak out and trash the whole thing. What's odd is that the bolt is nowhere to be found. It's not in the bellhousing, it's not on the ground, it's not trapped in the pressure plate, the only opening would be the clutch fork opening, and the rubber boot was in place and intact, so it didn't fly out there. No witness marks in the bellhousing or the pressure plate, flywheel or block where it ricocheted around in there.

Also, the clutch disc has contamination from the fluid, so that's junk. And the pressure plate and flywheel have hot-spotting as well, and the flywheel has been heavily cut once, and I don't like that the machine shop cut the dowel fins off of it. So I guess, it's getting it's 3rd clutch and 2nd flywheel in 5 years. Ugh. Also, is it odd for a clutch to have tapered wear? The outer edges of the friction material are noticeably worn more than the inner edges

Also, all the other input shaft plate bolts were not crazy tight but snug. I've never had the bolts out of this trans, but it's not original to the car (car was crashed badly at some point in it's life and it had a "1989" trans put in then, before I got it) and I never really thought to even check them when I had the trans out last year to put the new engine in.

My guess is that the bolt was never there since it's install, causing all of your clutch related problems.

That will teach you to top off the fluids, running a little low and driven easy probably would not have leaked at all.

In reply to akylekoz :

I doubt that it was never there, because it never filled the bellhousing up with gear lube before, and previous clutches didn't slip. The last clutch chattered a little but that likely more to do with the 1.6L with the leaky pan gasket and  rear main seal and the countless number of 4000-4500rpm clutch dumps at autocrosses. Also, it went 20k between clutches at one point and wasn't low on fluid when I pulled it. 

In reply to NickD :

Im willing to bet it fell out between clutches or even this clutch and it was not caught when trans was pulled. 

Is the bolt behind the flywheel? I re read but not sure if you have removed it yet. Also, is the bolt stuck to the starter (magnets?)?

If the bellhousing was full of fluid, are you sure the bolt didn't come out with that fluid when you separated the trans?

E36 M3ty situation.  Good thing miatas are easy to work on and so reliable (generally) that used parts are pretty trustworthy. Slap a trans in it. 

If it makes you feel any better, I had to pull a perfectly functional (at first..) miata trans out twice in a row this year because first my employee pulled the Jesus Bolt thinking it was the fill plug, and the second time because he forgot to reseal that input shaft retainer plate you're looking at. I also just had to r&r another manual trans under warranty because my builder either forgot to stake a nut or forgot to loctite it and it came loose and ate up some stuff. I didn't get paid for any of that. E36 M3 happens! 

Yeah, what's behind the flywheel?  If transmissions are cheap, I'd pitch that one and put another used one in.  Now, On The Cheap, you could put the clutch plate in the oven and cook it until it stops smoking then reuse it.  Best not to do this when Momma's around.  The flywheel, run it as it is after you pull it to look behind.

So, where'd the bolt go?  If the transmission noises are from within the transmission, then maybe the bolt head popped off, or was already popped off when you put it back in last time, and what was left of the bolt worked its way inside causing much mayhem?

Vigo said:

E36 M3ty situation.  Good thing miatas are easy to work on and so reliable (generally) that used parts are pretty trustworthy. Slap a trans in it. 

Mine is a little more difficult to work on now. To pull the header involves pulling the supercharger and and all the associated bracketry, which is a bit of a hassle.

Dr. Hess said:

Yeah, what's behind the flywheel?  If transmissions are cheap, I'd pitch that one and put another used one in.  Now, On The Cheap, you could put the clutch plate in the oven and cook it until it stops smoking then reuse it.  Best not to do this when Momma's around.  The flywheel, run it as it is after you pull it to look behind.

So, where'd the bolt go?  If the transmission noises are from within the transmission, then maybe the bolt head popped off, or was already popped off when you put it back in last time, and what was left of the bolt worked its way inside causing much mayhem?

I already have another transmission on hand, picked one up on the way home, since I had an empty U-haul van. Making the move to a 6-speed, since those are stronger. I really don't want to play around with pulling the trans again, so I'm just going to throw an entire clutch assembly at it while I'm in there. As I said, there's some weird clutch wear that I don't care for, and when I had the flywheel turned last year the machine shop couldn't get the dowel pins to come out, so they just milled them off. the more I think about that, the less I like it. If it was some truck motor or flathead Ford that was turning maybe 3000-4000rpm, I'd be less concerned, but I'm hitting 7000rpm+ frequently and I have thoughts of that clutch shifting around on the bolts and pounding out bearings.

Check the starter for the bolt!  I've seen pressure plate bolts jammed in to the starter before....

NickD said:

Vigo said:

E36 M3ty situation.  Good thing miatas are easy to work on and so reliable (generally) that used parts are pretty trustworthy. Slap a trans in it. 

Mine is a little more difficult to work on now. To pull the header involves pulling the supercharger and and all the associated bracketry, which is a bit of a hassle.

It’s snug but you shouldn’t have to pull the header to R&R the trans in an NA, BTDT with mine and had  no problems.   On the plus side, you can do it with the engine in the car, my monster was so tight that a transmission removal meant pulling the motor and trans together.  

if the outer ring of the clutch disc is worn more than the inner, that tells me that the hub of the clutch disc was not traveling as far forward as it's supposed to, ie something was blocking it.   i'm guessing your missing bolt spent some time lodged between the disc hub and the flywheel.   i had a similar clutch wear issue when the PO used the wrong bolts to attach flywheel to crank.   the bolt heads were too tall *and* he used split washers under them.

The Dragon ate your bolt. 

KyAllroad (Jeremy) said:

NickD said:

Vigo said:

E36 M3ty situation.  Good thing miatas are easy to work on and so reliable (generally) that used parts are pretty trustworthy. Slap a trans in it. 

Mine is a little more difficult to work on now. To pull the header involves pulling the supercharger and and all the associated bracketry, which is a bit of a hassle.

It’s snug but you shouldn’t have to pull the header to R&R the trans in an NA, BTDT with mine and had  no problems.   On the plus side, you can do it with the engine in the car, my monster was so tight that a transmission removal meant pulling the motor and trans together.  

We got the transmission out without pulling the header, but we had to turn the transmission sideways about 45 degrees and rotate it and there was no way we were getting it back in. The bellhousing solidly hit the header before it was fully disengaged from the clutch.

I have had those bolts back out before.  I have also had one of the bolts for the mid plate bearing retainer back out.  (That one was an instant de-toothing of some gears when it got caught up in them)  They "shouldn't" see much end loads but they do.

Every time I replace a trans, I get to as many of those bolts as I can and Loctite them.  Takes maybe a half hour with practice, eliminates a weird thing that could be prevented easily.  Unfortunately there is plenty of opportunity to get practice.  (First you remove the tail housing, then the shift fingers, then the mid housing, and then you can access the mid plate bearing retainer bolts.  Can't get to all of them but some is better than none)

When I started using ACT pressure plates, I also started experiencing breakage of the clutch fork and/or pivot ball.  I reinforce the snot out of the ball with weld, and reinforce the clutch fork with a strip of metal across the front to keep the ball socket from punching out.

As far as clutch wear around the outside of the disc, could be from the disc wobbling due to slightly excessive clearance on the input shaft splines-to-hub. Normally i would check this by having the rear up on stands and revving the engine up near redline with the clutch pushed (in gear) to see if it starts spinning the back wheels at high rpm.  I wouldn't spend much time trying to figure it out though since you're replacing the clutch anyway.

Knurled. said:

When I started using ACT pressure plates, I also started experiencing breakage of the clutch fork and/or pivot ball.  I reinforce the snot out of the ball with weld, and reinforce the clutch fork with a strip of metal across the front to keep the ball socket from punching out.

I don't think I'm going back to an ACT. I had the FM Happy Meal in it originally, but when I had to do the unexpected clutch change I needed a clutch in a hurry and they didn't have fast shipping options at the time and I didn't want to wait a week and a half, so I priority-mailed it from Good-Win

In reply to NickD :

EvanB has the Happy Meal in his Miata.  I thought he had a stock clutch due to the light and controllable feel.  Very much excellent clutch.

I only have ACT clutches because I bought a car and later an engine that came with them. 

I found the bolt. It was actually hiding in the fold of the rubber clutch fork boot. Head was fine, just the last two threads were gacked. That's a $2100+ bolt. ($750 transmission + $700 clutch + $700+ ring and pinion)

That makes sense.  It had to be somewhere.  Kinda like that time I blew a turbo.  It shot the nut up into the air intake system, unbeknownst to me.  Put the new turbo on, started it up, much bad noises and $700 down the drain.