What did the PO screw up? Speculating is easier than working on it - Miata clutch content

I've been very slowly (with minumum effort) rehabbing a beater 1.8 NA with ~180k that I bought last year for $1200.

One of the things that stood out when I bought it was just how bad the clutch was.  The entire engagement was the top .75-1" of the pedal, the rest of the throw did nothing (but it didn't hurt anything, either).   But it did function completely normally, apart from being kinda grabby on engagement.  I attribute that to the lack of control in the miniscule engagement window and worn motor mounts.  I adjusted the pedal a bit (and got the usable range down to ~1.25-1.5"), but otherwise have driven on.

I've been driving it for a year now, and it's not really gotten worse.  I was expecting it to be noticeably slipping by now, but it always seems to hold.  It is getting more grabby on engagement recently (I'm guessing it has a rear main seal leak), so I figured christmas break was the time to replace it.

The other night, I started in on it and got as far as getting the car up in the air and the PPF out and driveshaft removed.  It's pretty obvious that a PO was in here before, and badly.  The driveshaft was missing half the lock washers, and most of the plastic clips to hold the wiring harness to the PPF were broken.

So now I'm thinking that maybe it's not just a clutch that's failing after 180k, maybe the PO screwed something up? 

Put in your speculation now as to what the problem is?  I'm guessing the grabbiness is from oil contamination due to leaking rear main seal.   What's the cause of "only using the travel of the pedal?"  Bent pressure plate fingers?

Air in the line. Or bad hydraulics. 

Last vote is disc in backwards. 

There isn't very much a person can do to make a clutch engage right at the top of the travel and not slip.  That is usually a sign of a mostly worn out, but not greasy or bent clutch disc.

Dusterbd13-michael (Forum Supporter) said:

Air in the line. Or bad hydraulics. 

Last vote is disc in backwards. 

I forgot to mention that I had replaced the slave cylinder due to leak at one point...  Do you think it's worth looking closer at the master?

Streetwiseguy said:

There isn't very much a person can do to make a clutch engage right at the top of the travel and not slip.  That is usually a sign of a mostly worn out, but not greasy or bent clutch disc.

That was my original thought, but any cars I've previously driven with this sort of engagement were ~500 miles from slipping.  This one has done a few thousand this way (probably 5000 at this point?).

Dusterbd13-michael (Forum Supporter) said:

Air in the line. Or bad hydraulics. 

Last vote is disc in backwards. 

Backwards usually slips and drags, IIRC. This doesn't sound right.

Maybe it's just a crap clutch. Some sort of "improved" puck thing.

Keith Tanner said:

Maybe it's just a crap clutch. Some sort of "improved" puck thing.

You know, the funny thing is that that is the one scenario I hadn't thought of...  That would totally fit, though.

Slave cylinder on its way out?

EDIT: I see you already dealt with that. Ignore me. 

In reply to WonkoTheSane (FS) :

Shameless shilling for myself here but if you feel like doing a nice upgrade I have one too many clutches in my inventory just now.  A Happy Meal stage 1 (pressure plate, clutch disc, lightweight flywheel) with zero miles on it.  I'd knock a couple hundred dollars off retail if you want it.  So $500 shipped if you're interested.

KyAllroad (Jeremy) (Forum Supporter) said:

In reply to WonkoTheSane (FS) :

Shameless shilling for myself here but if you feel like doing a nice upgrade I have one too many clutches in my inventory just now.  A Happy Meal stage 1 (pressure plate, clutch disc, lightweight flywheel) with zero miles on it.  I'd knock a couple hundred dollars off retail if you want it.  So $500 shipped if you're interested.

Thanks for the offer, Jeremy!  This one calls for cheapest viable option, so I went with an Excedy clutch kit from Rock Auto.  I think I'm under $300 for a clutch kit, flywheel, rear main & transmission output seals and a shifter rebuild setup from Flyin Miata.  I'd take you up on the offer for my track car, but I have a lightly used happy meal setup sitting on the shelf for it :)

Unfortunately, last night I only had about 45 minutes to play (gotta love the lead up to Christmas), so I got the exhaust off of the header.  Those 3 nuts took all of that time, but they came out!  Those were the 3 I was most worried about on this project (I've more than a few Miata transmissions).   The rest should be smooth sailing.

Sometimes reality is stupider than fiction.  

Here's the whole reason I had to take this apart:

Give up?

Yes, that's right, the PO put washers under the pressure plate.

Uhm... and why would someone even think of doing that?

The pressure plate was "bending" when they tried to bolt it down?

aircooled said:

Uhm... and why would someone even think of doing that?

The pressure plate was "bending" when they tried to bolt it down?

 

No idea!  There was one under each bolt at least?

It confused the shiat outta me when I started pulling the bolts out and these washers started dropping down!

Is the pressure plate and disc correct for the application? I would check whatever part numbers are visible. They did that for a reason and at the time they thought is was a good reason.

In reply to NOHOME :

Lots of dumb people think they have a reason for doing dumb things.

That still doesn't explain it to me, because the hydraulics should auto adjust for any difference in pressure plate finger distance.  The only thing it should do is reduce the clamping force of the pressure plate.

I mean, MAAAYBE the cosine (sine?) difference is enough to change the motion ratio enough that the clutch disengages faster?

If it wasn't a 9000rpm grenade aimed at my feet, I'd try it.  I prefer a clutch that disengages quick and high up.

In reply to Stampie (FS) :

Agreed, but to assume it was done for no good reason, bolt it back together sans washers and find out that there might have been a reason wont make you smart. 

I do a lot of dumb things in hopes of getting away with it, but there is always a reason.

I would want new parts at this point just to start fresh. 

What does the flywheel look like?

Pete. (l33t FS) said:

That still doesn't explain it to me, because the hydraulics should auto adjust for any difference in pressure plate finger distance.  The only thing it should do is reduce the clamping force of the pressure plate.

 

I mean, MAAAYBE the cosine (sine?) difference is enough to change the motion ratio enough that the clutch disengages faster?

 

If it wasn't a 9000rpm grenade aimed at my feet, I'd try it.  I prefer a clutch that disengages quick and high up.

Maybe it hit the limit of adjustment of the hydraulics. Whatever the reason, it's hilarious. You're not going to guess that one ahead of time. This is why some of the questions I ask when troubleshooting seem really basic and ridiculous, after 20 years or so you have learned that maybe today is the day something really random happens.

If you want a high, fast disengagement I'd be messing with either pedal ratios or MC sizes.

Hmm, yeah.... maybe it was always partially disengaged but not slipping enough to notice (the grabbiness may have helped here) so depressing the clutch pedal was just disengaging it the rest of the way?

Maybe it was grabby because the friction disc was pre-heated :)

That is a new one for me. 

So I had to take a break for lunch, but I was also really curious whether the numbers and such would match up for a Miatas application..

I can't find them anywhere online?  I mean, when was the last time google's and bing's result pages were actually blank for you?

It's a "PHT" clutch and PP.  Disc #s D80117 & 3510.  So I'm at a loss there.

I can tell you it lines up with the new excedy stuff I got for it:

And, shockingly enough, the PP fingers seems to have excessive wear!

The flywheel itself is fairly worn, minor inside to outside rippling, with minor overheating cracks on the surface.  

I've joked that on the fully caged car, it's easier to replace the clutch than adjust the pedal, but it was a joke!

Oh, and yeah, I've got a new flywheel, excedy clutch kit, rear main seal, shifter rebuild, and fluid while I'm in there, so, it's really just an enigma.  New stuff is going in.