Help diagnosing clutch issue

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Help diagnosing clutch issue

Postby 07miata » Sat Mar 23, 2013 6:23 am

Good morning,
I have a street/track 2007 NC1 with an Exedy clutch with 49,000 miles on it, that has become noticeably more difficult to shift both out of, and into gear, over the last year or so. My clutch was installed ~3 years ago and I didn't notice any difficulty then. I figure it must(?) be either the fluid, clutch adjustment, slave cylinder, throw-out bearing, and/or synchros. Below are some tests I've done to try and rule things in and out, and I'm at a loss what to try next. Any help is appreciated.

1. There is no grinding when going into or out of gear, so I doubt it's the synchros, especially on such a young tranny

2. There's no rattling or whirring with the clutch in or out, so I doubt it's the throw-out bearing. Is there another test without dropping the tranny?

3. I fully bled the entire brake and clutch system several times with no noticeable change in difficulty shifting

4. It's most pronounced at the track after it gets hot. I usually resort to double-clutching to change gears. At first I thought the double-clutching worked around bad synchros, but now I wonder if the double-clutching builds up more pressure in the hydraulic system that's lacking, which is why it helps?

5. With the car jacked-up and in NEUTRAL, and the clutch in, I rev to 7K RPM, nothing happens. If I let the clutch out and rev up to 7K RPM, the rear wheels start spinning, which obviously shouldn't happen because in theory the car's in neutral??

6. If I shift regularly the difficulty is maybe 6 out of 10. If I hold the clutch in for 3 minutes then shift the difficulty seems to get worse, maybe 7 or 8 out of ten. Could the slave cylinder be leaking fluid back into the reservoir?

7. Pulling back the rubber boot on the slave cylinder it's bone dry. Does that mean it's not broken and it can be ruled out? (I was hoping it was soaked!!!)

8. The shift point on the clutch pedal is very high off the floor, and hasn't changed in any way over the years. I'd imagine if it was out of adjustment, the shift point would be moving closer to the floor? I really have no complaints about the shift point -- the fact it's so high off the floor means it should be grabbing plenty of fresh fluid per shift, no?

If anyone can think of another test I can do without dropping the tranny let me know, otherwise I may take it into a local shop or replace the slave cylinder myself just to rule that out. Thanks!
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Joined: Mon Nov 05, 2007 9:17 am

Re: Help diagnosing clutch issue

Postby 07miata » Sat Mar 23, 2013 6:52 am

FYI, in case it matters, I use ATE Superblue brake/clutch fluid and Red Line MT-90 tranny fluid, and have forever, so that hasn't changed.
Posts: 112
Joined: Mon Nov 05, 2007 9:17 am

Re: Help diagnosing clutch issue

Postby jboemler » Sat Mar 23, 2013 1:04 pm

1. Agreed.

2. If a throwout bearing doesn't fail all at once (usually won't disengage), it starts by making noise when the clutch starts to disengage. Doesn't sound you've got any of that.

3. Not surprising, I doubt the problem is hydraulic.

4. Not impossible, but I doubt it if you've bled the system.

5. Perfectly normal, movement is being carried by the gear lube in the transmission. You can stop the wheels with the brakes and the engine will keep going.

6. Holding the clutch in for three minutes is just abuse of the throwout bearing, not sure why you would even do that. But no, the fluid in the slave can't leak back into the reservoir -- there's only one line.

7. This is the test for a bad slave. If it's dry in there, the slave is fine.

8. You have to be careful about the high pedal. The master gets new fluid from the reservoir through a hole that's only exposed when the master is completely withdrawn. If you adjust the pedal too high, the rod becomes too long to allow the hole to be exposed, and you've got a sealed hydraulic system. At that point the actuation point will vary with temperature (of the fluid). The trick is to go under the dash and wiggle the rod, to be sure that there's really play in it when the clutch pedal up. It doesn't take much play, but the rod needs to be free.

Overall, my guess is that you've bent a rod or fork inside the transmission, and there's just nothing outside that's going to help, but check the pedal adjustment before you go pulling the trans.
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Location: Mukilteo WA

Re: Help diagnosing clutch issue

Postby 07miata » Sat Mar 23, 2013 3:35 pm

Thanks for the help, I appreciate it. For #6, someone suggested that test to see if the slave was leaking fluid back due to a bad seal, but they weren't as familiar with Miatas as you are, so good to know. That would suck if I bent something inside the tranny. :( I will readjust the clutch pedal to see if that helps, just need to buy a blowtorch to loosen this lock nut!
Posts: 112
Joined: Mon Nov 05, 2007 9:17 am

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