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amg_rx7
amg_rx7 HalfDork
7/3/10 2:23 a.m.

I'm trying to figure out what might be causing this...

1990 base model, 180k miles. Don't know age of clutch but it has been replaced at least twice in its life. Stock car but there is a lightweight flywheel in there.

This just happened rather suddenly although the car hasn't been driven much over the last 5 years. The car was on jack stands for the last couple of months with suspension, control arms and everything in pieces to refresh everything including calipers and brakes. Clutch felt normal before I took it down to do this maintenance.

The Clutch failed while I was bedding in the brake pads after a few repeated 2nd gear runs to redline, push in clutch, hit brakes slow down to 10 MPH, rinse repeat.

On one of those cycles, hit the clutch and brakes and the trans wouldn't pull out of gear.

The clutch fluid looked terrible so I replaced the slave and bled. No difference. Did the master next and bled. No difference. Clutch fork seems to move about 1" when actuating clutch.

Not able to get in gear w/ car running but, once moving, the trans will shift if forced and I get lucky matching revs - like driving w/o a clutch.

Seems like there is a problem with the clutch itself. Either PP or something else. Any ideas?

Thanks

Kramer
Kramer HalfDork
7/3/10 7:37 a.m.

Replace slave, try again. If problem still exists, replace master. That should fix it, relatively inexpensively.

Jensenman
Jensenman SuperDork
7/3/10 8:05 a.m.

Sounds to me like what Kramer says: hydraulic failure. Not terribly uncommon. IIRC the fork should move somewhere around 1 1/4", so if it's only moving 1" that's not enough. Check the hoses, I had an MG hose that would seal tightly under pressure but when the pedal was released the hose would not seal at the crimp, that sucked air back into the system. No matter how many times i bled the friggin' thing, I kept getting a soft pedal and no disengagement. Now THAT was weird.

A guy showed me a disc once that had the facing come off of one side, it remained all in one piece. It wedged between the PP and the disc, the clutch wouldn't release.

A real long shot: seized pilot bearing. That generally includes some noises though.

moxnix
moxnix Reader
7/3/10 8:19 a.m.
Jensenman wrote: A guy showed me a disc once that had the facing come off of one side, it remained all in one piece. It wedged between the PP and the disc, the clutch wouldn't release.

I had something like that happen to my miata. Parts of of clutch broke off got stuck in there not letting me shift and everybody kept telling me I was just not bleeding it enough. I replaced both the slave and master before tearing out the clutch. Once I pulled the clutch I found this.

Those little pieces got stuck somehow preventing the pressure plate fingers from doing what they should and I had no weird noises.

amg_rx7
amg_rx7 HalfDork
7/3/10 12:41 p.m.

Hydraulics already replaced guys.

I'll remeasure clutch fork movement as I've only eyeballed it.

Thanks.

fastmiata
fastmiata Reader
7/3/10 7:47 p.m.

I have found that the slave cylinder goes bad when the car sits for long period and that it takes massive effort to bleed the new cylinder and lines to get it all working together. Bleed and bleed again. YMMV

carzan
carzan Reader
7/3/10 8:28 p.m.
amg_rx7 wrote: ...I'll remeasure clutch fork movement as I've only eyeballed it. Thanks.

Yes, I think the clutch fork movement is key here. If you have full movement, I think the problem is most likely something within the bellhousing. If you don't have full movement of the clutch fork, it's most likely to be hydraulic (assuming you have full pedal movement). My next step, if I were you, would be to replace the hose, if you haven't already, in case it is ballooning somewhere. I would imagine that is still original/20 years old and relatively cheap.

Streetwiseguy
Streetwiseguy Reader
7/3/10 10:18 p.m.

If you have a hydraulic problem, you will be able to feel it in the pedal. On a hydraulic clutch, if you are paying attention, there are three distinct elements- you should feel a mm or two of pedal movement with no pressure whatsoever- thats taking up the slack between the pedal and the pushrod, and the pushrod and piston. Second stage is the hydraulic pressure taking up the slack between the slave and the pushrod, and release bearing to pressure plate. Thats what we used to call freeplay back when stuff was adjustable. Third stage is the actual movement of the release bearing.

What you need to pay attention to is the second stage- the easy travel before things really start moving. Any more than about 10-15 mm of pedal travel there, and you've still got air or hydraulic problems. If the slack takes up in less than 15 mm, you probably have a mechanical issue with the disc or pressure plate.

amg_rx7
amg_rx7 HalfDork
7/4/10 5:07 p.m.

The line is in good shape. No ballooning or leaks.

The clutch pedal engages at the very bottom - about 1 - 2" off the floor. It only seems to have tension at the very bottom. The clutch fork only seems to move about 1/2 - 3/4" with that small amount of pedal movement at the bottom.

If feels like when my clutch fork broke on my RX7 (FD). I really don't think its hydraulic. Clutch forks don't seem to be a problem on Miatas from what I have researched searching M.net.

It does indeed seem to be a mechanical failure with the clutch itself.

unevolved
unevolved HalfDork
7/4/10 5:25 p.m.

The pedal travel is adjustable. Think it could be something as simple as that?

Streetwiseguy
Streetwiseguy Reader
7/4/10 6:46 p.m.
amg_rx7 wrote: The line is in good shape. No ballooning or leaks. The clutch pedal engages at the very bottom - about 1 - 2" off the floor. It only seems to have tension at the very bottom. The clutch fork only seems to move about 1/2 - 3/4" with that small amount of pedal movement at the bottom. If feels like when my clutch fork broke on my RX7 (FD). I really don't think its hydraulic. Clutch forks don't seem to be a problem on Miatas from what I have researched searching M.net. It does indeed seem to be a mechanical failure with the clutch itself.

If the pedal is soft to the bottom, you have air in the system. Hydraulic clutches can be a bear to bleed, and its pretty much impossible if you are pumping the pedal with the bleeder open. I pressure bleed, pushing fluid up from the bottom. Thats tough to do without the right equipment.

Jensenman
Jensenman SuperDork
7/4/10 10:15 p.m.

Soggy with 'feel' at the bottom sounds like air in the hydraulics to me, too. Get one of those 'one man' brake bleeders or use a piece of vacuum hose and a jar or cup and have at it. The olde tyme 'one guy pumpin', one guy working the bleed screw' system works real well, too.

unevolved
unevolved HalfDork
7/4/10 11:20 p.m.

A vacuum bleeder won't work on a Mazda clutch slave. Something about the pressure (or lack thereof) collapsing something inside the cylinder, you will be sitting there all day pumping away. Ask me how I know. The only dependable way, short of a pressure bleeder, is a friend.

amg_rx7
amg_rx7 HalfDork
7/5/10 1:51 a.m.
Jensenman wrote: Soggy with 'feel' at the bottom sounds like air in the hydraulics to me, too. Get one of those 'one man' brake bleeders or use a piece of vacuum hose and a jar or cup and have at it. The olde tyme 'one guy pumpin', one guy working the bleed screw' system works real well, too.

Already bled it 3 times. Did the 2 person bleed.

It is solid feeling at the bottom but engages very low. Even with the clutch pedal pressed to the floor, the clutch remains partially engaged and can move the car. 1" off the floor, the clutch if fully engaged.

Annoying...

44Dwarf
44Dwarf HalfDork
7/5/10 6:30 a.m.

You need to vacuum bleed it from the master cyl. You said you replaced it already so take the old cap and drill a hole one size smaller then the hose on your mighty vac. now stuff the hose in it and push it down so the hose goes in the the res about 1/2 down. hook other end to your might vac canister and then to the pump. Down at the slave hook up a hose to the bleeder, put other end in to a jar of brake fluid. Now YOU MUST do this next steep the make this work faster. Bleed the hose from the slave just like you would normally. You don't want to pull the air in the hose all the way to the master. After a few pumps of the master and closing of the bleeder the air should be out of the hose. Now pump up your mighty vac and open the bleeder this should draw fluid from the jar and out the master as air wants to raise it will go up and out the master cap.

You can buy and injection syringe to do this but they don't hold much, and you need allot of fluid at least a full quart to do it right.

Motorcycle brakes are a pain like this as many have hard lins half way down.

44

Jensenman
Jensenman SuperDork
7/5/10 9:18 a.m.

+1 on motorcycle brakes being a PITA to bleed if they get air in them. Any loops in the lines which are higher than the M/C bore will hold an air pocket, the only way to get the damn things out is to push, not pull, the fluid. In fact, any time the lines have a 'high' point they can hold an air pocket even if it's not higher than the M/C. BTDT. Here's the kind of 'loop' I'm talking about:

On really tough car systems (like old Isuzu Troopers) I have done this: first, make sure the M/C pushrod is properly adjusted. On most cars this means ~ 1 mm of movement, measured at the pedal pivot point, before the piston starts to move. Get a friend in the car who has nothing better to do for a while. Stuff rags under the clutch master cylinder. Then have the friend pump the pedal a few times and hold it, now loosen the flare nut on the M/C so fluid will run out around it. Usually you will get all kinds of foamy crap, that's a sign the M/C has air in it. Do this 3 or 4 times or until you no longer get foamy stuff. Keep the M/C full, of course.

Now go down the line, repeating the loosening and bleeding at each connection, all the way down to the slave cylinder and then bleed it yet again. That will usually fix the hard cases.

amg_rx7
amg_rx7 HalfDork
7/5/10 12:38 p.m.

Good tips.

One more data point that I'd like your opinions on.

The clutch felt the same (same behavior) with the old master and slave as with the new one I installed. Does that mean anything to you guys?

Thanks.

carzan
carzan HalfDork
7/5/10 2:04 p.m.
amg_rx7 wrote: Good tips. One more data point that I'd like your opinions on. The clutch felt the same (same behavior) with the old master and slave as with the new one I installed. Does that mean anything to you guys? Thanks.

I see what you are saying and have been mulling it over since your original post. You would think that if it were a hydraulic problem, replacing the cylinders would resolve it.

Personally, of the many Miata clutch master/slave replacements I have done, I have never had any real problem getting them bled. I certainly haven't had to go to the lengths others have posted here (although all good ideas), so I can understand why you would think it was an issue within the bellhousing.

Again, I feel that the movement of the fork (or lack of) is a clue and it would seem to point to lack of hydraulic pressure whether due to air in the system, maladjusted linkage etc. I mean, if the hydraulics are working properly, wouldn't you see full movement of the fork regardless of whether there was a PP/disk fault?

The only reason I can think of that would give the symptoms you describe and be a component within the bellhousing would be if the pivot arm isn't returning to the "home" position with each pedal press, but I would think you would have noticed that when you replaced the slave cylinder. (That doesn't mean it isn't possible, I just can't think of anything).

Good luck and I'd really like to know how this turns out.

amg_rx7
amg_rx7 HalfDork
7/5/10 5:44 p.m.
carzan wrote:
amg_rx7 wrote: Good tips. One more data point that I'd like your opinions on. The clutch felt the same (same behavior) with the old master and slave as with the new one I installed. Does that mean anything to you guys? Thanks.
I see what you are saying and have been mulling it over since your original post. You would think that if it were a hydraulic problem, replacing the cylinders would resolve it. Personally, of the many Miata clutch master/slave replacements I have done, I have never had any real problem getting them bled. I certainly haven't had to go to the lengths others have posted here (although all good ideas), so I can understand why you would think it was an issue within the bellhousing. Again, I feel that the movement of the fork (or lack of) is a clue and it would seem to point to lack of hydraulic pressure whether due to air in the system, maladjusted linkage etc. I mean, if the hydraulics are working properly, wouldn't you see full movement of the fork regardless of whether there was a PP/disk fault? The only reason I can think of that would give the symptoms you describe and be a component within the bellhousing would be if the pivot arm isn't returning to the "home" position with each pedal press, but I would think you would have noticed that when you replaced the slave cylinder. (That doesn't mean it isn't possible, I just can't think of anything). Good luck and I'd really like to know how this turns out.

Actually, I wasn't paying attention at all. I just replaced it following the recommendations of everyone else. I haven't had the Miata long. Belonged to a good friend before me and I've been reviving it. I'd like to find another local Miata guy after the holiday so I can compare clutch fork throw length.

Streetwiseguy
Streetwiseguy Reader
7/5/10 8:11 p.m.
amg_rx7 wrote: Again, I feel that the movement of the fork (or lack of) is a clue and it would seem to point to lack of hydraulic pressure whether due to air in the system, maladjusted linkage etc. I mean, if the hydraulics are working properly, wouldn't you see full movement of the fork regardless of whether there was a PP/disk fault?

This.

Jensenman
Jensenman SuperDork
7/5/10 9:01 p.m.

Miatas have (at least to me) very light clutch pedal resistance, so I can see where it might feel very similar before and after.

amg_rx7
amg_rx7 HalfDork
7/12/10 1:52 p.m.

Looks like my clutch fork is broken.

http://www.youtube.com/watch?v=L6TdipaIQ0c

Keith
Keith GRM+ Memberand SuperDork
7/12/10 3:53 p.m.

I was offline for a couple of weeks, sorry I missed this. If you have nearly 1" of travel at the slave, nothing's wrong with the Miata hydraulics.

I don't know if the fork is actually broken due to that video, it might simply have fallen off the throwout bearing (although I cannot explain how). But regardless, the fix is inside the bellhousing.

amg_rx7
amg_rx7 HalfDork
7/12/10 4:36 p.m.

Yes, so it seems.

Thanks for the input.

gswaybright
gswaybright None
9/11/11 11:00 p.m.

Did you ever get this clutch issue fixed? What finally resolved it. I've been battling the same problem with hydraulics.

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