Clutch Issues

[jayb]

So, I've got about 1000 miles on my 68 Mustang now, with the 428 CJ (my former dyno mule), and the T56 Magnum transmission.  I got the complete transmission setup from American Powertrain.  The T56 is wonderful, shifts like a dream, all the gears are easy to find, etc. etc.  However, my clutch is behaving strangely.  I have the hydraulic clutch master cylinder and hydraulic throwout bearing that came with the kit, they installed and bled fine, and mounting the master cylinder was no real problem.  However, from day 1 with this combination, the clutch pedal has been sticky.  When you try to release the clutch pedal from the floor, it comes up about a third of the way feeling normal, then it seems to stick.  If you then start letting off the pedal pressure it will not move at first, but when it hits a certain foot pressure level it will suddenly pop up to about two thirds of the way up, and then stick again.  Again, to get it to move you have to release the pedal pressure.  Then, since you have started releasing some of the pressure it comes up too fast and engages with a lurch; you can't control it.  Seems to do it more when it is cold, but the issue is present all the time.  Makes pulling away from stoplights or stop signs rather problematic.

After I got the car put together and this problem persisted for a few hundred miles, I concluded that it must be a clutch pedal or linkage issue.  I took it all back apart, and made sure to lube the pedal cross shaft where it goes into the pedal tree, and replaced the plastic bushings in the pedal tree.  But the old bushings looked fine.  There didn't seem to be any binding on the rod from the pedal to the clutch cylinder, but I made sure that the rod cleared the firewall properly, and that there was no binding where it connected to the pedal.  After going through all this, there has been no change; the problem is exactly the same.

This clutch is a dual disc McCleod diaphram style clutch.  Is it possible for the fingers to stick on these things, or is this something that can be encountered with a hydraulic clutch setup?  Could this be an adjustment issue?  I'm beginning to think I should have put an automatic in this thing...

[blykins]

Twin disc or dual friction?

If it's a mechanical linkage and a diaphragm plate, you could be overcentering the pressure plate.

[jayb]

Sorry, I just looked up the sales order and it says the clutch is a Science Friction Atomic Twin SFAT26AF clutch, 950 ft-lb rated, Ceramix discs.  Two clutch discs with a floater plate.

[blykins]

Never heard of them. 

I jumped the gun on overcentering.  Just reread and saw it's all hydraulic.  Less likely to do it with hydraulics.

Have any return springs anywhere?

[Tom Gahman]

Is it a slave cylinder or a hyd. t/o bearing?
I've had slaves that acted like that. (import)
With the bleeder open you could feel the stroke wasn't smooth.
should be the same for the master.

[jayb]

Never heard of them. 

I jumped the gun on overcentering.  Just reread and saw it's all hydraulic.  Less likely to do it with hydraulics.

Have any return springs anywhere?

Great, I've got a brand X clutch    No return springs, in fact I took out the over center spring in the clutch pedal assembly because I thought that might be causing the problem.  Didn't help.

[jayb]

Is it a slave cylinder or a hyd. t/o bearing?
I've had slaves that acted like that. (import)
With the bleeder open you could feel the stroke wasn't smooth.
should be the same for the master.

It's a hydraulic throwout bearing, not a slave cylinder.  I may try opening the bleeder and working the pedal back and forth, at least that would eliminate the master cylinder from consideration if it felt smooth...

[Stangman]

I would have bet it was the bushings, could the throwout bearing be coking or the middle plate in between clutches. Is the pedal pressure smooth going in. Installed like the same setup in a 69 chevelle with a TKO was very smooth. Now the one that he gave me  made rattling noises when doing small menuvuers and he said he got the one with out the bushings that keeps the disc from rattling around, does yours maybe have those bushings inside and something is getting in the way. 

[WConley]

Jay -

Do you have that big clutch assist spring attached to your clutch pedal under the dash?  That could be the culprit.  Your setup may require lower pedal effort than stock, so the spring may be too strong.  Try taking the spring off.

[jayb]

Pedal pressure is smooth going in, just sticky coming out.  I can't recall if there are bushings in that center plate or not...

[stubbie]

Did you set up the depth of the clutch release bearing correctly?

[My427stang]

It is your car showing you it's unhappy that you didn't just go with a factory Z bar and heim joints and it will continue at least until you stop threatening it with a slushbox LOL

Seriously, it sounds to me like one of 3 things: a bad hyd TB, a kinked or damaged line, or maybe a bad master cylinder.  I seriously doubt it is the clutch itself.  I think I'd be leaning toward the TB, but, I'd probably reverse the line and see what happens first for laughs in case it's acting like a check valve

[jayb]

I set the depth of the throwout bearing as described in the instructions, something like 0.090" gap between the face of the throwout bearing and the clutch fingers.  Maybe I should get in there and try moving that around some.  The line isn't kinked at all, its a braided steel line and is nice and smooth all the way into the bellhousing.  You'd think with all the automatic cars around here that clutch would get wise and shape up...

[stubbie]

Just saw this about magnum T56 gearbox's and twin clutch plates (One other thing you’ll need to look at is the stack height of the clutch assembly. This is the thickness of the assembly when it is bolted together. Some twin-disc setups are thicker than stock clutch assemblies, and if this is the case in your application, you may need to trim the bearing retainer on the input shaft of the transmission to prevent it from pinching the clutch discs to the flywheel)
According to some gap should be 0.15-0.20"

[Heo]

Jay on Mercedes with hydraulic clutch there is the same
kind of "rat trap" spring on the clutch pedal as Ford have
And sometimes when the master cylinder goes bad like rusty
with piston sticking to the bore there is exactly the
problems you describe