Clutch master problems

[Lukens]

Help me out here. I'm either overlooking the obvious or I'm as dumb as I look.

I lost my clutch today in a course of maybe five miles (all okay yesterday).
I have a TR3 with separate brake and clutch masters.
Tin can reservoir is full.
No signs of leakage at master or slave.
Clutch is dead soft.
It appears that no juice is being pumped out of the master.
1) I assume IF the piston seals in the master or slave were leaking, juice would be pouring out. So I've ruled that out?
2) I also assume that there's a check valve of sorts on the inlet line. I don't see the level in the reservoir going up with the pedal going down, so I've ruled that out?
3) I'm guessing the master is full of air and needs bled but I can't understand how air got in.
Am I missing something? If the master needs bled, can I pressure bleed it from the slave (like I've done motorcycles)?
I hate the idea of having Dot 4 all over my firewall.
Any and all info will be greatly appreciated.
Russ

 

[TR3driver]

This sounds really familiar ... wasn't Moseso or someone complaining about this exact same problem a few months back? Unfortunately I don't recall what the conclusion was, but you might search through the old threads and see what you can find.

Have you checked that the slave isn't actually moving when you press the pedal? Since the TR3 uses a return spring on the slave, a broken taper pin would act like this. The slave would move, but the fork inside the housing just turns on the shaft due to the broken pin.

 

[Lukens]

Have you checked that the slave isn't actually moving when you press the pedal? Since the TR3 uses a return spring on the slave, a broken taper pin would act like this. The slave would move, but the fork inside the housing just turns on the shaft due to the broken pin.

You've lost me here. I'm certain the rod is not extending out of the slave. Taper pin?

 

[bobhustead]

No fluid leaks at slave? Master reservoir still full? The prior thread to which Randall refers ended with a failed check valve in the M/C.
Bob

 

[bobhustead]

Do you mean that the pushrod at the slave is not moving?
Bob

 

[Lukens]

No visible leaks above or below. Reservoir right up to top.
The slave pushrod extends about 1/4".

 

[TR3driver]

You've lost me here. I'm certain the rod is not extending out of the slave. Taper pin?

If the rod is not extending, then you can ignore this theory.

The slave push rod pushes the lever, which turns the shaft that runs through the bellhousing. In the middle of the shaft (inside the bellhousing), there is a fork that reaches up around the shaft and pushes against the throwout bearing, which in turn operates the clutch. The fork is located to the shaft by a taper pin, which sometimes breaks. When it breaks, the fork turns on the shaft a little (usually until the other end of the pin comes up against the hole), just enough to screw up the action of the slave cylinder. Curse words usually ensue, since it is a major PITA to remove the gearbox just to replace a $3.95 part! Got the greasy T-shirt ...

Because of the various ratios involved, a full stroke of the pedal only moves the pushrod by a bit over 1/2", so any lost motion at the shaft/fork joint is fatal to clutch operation. But it can be hard to detect when that happens.

 

[bobhustead]

Slave pushrod extension seems inadequate. Try bleeding via the fitting on the slave.
Piston rubber failures don't always immediately show leaks. Trying the bleed will show you how well the master is working. If it looks good, next stop is repair or replacement of the slave.
Bob

 

[Lukens]

No fluid leaks at slave? Master reservoir still full? The prior thread to which Randall refers ended with a failed check valve in the M/C.
Bob

A failed check valve makes sense... pushing fluid right back to reservoir. However, I see no motion or rise in the reservoir when I push the pedal.

I think I'm going to pump some fluid up through the slave bleed screw and see if it goes in the reservoir.
Like I said earlier, I hate the idea of Dot 4 squirting all over my "little baby". :frown-new:

 

[bobhustead]

See what comes out of the slave bleed valve when the pedal is pushed.
Bob

 

[Lukens]

Update
From my motorcycle days - I drained the reservoir down about an inch, filled a LARGE syringe with fluid, and connected it to the slave bleed screw via tubing. I forced about an ounce backwards up through the slave, through the master, and into the reservoir. Clutch is now working... but I'm confused.


I'm not familiar with the operation of the master cylinder, but I'm guessing that as the piston advances a bit, it seals off a port from the reservoir. This would explain how I was able to push fluid backwards in the "pedal up" position.
Doing this alone, I was not able to see whether or not I pumped any air into the reservoir.
Now I'm not sure where I am. I guess I'll keep an eye on it and carry some extra tools and fluid.

 

[drambuie]

I used to own triumphs, Tr6, Tr4s I am assuming the Clutch and Brake masters are close to the same.... Try checking under the dash where the master cylinder connects to your clutch peddle, pull the rubber dust cover back and see if there is leakage there! I would NOT bleed the Master at the fire wall! I had my Tr6 clutch go dead soft one time....It was a broken clutch fork pin! Triumphs are famous for that! I bought a upgraded clutch fork pin at TRF...as well as a new throw out bearing and everything else as long as i had the tranny out! I even converted it to a J-type overdrive!.... one thing leads to another! If you ever rebuild your system, Go with Dot 5, I really like it very much over the paint eating Dot 3. Anyway, I own a Healey BJ8 now, But i still miss my TR-6!

One last thing before you dig to deep.... Try just rebuilding or replacing the clutch master and slave cylinder, then bleed at the slave..... that alone may be your whole problem! If not.... I would suspect a broken clutch fork pin!

 

[Moseso]

Yes... I did have similar issues last summer. In the end, I remain mystified as to the cause, but my clutch system was sucking air in, somehow, without any fluid loss. Periodic bleeding of the clutch would get rid of the bubbles and restore function -- until it sucked more air in. Rebuilding the master cylinder seems to have cured it. If the symptoms return, I will get the MC sleeved and try it again.
Virtually EVERY mechanic I talked to about what was happening said he'd never heard of such a thing. I know I'd never seen the like before. Fortunately, throwing a new seal kit into the MC and the slave is one of the easier jobs on a TR3.

 

[Lukens]

Yes... I did have similar issues last summer. In the end, I remain mystified as to the cause, but my clutch system was sucking air in, somehow, without any fluid loss. Periodic bleeding of the clutch would get rid of the bubbles and restore function -- until it sucked more air in. Rebuilding the master cylinder seems to have cured it. If the symptoms return, I will get the MC sleeved and try it again.
Virtually EVERY mechanic I talked to about what was happening said he'd never heard of such a thing. I know I'd never seen the like before. Fortunately, throwing a new seal kit into the MC and the slave is one of the easier jobs on a TR3.

I've already ordered both rebuild kits. I'm hoping the cylinder bores are decent and don't need attention.

Am I right that both bores are the same (TS-45693)? If so then the slave should advance 1 to 1 with the master... assuming I've bled all the air out?

Thanks for all the replies. This internet is a wonderful tool.

 

[PKPoole]

Wow. I'm waiting for the final conclusion to this story. My best guess is that you clutch master (main) seal is weak. Since the seal has its lip pointing in the direction of motion it will still seal when pushing. However, it will suck air when the pedal spring forces it back, thus letting air into the clutch cylinder. Good luck, and let us know! Pat

 

[TR3driver]

Wow. I'm waiting for the final conclusion to this story. My best guess is that you clutch master (main) seal is weak. Since the seal has its lip pointing in the direction of motion it will still seal when pushing. However, it will suck air when the pedal spring forces it back, thus letting air into the clutch cylinder. Good luck, and let us know! Pat

I don't think so. The pedal spring cannot force the piston back, there isn't a solid connection between the piston & pushrod. The pedal will return even if the piston is stuck at the bottom of the bore.
The MC internal return spring does force the piston back, but normally it is not as strong as the slave return spring, so I think the pressure should always stay very slightly positive. At any rate, I've worn out that seal several times over the years, and I've never had it suck air until the reservoir was dry.

 

[Bob Claffie]

When the seal in the MC fails, many times the piston will create nominal pressure (the 1/4" movement at the slave) and allow the fluid in the MC to bypass the seal. Result is next to no pressure and no leakage. The fluid is just riding back and forth in the MC and doing no meaningful "work". Bob

 

[TR3driver]

Am I right that both bores are the same (TS-45693)? If so then the slave should advance 1 to 1 with the master... assuming I've bled all the air out?

IIRC, the slave is larger diameter than the master. 1" and .75" are the numbers stuck in my head, but I could be mistaken. If those are right, then the slave only moves about half as far as the master (the motion ratio is the square of the bore ratio).

 

[Lukens]

When the seal in the MC fails, many times the piston will create nominal pressure (the 1/4" movement at the slave) and allow the fluid in the MC to bypass the seal. Result is next to no pressure and no leakage. The fluid is just riding back and forth in the MC and doing no meaningful "work". Bob

Wouldn't the fluid leak past the seal and out the cylinder?
I'm anxious to tear the Mastercylinder down, then I'll have a better understanding of the internals. None of my literature shows that well.

 

[Lukens]

Like I said, I've got a Haynes manual and all 3 suppliers catalogs (plus the net) and I haven't found a decent explanation or drawings of the internals. Sure would help.

IIRC, the slave is larger diameter than the master. 1" and .75" are the numbers stuck in my head, but I could be mistaken. If those are right, then the slave only moves about half as far as the master (the motion ratio is the square of the bore ratio).