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clutch slave cylinder

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Hairyone

Hairyone

Jedi Trainee
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bugeye with 1275 engine & box:
I've just had to change my dual master cylinder coz it was weeping. It was a 7/8" I've discs up front so brought the 3/4" master. I know the clutch is a bugger to bleed & have searched on here how to do it. I now have the slave cylinder removed & hanging down under the car & it's inside diameter looks a little big, about 1".
Who knows what the slave diameter should be for a 1275 with disc brakes & a 3/4" master?
Thanks
 
Clutch woes:
I know this is a bugger to bleed & I know I've got all air out now, having read all about it here. But I still can't dis-engage clutch.

I've done some calculations on clutch slave travel (in metric as it's so much easier, 1" = 2.54cm).

I had a 7/8" master & the 1" slave: Presume the master pushrod travels 2cm (3/4") into the master, may be a little OTT. The fluid displacement = 7.74cc put that into a 1" slave and it's pushrod travels 1.52cm.
Now with the 3/4" master and the 1" slave travels 1.12cm, considerably less.

I know my clutch slave pushrod is worn (elongated hole) but the piston is also near the end of the cylinder. This says to me one of two things:
1/ my pushrod is too short, mine is 2 5/8" from end to middle of hole. I need a new one, but how long is it supposed to be?

2/my clutch or bearings etc are near end of life.

What have others uses with this combination? My thoughts are 7/8 slave which will give me 1.34cm of travel. ??????????? :hammer:
 
One other thought is that the inside of your MC (and/or maybe your slave) is pitted. I could not get my clutch pedal to return properly and that is what it was - at that point it was time for a new MC.
 
um nice wrench, but I don't have a problem with bleeding. I un-bolted the slave, pushed up the piston & clamped it up & used an eazybleed @ 15psi.
My cylinder is clean inside, no rust & 1" dia. My master is new 2/3" I was just wondering if this is the correct size combination???
 
I don't recall for sure but it seems like I remember hearing about different length pushrods.

???

JACK
 
Harry
Don't bother with getting another slave, I seriously doubt that it will work.
One of the easiest ways to remedy (notice that I DIDN'T say "fix") this condition is to remove the slave push-rod, thread it to 5/16-24 UNF and thread a nut in it (preferably a "coupling nut" which is about 1" long) and rreplace the unit in the car. Now unscrew the nut until the slave is pushed almost all of the way into the cylinder (giving the linkage about 1/8" slop).
It should now work just like advertised.
BillM
 
Did you put the rods from the 7/8 master in the 3/4 master?
The 7/8 master rods are much longer and will not work in a 3/4 master.
 
I don't know what rod is in there but it's 2 5/8" long, which seems a little short as the slave is nearly all the way out.

I believe I need a longer one (don't we all :cooler: ), but also more movement, hence my calculations & I've lost a bit of that when swapping to the 3/4" master.

Does anyone have part numbers for the longer pushrods & perhaps the 7/8 slave?
 
Longer rods are easy, always wanted to say that, even adjustable ones. Have a bolt brazed on the end of the rod and grind it round..

HOWEVER, first put a nut in the cylinder so the rod will push on it and see if the longer rod is appropiate.
 
By going to the 3/4" master, you've lost about a quarter of your motion at the clutch release lever. That's not good, but I'd think you could still release the clutch if all else is OK.

The slave cylinder is "self adjusting": it should pump up until there is very little slack in the pushrod; i.e., the release bearing is almost in contact with its mating surface on the clutch pressure plate. Then as long as things are adjusted right so there is no slop at the master cylinder, so you get a full stroke when you push in the clutch, you're doing about as well as you can.

It's possible to have a master cylinder rebored or sleeved so you can have 3/4" for the brakes and 7/8" for the clutch. Take a look at Sierra Specialties' web site, https://www.brakecylinder.com/, or similar places.

Also, if you can't get all the slack out of the pushrod/release lever assembly, consider BillM's solution seriously. I've had to make my own pushrod on occasion to make it all work right. If the pushrod is too short, the piston in the slave can hit the retaining snap ring, preventing you from getting enough motion. Not all slaves have those, however.
 
Thanks all for advice. I'm doing two things; ordered a longer pushrod & a 7/8 slave. Once installed next week sometime, I'll report back with success rate, part numbers & pushrod length.
Ta.
 
Yipee, all works now:
Here's what I have for anyone else in this situation:
Frogeye with 1275 engine & box, converted to disc brakes but using the dual master.
new 3/4" dual master.
new master pushrods (Moss 13H3655) cut down to suit (1/2" off)
7/8" clutch slave (minispares GSY110 (LL10469))
Slave pushrod (moss AHA6409) with the spare bit from the master pushrod welded on the end.
master pipe GPP56AA (this is the smaller diameter pipe).
Goodridge Flexi hose C-AJJ4025

Results: clutch a little softer. Brakes work well, but not tried in anger yet. :driving:
 
Lovely, glad it worked out.
 
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