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Sticking M/C piston

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M

mapleaf

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After rebuilding the clutch m/c and slave cylinders on my TR3A I'm now having trouble getting the system bled and the clutch pedal to feel normal. Using the pump and wait, pump and wait system of bleeding results in loss of all pressure after about 20 minutes. By disconnecting the pushrod and pushing it into the m/c manually I noticed that the piston was sticking in the bore and not returning smoothly or not at all. When rebuilding the cylinders the bores seemed smooth enough but I used repair kits that had been on my shelf for a dozen years (probably a mistake?). Anyway, would appreciated hearing of any causes for the piston getting hung up.
Thanks, Barry
 
This may not be the same issue - but had a similar problem on the Bugeye due to the best available seals being oversized. Got better with some use, but I had to really work them before they moved freely.

Make sure the seals are correct for the application, bore is completely smooth etc.

Others will jump in with other/better ideas.
 
Hey Barry,

Don't feel too bad. I used brand new parts in my rebuild about 6 months ago, and mine are doing the same thing. They worked fine after the rebuild, but now neither the brake nor the clutch piston will fully return. I used DOT5 fluid for the first time.

Just ordered new cylinders...but what a mess breaking all those lines apart!

I'll be interested to hear what the old heads have to say...

John
 
Thanks guys. I'll spend a little more time working it to see if it will loosen up. If not, and the bore is smooth, then a new repair kit and internal spring should solve the problem. Can't think of anything else?
Barry
 
Just got the new cylinders from Moss. Should have asked first, but are all the problems (talked about on the permanent thread above) resolved?

John
 
I also recieved my repalcement Moss MC's recently.
The dirt boots,while appearing more functional are different bellows type,and a large rubber band that secures it to the /mc body that doesnt allow the clyinder to be installed without removing and relacing after mounting.Also the outlet has an adapter that the MCgold and originals didnt have.No manufactrurer on casting,but a call to Moss and they said the are made by Girling in Europe.
I havent used so no performance feedback.
Tom
 
A couple of suggestions. Make sure you install the MC seals facing the correct way. Also the slave cylinders came in 2 sizes, 1" and 1 1/8", make sure you had the correct rebuilding kit for your car. Lastly, the "different" feel of your clutch pedal may actually be the way it should feel. If you have put a lot of miles on your car the clutch may have slowly over time started to fail, but since this is the "feel" you grew accutomed to you consider it normal. Everytime I have rebuilt a clutch hydraulic system it took me a few drives to get used to the new system and how it felt. Good luck.
 
Mine is all brand new and never even started yet...it's in the MC. The pistons just stick. I opened the slave bleed screw and blew air in, and the piston pops right out, but it sticks again as soon as you push the pedal. The seals are in correctly, but they could be the wrong size, as mentioned above. I even went as far in the rebuild as to hone and then polish the bores to a mirror shine.

Hope the new ones fix the problem...

John
 
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