95 1/2 ton Chevy P/U Clutch Master Cyl

corvettecat · 06-07-2007, 09:05 AM

Just had clutch replaced..........added new clutch master cylinder and slave cylinder........they are plastic.........shifting is fine and smooth until the master cylinder body cracks......I've replaced 3 master cylinders and 1 slave cylinder.....Anyone know why the master cylinders keep cracking? Could pressure build up somehow and cause this or are they just cheap?

75K30 · 06-07-2007, 09:34 AM

Welcome to the site.
That is very interesting. I have never heard of a master cylinder breaking the way you described, and to have it happen more than once, and to two different components is just plain odd.
Is it possible that the rod that pushes the piston is too long, and is going in too deep, causing strain on the body?
Of course I am assuming that these are breaking at the flange itself. Is that where these are breaking?

corvettecat · 06-08-2007, 07:51 AM

The clutch master cylinder body is plastic. The body has a molding seam down the middle at the bottom. It cracks open there.

75K30 · 06-08-2007, 11:00 AM

I have some earlier plastic master cylinders, and I tried a little experiment. I tried to break one using pressure. A was able to get over 11,000 psi out of a plastic body without failure. After that I started to get a little scared. I was not sure that my saftey devices were going to hold up to flying parts at those pressures.
I also looked into some later model applications, and have come to the conclusion that you might consider upgrading you masters to aluminum bodies. Plenty of later chevys used the upgrade masters, and have the same capacities as your existing units. They bolt up the same, and will be much stronger. While I am unsure of your actual problem, I do feel that the solution would be an upgrade that will not break. Not to worry, the later model units did have provisions for the same low fluid sensors too, so they will work electrically too.

06-07-2007, 09:05 AM	#1
corvettecat Junior Member Join Date: Jun 2007 Posts: 2	95 1/2 ton Chevy P/U Clutch Master Cyl Just had clutch replaced..........added new clutch master cylinder and slave cylinder........they are plastic.........shifting is fine and smooth until the master cylinder body cracks......I've replaced 3 master cylinders and 1 slave cylinder.....Anyone know why the master cylinders keep cracking? Could pressure build up somehow and cause this or are they just cheap?

06-08-2007, 07:51 AM	#3
corvettecat Junior Member Join Date: Jun 2007 Posts: 2	Reply The clutch master cylinder body is plastic. The body has a molding seam down the middle at the bottom. It cracks open there.

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06-07-2007, 09:34 AM	#2
75K30 Senior Member Join Date: Jul 2006 Posts: 2,992	Welcome to the site. That is very interesting. I have never heard of a master cylinder breaking the way you described, and to have it happen more than once, and to two different components is just plain odd. Is it possible that the rod that pushes the piston is too long, and is going in too deep, causing strain on the body? Of course I am assuming that these are breaking at the flange itself. Is that where these are breaking?

06-08-2007, 11:00 AM	#4
75K30 Senior Member Join Date: Jul 2006 Posts: 2,992	I have some earlier plastic master cylinders, and I tried a little experiment. I tried to break one using pressure. A was able to get over 11,000 psi out of a plastic body without failure. After that I started to get a little scared. I was not sure that my saftey devices were going to hold up to flying parts at those pressures. I also looked into some later model applications, and have come to the conclusion that you might consider upgrading you masters to aluminum bodies. Plenty of later chevys used the upgrade masters, and have the same capacities as your existing units. They bolt up the same, and will be much stronger. While I am unsure of your actual problem, I do feel that the solution would be an upgrade that will not break. Not to worry, the later model units did have provisions for the same low fluid sensors too, so they will work electrically too.