8700 Master Cylinder

Fred Werring

Well-known Member
Been posting on the Tractor Talk forum, and had posted here last year, thought I'd post a summary.

A dual MC (clutch/brake) for a 1966 Chevy C10 is the same as the MC's on the 8700...except for the seals/cups, and reservoir cover.

The seals in the Chevy MC are made for DOT3 brake and will swell over time making the bores stick.

I know this cause I took a chance when I bought it last year and installed it as is hoping the seals would be compatible. Worked fine last summer/fall. Got the tractor out a week ago, pistons were sticking in the bores, locking up the brakes. Cups swollen big time.

So if you've got one of these MC's with the bores so pitted you can't get them honed out, buy an MC like linked to below, pull the guts out (there is a seal under the spring in one of the bores, don't miss it), clean it out good, and replace guts with a rebuild kit sold for an 8700. I'm using one of the aftermarket rebuild kits from YTmag for $58 vs the $200 kit from New Holland, not sure what the difference is. Price out a new or rebuilt MC from New Holland if you want severe sticker shock.

Lessons learned.
You need to swap the reservoir covers, but the threads are not the same between the 2 MC's for the bolt that holds it down. Figure on getting a longer bolt.
I should have left the flat cover on when the new MC was getting installed (to keep dirt out) and swapped the covers once the MC was bolted to the firewall...my tractor has a cab, took a fair amount of manipulating to get that MC in there with the taller cover on it.
Takes forever to get it bled if it's installed dry. If this ever has to come out again, I'll get a couple plugs for the line ports to retain fluid after bench bleeding it. Tried bench bleeding last year, but the way the MC gets twisted around during installation, lost all the fluid anyway. If I had plugs, could have done it.

FWIW

Fred
1966 Chevy C10 MC on Amazon
 
I think that is similar to my 8000 in that it does not use brake fluid but a mineral oil. I had no brakes on the 8000 and pulled the MC apart and found the seals/cups completely shot. Rebuilt it with a YT kit and bled the system with the proper fluid and it works great now.
 
Knew it took mineral oil, never had DOT3 fluid in it as far as I know. Sure hope not, hate to think about replacing the brake seals in the axle.

But now I do know that the seals in an MC for a 66 Chevy C10 were made for DOT3 and are not compatible with mineral oil.

Fred
 
You're welcome.

I've picked a lot of information off these forums over the years, I return the favor when I can.

Fred
 

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