Ford 8700 Brakes MC rebuild

Bought an 8700 last year for a baling tractor.

Was losing brake fluid out of the back of the master cyl. Just added fluid (ford mineral
oil) every time before I went out to bale, said "i'll fix it this winter"

Photos show the rust/crud out of master cylinder.

Spending a lot of quality time with a drill mounted brake hone trying to get the MC bores
cleaned up. Can't get the piston springs to return the new piston/seals yet.

I realize some of this has probably gotten into the brake cylinders, going to blow out the
brake lines before I put it back together and hope for the best. Can't seem to break loose
the brake lines at the axles without boogering up the lines. Thinking about blowing back
through the bleeder valve with the lines off at the MC...can anybody tell me why this
would be a bad idea?

Fred

Gravity will work against you. TW tractors have a drain plug at the bottom of the piston chamber in the trumpet housings. Maybe the 8700 does as well?

No such luck, no drain plug. That would've been too easy.

Thanks

Fred

if it were me I?d get the cylinder clean put the rebuild kit in it and see if it?ll pump up. The tractor doesn?t have wheel cylinders like automotive brakes. The fluid pushes a plate against a brake disc. Servicing those requires removing the final drives

I'm wondering if someone put brake fluid in it by not knowing the system.

You might get the lines loose by heating (heat gun,hair dryer) close to the nut and stick a candle where the line goes into the nut. That wax trick will get some stubborn stuff out. It wouldnt get my rockshaft out though, I had to use the blue wrench.

riveroadrat wrote "I'm wondering if someone put brake fluid in it by not knowing the system"

40 year old tractor, who knows? Hope not.

I will say that last year the brakes worked fine until all the fluid leaked out the back of the MC...could go out and bale 4-5 hours at a time with
no issues.

Thanks

Fred

Fred, I have same problem with my 8700. Did you use OEM seal kit from CNH or aftermarket? I?ve also heard that if your MC is to bad, a 1960?s Chev C10 MC can be used if you change the seals to the mineral brake oil compatible ones.
Chris

chris in sk, where were you a few days ago when I needed you?

I went with the aftermarket rebuild kit due to price...$58 vs $200 for New Holland.

My problem with the aftermarket (maybe the NH is the same, I don't know) is they use o-rings on the back part of the pistons to keep oil from leaking past the pushrods. My original pistons had cups.

Granted, I had to hone the cylinders forever to clean them up, but with return spring pressure only, the new pistons would not return. If I greased up the bores they would, but the mineral oil brake fluid didn't have the lubricity to let them slide.

The orings that came with the rebuild kit were 1-1/8 OD x 1/8 thick....I stretched some 1-1/16 OD x 1/8 orings on there, now the pistons will return. Don't know how this will be for the long haul, but no leaks so far.

For kicks, I looked up a master cyl for a 1966 C10....sure looks the same. That's what the pics and link are. Have to re-use your cap. And $40 plus core??? waaaay cheaper than what I was finding when looking for 8700 master cylinders.

I thought....probably wrong....that seals made for brake fluid would work with mineral oil, but not the other way around. Anybody know for sure? And if not, where's a source for cups?

Fred


master cylinder at autozone

Fred, sorry, that?s about all I know. As I said, I have to do the same repair on my 8700, just been putting it off. I?m pretty sure my MC will be rusty. I don?t know how the normal brake fluid seals in the C10 MC will stand up to mineral oil, but I?m thinking if they only last a few years it will be easier and cheaper than the NH seal kit in honed but probably still pitted bores. If you find those cup seals, please post back.
Chris

chris in sk, I asked the question about the seal compatibility in the tractor talk forum. Link below.

About halfway down, Bob points out that 1 side of the dual cylinder c10 MC is for the clutch, and the pistons may not be valved correctly. Really wouldn't know until you took one apart and looked.

So you may wind up buying the C10 MC just for the good core and rebuilding it anyway.

We'll get something figured out on this eventually

Fred
Discussion in Tractor Talk

I know of a couple of guys in UK that have used the C10 MC on Ford TW?s successfully. I think they fitted the correct NH seal kits though. I?ll try and track them down and get more info.

Thought to grab the old pistons/seals out of the trash before it got hauled off.

The seals have Bendix part numbers, that don't show up when you search their website. Got an email in to them about updated part numbers, we'll see what happens. Told them they were for a mineral oil system.

The cup is bendix no 2227759, the rear seal is 2227754. Google search brings up zilch.

Maybe you'll do better...let me know if you do.

Decided my old pistons/seals are going in the cabinet until this gets sorted out. It's hard being frugal.

Fred