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master cylinder help

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master cylinder help
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asphaltaddict

Jeeper
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143
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Location
asheville nc
Vehicle(s)
88 Ford F150, 78 Jeep CJ7. 73 Jeep CJ5
I'm trying to track down the rubber gasket for the master cylinder on my 73 CJ5 . I have the stock AMC 304 . Anyone know where i can order one?
 
I'm gonna' tag along on this one - I've got one that needs replacing, too. Once in a while NAPA and AdvanceAuto have random master cylinder cap seals on the rack (HELP section in NAPA), but I haven't spotted one that fits yet.
 
I'm pretty sure they're different, but I'm not positive.

What we need to do is find a bunch of old beat-to-death heaps rotting in a field someplace, scavenge out a boxful of the dang things, & market 'em. :)

I'm pretty tempted to make one, if I can find the right material to do it with. Ordinary rubber will just dissolve in brake fluid, after it bloats up like a dead cow. That'd save quite a few dollars at the parts house or a trip to the salvage yard.
 
asphaltaddict said:
no joke. if i have to buy a new master cylinder, this will be the most expensive gasket ever!
Click to expand...
so you guys are looking for the "condom" the shaft fits through??
 
asphaltaddict said:
no, I'm looking for the rubber piece that goes into the lid.
Click to expand...

well, that is a different story. got a picture? tale one next to a ruler so I can see scale. I wouldn't think there were that many different styles and sizes. Hmmmm :confused:
 
the rubber piece won't fit. i was thinking of just changing the entire master cylinder from the 78 to the 73. i need to see what parts will fit both. they both have a AMC 304 and the carb on the newer one was recently rebuilt too.
 
Updating to a more modern brake master cylinder might not be a bad idea. I have seen some funky things happen to the rubber in old systems when guys switched to synthetic brake fluid.
 
after pondering this for a bit it occurred to me that if the gasket in the lid is shot, how far behind could the rest of the rubber in the master be.:dunno:
 
If we do... we'll need to be sure to pick one that's compatible with the brake types we've got... drums all around (unless we upgrade that, too).

The MC is an iron two-compartment MC with both chambers the same size, rounded at both ends. I'll try & get a photo in the morning when it's a little brighter out.
 
When I upgrade my brake system I bought thr Ford truck MC and put the back presure valves I wanted in either chamber
TDHofstetter said:
If we do... we'll need to be sure to pick one that's compatible with the brake types we've got... drums all around (unless we upgrade that, too).

The MC is an iron two-compartment MC with both chambers the same size, rounded at both ends. I'll try & get a photo in the morning when it's a little brighter out.
Click to expand...
 
BajaEdition said:
When I upgrade my brake system I bought thr Ford truck MC and put the back presure valves I wanted in either chamber
Click to expand...
It is obvious , once again, that you know more about this than I do. are the back pressure valves, you speak of, a form of proportioning valve or is this something else??:cool:
 
IOPort51 said:
after pondering this for a bit it occurred to me that if the gasket in the lid is shot, how far behind could the rest of the rubber in the master be.:dunno:
Click to expand...

Could be a long way. A master cylinder kit doesn't come with that lid seal, so it could easily have been rebuilt several times & still have the original seal.

The seal's exposed, too... and if any motor oil gets on it, it swells up the same way an engine seal swells up when it's exposed to ATF.

Even if the internal pressure cups are ready for replacement... a master cylinder kit's cheap & so's a hone. :)

...long as there's no rust pocket in the bore... that makes a rebuild kinda' interesting.
 
IOPort51 said:
It is obvious , once again, that you know more about this than I do. are the back pressure valves, you speak of, a form of proportioning valve or is this something else??:cool:
Click to expand...

There actually is a little valve in some master cylinders that holds a small amount of pressure on disk brakes to keep 'em seated against the rotor. It's almost always on the front chamber, if it's there at all. Usually those are unequal-chamber master cylinders, though, 'cause disk brakes and drum brakes don't need the same amount of reserve fluid.

In this case, it's pretty moot unless we do the disk-brake upgrade for the front. If we do that, we hafta' switch to a different master cylinder & add a proportioning valve.
 
Don't know if this helps but I've seen lid gaskets or whatever there called in the HELP sections of some Auto Parts Stores.
Mike
 
TDHofstetter said:
There actually is a little valve in some master cylinders that holds a small amount of pressure on disk brakes to keep 'em seated against the rotor. It's almost always on the front chamber, if it's there at all. Usually those are unequal-chamber master cylinders, though, 'cause disk brakes and drum brakes don't need the same amount of reserve fluid.

In this case, it's pretty moot unless we do the disk-brake upgrade for the front. If we do that, we hafta' switch to a different master cylinder & add a proportioning valve.
Click to expand...
check vales, back pressure vales etc, kinda the same name for the same thing.
each type of brake, or even manufacturer of brakes, even the size can use a different amount of back pressure to keep the rubber full of fluid, pads seated, etc. Just depends on what you are doing. Ford makes a great MC, but it may not be compatible to your brake system. nd brakes are such an important thing.
REMEBER your brakes are the hardest working system on the vehicle, in relation to calorie to amount of energy produced these things kick <-BAD WORD->. They also can kill you if done wrong or get you in a legally liable position where you can loose everything real quick. Anytime you change to a different brake proponent you need to make sure everything matches. Fortunately if you are going from most American 4 wheel drum systems to another 4 wheel drum system the technology they use is fron the 1920s and they all match, THE ONLY THING you need to check is if it is a dual cylinder system that the proportion of liquid moved in reference to the front and rear are the same. Getting to much pressure in the rear brakes can get your rear trying to swap with your front when you brake hard, not a fun thing. If these are not the same then a proportioning valve needs to be cut into the rear brakes so you can reduce the amount of liquid moved in the rear making them work less than the front. Or premature rear brake locking.
Biggest reason I like the Ford truck MC is that it works well with disc brake set ups. and also it holds loads of fluid. I usually add disc to the front of any jeep, and this means a different check valve in the front cylinder than I use in the rear for the drums.
Another factor that seems strange, but actually is affected is the self adjusting drum brake system can be affected by wrong back pressure. I have read quite a few tech articles that the answer to this was they had the wrong check valve in.
Now having just run off into a bit of a disarray on brakes and probably confusing everyone who read it. I think I need to write an article about designing and maintaining a brake system so we get it right.
Remember anytime you mess with brakes you need to tune them till they are working correctly as this is a safety factor that is very important.
 
so, if one was to put disks on the rear axle, a Dana 44 to be precise, would it be necessary to install check valves in the rear reservoir? I have read that the proportioning valve does not need to be changed. when you say "tuned" that would lead me to believe there was some kind of adjustment in the system.
I can hardly wait for the article.
 
The check valve needs to be added to whichever reservoir in the master cylinder drives the DISK brakes. In a drums-all-around vehicle, either reservoir can run either set of brakes & sometimes they get swapped.

The proportioning valve will need to be a disk/drum proportioning valve because calipers take more fluid than wheel cylinders do.

A typical disk/drum master cylinder will have the front reservoir running the front brakes, and larger than the rear reservoir to manage the larger fluid requirement for the disk brakes. The front piston will move more fluid than the rear piston, too.
 
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