'76 brake MC question

[hdgapeach]

My '76 CJ5 has manual front disc, drum rear brakes. The master cylinder is leaking out the rear reservoir, out the weep hole and down the engine compartment side of the firewall. Brake fluid is a great paint remover, by the way!

Anyway, I have to get another master cylinder this evening and get it going before tomorrow. The local chain parts house is the only option I have since it's late on a Saturday. Advance has a rebuilt Cardone MC in stock. I looked it up online and the description says for a drum / drum setup. Mine is disc / drum. The MC pretty much looks like what I have on the Jeep now except for a couple of bleeder screws on the side of the one on my CJ that the rebuilt unit doesn't have.

Do y'all know if there's a problem with installing the rebuilt drum / drum unit or should it basically be the same since I have manual brakes? I do have a proportioning valve downstream from the MC that I believe is functioning correctly. Appreciate any insight on this!

 

[Barry2]

Sounds like it might have been overfull, did you work on the brakes recently?

 

[mtnwhlr]

No a drum drum will not work with discs on the front because discs take more pressure and the reservoir will be bigger for the front. And you are right when they start leaking out the back it's time to replace it.

 

[hdgapeach]

Sounds like it might have been overfull, did you work on the brakes recently?

Wish that was the issue. I couldn't get that lucky.

Nah, it's definitely a seal leaking. The little hole at the bottom of the MC, just forward of the firewall has a pesky leak. The spongy pedal is what caused me to look at the MC to begin with (after I checked for brake fluid leaks at all four corners and found none). Took the lid off the MC and saw the rear reservoir was about empty. Filled it up with DOT 3 and watched it "self bleed" for a few minutes. Right now it's a very slow leak (meaning it takes several days to leak down to where it is now).

 

[hdgapeach]

No a drum drum will not work with discs on the front because discs take more pressure and the reservoir will be bigger for the front. And you are right when they start leaking out the back it's time to replace it.

That about figures......

Doesn't matter anyway. The danged dude behind the counter didn't bother to check the shelf to make sure they had one. He went by what their computer said was in inventory. I even asked him to check before I made the 26 mile round trip for nothing. He assured me they had it.

Well, other than filling the tank with gas, it was a wasted trip. Computer said it was in stock and no one at the store could find it on the shelf. I didn't even get the opportunity to compare it to the one I have. Guess I'll have to keep it full until Monday after CARQUEST / NAPA opens. I'm sure they'll have what I need (as usual).

 

[hdgapeach]

Since my part purchase fail gives me plenty of spare time to research, I'll go ahead and ask y'all;

Anybody know what brand and/or part number I need for a replacement manual brake master cylinder for a '76 CJ5 with disc front and drum rear brakes. Other pertinent info: AMC 304 , 3 speed stick, power steering.

Everything I'm finding so far on the web states it's for drum / drum only. I'm beginning to think I have a FrankenJeep!

 

[mtnwhlr]

Be sure you bench bleed it before you install it a step alot of people don't do that causes lots of headachs.

 

[hdgapeach]

Be sure you bench bleed it before you install it a step alot of people don't do that causes lots of headachs.

Oh yeah, I learned that one many years ago, the hard way . I'll just be thrilled to actually find the correct one to bench bleed! I considered rebuilding the one I have myself, but the rebuild parts cost more than a complete rebuilt MC (that is, if I could actually find one). Never would've thought the parts to do it would be more than the complete refurbished unit.

 

[IOPort51]

Cardone Remanufactured 10-1670 - Master Cylinder | O'Reilly Auto Parts

I would be willing to bet lunch that this will work quite well.

 

[Barry2]

My mistake, I thought it was leaking from the hole in the cover as in overfull.

 

[hdgapeach]

Cardone Remanufactured 10-1670 - Master Cylinder | O'Reilly Auto Parts

I would be willing to bet lunch that this will work quite well.

Thank you, sir. I'll call to see if they have one on the shelf this afternoon.