Rear drum brake question

[jlmnjem]

I recently acquired a 78 CJ7 with manual disc/drum brakes. I pulled the rear drums to inspect and everything looked ok so I put the drum back on and adjusted the shoes back out to where I could hear them lightly drag when I turned the wheel. To further check their function, I had my dad push the brake pedal to see how well they grabbed, but they didn't on either side. I had him pump the pedal and I opened the bleeders on each side to be sure I didn't have a clogged line or MC port but I got all fluid from the bleeders. I pulled the PS drum off to observe the wheel cylinder while he pushed the pedal and it didn't move at all. The initial diagnosis is that both wheel cylinders are frozen. Then I started reading about the combination proportioning valve, and having to bypass it when bleeding the brakes. That makes me wonder if not getting the rear brakes to grab has anything to do with its function (directing all hydraulic power to the front discs first?), or perhaps it's malfunction. Please educate me on this valve and whether it could cause this.

 

[Posi]

You didn’t mention anything about the brake pedal and how it feels.
If you have a normal or hard pedal it would suggest your wheel cylinders are frozen.

 

[cglax6]

You didn’t mention anything about the brake pedal and how it feels.
If you have a normal or hard pedal it would suggest your wheel cylinders are frozen.

I second this...

Wheel cylinders are cheap enough to where I'd just go ahead and replace them anyway. I did a complete brake job on my '76 when I got it. Didn't want to mess around. Brake rebuild kits are very cheap too...if you don't replace everything, then take it apart and give every spring, cable, linkage, etc a good cleaning.

If you're not familiar with drum brakes, they can seem intimidating, but there are plenty of good youtube videos out there on how to rebuild. It's just a PITA to get the springs off and on because they're under so much tension.

 

[Lumpy Grits]

Did you have both drums installed?
LG

 

[Torxhead]

Did you have both drums installed?
LG

Yes, or the brakes will not operate correctly without the drums installed. There is a primary pad which makes contact first then the secondary pad comes on.

 

[jlmnjem]

Thanks for the replies. I'm going to replace the wheel cylinders. I just wanted to be sure the issue wasn't caused by the normal function of the valve before I started replacing things.

 

[cglax6]

Thanks for the replies. I'm going to replace the wheel cylinders. I just wanted to be sure the issue wasn't caused by the normal function of the valve before I started replacing things.

Without the drum on, one side of the wheel cylinder will work. If you're not getting any movement on either side of the cylinder with the drum off, then I'd start with replacing the wheel cylinder.

Don't forget to bleed when you're done...

 

[Idahododgeram]

I agree with all of the above. As an owner of a '77 CJ5 I would recommend you be prepared to buy a couple of cylinders before you get a new one that doesn't leak. I have gone through several this year, all new. Maybe manufacturing has gone down hill?

 

[cglax6]

I have gone through several this year, all new. Maybe manufacturing has gone down hill?

Dang, I might just be lucky...no issues with the two I bought from O'Reilly's.

Speaking of lucky, I drove through Coeur d'Alene when I moved to/from Alaska by way of the ferry system out of Washington. Told the wife I'd like to retire out that way...so beautiful.