5n ton non air brake question

[812]

i have a 1977 juice brake 5 ton that when i pump the brakes a few times the shoes wont release on both back axles unless i open one bleeder screw on one wheel to release fluid pressure, i have replaced the back hoses and by passed the mirco lock solenoid, its as if master cylinder will apply but wont let fluid return. any thoughts before i bite the bullet for a MC?

 

[kendelrio]

Check your return port on your MC. You may have trash in the line.

I've had this issue on motorcycle brakes and clutches and 9 times out of ten, it was old fluid that had gummed up the return port. I would use a bristle from a wire brush to punch it out and they would work fine from there.

 

[Mullaney]

i have a 1977 juice brake 5 ton that when i pump the brakes a few times the shoes wont release on both back axles unless i open one bleeder screw on one wheel to release fluid pressure, i have replaced the back hoses and by passed the mirco lock solenoid, its as if master cylinder will apply but wont let fluid return. any thoughts before i bite the bullet for a MC?

.
I agree with @kendelrio . Crud in the brake lines will often cause the problem that you described. The brake booster is next if your brake fluid comes out clean and clear. Opening the bleeder screw at the brake booster could free up the shoes too. The rubber hoses will collapse from the inside as well - but your post mentions you have already done that...

 

[kendelrio]

.The rubber hoses will collapse from the inside as well - but your post mentions you have already done that...

That was my initial thought too until I read that he had changed them.

 

[kendelrio]

I would recommend a thorough flushing to clear everything up before you throw any more parts at it.

 

[812]

I would recommend a thorough flushing to clear everything up before you throw any more parts at it.

I would recommend a thorough flushing to clear everything up before you throw any more parts at it.

i flushed the system and still doing the same thing, i'm thinking master cylinder or air pack they are both orig as far as i can tell

 

[G744]

Could be the push rod going into the MC might be adjusted too long.

That in turn won't let the piston return, and keeps pressure in the lines.

You can do a simple test: wiggle the rubber boot and see if there is a bit of free play in the rod. It only needs about 1/16" to be OK.

 

[162tcat]

Try cracking the bleed port on the master cylinder when it’s locked up. If this has residual pressure, that’s your issue. Mine did this and no amount of flushing, bleeding or adjusting fixed it. Replaced the MC and it worked great.


Sent from my iPhone using Tapatalk

 

[812]

Try cracking the bleed port on the master cylinder when it’s locked up. If this has residual pressure, that’s your issue. Mine did this and no amount of flushing, bleeding or adjusting fixed it. Replaced the MC and it worked great.


Sent from my iPhone using Tapatalk

Thanks for the info, Have a M/C on the way

 

[Mullaney]

Thanks for the info, Have a M/C on the way

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Save the old master cylinder if it didn't have to be returned for a core.
Pulling it apart, inspecting the bore, and the piston will help you decide what happened AND if you can find repair parts.