It has an brake problem sometimes they work sometimes they don't.

GANDALF776

MEMBER
1951 CHEVROLET
500 MILES

My girlfriend bought a 1951 chevy p/u with a 350 v8 that has been customized. It has a 90-96 ford f150 power brake booster and master cyl. And 76-81 chevy camero frt. Disc and rear drum. Checked all four wheels for leaks found several of the line fittings were not tight and Teflon tape on bleeder screws. Tightened all fittings and cleaned bleeder screws and bled system. That made no difference. One pump the brakes grab and hold the next pump they may or may not hold. Checked for fluid between booster and master cyl. Found none. The booster did not have a check valve so I installed one. Still same problem. I did notice what appears to be grease coming from inside the booster on the piston rod. I am thinking that the master cyl. Is bypassing internally. How can I be sure the booster is working properly?

5 Replies

HMAC300

MECHANIC
48,601 POSTS

If the pedal goes down fairly easily with the engine running then the booster should be working. One thing is that this should have a proportioning valve on the system. If there isn't that will be part of your problem. Also the larger of the mastre resevoir should go to the disc brake side. There also should be a little valve in the line going to the drum side of the brakes. That is very important as drum brakes require constant pressure whereas disc brakes don't. If there is no proportioning valve there are adjustable ones sold that can be installed. You might try power bleeding this system to see if that fixes it. If not it may be a bad master cylinder or one of the other things i've mentioned. It sounds as this has been hacked fairly well. It might not have the correctmaster for this system either as the ford may have had disc brakes all the way around whereas you don't on yoursystem and you will run into the previous problem mentioned. If your master looks similar to the pic shown you have the pp valve already and that line should go to the rear.

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Thursday, January 5th, 2012 AT 5:59 PM

GANDALF776

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10 POSTS

Thank you for your quick response. And yes I forgot to mention that there is an adjustable proportioning valve inline to the rear. Also it looks like the master cyl you showed is the same one that was used. Which I wondered what that fitting was on it. So if the cylinder has a built in valve then the inline one is not needed if I understand correctly. I will have to go back and look but I think the person who built the truck has that master cyl valve hooked to the frt brakes. So hopefully I have found the problem with your help thank you.

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Thursday, January 5th, 2012 AT 8:17 PM

HMAC300

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Just make sure you do this as correctly as you can Brakes an steering are not two things to hack on a vehicle.

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Thursday, January 5th, 2012 AT 8:19 PM

GANDALF776

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Yes that I do understand unlike my girlfriend who did not tell me of the problem. When they failed she got it back to her house added some fluid and wanted to test drive it. Backed out of the garage and found she had no brakes. Luckily her honda crv was in the drive way and stopped her from rolling out into traffic. So after I get the truck fixed (which is on stands w/ all wheels off) then I get to replace the headlight assy in her honda. I think she learned an important lesson. Thanks again for your help

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Thursday, January 5th, 2012 AT 9:25 PM

HMAC300

MECHANIC
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Hey no problem.I had to add the last reply due to not knowing your expertise, alot of people dont' no need to reply unless you still can't get it fixed.