Brake Help

[007]

Boys I'm about to give up. I'm on my second master cylinder and same results. When I bleed the master cylinder as per the documentation all goes well. I bleed it out and it gets firm and so on.

When I hook the lines to it and fire it up i have 25 or so vacuum to the booster but the thing is mush and the pedal won't return.

What the heck should I do next?


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[gutthans]

I'm thinking that your booster diaphragm is leaking???

I don't know your setup, but the MC has an internal spring that retracts the plunger back to near full pedal travel IF the vacuum is working in the booster.

Mushy pedal is symptomatic of air in the lines (you did bleed all 4 lines after the MC install right?) That could soften the return of the pedal a bit...even if the booster is tight.

Check out the repair section on Autozone for the basic power brake circuit diagnostics if you want...it'll list how to detect booster vacuum issues...I'd write it here, but my brain is so full of crud that I always go back and read that stuff anyway, as I only do the stuff every 6 to 8 months and I forget in between

 

[007]

My set up is a vacuum line running to a vacuum reservoir and the vacuum reservoir running to the booster. I have not yet bled all four wheels and I'm okay with the mushy pedal because of that but I'm not okay with not returning that doesn't make sense to me


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[007]

So I just sat in the jeep with the engine off and pumped the brakes again and they're reasonably tight and the pedal comes back just fine. It's almost as if vacuum is causing my problem as opposed to eliminating it - which I know is not the case.


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[Lumpy Grits]

How did you bleed the brake lines. Gravity bleed works well on these old Jeeps.
LG

 

[007]

I haven't bled anything but the new master cylinder. I was thinking I should have pedal return even with mushy un-bled brakes...shouldn't I?


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[Lumpy Grits]

You MUST bleed the entire brake system!
LG

 

[007]

Okay. I'm fine with that as it has to be done anyway but you're saying this will cure my non returning pedal?


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[Dan77CJ7]

you need to bleed the brakes you let air in the system when you replaced the master cylinder,even more the second time, you need to bleed the brakes starting with the Passenger rear then driver rear, then passenger front, driver front, if you havnt already done this, then it might be the problem, always bleed the brakes when air is let in. no matter what.

 

[007]

Okay. Will do. I just never imagined it would cause the pedal to not return. I'll do it and report back.


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[Lumpy Grits]

Air that you let in can compress and let the pedal 'sink'. BTW-low brake pedal is a classic sign of air in the lines on hydro. brake systems.
Water/brake fluids can not be compressed and the pedal sits where it should.
LG

 

[007]

I just saw your post LG. Thank you. I feel a lot better now. Gonna do this right this weekend it appears.


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[IOPort51]

Will the pedal return if the booster rod is off the peddle?? The peddle does have a spring on it to, at least help, return it to the top.