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78 CJ7 Master Cylinder Bleed

#1 User is offline   nyjeeper 

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Posted 07 January 2008 - 09:25 PM

I own a 1978 CJ7 brake lines in rear were replaced, since then, I can't get brake pedal pressure to return, even after bleeding all four brakes. Fluid spills out of MC and empties front small compartment only. Air bubbles come from rear brakes. No leaks are found. suspect frozen rear wheel cylinder, but why do they bleed??????????????? Am I missing something.....Looking for sound advice. Portion valve???? Appreciate any advice out there. :biggrin1:

#2 User is offline   Rollbar 

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Posted 07 January 2008 - 09:33 PM

How cold is it there, might have h20 in the system :biggrin1: . If memory serves the front small compartment is for the rear brakes. Pull the rear wheels & check your wheel cyl. U will not see any fluid until the rear shoes get saturated, most of the time. I suspect the rear wheel cyl(s) R bad. Spray brake cleaner around all your connections of the new rear line U installed to double check for leaks.
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#3 User is offline   nyjeeper 

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Posted 07 January 2008 - 09:45 PM

View PostRollbar, on Jan 7 2008, 09:33 PM, said:

How cold is it there, might have h20 in the system :scratch: . If memory serves the front small compartment is for the rear brakes. Pull the rear wheels & check your wheel cyl. U will not see any fluid until the rear shoes get saturated, most of the time. I suspect the rear wheel cyl(s) R bad. Spray brake cleaner around all your connections of the new rear line U installed to double check for leaks.

We live in Mexico Ny and it has been cold, could water be trapped, but I put so much fluid through it and bled the brakes out, nothing is discolored and nice clear fluid with air bubbles bleeding up to the front MC like what you had mentioned. After I bleed them and push on the brake pedal, I have NO pressure :banghead: Today, while it was warmer out, I bled the rear brakes again, had good pressure without the engine running as soon as I started the engine, put my foot on the brake went straight to the fllor, light came on and NO PRESSURE....Brakes at bottom of pedal. Temp 50 today. Ohter than that it has been below freezing daily. Thanks for such a rapid reply.

#4 User is offline   Rollbar 

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Posted 07 January 2008 - 09:51 PM

Might need to bench bleed (or just do it in the Jeep) the MC, but check the rear cylinders first. Good clear fluid, I would think there is not H20/contaminates in there.

U mentioned after U started the Jeep the pedal went to the floor? Do U have power brakes? If so the booster might have went.
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#5 User is offline   nyjeeper 

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Posted 07 January 2008 - 10:02 PM

View PostRollbar, on Jan 7 2008, 09:51 PM, said:

Might need to bench bleed (or just do it in the Jeep) the MC, but check the rear cylinders first. Good clear fluid, I would think there is not H20/contaminates in there.

U mentioned after U started the Jeep the pedal went to the floor? Do U have power brakes? If so the booster might have went.

Thanks for the fresh insight.....I am going to try your advice tomorrow. yes on the power brakes, but I haven't lost the vacuum would that make a difference. I would like to keep in touch with you on this issue.... We have some decent weather right now and I need the jeep for the snow...Just bought it about a month ago, but have had CJ7's for about 13 yrs. This is a challenge.

#6 User is offline   Rollbar 

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Posted 07 January 2008 - 10:07 PM

View Postnyjeeper, on Jan 7 2008, 10:02 PM, said:

Thanks for the fresh insight.....I am going to try your advice tomorrow. yes on the power brakes, but I haven't lost the vacuum would that make a difference. I would like to keep in touch with you on this issue.... We have some decent weather right now and I need the jeep for the snow...Just bought it about a month ago, but have had CJ7's for about 13 yrs. This is a challenge.



My '79 did the samething w/out fluid loss & the booster would hold but bleed down & I would loose pedal. Just a thought but look @ your rear wheel cyl first, sounds like the problem.
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#7 User is offline   nyjeeper 

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Posted 07 January 2008 - 10:20 PM

View PostRollbar, on Jan 7 2008, 10:07 PM, said:

My '79 did the samething w/out fluid loss & the booster would hold but bleed down & I would loose pedal. Just a thought but look @ your rear wheel cyl first, sounds like the problem.

you have been alot of help.....will get on that tomorrow. Will be in touch with you to let you know how I make out.

#8 User is offline   XrayDivr 

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Posted 08 January 2008 - 08:13 AM

you can test the booster to see if it has an vac leak by turning off the key and pumping the brakes the pedal should pump up hard
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#9 User is offline   nyjeeper 

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Posted 08 January 2008 - 10:12 PM

View Postxraydivr, on Jan 8 2008, 08:13 AM, said:

you can test the booster to see if it has an vac leak by turning off the key and pumping the brakes the pedal should pump up hard

I have done that and it does pump up hard...when I turn ignition on,,,goes spongy. Could I have air in MC or siezed non leaking wheel cylinder????
Baffled!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I am working on rollbars sug....but live in Upstate NY and it is chillin :biggrin1:

#10 User is offline   Rollbar 

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Posted 08 January 2008 - 10:16 PM

After U pull the rear wheels to look & if U do not find anything (doubtful since U R loosing fluid) U can have the system power bled & it will get 99% (well close) of the air out. A lot better then the pedal/vacuum pump method.
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#11 User is offline   nyjeeper 

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Posted 10 January 2008 - 05:35 PM

View Postnyjeeper, on Jan 7 2008, 10:20 PM, said:

you have been alot of help.....will get on that tomorrow. Will be in touch with you to let you know how I make out.

as you suspected....the passenger side rear wheel cylinder was fully seized up and leaking small amt fluid..not visible outside of the drum and the driver side was completely seized up and no leaks found...also, found the emergency brake was trashed....another project to tackle later..just purchased the before X-mas so still learning stuff about it. Hey.....thanks for the advice...appreciate it. I was reading alot of other different stuff from this site and would be interested in a link to CJ7's esp...specs on 1978. Sounds like the right person to ask.

#12 User is offline   Rollbar 

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Posted 10 January 2008 - 05:44 PM

Your :amazed:
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