jedm3

Master cylinder replacement-no pressure at rear lines?

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So bought a project car. Want to get brakes/clutch alive so I can verify drivetrain works prior to disassembly. Could not get brake pedal pressure so replaced master cylinder. Have worked to bleed new MC with pressure and also pedal bleeding. Have pressure to rear MC connections going to front brakes. Have fluid to all points with no identified air. Could not get good pressure to front MC connections to front or to rear brakes. Pulled MC and had good pressure at rear ports, good pressure on front ports to front brakes but no pressure to rear brakes(MC on bench pumping by hand). Am I missing something? 

Can put pressure bleeder on with 15psi and no leaks. Rear brakes adjusted roughly but do have drag.

Bad MC or bad operation? Any thoughts or feedback appreciated.

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I would replace all 5 flex hoses first... unless your have evidence a PO changed them in last 5 yrs.

I understand you are saying that Mcyl is ok but no pressure/flow to wheels... that sounds like flex hoses

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To clarify, with the pressure bleeder, I get solid brake fluid to the rear wheel cyl bleeders and can bleed from them. However, am unable to develop pressure on the rear brake port of the mc(had pressure at all 4 front ports). Have pulled mc back out and will work to bench bleed to confirm I can get pressure on that port. If not, mc issue. If so, brake line issue. 

Front flexes were all replaced and rears will be during refurbish.

Thanks for the feedback!

John

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so you bled the rear brakes successfully with pressure bleeder,  but pedal won't push fluid out bleeders /operate rear brakes?

Edited by Hans

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Correct. and when I pulled MC back out and operated manually, fluid was pumped from 4 front brake ports, not from the rear brake port

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Is it possible that the pressure retention valve for the rear brakes is at fault, don't think I've heard of that but worth trying the old one?  

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Perhaps rear wheel cylinders/calipers are seized....I would test drive to see if you can free them up. If not rust may have developed rust rings preventing piston travel in the cylinders, or calipers. Brake fluid is hygroscopic and will make rust your enemy in 2002 brake systems. Also the rubber brake hoses can close up similar to cholesterol. If your master is putting out fluid, then physically check rear bake cylinders for movement. adjust shoes while there etc. Good luck!

 

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Disassemble the master cylinder. I think your problem will present itself upon inspection. It sounds like a pitted bore or torn seal to me.

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I think it is a new MC. Seized cylinders is a possibility, easy enough to see if  pistons move back into bores. Odd coincidence that both were seized.  But I'd change flex hoses before tearing into the MC . My clutch hose once did that : fluid appeared on bleeding, but not enough flow to operate clutch.

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