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[Dave69]

I'm stumped by this one so throw some ideas no matter what they are.

mk 1 cherokee 4ltr auto.

had the jeep in for an mot and it failed on the brake bias and an unrestrained hard brake pipe by the master cyclinder (frhs wheel). so the brakes were working fine.

* swapped both front calipers for some spare i had (reasonable condition and no leaks)
* i then replaced the hard brake pipe for a new one but slightly shorter
* brakes were bled fully but when the bleed nipples locked off the brake pedal still had to be pumped to get resistance as normally would be felt.
starting the engine and the pedal drops straight to the floor and eventually resistance is felt after alot of pedal pumping.
* the brakes will hold the jeep staitionary when in drive and no throttle.

* the confusing point is that the brake system is pressurising back to the brake reservoir forcing the brake fluid out of the reservoir. Undo the cap and there is the sound of pressure release.


The amount of years i've worked with brakes i've never encountered the reverse pressure symtoms.

Any ideas before i rip out the booster and master cylinder and swap it for a unit of the 2.5 sport to see if that will work

[Bubba]

sounds like you have air in the master cylinder they be trickey litle bastards

[scrw]

Had a similar issue on another motor, the MC seals had turned inside out and were facing the wrong way in the bore. I would strip the MC and check the condition of the seals

[greggmo]

do you recon a vacuum bleed might help?

[dxmedia]

If it's got ABS the engine needs to be running to bleed the abs pump. You'll get brakes with the engine off, but as soon as you start the pedal will go straight to the floor otherwise.

[Dave69]

the ABS unit has been removed

[dxmedia]

* the confusing point is that the brake system is pressurising back to the brake reservoir forcing the brake fluid out of the reservoir. Undo the cap and there is the sound of pressure release.

shouldn't do that IMO. Sounds like a problem with the seals in the master cylinder if it's pressuring when you take the cap off?

[Dave69]

looks like a problem with the rear seal as it is frothing the fluid in that chamber.  Is there a seal kit avalable for the m/cylinder