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Discussion Starter · #1 ·
I have a bit of problem with my brakes, i have a 94 qg 4.2d trayback, brakes work great on road with normal braking, however if you hold brakes on, they slowly fade to the floor.
I have replaced the master cylinder, and have had brake lines tested to see if they are damaged, but mechanic says there all good, bleed the system, etc, etc....I also got told that its a design fault with the year and make of my patrol. Does any one know how true this is? Or have an answer to my problem? Any help is appreciated!

thanks simon
 

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I have a bit of problem with my brakes, i have a 94 qg 4.2d trayback, brakes work great on road with normal braking, however if you hold brakes on, they slowly fade to the floor.
I have replaced the master cylinder, and have had brake lines tested to see if they are damaged, but mechanic says there all good, bleed the system, etc, etc....I also got told that its a design fault with the year and make of my patrol. Does any one know how true this is? Or have an answer to my problem? Any help is appreciated!

thanks simon
I've owned a 94 tray before and it never did that. Any car I've owned where brake pedal fades to the floor has been fixed with a new master cylinder. Are you losing fluid at all?
 

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Discussion Starter · #3 ·
We put it up in the air and pumped the brakes but couldn't see any leaks then the mechanic had it for 2 days and it wasnt leaking, so unless it leaks into somewere u can't see it? i got no idea. We also replaced 2 siezed piston, and put in a new caliper kit, if that helps.
 

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This might be a long shot, but check for vaccum leaks too. Sometimes trying to pull a 7 point turn at idle, my brakes and steering will get heavy, because the vaccum pump / reservoirs have been overwhelmed, resulting in no power assist. This can cause you to push harder than normal on the pedal and therefore notice the pedal sinking closer to the floor. I once noticed this on road (pedal going almost to the floor) after multiple river crossings and not tapping / dragging / drying the brakes properly. After scaring the crap out of myself and pulling over I went fault finding and found the pedal going almost to the floor - hence suspecting a problem. I then realised, I was pumping the brakes at idle (almost no vaccum), and there were no other dectectable problems. After hitting the road again (cautiously) and being sure to dry the brakes, they were fine and have been for 8-9 mths since.
 

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I agree with BennoGU28 the steering has nothing to do with the vacuum system. Sounds like bypass in the master cylinder. Master cylinders can also leak back into the power booster also.
 

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Just found the same problem with my 1989 GQ YD42. Engine off and pump the brake pedal up and she's hard as a rock with no pedal movement at all, but with the cars running pump it up hard and hold the pedal on and she ever so slowly starts going down. Could it be bypassing due to too much pressure?????? Would be very interested to know how you got on with your problem bigsim1
 

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My 1993 GQ 4.2 used to do the same as your 94, brake pedal going to the floor, found no leaks and replaced all the brake pads and bled the system. Put a new kit in the master cyl but all to no avail.
I ended up but putting a brand new master cyl on and that fixed the problem.
 
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