Loss Of Power Brakes On Sudden Stopping VS UTE

[AmericanGuyInAUte]

Hi all... Having a hard time and need help because I'm having a braking problem on my 95 VS Ute.

If I drive normally, everything feels perfect!

If I slam on my brakes during say a panic stop, I lose power brakes or have too little power brakes.

I have no hissing from the booster, no idle change during braking.

Things I've tried. I bought a used Brake Booster (with check valve) and installed it as well as a new brake master cylinder. It's exactly the same. THe booster is some crap plastic.

Question... what is the little brake valve connected to the rear Diff with a little chain do? Could that be causing my problem? I had the diff out to replace bushings.

THANKS!!

 

[jeepster]

The valve at the rear is load proportioning valve to limit rear brakes when tray is empty. Probably not causing the failure, as in a panic stop, most of the braking will be on front wheels. I presume it doesn't have ABS, being series 1 ute.

 

[AmericanGuyInAUte]

The valve at the rear is load proportioning valve to limit rear brakes when tray is empty. Probably not causing the failure, as in a panic stop, most of the braking will be on front wheels. I presume it doesn't have ABS, being series 1 ute.

correct. no ABS,

 

[Fu Manchu]

I would do a smoke test on the top end of the motor to find vacuum leaks. It will find a leak every time. Easy to make one for the job.

Inspect every brake cylinder for leaks.

Inspect the lines for signs of a split or leaks.

You can buy a vacuum pump, handy for bleeding the brakes too. They often come with the better bleed kits. You’ll be able to test the booster for a vacuum leak. Has a gauge to show if it holds vacuum.

Get the master cylinder off and dismantle. Make sure the rubber seals are orientated the right way around. Double check it’s a ute master cylinder. Double check bench bleeding is done correctly.

Bleed the lines.

 

[BlackVXGTS]

The only time I have experience a similar problem was when I was using my VS Calais V8 on high performance training days at Sandown Raceway in Melbourne. On one occasion, I assumed that the brake fluid had been replaced, when in fact it hadn't. No matter how hard I pressed the brake pedal at the end of the straight, it wouldn't stop any faster. During all your machinations, have you use new brake fluid, or have you re-used some/all of the old fluid?

 

[AmericanGuyInAUte]

I would do a smoke test on the top end of the motor to find vacuum leaks. It will find a leak every time. Easy to make one for the job.

Inspect every brake cylinder for leaks.

Inspect the lines for signs of a split or leaks.

You can buy a vacuum pump, handy for bleeding the brakes too. They often come with the better bleed kits. You’ll be able to test the booster for a vacuum leak. Has a gauge to show if it holds vacuum.

Get the master cylinder off and dismantle. Make sure the rubber seals are orientated the right way around. Double check it’s a ute master cylinder. Double check bench bleeding is done correctly.

Bleed the lines.

THe Vacuum pump is a good idea and I do have a smoke tester at work. I will give it a look see. I don't believe that I have air in the lines as my pedal has no "spongy or sinking". THe rear brake lines were replaces (they were rusty). Will check to see if I have the correct master cylinder.

 

[AmericanGuyInAUte]

The only time I have experience a similar problem was when I was using my VS Calais V8 on high performance training days at Sandown Raceway in Melbourne. On one occasion, I assumed that the brake fluid had been replaced, when in fact it hadn't. No matter how hard I pressed the brake pedal at the end of the straight, it wouldn't stop any faster. During all your machinations, have you use new brake fluid, or have you re-used some/all of the old fluid?

I used a lot of new fluid because of replacing the rear brake lines and the master. It's possbile that the drum of brake fluid in messed up due to moisture. I've seen that before. I have one of those little moisture dector meters. Will check the fluid at work on monday. Thanks for the sugggestion!

 

[AmericanGuyInAUte]

I would do a smoke test on the top end of the motor to find vacuum leaks. It will find a leak every time. Easy to make one for the job.

Inspect every brake cylinder for leaks.

Inspect the lines for signs of a split or leaks.

You can buy a vacuum pump, handy for bleeding the brakes too. They often come with the better bleed kits. You’ll be able to test the booster for a vacuum leak. Has a gauge to show if it holds vacuum.

Get the master cylinder off and dismantle. Make sure the rubber seals are orientated the right way around. Double check it’s a ute master cylinder. Double check bench bleeding is done correctly.

Bleed the lines.

Thanks again for your help. I've still not found the problem but have eliminated my booster as the problem. I've tested the check valve and used a vacuum gauge to test for vacuum at the engine. I've also started the car and then turned it off, booster assisted me for longer way longer than 30 seconds and when i start the car I can feel the booster "sink the pedal" some. Hooked a vacuum gauge up to the booster (no valve ) and pumped the little hand pump for a looooog time. Got some vacuum on it and it held. I repeated this test with my original booster with the same results.

No how to make sure how to tell if I have the correct new master cylinder or not. It has numbers on the PBR master but can't find a Catalogue to tell me if it's correct. The numbers on the master do not match the part numbers at the store.

Another stupid questions. I changed some rear brake lines. Could this happed if I crossed them somehow (very unlikely I did this but too many drugs in high school never know).

Next I will try what BlackVXGTS suggested, changing the brake fluid and bleeding the system again. I've felt many cars that had air in the system and never had it "remove" most of my power brake assisit but it's a good suggestion and an easy test.

 

[vc commodore]

Bit hard crossing the rear lines.....They are 2 different lengths to start with.....And all they do is channel the fluid from the junction to the caliper....

Maybe look at the T-piece hasn't got crud in it, if you are thinking about re-bleeding.....

 

[Fu Manchu]

What is the condition of the rubber hoses to the front callipers? Maybe with hard braking they are expanding a lot?