Brake issues

[Chris078]

My Mechanic and I are at our wits end. I cannot get the brake pedal hard enough to lock the brakes.
It stops reasonably well, but no matter how hard you push the brake pedal, they won't lock up.

I've put new calipers and pads on the front, replaced the front and rear flex lines. Had the fluid flushed and replaced 3 times.

The brake master cylinder looks new. The booster doesn't appear to be in bad condition.

The rear cylinders, shoes and pads were replaced 2 years ago.

Any suggestions?

[Phil B]

My Mechanic and I are at our wits end. I cannot get the brake pedal hard enough to lock the brakes.
It stops reasonably well, but no matter how hard you push the brake pedal, they won't lock up.

I've put new calipers and pads on the front, replaced the front and rear flex lines. Had the fluid flushed and replaced 3 times.

The brake master cylinder looks new. The booster doesn't appear to be in bad condition.

The rear cylinders, shoes and pads were replaced 2 years ago.

Any suggestions?




Sounds like the only thing left to check is the vacuum pump on the back of the alternator and the vacuum line to the booster.
I'm not sure how much vacuum it should pull (others can help here I'm sure) but if you remove the line from the booster you should have a reasonable vacuum with the engine running.
Possible causes for lack of or low vacuum:
1. worn out pump
2. cracked/broken vacuum lines
3. leaking diff lock switch and / or lines to and from the gearbox
4. leaking booster non return valve.


You may also be expecting too much out of the brakes. The design is 30yrs old and the combination disc/drum set up is not perfect. Add to this the 2 1/2 tons of vehicle, expecting the brakes to lock up might be optimistic !!;)


Hope this helps.


Regards,

[BathurstTom]

ABS or Non ABS? Have you tried putting your foot on the brake pedal several times until vacuum runs out and THEN starting the motor to see if the booster is working?

When you say you can't get the brake pedal hard enough - does that mean that it is soft or sinks to the floor?

Tom.

[BadCo.]

When you do manage to get the brakes to lock up, let us know how you did it. I thought it would be impossibly haha.

[Chris078]

BathurstTom - It's a perentie so no ABS.

If anyone has some numbers on what the vacuum should be on the line to the brake booster, I'd be most grateful.

This would be the only car I've ever had where I couldn't lock the brakes, and I used to have an old corolla with 4 drums!

I may be asking too much of it, but I thought it would be at least capable of locking the brakes when the truck is empty and I'm shoving the pedal to the floor.

[Bearman]

BathurstTom - It's a perentie so no ABS.

If anyone has some numbers on what the vacuum should be on the line to the brake booster, I'd be most grateful.

This would be the only car I've ever had where I couldn't lock the brakes, and I used to have an old corolla with 4 drums!

I may be asking too much of it, but I thought it would be at least capable of locking the brakes when the truck is empty and I'm shoving the pedal to the floor.

Yep you're expecting too much if you are wanting to lock up on tar Chris!!! And you are better off as far as braking goes by not locking up.

[Blknight.aus]

disconnect the brake booster, you should then be able to lock up the back brakes.

if you cant somethings wrong. if you have to pump up the brakes to get that to work you have damaged snails and possibly have the backing plates on the wrong sides, the extra fluid travel requirement to get them to begin to work properly is robbing the pressure out of the front end

My default starting point to work out if it was mechanical adjustment or a proper contaminated hydraulics issue was the double stab (which should lift the pedal point right to the top) and both feet on the brakes trying to break the back off the seat with reaction force level brake pressure application.

If that locked it up, it was usually an adjustment problem. if it didnt and the pedal was spongy it was usually MC/booster/lazy vac pump.