brake help please!! - cant get front brakes to lock - tried everything (1 Viewer)

[roverx]

hi guys!
I'm in a real mess, really need ur help!

My bj40 brakes were super until a few days back when the brake peddle went soft (about half the normal resistance) and the peddle dorps to the floor before the front wheels lock- need about 10meters to stop with feddle to the floor.

no fluid loss
checked all wheel cylindsers for leaks - none
bled the system completely a couple of times
adjusted all wheel sylinders
adjusted brake peddle to master sylinder linkage play
all brake pads are almost new

no change , the rear wheels lock but only slight force on front wheels - but fluid blrrds well from both front hoases

changed the master sylinder ---> still peddle drops to the floor with the engine on but only rear wheels lock

I'm all out of ideas'
what could be the falt - I've checked everything twise!!

please please gimme some advise!

 

[lostmarbles]

I would have said that the seals had "gone" in the "mastercylinder intermediate piston" allowing the fluid that was meant to go to the front drums (from the front section of the mastercylinder) to bypass around the piston back to the "rear brake application chamber". But you say you replaced the mastercylinder so that should "count out" that theory.
The only other thing I can think of is that one of your front brake hoses is damaged and is "bulging out" with fluid rather than allowing the fluid to push the wheel cylinder pistons out. This would be highly unlikely though because those hoses are reinforced to stop this and would be much more likely to rupture than bulge.
This leaves you with a sudden unexplained change in the front brake drum area. I once had a new shoe lining come unstuck from the shoe itself. Maybe this is a possibility. It could cause the a wheel cylinder piston to move as normal (and further) without applying the braking force to the drums. But then with ALL the work you've done and your obvious "sound knowledge" I would have thought you would have uncovered this before now. So really I'm "dumbfounded" like you!
A lot of people will tell you just to replace your front drums with disks but my drums-all-round have always been great and I'll never dump them. (Any possibilty your new m/cyl is the wrong one and meant for front disks instead? Your front drums have 8 pistons in all and need a lot of fluid!)
Cheers

 

[Mainer7]

I just went through the opposite, sort of. My front brakes would lock up after using them 3-5 times and then I'd have to crack the line at the MC to release the pistons! After replacing too many parts, it finally eneded up being a faulty Booster. After the old booster came out, it felt like a bunch of things inside of it were really loose or just jammed up. The new booster completely fixed the problem, so check your booster out. Also there is an adjusting rod/nut between the booster and master that plays a big role here. Good luck!

 

[bsmith123]

I had the same sort of problem on an old Triumph Dolomite in the UK and it was the booster, Since the parts are probably made by a brake specialty company like lockheed etc even if you can't get a new one I bet you can get a rebuild kit. I did and it was really easy to do.

Good suggestion on the bulging brake lines.

I don't know your level of experience but sometimes bleeing is just not done enough
bleed the hell out of em. since it sounds like it just happened and wasn't maintenance related it does sound like a failure.

make sure the shoes are adjusted out enough even if the are auto adjusters

after that if it were me i would try isolating out the problem by capping the rear and see if the front gets better or cobble up some crossover lines to make the rear pressure go to the front and see if it still happens etc may lead to something more definite.

Good Luck!

 

[lostmarbles]

if it were me i would try isolating out the problem by capping the rear and see if the front

Good Luck!

Or alternatively could use some type of vicegrips to gently squash/close the flexible brake line connecting the chassis to the front diff and see if this gives a "hard pedal" (thus isolating the fault to beyond that point) - and so on.

Have to be very careful the hoses don't get damaged though!

 

[roverx]

Thanka

hey thanks so much for all your advice!!

I turned out to be the the adjustment between the booster and the master cylinder was incorrect after I fit the replacement Master cylinder it had to be adjusted a little bit towards the cylinder side so that it is quite near the cylinde at resting position.

The "peddle going soft" was actually the vaccume assist "kicking in" with the buildup of vaccum in the booster!

This only occues after a lot of vigarous pumping clearing all the vaccum!

anyway back on the road again

 

[lostmarbles]

Glad you got it fixed.
We weren't really much help but your persistence paid off

 

[bsmith123]

Good Job

half the battle is eliminating other causes--I guess that was our role this time! ha ha!

I'm glad to se you posted the final fix--that helps