Thread: brake question

if you have drum rears you have one of 2 problems

1. the shoes are in ass about.
2. the snail cam adjusters arent doing their job and slipping back, letting the shoes off further and you have to pump them out to make the brakes work again..

to test your booster... sa I mentioned abouve pump up the brakes and then with the brakes held start the car. if the pedal sinks your boosters mechanism is ok..

now nice and slowly let the vehicle roll and turn the engine off, angel gear is what your after on a very slight slope.

apply the brakes and then let it roll for 10 m or so then go again.

you should get 2 applications as tho the engine was still running maybe 3

if that happens then the one way valve and booster are still air tight and doing their job and your brake problem lies within the hydraulics somewhere, be it excessive knock back, bad setup on the rear, flexing hoses, air in the system, the secondary master cylinder bleeding back into the primary or vice versa.

if you have discs all around due to the size of the pistons in the caliper if all of your rotors are on the maximum allowable limit of lateral run out (.2mm per disc) my rough calculations indicate that you will need 3/4 of a stroke of the master cylinder to get the pistons back into position. This is without allowing for any bearing run out.

(it was a slow day on the drivers course so I did some rough measurements on the calipers and master cylinders on the shelf)

I hope this is helpful to all of you...

if you have discs all around due to the size of the pistons in the caliper if all of your rotors are on the maximum allowable limit of lateral run out (.2mm per disc) my rough calculations indicate that you will need 3/4 of a stroke of the master cylinder to get the pistons back into position. This is without allowing for any bearing run out.

Mate, you've done well!, but on the pedal, how much is 3/4 of a stroke of the master(roughly) and what booster do you guy's use on the 4be4 Perenties with disc's all 'round.

3/4 of a stroke of the master

belongs in the Mud Pit!.

thats simple...

see the pedal height when its fully up?


measure that from the bottom of the fire wall (along its arc where it would hit the fire wall if you lost all the fluid) 3/4 of that distance is about 3/4 of the piston stroke in the master cylinder



IMHO, with all else being within tolerance and working correctly, the outside limits for travel (in 1/4s of overall stroke) are

1/4 of the pedal travel being used before brake feel is found (taking up slack in the system)

the next 1/4 of travel should see your brakes progressing to normal everyday braking applications

somewhere (the earlier the better) in the next 1/4 your brake pedal should stop moving and you should be at essentially the panic stop lock em all right now brake position

and the final 1/4 (and whats not used of the panic stop 1/4) should be your pedal reserve.

There are actual specs for this but they mix fractions like a mad scientist, the rough and ready that Ive just given will see you doing adjustments more often than required but IMHO thats ok these are brakes we're talking about here.

ABS systems will typically have a bit more in the normal braking 1/4 and a touch less reserve if you do your pedal checks with the vehicle stationary but thats just the nature of the beast, if you can adjust it up to the 1/4 rule your laughing, if your a mickey out dont panic you wont get all the way through your panic stop position before the ABS kicks in anyway.

also............


if the drums are out of round......which is pretty common......you will not be able to adjust the rear brakes correctly......
instantly losing a fair bit of pedal travel.........

combine this with a slight bit of disc run out........and you will need to pump that pedal to have any brakes......




why....?
beacuse if the drums are out of round.......you cant adjust the rear shoes correctly because they will
bind up on the high spots of the drum......and be too loose on the low spots......

this will also give the symptom of a pulsating pedal whilst braking......

if the front rotors are warped......you will feel the steering wheel wobble whilst braking......

thanks Dave and everyone.

I haven't measured it yet. However, the pedal probably travels about a 1/4, so may is normal. Since getting it back after wheel bearings being checked the brakes are more consistent. Normal just feels soft compared to a car I suppose. It has only been on the road for a short while so not much to compare it against.

I remember having rear drums on the previous county. The drums were machined over limit with oversize shoes to compensate. Drums are not that expensive so i don't know why the prev owner did this. The cams would slip back which affected brakes badly. New drums fixed the problem. However, I never mastered the double adjustment on them. I always ended up with uneven wear. Consequently, I was attracted to self adjusting disc brakes.

just a side thought, have you checked the firewall for towerflex when you put the boot on the brakes. Dont forget to check the tower back for flex/loose bolts.