Brakes!!

[Peetee]

My Mogs brakes are rubbish. they have a lot of travel and then respond fairly well but with not enough vigor to be safe. I have inspected the wheel cylinders for leaks, bled the brakes twice, checked the master cylinder level, adjusted the shoes, all to no avail. The drums do seem a bit oval (binding intermittantly as the drum is rotated with cam set to 'closest' notch) but I wonder if this would be enough to create so much travel?

I have bought a M/C repair kit on the assumption that the rubbers are shot but if this were the case would it not be a bit unlikely that the brake operation would be so consistantly poor? surely if fluid was leaking past the seals, then at times there would be no brakes at all?

[bmcecosse]

Are all the linings in good condition - are ALL the wheel cylinders moving freely ? Maybe a general replacement of just about everything is called for !

[tufty]

Having fitted a servo to my moggy i found the brakes to be very disappointing. I eventually traced the problem to the rubber hoses on both front wheels and rear axle. I built a rig to test the pipes and found that they panted even with very little pressure. When braking pressure was applied to them they took an extra 10% of fluid to get the same braking effect ie, the pedal has to move futher for the same amount of braking.

[bmcecosse]

Usually heavier duty hoses are specified for cars with servos -- ie the Cooper S had 'double green band" hoses.

[Willie]

If you had a leak or the Master Cylinder rubbers were not working
properly you should find that when you depress the brake pedal
HARD and keep it pressed that your foot will then slowly move
further down. If the pedal action improves when you pump it
rapidly then your brake shoes are too far away from the drums.
Regarding the leaks, there is no way that you can tolerate ANY sort
of leak in the system so that you "eventually run out of brakes".
If the fluid level in the reservoir drops then you MUST find the culprit.

[Peetee]

well i don't eventually run out of brakes, it's simply that the brake action does not begin until the pedal is well down. they then work OK but of course they are limited because the floor gets in the way!! As I say the snail cams have been adjusted all round.

Could it be that the slave cylinders are not working on one or more wheel and that the master cylinder seals are poor. Am I right in thinking that any fluid leaking past the M/C seals would return when the pedal pressure is released?

[bmcecosse]

I think you should try again with the adjusters ! Are you sure each one has been pulled up really as far as it will go ? ie -Pulled up till the drum won't turn, then backed off 1 notch only.

[chickenjohn]

A classic one to miss! (it caught me out once:( ) Did you bleed the brakes in the correct order? The wheel cylinders should be bled in the order of furthest away from the master cylinder, so : rear left, rear right, front left, finally front right.

"Could it be that the slave cylinders are not working on one or more wheel and that the master cylinder seals are poor. Am I right in thinking that any fluid leaking past the M/C seals would return when the pedal pressure is released?"

No, this fluid will end up in the dirt at the bottom of the chassis member.

[rayofleamington]

No, this fluid will end up in the dirt at the bottom of the chassis member.

Fluid that gets into the chassis leg will be from a leaking secondary seal (on the low pressure side). It's the primary seal that affects the brake pressure - any leaks on this seal will go back to tank.

Personally I expect it is either adjustment or bleeding needed (or a bit of both).

[Peetee]

Fluid that gets into the chassis leg will be from a leaking secondary seal (on the low pressure side). It's the primary seal that affects the brake pressure - any leaks on this seal will go back to tank.

I think thats what I was getting at. Is it possible that as the brakes are applying, and pressure in the system is increasing, one of the seals is leaking and fluid is escaping back to the reservoir rather than advancing down the system?

[chickenjohn]

If thats the case- you need a new master cylinder!! Best change it before it fails half way down a very steep hill!

[tufty]

I have found that it is hopeless to try adjusting the brake without first removing the drum and cleaning out the muck (do this with a wet sponge or proprietery cleaner) caused by the lining wearing in the first place. Refit the drum and then adjust the snail cams. Carrying out this procedure has the advantage of checking the slave cylinder seals and handbrake mechanism in the rear wheels (wheel cylinders free in back plate). Also has the master cylinder been changed and then not adjusted. There is an adjustment for free play built into the pedal to master cylinder linkage, have you checked the linkage for wear in the cross shaft small amounts of wear in all the joints may add up to the lost travel!

[bmcecosse]

The 'snails' can sometimes come up against a faulse 'stop' when the edge catches - you need to get them beyond that to be sure the shoes are tight enough. So it's essential to lock the drum and then back-off one click only. Then repeat with the other adjuster.

[woo]

bmcecosse said:

lock the drum and then back-off one click only.

When I just back-off with one click the drum does not turn completely freely. Does this mean that I should perhaps back-off until it does not 'catch' while turning the wheel?

[rayofleamington]

When I just back-off with one click the drum does not turn completely freely. Does this mean that I should perhaps back-off until it does not 'catch' while turning the wheel?

Personally I leave them rubbing slightly to make sure the pedal travel is nearly zero (any rubbing soon goes once you've done some mileage), but I'm sure that others don't like that method.

When the drum is off - check for the false stop! i've seen this more than once and it is cured by removing a bit of the steel from the shoe (file / angle grinder etc...) to allow the adjuster to keep rotation.

[Matt]

Personally I leave them rubbing slightly to make sure the pedal travel is nearly zero (any rubbing soon goes once you've done some mileage),

Thats what I do too....

[TerryG]

Quote:

Personally I leave them rubbing slightly to make sure the pedal travel is nearly zero (any rubbing soon goes once you've done some mileage),

Me too!
Thats what I do too....

[Theo]

How much pedal travel is normal? I changed the front wheel cylinders and brake shoes, bleeded and adjusted all 4 brakes. Now I can create blocking wheels by braking at 30 mph, but have to push the pedal almost up to the floor. Is this normal, or should I have smaller pedal travel?

[andrewsxt]

I would say this is far from normal, I have the same problem and have done everything apart from change the master cylinder so I am assuming this is the problem.

[bmcecosse]

Look at the shoe adjusters - they sometimes go so far and then 'jam' against the shoe but before they have brought the shoes right up to the drum - a little touch with the angle grinder (or some filing) gives clearance. Be sure to slacken off the handbrake cables - then adjust the rear brakes - then tighten the cables again little by little and each side in turn - but check they don't cause the rear shoes to drag when doing this. If the travel is less when you 'pump' the pedal then there is still some air in the system. Other problem could be flexi hoses 'bulging' under pressure - get someone to stand on the pedal while you inspect them. Obviously this is very dangerous - and if bulging they need replacing immediately !!