Bleeding brakes - what am I doing wrong?

[Alex'n'Ane]

My feelings on useing a one way valve as he is, is that air can be drawn in on the oedal upstroke between the bleed nipple and the threads/tapered seat

I do agree that that is a possibility, can u not just get anyone to steadily push the pedal down, wait till you tighten it up, then raise the pedal again? And repeat..

[bmcecosse]

Oh dear - all these master cylinders that are needlessly changed.......

[gatsby989]

are you 100% certain that you are adjusting the brakes properly,badly adjusted brakes will give you the exact symptoms you are describing,air in the system usually feels like a soft pedal at all times.

No, I am not 100% certain about that. I haven't messed with the front brakes at all, only the back brakes. I installed new shoes when I installed the new rear cylinders. Could you please explain, or point me to an explanation, of how to properly adjust the brakes? Maybe I'm chasing a wild goose.

I do not think it is the master cylinder because I've been driving the car daily for the last several months, and the pedal was fine. The brakes mostly worked. The main problem I was having is that the emergency brake would not lock up, no matter how tight I got it. I replaced the cables, to no avail, and then decided to replace the rear cylinders as they barely moved when either the foot brake or handbrake was applied. Apparently the front brakes have been doing all the work.

Edit to add: I have no servo, no front disks, nothing out of the ordinary. Just the standard 7" drums all around.

[mike.perry]

I was getting very little action from the handbrake on the slope outside my garage and the pistons did not appear to be working well - and I had an MOT coming up. I checked the rear brakes on the local garage tester and got very poor results.
I changed both rear cylinders and as I had to cut the pipes off, they were changed as well. One pipe was found to be crushed which did not help. The cables were greased including the ends where the inners come out of the outer cables as this part can rust and often frays. The inner cables were pulled back and forwards to check that they were moving freely.
The rear cylinders were adjusted fully and bled then slackened and the brake pedal pushed firmly to centralise the shoes, then adjusted again and checked
The handbrake cables were attached and the handbrake applied and the drums checked that they were locked on. The wheels were replaced and checked and the handbrake released one notch. The cables were adjusted so that there was equal resistance on both wheels, then checked again with the handbrake fully applied
There was a lot of checking so that I knew that each stage was correct. The Traveller passed the MOT and with the back brakes working correctly, the car at last felt that the Wolseley front brakes were able to perform to their full capability

[bmcecosse]

[autolycus]

For this purpose, adjust all the brakes, using a screwdriver through the holes in the drums, until the wheels are locked. You may then find the problem has disappeared. If not, each wheel cylinder will then have minimum piston travel, so the maximum amount of fluid will be available to sweep out any bubbles.

You should then have a very firm pedal, with minimal travel. Then adjust the brakes as normal, backing off the adjusters till the brakes rub only very slightly. Then adjust the handbrake cable as Mike advises.

It is very occasionally necessary to use hose clamps to isolate parts of the brake system when searching for obscure faults, but don't do this unless necessary.

Finally, I've had far more master cylinders fail during bleeding than in normal use. The extra travel of the seals, into uncharted bore territories, can finish them off. That's another advantage of Eezibleeds or vacuum bleeders - or, if you live in Scotland, gravity, since, like everything else, it is so much stronger up there.

Kevin

[MarkyB]

Very good point about the extra travel when bleeding the brakes.

If with gentle progressive pressure from your hand or foot the pedal will go all the way to the floor the MC is knackered.

Are you getting more air out when you bleed the brakes? This is another possible sign of MC problems.

[bmcecosse]

" if you live in Scotland, gravity, since, like everything else, it is so much stronger up there "

[MarkyB]

Urban myth brought on by Irn brew adverts

[charlie_morris_minor]

Urban myth brought on by Irn brew adverts

er gravity is stronger in scotland than in the usa..

http://www.guardian.co.uk/science/2011/ ... th-gravity

[bmcecosse]

Irn Bru - made from girders.......

[kennatt]

if its only the back brakes that you have changed,then the fronts should still be adjusted,with the drum on turn the adjsuter screw untill the drum is held fast then back off one click at a time untill it just rotates with a very slight rub.If still no joy,it may be that you need to clamp off the brake hoses (People will come on and say that it damages the hose)I've done it for 35 year and never damaged one yet,but your decision,if you havent got a hose clamp, use a vice clamp or gclamp with a couple of wooden blocks between the jaws to spread the load it dos'nt need to be very tight and you dont need to stamp on the brake just gently press the pedal you'll soon see if it is now firm and then know where to start remedial work.clamp one at a time and leave the clamps on when all are clamped if still going down to the floor then suspect master or still a LOT of air in the system. good luck

[gatsby989]

Thanks again for the suggestions. My rear brakes do not have flexible hoses. The metal pipe goes straight into the cylinders. So afraid I can't clamp the rear ones. I bled them a little more using Charlie's method, and I also re-adjusted all the brakes, front and back. That certainly helped, but the pedal's still not quite as it was before. I wonder if part of that is just because both rear cylinders were pretty much seized, so there wasn't as much travel before. Took the car out for a bit this morning, and it performed fine. The handbrake finally works as it's supposed to.

I plan to soon swap out the front 7" for 8" drums. The current front brake cylinders work fine. The same cylinders are used for 7" and 8", correct? When I disassemble the front to change the backplates, are their gaskets / oil seals that I will need to replace?

I just saw in the workshop manual that one of the potential causes of excessive pedal travel is "master cylinder cup worn." When I do the front brakes, I might try a repair kit for the master just in case. I see there are two sizes of kits for MCs, 13/16 and 7/8" My car is ostensibly a '57, so as I understand it, it should have the 7/8" bore. However, I know the master has been taken out before, so I don't know for certain that this is the original. Is there an easy way to tell which size I have?

[Alex'n'Ane]

The rear flexi is a single pipe that goes between the body. And the rear axle, its at the middle of the car, by the diff. Also - wouldnt bother trying to fit new seals, not worth the hassle. If removing the old mc, just fit a new one, as the bore could well be rusted etc on ur current one anyway.

[bmcecosse]

Well done. There is a single flexi to the rear brakes - but I am dead against ever clamping flexis - I feel it will shorten their life and come back to haunt you..... Yes - same cylinders, No - no gaskets etc. As you say - you may be used to the seized up rear cylinders having NO movement whatsoever. You may well find that the new rear brakes need 'nipping up' now that you have had a run in the car. The 8" drums will be MUCH better for you. My advise - leave the mastercylinder alone until you are sure there is no other possible reason.....

[kennatt]

[quote="bmcecosse"]- but I am dead against ever clamping flexis - Like I said but two days later yes the seized rears would have resulted in a hard pedal,now they are moving then there should be a bit more travel. A solid pedal is infact a good test for siezed cylinders.

[bmcecosse]

Yes - I was agreeing with your analysis.....

[Trickydicky]

Just for info everyone,

I adjusted my brakes all round the other day as the minor was going in for a "pre mot" the brake pedal has now proceeded to have full travel to the floor. (yep it failed on the brakes) I thought one of the adjusters could have sprung back, which would cause excesive foot pedal travel but after checking each corner, all are fully adjusted.
So I thought "check the fluid level" removed the plug to find very little fluid in the M/C, removed the cover plate to find plenty of fluid in the chassis leg......

Anyway I have ordered a new M/C as it is most likley a worn/aged seal on the cylinder.

The moral of the story is that if you are adjusting/replacing brake shoes or new wheel cylinders be mindful of the fact that if the M/C is old and worn putting extra pressure on the system will invariably find the weakest link ( in my case the M/C)