Brake bleeding question

Post by **chrisd87** » Thu Feb 05, 2009 5:06 pm

Sarah's brakes weren't working all that well and were pulling to the left, so with the MOT approaching I investigated and decided to replace all the front wheel cylinders, pipework, flexi-hoses and the brass union (due to the pipes being thoroughly seized into it).

Today I've been trying to bleed the brakes through but I've come up against a slightly strange problem - I can't get a firm pedal. I've bled through the entire system until no bubbles were apparent in the bleed tube but the only way I can get a pedal is to pump it. Once pumped you can apply loads of pressure to the pedal and it doesn't sink, so I don't think there's a fluid leak anywhere (no signs of one either).

I'm really baffled - it's as if there's air in the system, but I don't see how there can be. Any suggestions? The only thing I can think of is that I bled the system with the handbrake on, but there's no mention of it needing to be on or off in the Haynes.

Post by **8009STEVE** » Thu Feb 05, 2009 5:14 pm

This wil take 2 people. Apply pressure to the footbrake, with a firm pedal , and then bleed the nearest. Just let the pedal go to the floor, then lock off the nipple. do this to all bleed nipples. then bleed the whole system as normal and you should get a good pedal

Post by **PSL184** » Thu Feb 05, 2009 5:15 pm

see here for more tips....

http://www.mmoc.org.uk/index.php?name=P ... pic&t=8563

Post by **jonathon** » Thu Feb 05, 2009 5:28 pm

The brakes should be bled with all adjusters off and the handbrake released. Bleed in the correct order and if you still have a soft pedal then adust the rod on the pedal to see if this improves things.As Steve suggests you can pump up the pedal to achieve pressure but still bleed them in the correct order.

Post by **bmcecosse** » Thu Feb 05, 2009 5:32 pm

I disagree J - in my experience the adjusters should be tightened up so the shoes are 'skimming' the drums. This gives least possible movement in the wheel cylinders and ensures the air is expelled. handbrake OFF I agree !
In fact - I suspect the problem here is that the shoes are needing to be adjusted up - that's why there is a long pedal even after all the air has gone.

Post by **jonathon** » Thu Feb 05, 2009 6:07 pm

Its worked well for me over the last 15 years BM

Post by **alainmoran** » Thu Feb 05, 2009 6:31 pm

I agree with Jonathon ... I had real mares with trying to get my brakes to work correctly until I disconnected the handbrake cables, bled the system (for me I used the most distant first), adjusted the shoes, then reconnected the cables and adjusted them to suit.

Post by **kennatt** » Thu Feb 05, 2009 9:27 pm

i'm with bm bet simple adjustment of the front and back shoes will give a good pedal

Post by **jonathon** » Thu Feb 05, 2009 9:57 pm

For bleeding the route I mentioned works well, you do need obviously to adjust the shoes afterwards to obtain a good pedal

Post by **Dean** » Thu Feb 05, 2009 10:01 pm

What is the correct order? I need to bleed mine...

Post by **alanworland** » Thu Feb 05, 2009 10:23 pm

I have the brakes adjusted correctly, then, via a home made adapter I apply 8/10 psi through the small hole in the master cylinder cap ( a WD40 tube works well)
Then I undo the bleed screws (furthest first) and allow the fluid to be piped into a jar.
Keep an eye on the level in the master cylinder, I find it works a treat!

Post by **bmcecosse** » Thu Feb 05, 2009 11:27 pm

As you all know - I just rely on gravity!
Worked for me for 40+ years now J - I've been at it for longer than you!!

Post by **kennatt** » Fri Feb 06, 2009 8:06 am

and me 45 years +

Post by **Dean** » Fri Feb 06, 2009 8:19 am

I've been at it for 6 months and I still haven't a clue!

Post by **jonathon** » Fri Feb 06, 2009 8:28 am

Bleed sequence is N/S/R, O/S/R,N/S/F,O/S/F.
BM, well at least you now know how to do it properly

Post by **chrisd87** » Fri Feb 06, 2009 5:33 pm

Thanks for that everyone - I've managed to get it sorted now. Me and a friend pumped the pedal up and then undid the bleed nipples in turn which got a bit more air out of the system. Then I adjusted the shoes which has given me a reasonable pedal.

Post by **jonathon** » Fri Feb 06, 2009 6:10 pm

Excellent !!

Post by **rayofleamington** » Fri Feb 06, 2009 6:24 pm

Yes - poor shoe adjustment will give a need for some pumping before you get a firm pedal. However it shouldn't give a spongy pedal - a spongy pedal will always be an air problem [unless you've just fitted new shoes]

I disagree J - in my experience the adjusters should be tightened up so the shoes are 'skimming' the drums. This gives least possible movement in the wheel cylinders and ensures the air is expelled.

Worst thing you can do for final bleeding is have no movement at the cylinders!! Air is easily trapped and removal needs significant fluid FLOW.
Therefore bleed with the adjusters fully off. After bleeding re-adjust shoes so there's no play.

The rear shoes are designed to trap air - the original seal design (cup seal) was not so bad but recent cylinders are likely to hve a ring seal and this configurations leaves much more room for trapped air.
Tips to assist with that are shown in the link on P1 of the thread.

If you've just fitted new brakes shoes you're unlikely to get a good pedal

New shoes are nearly always badly made these days and they take a fair degree of 'bedding in' before they fit neatly to the drums. The spongy pedal may be flex in the brake shoes!

The quickest and dirty way to bed new shoes in is to adjust until you can hardly turn the drum. Then do some short drives with a fair bit of braking. In bad cases you may need to do this more than once.
Needless to say your brakes will be shoddy to start with so make sure any driving is done with due care and attention - on a private road etc...

linearaudio · Post by **linearaudio** » Fri Feb 06, 2009 6:26 pm

Just a thought, did you strip/check the REAR cylinders? They can seize and give odd problems, yet handbrake will still work(ish). Just mention it as you don't sound totally convinced that you have it cracked!!

Post by **bmcecosse** » Sat Feb 07, 2009 5:50 pm

Never had any problems bleeding - with shoes adjusted right up! The idea is to flow oil through - no need to move the pistons. No problems with 'trapped air' at the rear cylinders either - although I concede all mine are 'cup' seal - not had any ring seal cylinders at the rear.