Brake bleed sequence

[SteveOS3]

I will need to bleed all the brakes very soon and was wondering in which sequence if any, it needs to be done.

I have the Saab servo/cylinder setup if that makes any difference.

Thanks,

Steve

[Marc C]

Generally, bleed the most distant first, if the system is completely empty you may need to bleed through the brake bias valve aswell

[Ceejay73]

The way these cars are plumbed, longest pipe run first to shortest, bleed order would be;
OSR
NSR
NSF
OSF

BUT I would recommend NSR Then OSR as the pipe to OSR runs higher in the chassis than NSR.

HTH
Carl.

Edited by Ceejay73 on Tuesday 1st September 19:09

[greymrj]

I would agree with that. One other thing, I have found it better to bleed an empty system on the S with the handbrake about 3/4 on first which limits the slave travel. I had a bugger of a job getting the rears clear otherwise. Might just be me!

[phillpot]

greymrj said:

the handbrake about 3/4 on first which limits the slave travel.

Strange? ...... with the bleed nipple open on the wheel cylinder the pistons shouldn't be moving, but if it works go with it

[SteveOS3]

Thanks gents.

Hoping to fit new seals to the master cylinder today.

Steve

[greymrj]

phillpot said:

Strange? ...... with the bleed nipple open on the wheel cylinder the pistons shouldn't be moving, but if it works go with it

What I think is happening Mike, and it does in other hydraulic applications, is that the fluid input to the cylinder is adjacent to the bleed valve so unless the 'pumping' is very gentle, fluid goes straight from the input to the output (which is smaller in diameter) and slightly pressurised air can get trapped against the pistons, more probably if they are some way out from centre. Keeping the pistons close together until the cylinder is refilled with fluid minimises this. In a way I suppose it is acting like priming the slave cylinder.

[tvrgit]

greymrj said:

What I think is happening Mike, and it does in other hydraulic applications, is that the fluid input to the cylinder is adjacent to the bleed valve so unless the 'pumping' is very gentle, fluid goes straight from the input to the output (which is smaller in diameter) and slightly pressurised air can get trapped against the pistons, more probably if they are some way out from centre. Keeping the pistons close together until the cylinder is refilled with fluid minimises this. In a way I suppose it is acting like priming the slave cylinder.

But but but... putting the handbrake on moves the brake shoes out, right? And moving the shoes out takes away (or at least reduces) the spring pressure pulling the shoes together (i.e. pulling the brakes "off"), right"

So with the handbrake on, there is LESS pressure (from the shoe springs) acting back against the pistons, then they are MORE likely to move out while bleeding, so how can putting the handbrake on hold the pistons closer together?

I have sometimes bled brakes with the handbrake partly on before - I thought it was because you were more likely to fill a bigger space (if the shoes can move out) without trapping air

[phillpot]

greymrj said:

unless the 'pumping' is very gentle

Being "Billy no mates" I use a Gunson Easibleed with a spare wheel at low PSI rather than up down up down on the pedal

[SteveOS3]

Shouldn't a gentle pumping involve going down before going up?

[greymrj]

tvrgit said:

But but but... putting the handbrake on moves the brake shoes out, right? And moving the shoes out takes away (or at least reduces) the spring pressure pulling the shoes together (i.e. pulling the brakes "off"), right"

So with the handbrake on, there is LESS pressure (from the shoe springs) acting back against the pistons, then they are MORE likely to move out while bleeding, so how can putting the handbrake on hold the pistons closer together?

I have sometimes bled brakes with the handbrake partly on before - I thought it was because you were more likely to fill a bigger space (if the shoes can move out) without trapping air

I think I need to go to the corner with a tall hat with the letter D on it. Lesson one: engage brain before touching keyboard.

I know it has something to do with fluid being pushed into the cylinder faster than air can get out and air getting trapped. I think that would only happen with pumping rather than Mikes method?

As far as going down before coming up is concerned, it is before the 9pm watershed so I wont dwell on that!