most bits changed - BUT STILL NO BRAKES!! Thoughts please.

[BartonStag]

Hi all, tried this twice last night and it wouldn't let me post??!! So I'll keep it short - just in case. Basically I've replaced the rear shoes and wheel cylinders, fitted braided hoses all round and replaced the front calliper seals, pads, retaining clips etc. The only seals NOT replaced are the square sectioned ones between the two halves of the callipers (none supplied with o'haul kit). I'm using a Gunson auto bleed unit and am getting plenty of air coming through - especially from the rears.There are no apparent leaks evident, although I cannot prove the system is NOT drawing air in anywhere (how do you prove that?). Despite all this I still have no pedal pressure. The PDWA valve is sitting centrally. I believe it points to the master cylinder/servo although I have also replaced these components with supposedly tested parts. Any advice gratefully received if you've come up against this one folks.

Thanks
Gord

[Stagsongas]

Gord,

Start right at the beginning by proving (or disproving) that the master cylinder is working. Get someone to pump the pedal and slacken the pipe unions connected to the master. If fluid comes out, it's working, but check both pipes. Mind your face, eyes and the car though.

Good Luck

Steve

[4x4]

Have you got all the bleed screws closed except the one you are trying to clear?

[73stagman]

I think the master cylinder will only be proven ok once you have pedal pressure. We had some trouble breeding Brians brake system and ended up throwing away the one man bleed kit. We put fluid in the jar to cover the end of the hose connected to the furthest away bleed nipple. Opened the bleed nipple and just kept pumping till we filled the jar with fluid. Closed the bleed nipple and then convention took over. Pump the pedal till its hard let go of bleed nipple let all air fizz out close nipple pump pedal again. Repeat again and again and again and......

[jleyton]

We had some trouble breeding Brians brake system

I bet you did

Sorry Neil - I need anything to smile at right now

Cheers

Julian

[Mike Stevens]

I tend to use the 2-person 'down, down, up, up' method. One on the pedal and the other opening/closing the bleed nipple on each wheel in turn. Open the nipple, press the pedal down, close the nipple, let the pedal up. That way you should not let air back in again as long as you have a short length of pipe on the nipple. Start with the brake furthest from the master.

Initially, you just get air out but then air and fluid, finally hopefully just fluid. If you do, then that master 'half' is pumping OK. You won't get a hard pedal until all 4 wheel are bled.

Cheers,
Mike.

[BartonStag]

Hi again all. Apologies for not replying prior to now -- but again I've been unable to post??? Email now sent to administrators! I originally bled the brakes using the two man method but with limited success. At this point I changed the master cylinder/servo for a supposedly tested unit from a SOC member. From this point I've used the Gunson method. I have free flowing fluid complete with air bubbles from every brake bleed point (all bleed points locked up 4x4). It appears that that the master cylinder works sufficiently well to push fluid thru to each brake unit, but when I try to achieve full pressure on the system it lets by?? I'll get a reconditioned master if I have to, but due to cost I need to be sure that's the problem.
Thanks again
Gord

[wilf]

With that much air in the system I doubt you will build any pressure.

Persevere with the bleeding, at some point air should stop coming out with the bled fluid and then you might start to see pressure building.

If not, your suspicions are well founded, but a can of fluid is cheaper than another mc.

[stagmuffin]

one thing worth noting , the master cylinder does not like being used to the full extent of its travel and this will only happen when one circuit fails or the brakes are bled using the pedal pumping method . the piston travels down the bore to a previously unused part of the bore which 9 times out of ten is rusty because of the moisture in the system ! this then rips the s**t out of the seals which then can lead to what you are experiencing .
solution is to fit an LD parts remanufactured m/cylinder with machined out and fitted with stainless steel sleeve ,this is a fit and forget option and is the route I personally have taken. I also use a mityvac vacuum tool to draw the fluid through it is much more efficient.
steve

[BartonStag]

[QUOTE=wilf;246890]With that much air in the system I doubt you will build any pressure.

Don't think expressed things very clearly there Wilf. I meant to say I've pushed air bubbles through at ALL the bleed points - but that's stopped now - still NO pedal pressure. It maybe Steve has identified the issue - I did read about not pushing the pedal down full stroke, but didn't actually realise why. However my fifteen year old who assisted doesn't have any experience with brake pedals. Looks like a new cylinder then folks!!

Thanks to all who have responded
Gord

PS All the best to you new moderator boys. Thanks for making the effort - good luck with it.

[wilf]

Ok, understood. Think Stagmuffin may be right now.

[Stagsongas]

He is right - full travel is normally unattainable in service life of the MC and should be avoided.

Regards

Steve

[BartonStag]

He is right - full travel is normally unattainable in service life of the MC and should be avoided.

Regards

Steve

Sounds fair enough Steve. But if I get a new one and use the Gunson one man bleed unit, when the pedal is pressed in the first instance can any damage occur internally due to "overtravel" or is that likely only (as the other Steve) explained in an older previously used cylinder?

Cheers
Gord

[Stagsongas]

Sorry, but I don't know of any 'hard and fast' rule, it's avoidance which does not help us much.

You can initially charge the master by bleeding at the outlet pipes, and then instruct your pedal-pumper not to go right to the floor I guess. Any self-bleed arrangement (like Gunson) that does not require pedal pumping has to be a good thing for aviodance but it's still good to finish off by having the pedal pumped, although by that time you should have some kind of 'pedal' which will not then allow too much MC travel.

Some times you can pre-charge most of a system with fluid just by having the MC reservoir full and opening one or more bleed nipples, the fluid may flow out of the nipples just due to siphoning, and I will often do that to get a system intially 'wet'.

All in all, damage due to too much MC travel is not a massively common problem, I think the advice was offered, like other advice, to try and explain what happened in your particular case, which is unusual anyway. A good master and good prep. should see you bleeding it all up in no time.

Good Luck

Steve