need help bleeding/fixing brakes on a GQ

[werafa]

Hi all. I've run out of ideas, and am now into the 'gaining experience' zone, except I don't know what experience to gain. I hope someone can help.

1. I replaced the brake cylinders on the rear wheels (drum brakes), and drained all the brake fluid while I was at it.

2. I added new fluid, and bled the system until new clean fluid was coming out at each brake cylinder.

3. after two attempts to get rid of all the air, I discovered that there is a fifth bleed point in the rear axle (power transfer valve), and bled the whole system again.

4. the pedal is still unacceptably spongy (over half the pedal travel is 'soft'), so I bled the entire system again, but found no air; and made no change to the pedal action.

can anyone suggest what might be wrong, and how I can fix it? :smileyvault-cute-bi

many thanks

[Bigrig]

Sounds like one for Tony, Patch and crew ... hang tight mate, they'll be along to assist no doubt!!

[the ferret]

Have you adjusted the rears up?
Start bleeding at the rear left, power valve, rear right, then front left then front right, don't push the pedal all the way to the floor, lock the bleeder before letting the pedal back.
Sometimes it needs a "gravity" bleed where you open the bleeder and let the fluid bleed itself.
Have your catchment bottle higher than the bleeder using beverage tube to the bottom of the bottle.
Bleed the master cylinder several times.
You may need a "pressure" bleed if all else fails.
Cheers, the ferret.

[werafa]

I was careful not to change the adjuster on the rears - just made sure they were free to turn.
for bleeding, I used a non return valve on the bleed tube, but when I struck trouble I went back to the karate kid method (brakes on....brakes off)
last time around, I pumped about half a resovoir through to the load adjuster valve to try to shift any air locks.

since starting this post, I checked the connector at the top of the master cylinder, and had a fluid leak the instant I cracked it - but there is a downside up u bend just above this point - perfect for a hard to shift air lock.

what do I need to get to do a pressure bleed?

Thanks

[the ferret]

Try Supercrap.
I think they sell a kit, but try the old gravity bleed method first.
If you still want to pedal bleed it, just go steady and don't pump it like a rabbit scratchin flees!!
Cheers, the ferret
EDIT.
There may be more than one bleeder on the load sensing valve.

[werafa]

thanks

will check the valve - but I think it only has the one on the top.
I have the visibleed tube - and this is what I used to begin with.

Am starting to think I might put this back on to one of the rear brake lines, and try to pressurize the resovoir with my mini compressor - I think the most likely culprit is an airlock somewhere early in the system. Everything was good until I fixed it.

[the ferret]

If the pedal won't hold pressure and slowly goes to the floor, then you may have a leak, or the master cylinder needs an overhaul.
Cheers, the ferret.

[werafa]

The pedal goes half way under light pressure, then goes hard and starts to apply the brakes. once it is on hard, it goes no further

[the ferret]

So The master cylinder is ok, you still have air in the system, more bleeding needed.
Adjust the rears up tight and bleed system again.
Check that no hoses are expanding when the brakes are on hard.
Cheers, the ferret.

[werafa]

:jawdrop::1087::blowup:

oh we're happy little vegimites...........

will let you know how I go.

[werafa]

Ok, just pumped an entire reservoir of fluid through to the rear passenger side bleed valve.

as for all the other ploblems, the brakes were rock solid until I replaced the rear cylinders and drained the fluid
will see how it feels in the morning

[werafa]

Hmm. no change.

even worse; if I hit the brakes hard, I can feel them sag for a bit - methinks it could be the master cylinder. anyone got any better ideas?

[the ferret]

Havn't got the rear brake shoes in arze about have you??
That would also cause the brakes to lock when moving forward.
Might pay to go back over the rear wheel cylinders and make sure they havn't popped or the push rod hasn't slipped sideways., but that should also cause a fluid leak.

[Robo]

Hi bud.

This is DA maverick spec, but 1 would think same
adjust brake shoe clearance.
Min .25mm -- Max .4mm .

again da mav spec.
Bleed.
LSV first---left rear --- right rear ---left front ---right front.

If you are having trouble with bleed screws leaking air/fluid on their threads " my trick " is try some plumbers thread tape on em, be careful not to allow tape beyond thread of bleeder screw and into cylinder.
found this helps alot.
you need a temp plug to stop losing fluid while you put tape on screw.
personally found it easier to have bleed tube going up vertical to some degree after screw to help prevent air re-entering cyl.
use ring spanner on bleeder as you never want to round one of these suckers off.
If this doesn't work , you may need to look further for leaks.

cheers

[werafa]

last update - It was the master cylinder. Draining the old fluid allowed the cups to collapse - they were a bit over it, and this was the last straw. hence the advice never to empty the system. I can stop now.

doh

[jedskipow]

Those engine cleaning guns that work on the air compressor and suck out off tub under neath. Take tub off, duct tape longer hose on, hook on brakes. Longer hose is so you retain paint work on car. I do the clutch, brakes like that.