Bleeding Brakes

[Hodgy]

Hi everyone, having trouble bleeding the brakes on our HZJ 75.

Just fitted a new master cylinder to it and am now trying to bleed it.

The rear is fine, no bubbles and the brakes work ok.

The front is the problem, when the brake pedal is pushed for the first time then fluid comes from the port but when the pedal is released it sucks air back in the port instead of more fluid from the reservoir. We don't have a speed-bleeder or an easi-bleed and can't get them here.

Any ideas how to continue and does anyone have a diagram or photo of how the seals are supposed to be assembled?

Thanks all

Joe

 

[Hodgy]

Just got a pic of the internals....and just to clarify...I fitted a rebuild kit...seals only...not a complete new master cylinder.



'Cos I'm clever I didn't take a pic before I took the old one apart....

So here's hoping you can help!

 

[boogie74]

You may need to bench bleed the master. No need to remove it from the firewall tho.
Run a tube from the fluid resevior to the where the front brake line connects to the master
and give the pedal a few pumps. This will get fluid into the master, prime it. Google 'Bench
Bleed Master' and you'll find heaps of info. I had the same problem with my clutch when I
put a rebuild kit through it.

Cheers.

 

[Hodgy]

G'day Boogie.... :upside down smiley:



First a bit of history...the brakes had been sticking on. Gradually as you drove the front brakes would start to stick on and the pedal was hard, even the a short push would lock the brakes.

I tried...

cleaning the caliper pistons

cleaning the brake disks and replacing the pads

adjusting the booster pushrod so it was backed waaay off - no chance of it pushing on the master when the brake pedal was released

adjusting the stopper on the pedal side - no displacement of the booster pushrod when the pedal is at the top of it's travel

and

cleaning out the front circuit brake pipes with an air line


Thats when I took the master cylinder off to clean out the ports, my thinking being that anything that could obstruct the brake fluid as it travels BACK to the master cyl./reservoir could cause the brakes to progressively stick on. I found that one of the seals for the front circuit had a chunk taken out of it (second from left in the above picture), so thats when we bought a seal repair kit.

So now I'm having trouble bleeding it all back up. I tried bench bleeding just now and the problem is the same, with the master bench bled, as soon as I release the pedal the master sucks the fluid it pushed out back in again. For some reason the master doesn't take fresh fluid from the reervoir. Though as I said the ports are all clear.


I think either....

The seals for the front circuit are set wrong

As the front brake pipes are empty there isn't enough of a vacuum formed tro overcome the suction from the master cylinder and thus for the recuperation seals to allow fresh fluid through.

or

I've backed off the booster push rod too much and the front circuit is not getting enough 'push' from the master.

or

I'm an idiot and overlooked something blindingly simple



Thanks everyone

Joe

 

[Jim_Hbar]

Joe:

A quick search came up with thisHow a master cylinder works.

It talks about your previous locking problem etc..

First, make sure the springs and seals are correctly oriented in the master cylinder, and then bench bleed the master cylinder - the pipes that return fluid back to the reservoir MUST not suck air - the idea is to get all of the air out of the master cylinder.

Also, most people go about bleeding brakes incorrectly - they jump on the pedal and bump like hell, trying to build pressure, and get a bunch of air entrained in the fluid. DON"T DO THAT! If you don't believe me, take a partially filled can of brake fluid, shake it up well, and then wait for all of the air bubbles to come out of suspension.. The idea is to move the air through the plumbing..
To pedal bleed the system, Just push down firmly and slowly on the pedal, open the bleeder, push the pedal to the floor, and then close the bleeder... BTW, you will need two people to do that..

HTHs