Brake Bleed Problems....

[keithb7]

1998.5 24V. Rear wheel ABS.  Recent work included:  2 new rear wheel cylinders. New  rear shoes. New shoe springs & related hardware and new rear drums.  Two rear brake lines were so corroded they snapped off at the nut on wheel cylinders. I made new lines. Mounted everything up.   Unfortunately had to go to work, and could not get the new lines on for a day or two so master self drained. All rear shoes and hardware seemed to go on fine, and appears to be functioning properly.  Recently I read several posts about bleeding brakes. I filled up master and started with my mity-vac vacuum system at each corner. Attempted to bleed by myself.  Little results felt on the pedal. Tried again this morning with a helper and manually bled the system. Helper pumped and held down while cracked lines. I started at the master cylinder lines and bled, then on to the proportion valve line connections. Then the ABS connections.  Then left rear, then right rear cylinders. Then front right and finally front left. All the while constantly topping up the master cylinder reservoir. Not allowing any air in the system. Master cylinder is still too low. I have rear end jacked up, re-installed wheels and fired up the truck. Rotated wheels and applied the brakes. I am barely getting enough to stop the rear wheels. There are no leaks. I just can't seem to get enough power through the master to each wheel. Maybe there is more air in there? I've gone through a fair bit of brake fluid and pumping. 

 

Brakes worked fine before I touched them. I went in for a leaking rear seal and went further based on other findings. Front pads are decent. Going back out now to manually adjust the rears. Make sure they are right and try again.

 

Any tips? Thanks.

 

Keith 

[Mopar1973Man]

I've used a mayo jar for years and never used anything else. Bleed my brakes solo for years!

 

 

Check the frame for rear axle weight valve. If the weight on the rear axle is too light the valve restricts brake fluid to the rear axle. A lot of people detact the arm and tie it in the up position to improve braking performance. 

[keithb7]

Interesting!  So I went back out and tweaked the rear manual adjusters even more. Moving the shoes yet closer to the drum. I read that the proportion valve limits hydraulic braking power to the front, until there is enough pressure built up on the rear brakes. Some sort of system relief in the proportion valve determines this. The rear wheel pistons only travel so far. Really not much at all. With the rear drums out of adjustment, the rear hydraulic pressure does not built up quite enough to offer full equal braking front and rear, it seems.

 

Braking is better now. Like it was before I started this brake work. However, I'd still like the pedal higher with more positive feel. I suppose one should consider the 21 year old master cylinder at this point. Likely well past it's prime. The previous owners did not do a good job with brake maintenance.  Wheel cylinder brake fluid came out looking like the ganges river.

[Mopar1973Man]

No, there is a valve with a rod connected to the frame. As there is more weight in the bed of the truck the rod opens the valve supplying more brake fluid pressure to the rear axles. This was only for a few years and then given up for the 4 wheel ABS. 

 

Brake shoes should be adjusted just enough to barely touch the drum then backed off slightly. 

[JAG1]

When bleeding the wheel cylinders on the rear you are supposed to start with the right rear then go to the left rear, (you mentioned you started with the left rear) Always bleeding furthest away from the Master cylinder first is industry standard.