IIa Brakes

[rbbailey]

I'm trying to stiffen up the brakes on my 88. It has standard drums, but I have put a boosted Series III system in. Since then, I just can't get them to bleed right. It's not leaking anyplace, I'm not losing any fluid. I don't see any bubbles in the fluid that is coming out. I have my son on the pedal, I'm starting at the furthest point. Open, pump, pump, pump and hold, tighten. etc.... But I just can't get it to work.

Normal light braking isn't a problem, but if I have to step on it hard at all, it will lose pressure and I have to pump the brakes to continue the whole stopping thing.

Any pointers?

[SafeAirOne]

Are the brake shoes PROPERLY adjusted?

Even if the system(s) are fully bled, if the amount of brake shoe travel required (total wheel cylinder displacement) exceeds the master cylinder's output when you step on the brakes, it will take more than one pump to get the shoes to close the gap to the drums and to apply enough force on the shoes to get the desired result.

The purpose of the adjuster cams are to keep the shoes very close to the drums so it doesn't take a great amount of fluid displacement on the master cylinder's part to fully actuate the brakes.

[rbbailey]

The problem with that is there is I guess my drums... new drums, are warped because if I pull the wheel off the ground and spin it will grab, then release, then grab, etc.... So I adjusted them as tight as possible for the bleed, but have to back off in order to roll.

However, after adjusting and bleeding some more, all of a sudden a bunch of air did come out. I'm now still seeing very, very small bubbles. I've gone through a full gallon of fluid and no change.

I test drove the truck and the initial push on the brakes is very good. Very short travel with the pedal to get a lot of pressure on the drums. I can actually stop very well. BUT! After about four seconds they fade and the pedal continues to depress.

Going to have to sell the thing at this rate. Every time I touch it something else goes wrong.

[I Leak Oil]

Open, pump, pump, pump and hold, tighten. etc.... But I just can't get it to work.



You need to modify your proceedure. What you're currently doing might be more like:
Open, pump, release and suck in air, pump, release and suck in air....hold, tighten.

Just do it like this:
Pump, open, hold, close. Repeat.

But I agree that poor adjustment is a common cause of soft or double pump brakes. This is one of those cases where Rover never modernized their design. Never added self adjusters over the nearly 40 years of using drums.

[TeriAnn]

I test drove the truck and the initial push on the brakes is very good. Very short travel with the pedal to get a lot of pressure on the drums. I can actually stop very well. BUT! After about four seconds they fade and the pedal continues to depress.



That is a classic sign of a bad master cylinder with an internal leak.

BTW, pressure bleeding does wonder for removing bubbles. You only need about 5 to 7 lbs pressure to push the bubbles out.

[SafeAirOne]

You need to modify your proceedure.

Good catch. I didn't notice the procedure he described. Should be "pump, hold, open, close" then back to pump again.

[rbbailey]

OK, I'm looking at what Teriann is saying, I hope not, it's a new master. But I think you're right.

With my procedure, I sort of realized this on the last attempt. So I then told my son to put pressure on the pedal before I opened. Then pump three times, hold, close. Would this be bad as well?

But since after doing that I'm still getting bubbles, I'm thinking Teriann might be right, that the bubbles are actually coming from the master sucking air. I don't see any leak, but...

[SafeAirOne]

There should be no upward movement of the brake pedal whatsoever anytime the bleeder valve is open. This is draws air back in through the open bleeder instead of drawing new fluid in from the reservoir.

[siii8873]

I assumed when you say Pump pump pump these are all with bleeder closed to build good pressure, then press, open bleeder, hold, close bleeder release repeat. I was thinking master cylinder leak by also if air is out of system and still loosing pressure, no leakage.

[tmckeon88]

One other thing to check possibly is the large pin that the brake shoes pivot on, which is located at the bottom of the brake backing plate. That pin is usually tack welded or spot welded into the backing plate and it's possible that the welds can break and leave the pin sort of floating around there. That means that there's no amount of adjusting that can ever take up the slop in the whole brake system and you end up having to double pump your brakes. I had this problem for YEARS and when I finally located it and replaced that backing plate, it was like night and day. Haven't had a significant brake problem since.

Good luck -
Tom

[rbbailey]

Yes, but if the hose is attached to the valve and down in fluid, the only thing that could be going back in is a small bit of the fluid that was pushed out of the valve.

However, having read what others are saying here, I think maybe I am doing it slightly wrong. I need to build up more pressure before opening the valve.

[I Leak Oil]

If the tube is in the fluid it's possible it's sucking air in past the threads of the bleeder screw. Path of least resistance. It's easier to suck in air here than it is to pull all that fluid back up into the system. Best practice is to not let up on the pedal when the bleeder is open. You'll never have negative pressure in the system by doing that.

If you need the multiple pumps then do it first, hold, open, hold, close. repeat. Never let up with the bleeder open.

If you suspect the master cylinder then you can test it using a similar method. Easier to do it out of the vehicle on the bench.

[Partsman]

If the tube is in the fluid it's possible it's sucking air in past the threads of the bleeder screw. Path of least resistance. It's easier to suck in air here than it is to pull all that fluid back up into the system. Best practice is to not let up on the pedal when the bleeder is open. You'll never have negative pressure in the system by doing that.

If you need the multiple pumps then do it first, hold, open, hold, close. repeat. Never let up with the bleeder open.

If you suspect the master cylinder then you can test it using a similar method. Easier to do it out of the vehicle on the bench.
I find a bit of thick grease around the threads helps prevent air getting past them, but as Jason says don't let up on the pedal while bleeding.

[cedryck]

I feel and agree with Terri, pressure bleeding is much better at removing air, and actually easier as you do not need another person, although this helps having another person there. There are a number of different units on the market that work well.