Brake rebuilding time. Lots o' questions!

[Captain Obvious]

The Factory Manual, Chilton's and my primary reference, Autobook, shows the return spring inside the cylinder as having its larger end against the piston, smaller against the cylinder. But I know, on both of my cylinders, it was installed the other way because I had to jimmy it off the bolt-head like thing on the piston.

You're talking about the pre-77 rear cylinders, right? They're very different than the 77-78's.

I'm sure that spring you're talking about is supposed to fit narrow end snugly around the locating boss on the back of the piston and the wide end pushing against the inside of the cylinder. You're saying that all the pictures show that spring installed wide end against the piston???

[Jetaway]

You're talking about the pre-77 rear cylinders, right? They're very different than the 77-78's.

I'm sure that spring you're talking about is supposed to fit narrow end snugly around the locating boss on the back of the piston and the wide end pushing against the inside of the cylinder. You're saying that all the pictures show that spring installed wide end against the piston???

I think they are pre-77 cylinders, yes. They look like they were born with my '72 but I am beginning to put nothing past a determined P.O.

Yes, they are pre-77s. I'm looking at my downloaded service manual right now. Yes, the drawing has the big end against the piston. When I dismantled them, the springs were as you remembered, and as I reinstalled.

Weird, huh?

I really don't see how you could hope to keep the spring from wandering around in the bore if it were installed per Service Manual.

Chris

[Captain Obvious]

I really don't see how you could hope to keep the spring from wandering around in the bore if it were installed per Service Manual.

I agree. Must just be a mistake in the docs.

Sure is a good thing that I don't read directions, or I may have followed them!

[FastWoman]

Captain, all I can point to is one rather corroded cylinder. Maybe that was the smoking gun. I have no idea how long the fluid was leaking. I usually check the fluids with every oil change, but perhaps not reliably enough. I don't think the twisted-up brake line that I replaced was leaking. Anyway, in my experience, when there's a leak, even a slow one, it's brake rebuilding time. There's usually lots of stuff like I found. In the end, I straightened out one corroded cylinder, two corroded calipers (one of which wasn't really all that old), old brake fluid that needed flushing, some brake hoses that might have been past their prime, and some rusted-solid emergency brake mechanisms. I may have one master cylinder to go.

I finally got my MityVac today, so I'll do my final bleed tomorrow. I wasn't aggressive with the first bleed, because I didn't want to screw up my master cylinder. I might not have been successful in that regard. We'll see...

[Captain Obvious]

I'm sure you already know this, but just because the fluid level in your master cylinder is low, doesn't necessarily mean that you have a leak. At least not with simple disks like in the front. The volume behind the caliper pistons increases as the pads wear, and that extra volume is taken up by brake fluid from the master cyl reservoir.

With rear drums, I guess it's not that clear... The rear wheel cylinders should always relax to the same position, so there shouldn't really be any change in the reservoir level at rest, but if your rear adjusters weren't working properly, that may not have been the case. The rear pistons may not have been pushed all the way "home" and you may have used some of the fluid from the tank to take up the extra volume. I know, I'm reaching here, but that's all I got.

(On edit): Actually, thinking about it some more, the rear cylinders push directly on the shoes, not on the adjuster mechanism. So the pistons should not be pushed home as the shoes wear. The adjuster mechanism should hold the shoes apart, so I guess the same situation exists in the rear as the front. The brake fluid in the master cyl will drop as the shoes wear. What you could end up with if the adjusters aren't working correctly is excessive pedal travel.

Only other info I've got would be that I've seen the same white crumbly corrosion on aluminum brake parts in the past. My theory is that it is a slow leak, and the brake fluid (being hygroscopic) is attracting moisture from the atmosphere and that combination of brake fluid and water is causing the aluminum to corrode.

In any event, with all the issues you did find, it sure wasn't a wasted effort!!

Edited October 26, 2011 by Captain Obvious
Hadn't had my coffee yet

[FastWoman]

Well, that's true. However, the fluid had disappeared over maybe 2000 mi. I suppose I might have explored more, but as far as I could ascertain from the PO, the brakes had been "maintained" (replacing a part here or there), but the hydraulics were at least 15 years old for the most part, without the benefit of regular use at various points in their life. So a light had already gone off in my head when I first bought the car that a brake rebuild would probably lie not far down the road. In fact I was tempted when I first got the car to tear into the brakes, but the car seemed to stop fine, and the engine was begging a bit harder for my attention.

[FastWoman]

Well, I've bled my brakes with my fancy MityVac. The verdict? I didn't think it did as good a job as an assistant and a manual opening/closing of the bleeder screw. Anyway, my brakes work, and I can stand the car on its nose, but the pedal is still somewhat soft. The pedal travels maybe 2", making a light wheezing noise as it travels. Of course the brake shoes are not perfectly shaped to the drum yet. They have a VERY smaller diameter than the drum, so I imagine the rear cylinder travels just a bit further for now. Would that make the brakes somewhat spongy?

Any thoughts? Buy more brake fluid, and do it again?

[robftw]

Take a bottle, fill it with brake fluid 1/2 way

Run a hose from the bleeder to the bottle, submerge it in brake fluid and crack the bleeder

Go top off the the brake fluid and start pumping, do it about 10 times and check the fluid

Repeat the process 3-4 times per wheel.

Close the bleeder before you remove the hose!

[beermanpete]

Well, I've bled my brakes with my fancy MityVac. The verdict? I didn't think it did as good a job as an assistant and a manual opening/closing of the bleeder screw. Anyway, my brakes work, and I can stand the car on its nose, but the pedal is still somewhat soft. The pedal travels maybe 2", making a light wheezing noise as it travels. Of course the brake shoes are not perfectly shaped to the drum yet. They have a VERY smaller diameter than the drum, so I imagine the rear cylinder travels just a bit further for now. Would that make the brakes somewhat spongy?

Any thoughts? Buy more brake fluid, and do it again?

A slightly vague pedal is normal until the brakes bed-in. As you said, the shoes and drums are not the same diameter so the shoes flex more than normal unlit the diameters match. The pads in front will do the same thing to a lesser degree until bedded in. The bed-in will take a few hundred miles.

The brake fluid level for the front brakes (larger reservoir, closer to firewall) will drop slowly as the pads wear. The rear brakes will not do this. The rear brake slave cylinder will always return fully unless they are stuck for some reason.

[FastWoman]

Thanks, guys! Well, I guess I'll drive the car a few hundred miles and see how it goes.

Rob, I've not tried that technique, but it sounds good. I have a check-valve bleeder that does almost that, except the fluid doesn't re-enter. I do the last couple of squirts by having someone depress the pedal for me while I burp the bleeder plug.

[to4tz]

www.silverminemotors.com offers a more complete kit for less $$. I have their stage 4 front & rear and it was worth it. The fronts are from a Toyota 4runner & the rear are a Mustang GT 500

Thanks for the information, I have been looking for a complete system at a fair price for some time. I wanted vented discs, 4 piston front and rears single or dual piston to work with e-brake.

Question - front disc are 10.8" and rear are 11.8". Normally the larger would be on the front. Will the 11.8" disc work on the front?

Planning to buy 16" wheels - any suggestions?