1988 Pickup Brakes...

This one's easy. The pistons in the calipers are not fully retracted into their bores. You need a long C-clamp, probably an eight or ten incher. Pull the cover on the master cylinder and remove about one third of the brake fluid from it. Replace master cylinder cover. Unscrew the clamp and put the non-moving part on the outside of the caliper. Screw the moving part of the clamp down into the piston or "hockey puck" until it contacts the piston. Slowly screw down the clamp and push the piston completely into the caliper, until it can go no further. Now, look at the master cylinder fluid level, it will have risen some. If needed, pull more fluid from the master cylinder. Repeat on the other side. You'll notice now that new pads will fit just fine. After brakes are installed, don't forget to check fluid level once again.

Opening the bleeder valves may help.

-- Mike Harris Austin, TX

Question: right out of the box, how difficult should these pistons be to depress? Neither seemed to budge right out of the box using an 8" vice and a block of wood; could one or both be seized before I even use them? How hard do I really need to turn the clamp to get these pistons to move?

Thanks,

mothy

Lhead wrote:

Yes - help lots of air (and possibly dirt) get into the brake system, and then he has to learn the wonders of brake bleeding the hard way. BAD IDEA, GUY... :(

"Please step away from the bleeder valves..." ;-)

The fluid should go back to the master cylinder just fine with a C-clamp or a proper brake caliper retractor tool. The only reason it wouldn't work would be a mis-adjusted master cylinder pushrod, if the Master piston isn't fully retracting and the return ports aren't opening up - but the OP would be complaining about dragging brakes.

And get the brake fluid level down before retracting the pistons, as LHead mentioned, or the reservoir will overflow when you retract them. You don't want that, because the fluid will spit out the vent hole in the lid, and wherever the brake fluid goes the car paint will be destroyed and it'll peel off to bare metal - top of the hood, along the firewall, and if the hood's open and it spits out onto the fender...

Go down to the "99c Only" store and buy a cheap turkey baster, and mark it with a permanent marker "For Automotive Use Only". Trust me, you won't want to use it in the kitchen after it has had brake fluid in it.

Do NOT put the old fluid you suck out back into the clean fluid bottle, and do NOT mix it with used motor oil or coolant - go get a clean 3-gallon or 5-gallon plastic bucket with a gasketed lid, and mark it "Used Brake Fluid". You also use this bucket as a catch when bleeding the brakes. And when the bucket starts getting full, take it in for recycling.

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I do it all the time. I also use a plastic tube connected to the bleeder, with the other end clipped into a jar of clean brake fluid so as not to take in air or dirt should the pistons move the wrong direction. I'd rather have the old fluid as well as any crud caught on the far side of the pistons OUT of the system via the bleeders, instead of pushed back up towards the MC.

Perhaps I shouldn't assume a certain degree of mechanical competence among Usenet users?

-- Mike Harris "You actually listened to some guy on Usenet? There's your problem, right there." Austin, TX

Interestingly enough, both of my calipers were diagnosed as having been frozen prior to my replacing them. When I was trying to depress the old ones today to figure out how much pressure I must apply to get them to retract, they seemed to pop in pretty easily. Could a mis-adjusted master cylinder pushrod present the same symptoms as frozen calipers?

Thanks,

mothy

Absitively - if the piston doesn't fully retract, the drain ports do not fully open. The brakes on one end will work fine when cold, but when they heat up the fluid expands and has no place to go.

Third or fourth hard stop, they get hot, the fluid expands, and one end's brakes won't release, no matter what you do.

Don't ask me what the slop spec is, but there is one - probably one or two MM. I figure if the piston is fully retracted to the stop c-clip or pin, the pedal doesn't have a weak return spring and it's fully retracted to it's stop, and there's noticeable wiggle room for the pushrod, you should be fine.

If you're getting oddness like that., you may be by elapsed time alone better off to go through and change out the master cylinder, calipers and wheel cylinders, and rubber brake hoses - just on general principles of 18 to 19 years of the rubber parts' exposure to ozone and contaminants. Rebuilt parts are cheaper than a nasty collision.

I did it to my Corvair after several years of it sitting, and I'm told there were a few surprises found when he did a post-mortem on the brake parts. And with a Pre-1966-ish car with a single braking system any one failure knocks out the entire brake system. It's due again after another sitting parked for several years period.

Your truck has split brakes, but a front brake failure will still get exciting if it happens at a bad time, as the front brakes do most of the heavy work. The rears only will get you stopped - eventually. If you don't have the time or room for the extra distance...

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