Newly rebuilt calipers o. How do I know ok to install with out rebuilding the MC too.

[BReyes]

Newly rebuilt calipers just picked up (no problems with any corrosion to the pistons et al). How do I know it is ok to install them and use with out rebuilding the MC too. The car has been sitting.

Regards,

[Walt Fricke]

Well, you won't know if your MC has problems until you can use it. So install your rebuilt calipers (which you will have to do anyway) and see. If the MC has a significant problem, it should show up statically (i.e., without your having to drive the car). Your pedal won't behave right. These hydraulic systems are fairly simple and robust, so I'd not start out with the supposition that the MC is shot. It doesn't see anywhere near the heat the caliper seals see.

You can reduce the chance of problems with the MC by not overstroking it when bleeding the system after you have replaced the old brake fluid (which maybe is already mostly out of the MC and lines, having dribbled out when you pulled the calipers off).

The theory is that the normal stroke range inside the MC gets burnished by the seals as they move every time you apply the brakes. The part that is out of normal range (as in "my pedal went to the floor without any warning") might develop a little rust from the inevitable water that the brake fluid likes to accumulate. And that rust, not being burnished away constantly, can get jagged enough to damage the seals. I'm not sure just how true this is (does it always happen? I don't think so), but it is one of those pieces of conventional wisdom that has a plausible basis. And it takes but little extra effort to follow the directions. If you pump bleed, just caution the pumper to take half strokes only. If you use one of the many other bleeding methods, not an issue.

If you find your MC has problems, just remove it and get another one. That's not really any harder with calipers installed than not. Brake fluid (well, most kinds) is cheap. MC aren't awfully expensive, and for at least some rebuild kits are available though it the MC bore is pitted with rust, new seals aren't going to do the job. And the delta between a new MC and a rebuild kit is (at least for the ones I have been interested in) disappointingly small.

Walt Fricke

Walt Fricke