Can’t get brake fluid to move

Dear Mike: I’m trying to install a new master cylinder on my 1982 minivan. I wanted to flush the system of old, dirty fluid, so I blew all the brake lines clear with compressed air after opening all the bleeder bolts. I’ve tried bleeding the brakes every way that I can think of, but I still haven’t gotten any fresh fluid to come out of the calipers. The level of brake fluid in the reservoir doesn’t go down at all no matter how much I pump.

The local brake shop said they won’t work on it for any less money than the price I would have paid them to do the whole job themselves. I’ve spent so much time on this that I’m ready to shell out — but the van has no brakes and I’d have to pay them to tow it down there as well.

How can I get the fluid to move?

— J.S., via e-mail

A: You’re working with a dry master cylinder and a dry brake system, and that can make it difficult to bleed out the air. If you don’t have access to a pressure bleeder, at the very least you first need to bench-bleed the master cylinder to purge it of air.

Most new or rebuilt master cylinders come with bleeding adapters and instructions. Go back to the parts store where you got the master cylinder and acquire them. If you’re unable to do this because you can’t drive your van, you can make do with a couple of pieces of small-diameter hose.

•Be sure the hose is clean. Disconnect the brake pipes from the master cylinder and run the hose back into the reservoir. (Once, in an emergency, I cut up an old brake line and bent the two short ends back into the reservoir.)

•Now stroke the master cylinder piston in and out. If you do this before you install the master cylinder on the firewall, you’ll be able to move it easily with a Phillips screwdriver or a piece of dowel. Otherwise, you’ll have to pump the brake pedal.

•Within a few strokes, the master cylinder will start recycling brake fluid into the reservoir. Continue slowly until the fluid clears of all bubbles. Now you can install the regular brake pipes into the ports on the master cylinder, and proceed to bleed in the normal fashion.

Given your minivan’s age, it would not have ABS. Bleeding brake systems with ABS is a different, much more complex topic. I’ll leave it to another day.

Dear Mike: I take my car to the service station every 4,000 miles to have the oil changed. At 90,000 miles, the shop told me I needed to have an oversize drain plug installed because the old one was worn out. My mechanic said this should not be necessary because the threads on the oil pan where the drain plug screws in are hardened and that the drain plug is simply worn. He said an oversize plug is not needed — just a standard one. Who is correct?

— W.T.W., Houston

A: Who cares? Regardless of what’s worn out, the wear is excessive considering your car has had fewer than two dozen oil changes. Somebody is overtightening that plug. Make them stop, or eventually they will wear out the female half of the threads and you’ll have to replace the oil pan.

Maybe you can get them to install an aftermarket oil-change valve to replace the drain plug. Fram makes one called the SureDrain that has a removable hose. You’ll only need to make the threads seal once, or you can try a Helicoil thread insert.

Dear Mike: I had to take my car in to have the speedometer fixed. Since then, the heat and air conditioning system hasn’t worked properly. It blows air only when I release the gas pedal. If I pull away from a light, the air stops blowing until I stop. They tried hooking my car up to the computer to see what was wrong, but nothing showed up so they can’t fix it. Did they hook up something wrong?

— J.P.S., South Carolina

A: Yes. There’s a linkage or vacuum line hooked up incorrectly — or not hooked up at all. The mechanic who worked on your speedometer was right next to the heater controls. And any mechanic who thinks the computer is going to tell him what he misassembled under the dash is probably better suited to working with a shovel than a computer.