Drive it forever: Start with some penetrating oil

Dear Mike: I’m trying to remove the screws that hold the latch plate onto the B-pillar of my antique car. They don’t look particularly rusty. I can’t get them to budge, however. My Phillips screwdriver doesn’t fit very well, and the screwdriver bit simply pops out of the screw head when I try to turn it.

A: Start by using some penetrating oil. That might mean finding a way to squirt some oil on the threads inside the B-pillar where you can’t see them unless you remove some trim, or even drilling a one-eighth-inch hole in an unobtrusive place to insert the nozzle of the aerosol can.

Then grab a new or relatively new Phillips screwdriver. It won’t be partly worn out like a well-used one. And make sure that you are using a screwdriver of the appropriate size. Striker plates generally use a No. 3, rather than the smaller No. 2, which won’t generate enough torque before it cams out and slips.

One tweak I have used in the past is to dip the end of the bit in some abrasive, such as valve-lapping compound. Don’t happen to have a tin of valve-lapping compound around because you used it all up when you redid the cylinder heads on that Model A? You can substitute household cleanser — the gritty stuff, not the kind that’s advertised as “kinder and gentler.”

The abrasive will give the screwdriver bit substantially more bite on the screw head. Use a hammer to tap the screwdriver smartly into the screw head a couple of times. This will break up any corrosion and make the screw easier to turn. When you go to turn the screw, use one hand to push the screwdriver into the screw, hard, while the other concentrates on twisting.

Here’s another tip: Start by attempting to turn the screw in before trying to turn it out. The next escalation of effort, when that doesn’t work, is to use a tool called an impact driver, which you smack with a pretty big hammer. Depending on how fragile the sheet-metal door frame is — it may be rusty and frail — I’ll often simply drill the screw head off instead. Then I can remove the striker plate and deal with the stub of the screw using heat and Vise-Grips.

Dear Mike: I have a 2002 Mercury Grand Marquis with 120,000 miles on it. Last week, in the mountains, we were going uphill at about 50 miles per hour with the cruise control set at 55, and I needed to tap the brakes for a car in front of us. The pedal was rock hard. I pushed harder and it finally worked, but it acted as if the booster was not activating.

Could the cruise control use up all the available vacuum pressure that the car was producing under high throttle, thus preventing the brake booster from functioning? I was unable to reproduce the symptom, and it has worked perfectly ever since.

A: Extended periods of low vacuum — exactly what happens on long uphill grades — from heavy throttle application can reduce the amount of brake boost, although there’s supposed to be a check valve to reduce this. Your service brakes were not affected, so full braking was available if you pushed harder on the pedal.

I’d have that check valve checked, but otherwise I see no problem. Manifold vacuum would have returned within a second or two, as soon as the throttle dropped back to idle.

You might want to downshift on long, steep grades to keep a slightly higher engine RPM, which will in turn raise manifold vacuum.

Dear Mike: In a previous column you talked about being able to launder car covers. I have a Noah fitted car cover for my Mustang, and am curious what the best way to wash it is.

A: I simply throw mine in the washing machine. No starch.

Dear Mike: The rearview mirror in my car fell off and, when the mounting piece was glued back on, it was attached upside down. Now we can’t get the mounting piece to come off. Do you have any suggestions?

A: Use a crescent wrench to unscrew the button from the glass.