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Brake-booster leak could keep mom-in-law's car from stopping

Question - Recently, I drove my mother-in-law's car over to my house to take a look at her muffler. I backed her car into my driveway that slopes a bit downhill to the garage. When I got out, I could see I needed to back it up another foot or so to get clear of the front walk. I got back in the car and figured I would not bother to dig my keys out of my pocket again and just let it roll backward using the brakes.

The car is an '84 VW Quantum. I've studied Quantum mechanics, have an official factory repair manual for our '85 Quantum, and remembered that the owner's guide mentions that even with the engine off, the power brakes will still function, but more pedal pressure is required. I put my foot on the brake, shifted into neutral, released the foot brake, put my right hand on the steering wheel and my left hand on the slightlyopened door - looking backward to judge my position. The foot brake held the car in place with no problem.I eased just a bit off the foot brake to permit the car to roll a few feet, then I stepped on the brake to stop and found nothing. I pressed extremely hard, but the car continued to accelerate. I pumped the brake, fearing the master cylinder had leaked down . . . .nothing. By this time, I was still barely rolling, but I had started with the rear bumper only six feet from the garage door. Now I was closing in on it fast!

I rammed the shift lever into reverse, then grabbed at the emergency-brake handle, still holding the door with my left hand on the window sill as the car crashed through the garage door and finally halted when the driver's door hit the garage-door framing. The car got totaled out by the insurer. My mother-in-law bought a new VW Jetta. I repaired and repainted our garage, and yesterday, a new roll-up door was installed. But I'm wondering, what happened? - John

TOM: Oh, John, I could tell by the first sentence of your letter that things weren't going to turn out well.

RAY: Normally, you CAN stop a car with the foot brake, even if it has power brakes and the engine is off. That's because there's a reserve of vacuum that the power-brake system stores just for this purpose.

TOM: So my guess is that something was indeed wrong with your mother-in-law's car. And it was probably a leaking power-brake booster. The power-brake booster has a diaphragm in it that's supposed to hold a "vacuum reserve." That way, even with the engine off, there's still enough vacuum in the booster to "power" the brakes for another stop or two.

RAY: But if that diaphragm had a small hole in it, it wouldn't hold the vacuum reserve for very long. You wouldn't notice this during normal driving, because the engine is constantly creating new vacuum. But once you stop, air would leak in, and you'd lose that vacuum. Then you WOULDN'T have that cushion that's mentioned in the owner's manual, and it would take superhuman strength to stop the car. It can be done, but it's much harder than you might imagine.

TOM: So I'm sure you've learned a very valuable lesson here, John: Don't ever work on your mother-in-law's car.

Question - I've still got my first new car, a red 1987 Toyota MR2. We had a party for its 100,000th-mile birthday a year or two ago and it's still running well. I have a repainting question. One firm recommends painting it the same exact color, so they can cut corners and not paint the door jambs and other places where I won't really notice it. They say this will save me money because they won't have to take off body parts and hardware.

I have no objection to saving a little money, but I want to make sure I get a good paint job, since I plan on keeping this car through its 200,000th- and 300,000th-mile birthdays. Rust isn't a problem where I live. Should I have the car thoroughly repainted inside and out, or is it OK to save a few bucks and just paint the parts that show. - Marcy

TOM: If you were planning to, say, sell the car to your brother, then I'd say fine, cheap out and don't paint the door jambs.

RAY: But since you obviously love this car and are planning to keep it for the long haul, I'd get a real paint job, Marcy. It's not much more expensive, and a real body shop might even, for example, roll up the windows before spraying on the paint.

TOM: More important, Marcy, in my opinion, you can't paint the car the same color. After spending all that money, the goal is to feel like you've got a brand-new car. And to do that, it has to be a brand-new color.

RAY: Just don't make the same mistake my brother did. Be sure that the new exterior color you pick goes with the car's existing interior.

TOM: How was I supposed to know that a metallic burnt-orange body clashes with green seats?