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Automania/Repair and Maintenance
AUTO QUESTIONS AND ANSWERS FOR WEEK 25
by Bob Hagin
Q. Several years ago I purchased a 1990 Mercury Grand Marquis that had 22,000 miles on it. When I had occasion to apply the brakes quickly, the back wheels would lock up and skid briefly on the right side before the left brake applied. I had new tires put on the rear wheels but it did not solve the problem. I had new brake shoes put on the rear and new pad put on the front but it did not solve the problem either. The parking and emergency brake cable does not seem to be too tight and all parts of the brake system seem to be OK.
A. When brakes act erratically on modern cars, I'm always suspicious of a malfunctioning anti-skid brake system (ABS). Your letter doesn't indicate whether or not your Merc has ABS but if it does, have it checked out for uneven or non-existent operation. ABS electronically releases hydraulic brake fluid pressure to any of the individual brakes the instant that wheel begins to skid, then reapplies the pressure as the wheel begins to roll again. This all happens very quickly and if any of the ABS wheel sensors rust up or short out, uneven brake application can result. If your car doesn't have ABS, I'd be suspicious that one of the rear wheels cylinders is hanging up (the cure being to replace them both) or that the pressure delay valve on your hydraulic system is not working. A delay valve slows down the application of hydraulic pressure to the rear drum brakes a bit since it takes a little more time for the front disk brakes to go into action. Replacement of the valve is the cure. Whenever I replace the shoes on drum brakes, I always overhaul or replace the wheels cylinders since new shoes reposition the wheel cylinder cups deeper into the cylinders which can result in leakage.
Q. A 1951 Ford V8 skidded for 85 feet before broadsiding and totally destroying a 1967 Volkswagen, which then caused the Bug to bounce 10 to 15 feet further from the point of impact. How can one determine the speed the Ford was traveling before braking?
A. You need to talk to an accident reconstruction expert rather than a mechanic on this one. The things that the investigator takes into consideration are the coefficient of friction of the road surface (wet or dry, concrete or asphalt, level or on an incline), condition of the brakes and tires on the Ford (maybe pretty bad on a 46 year old vehicle), weight of the truck (loaded or empty), positioning of the Volkswagen at the time of impact (stationary or rolling) as well as a half-dozen other factors. By comparison, it takes a '97 Ford F-150 pickup 160 feet to drop from 60 MPH to a complete stop without skidding.
Q. My 1987 Honda CRX SCi has around 95,000 miles on it now and it has slowly developed a hesitation on acceleration and it also idles rough. It hesitates especially bad when I'm driving up a hill and then have to slow down and then accelerate again. I had the engine rebuilt not too long ago and now a mechanic who recently did a tuneup tells me that the spark plugs are beginning to foul out and show signs of carbon buildup on their tips. The engine doesn't use much oil.
A. You may have gotten an overhaul rather than a rebuild. A rebuild means pulling the engine to rebore the cylinders, resize the crank and in essence, remanufacture the engine completely. An overhaul means honing the cylinders so that a new set of rings will seal, grinding the valves and replacing all the gaskets. There's only a couple of ways that oil can get into a combustion chamber and foul plugs. The piston rings may not be sealing which would allow oil to be sucked up past the oil control ring or the valve guides (the "tubes" that the valves slide in) could be allowing oil to be sucked past them. A mechanic should be able to analyze the problem pretty easily.
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