I have a 1994 Chevy Lumina APV. It has a tow package on it, and we've used it to haul fairly heavy loads (2000 lbs or so). Recently the steering wheel began to shake violently when we'd be driving over 55 and put on the brakes, and there's a thudding or pounding that accompanies it coming from the front end. At about the same time, the ANTILOCK SERVICE light on the dash began coming on and staying on. Our mechanic (who is wonderful) took a look at the brakes and said they were okay - he did nothing with the rotors though. He told us to buy an antilock assembly, which we did, from a reputable local used parts dealer. We put it on, and it seemed better at first, but within a day had gone back to the violent shaking when we apply the brakes at speeds over 40 mph. Under 40 mph, there is no shaking. The thudding/pounding is back too. The ANTILOCK SERVICE light on the dash has not come back on. When we first installed it, the cruise control worked (it's never worked since we bought the van). The cruise control assembly is part of the device. It worked for a very short period of time - a few minutes - then stopped and still doesn't work. Don't know if this has anything to do with the problem at all, but thought I'd throw it in just in case it helps anybody with a diagnosis. Anybody have any ideas? Thanks very much. This has been a great vehicle!

After the dealer told me it was the catalytic convertor, and finding out it wasn't, I found the source of the loud clatter coming from some kind of shield below and just behind the motor. Has anyone else experienced this problem? Does anyone know what this "sheild" is?