Oct 10, 2020
RAY: A customer called up the other day and said that a brake job we had done had gone awry. We had put new pads and new disk rotors on his Volvo and it was all right for several months. But the customer says, “Gee, now when I step on the brakes I get a rumbling. The harder I step on the brakes the worse it is. In fact, I don't really feel it at low speeds or if I step on it gently even at high speeds, but if I really lay onto the brakes, I feel that shuddering in the car.”
He says one of those new disks must be warped. And we say we doubt it. Anyway, he brings the car in and we drive it around and sure enough, he's right. It is showing the classic symptom. We put the car up, we put the dial indicator on it, and determine that there's nothing wrong with the disk. We check all the bushings. We check everything. And we can find nothing wrong, but to humor him we put four new disks on.
We drive the car and exactly the same thing happens. Back up on the lift, it goes. And the hours go by. We have Ralph chained to his toolbox until he figures this out. He's standing there right smack in the middle of the car with wrenches in hand and he's ready to remove something. I ask him what he’s doing and he says, “I know what's wrong with it.”
RAY: Yes, Dick had a seized universal joint. What happens is when you step on the brakes hard, the car does something called nosing or diving, the front bumper dives to the ground. The drive shaft has universal joints on it which must flex, but if one of those universal joints is seized when you're asking it to flex to accommodate this new angle of operation, it begins to shake like crazy.
It was only doing it on hard braking. So Ralph figured out that it was because the thing was nosing and causing that seized joint to have to try to bend, and it couldn't, and that was causing the vibration. Pretty nifty, eh?