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Posted by D Sherman [24.32.202.83] on Friday, May 14, 2010 at 22:34:28 :
I took the old M37 up in the hills this afternoon for the first time this year and found a very strange intermittent pulsation in the brakes on the way down. They would pulsate severely, as in 1" to 2" up and down motion of the brake pedal under light pressure. Nothing made any sort of funny noise. I've had other brakes pulsate a bit, but nothing like that. The pulsation rate corresponded to the truck's speed, just like if it was a warped drum. What's weird is that after driving a bit further, I'd try the brakes and they'd be as smooth as can be. Then go a ways more and they'd pulsate as bad as ever. It has nothing to do with heat because I wasn't riding the brakes before they started pulsating. The last time they acted up was after a couple miles of gentle downgrade during which I didn't use the brakes at all, so they should have cooled off completely. Even when I was going down the steep part, I kept it in a low gear (lots of back firing) so I didn't use the brakes much.
The brakes on this truck have always been a bit funky. I don't have all the shoes very well adjusted, and the master cylinder is pitted so it leaks some even with a new kit in it. Sometimes I get a firm pedal after pumping it once, other times it leaks down slowly. Still, this 1"-2" pulsation is something entirely new and it seems to either do it that bad or not at all. When it pulsates or when it doesn't, the brakes still seem to work pretty well.
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