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Posted by Don in Missouri [69.69.205.226] on Thursday, November 29, 2012 at 11:50:17 :
In Reply to: Re: Brake Rotors? posted by Mike Hernke [63.151.218.18] on Thursday, November 29, 2012 at 09:47:12 :
I think my crew cab still uses the 1984 W350 proportioning valve. None of the rear ABS controls got transfered from the W250 extended cab truck when the diesel conversion was done.
I need to learn how proportioning valves work. Are there moving parts in the proportioning valve? Do they go bad? Over the years, there have been instances (rare) when the rear brakes locked up. It hasn't done that for a long time, and most every other brake component has been replaced, so that could have been related to the master cylinder?
I probably do have some wear in the spring bushings. The bouncing stops when I change the rotors. Maybe I should replace the spring buyshings and see what happens before swaping rotors again?
Are you talking about your Scout with the spring-over conversion? I would bet that the the rear is actually bouncing because of the driveshaft angle. When the rear brakes engage, it applies torque to the rear springs and tweaks the pinion angle. The pinion movement is exaggerated by the spring-over conversion and if the lift already challenged the driveshaft angle, the additional movement could cause driveshaft vibration. I think I have this problem with the Ramcharger. It started when I got the rear brakes working. Back when the rear brakes were in such a shambles that they basically did not work, there was no vibration. An easy check would be to drop the rear driveshaft, drive around in FWD and see if the rear still bounces when you stop w no rear shaft.
Once I confirm this to be the case in the Ramcharger, I'm thinking I may need a double cardan joint on the rear shaft.
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