coastn

I need help with the rear drum brakes on my Express 2500 van. To give you an idea of my abilities, I began doing brake jobs before disc brakes were available on passenger cars and though I do not make my living as a mechanic, I repair just about everything except rebuild auto transmissions. The van is a 97, 12 passenger with the 350 (5.7) and uses the 2" rear shoes. I did some searching on the site before posting a new thread, but everyone talked about front rotors warping. Initially, I had a moderate vibration in the brakes when applied so I replaced the front rotors and pads before checking anything else and the vibration did not disappear. I then replaced the shoes, springs and drums and the vibration went from moderate to severe! I then replaced both wheel cylinders with no improvement. I pinched off the flexible brake hose that feeds the rear brakes with vice grips and the thing stops smoothly, so the problem is definitely in the rear somewhere. While up on the lift, I started the van and put it in gear then slowly applied the brakes. The right rear wheel would suddenly lock up, release, then lock up, release and so on. While driving on the road, the right rear wheel will lock up momentarily if I hit the brakes hard. The right rear drum gets extremely hot after normal driving but the tire can be rotated by hand when jacked up, so it seems to me that it is not over adjusted. The shoes are installed properly with the longer brake shoe material at the rear and the shorter in the front. There is no grease or other foreign substance on the new shows or drums. There is no excess play in the axle indicating a bad bearing. I pulled the fuse on the anti lock brakes thinking maybe the system was faulty but that actually made it worse. I have not had someone else drive and hit the brakes so I can watch the rear wheels while braking, but the thing shakes horribly!!! I am at my wits end. Any suggestions are greatly appreciated. Thanks in advance.

tech2

for future diagnostic aids:
front brake shake will transfer into the steering wheel while rears transfer to the brake pedal. applying the ebrake would also help isolate the problem if the ebrake use the service brake linings.


I have seen quite a few drums 10 thou out of rounds right out of the box. I had to machine the new drums and that's what it took to correct it. That's why oem drums are 3x the price. if I get aftermarket anymore, they go right to the brake lathe before I install them.

coastn

Thanks for the info. I'll flip the drums as soon as time allows, left to right...right to left and see if the problem follows the drums. I'll let you know.

tech2

cross rotating the drums won't solve anything. how did you come to that conclusion?

coastn

The left rear wheel does not exhibit any problems, it stops smoothly when the e-brake is applied while the van is on the lift. It does not lock up momentarily like the right and does not get extremely hot after normal driving. If the right drum is out of round and the left one is not, then the problem should transfer to the left side when I interchange them, at least that's my logic.

coastn

I have to admit, I was a little skeptical about the new drums being out of round and causing the vibration, but you were 100% on the mark! I took them to the neighborhood auto store and $35 later, she stops SMOOOTH. They said they were about 12 thousands out. Thanks so much for sharing your experience, you saved me from many more hours of aggravation!

tech2

bad new parts can throw anyone for a loop.

canucklehead

So true.
My dad got a brand new big block chev for his hot rod back from an engine builder and after installing it found it had a slight vibration....
Took forever to trace it and turned out to be a bad spark plug.....go figure.

tech2

I had one bad plug on a new engine 2 months ago. Luckily, it was easy to locate and fix with modern obdII diagnostic platforms.