QuestionReplaced the rear drums and shoes with parts from local napa store (i.e. not GM parts). The front rotors and pads were replaced last year, so I'm assuming they're not an issue here, but have not inspected yet to confirm. The issue I have is that the new drums, during setup and driving, are behaving as if they're very slightly "out of round" (i.e. on setup, the drum free-wheels nicely, then grabs a bit, and then continues to free wheel. While driving, the vehicle surges a little bit while coming to a stop - not a smooth deacceleration). Thinking I'd bought a couple of bad drums, I took them back to the store. He said they were a tiny bit out and took off 10 thou to make them perfect. But after installing, still same issue. After closer inspection, I've noticed that the hole in the middle of the drum is a tiny tiny bit larger than the hub, we're only talking 1/2 a hair, but enough to allow the drum to move back and forth a tiny tiny bit. I'm thinking that this is the issue because if the drum is not perfectly centered on the hub, it's going to act like it's out of round. When I removed the original GM drums, I remember them being a bit tighter on the hub and not moving at all.
Am I correct in my observations here ? or is this just normal for an after market drum ? What do I need to do to get this out of round behavior fixed ?
Thanks, Dave
AnswerHi
If the "surge" is when the pedal is applied, I would HIGHLY suspect the front rotor(s) having excessive LRO (Lateral Run Out). This can be corrected by a resurfacing.
The slight variance in the drum to shoe difference is common (ie.. the grabbing while hand spinning).
The drum to hub difference is USUALLY taken up when the lugs are tightened.
As the drum spins, the variance between the drum and shoe SHOULD not be enough to cause a noticable shake. That being said, it dont take much.
If the pulsation is WITHOUT the pedal applied It MAY be a different cause...tire, rim, axle.
Please let me know if it is pedal applied or not.
Thanks
Pawl
