Weird Vibration from Rear

[ptcfast2]

Since I've owned my Lumina I've had vibration problems. I've managed to isolate and fix the causes one by one, but I'm stuck on this last puzzle!

I rebuilt the rear drum brakes on my Lumina a few months back (new pads, drums, cylinder, etc...) in an attempt to cure a vibration that was emanating from the rear end when I applied the brakes and decelerated the car. This vibration occurs from any speed over 50MPH when the brakes are applied. The vibration dissipates once you hit the 40MPH mark and the brake pedal feels normal. I know that the rear wheels are causing this as I've confirmed with the parking brake at high speeds.

I'm thinking that the bearings might just be worn out as they've got 226,000 miles on them. I've read a few places that worn/pitted bearings can cause vibrations at certain speeds & when a certain amount of force is applied in a general direction on the bearing due to wear.

Anyone have ideas/care to confirm my suspicions?

[jeffcoslacker]

Bearings like this usually rumble or moan when they have anything wrong. I can't say it's impossible, but doesn't sound likely.

I'd be trying to make sure I wasn't dealing with a chunked or missing trailing arm bushing or something like that...I guess you've already eliminated the tires as a cause? A broken tread belt will do stuff like that sometimes...

[ptcfast2]

Tires are pretty new (got them around this time last year). They aren't the best in the world (Goodyear touring tires) but they've done the job so far. Honestly, the only reason I've ruled them out at this point is because the vibration is only during decel and not acel (I would think the vibration would occur both ways). The trailing arms & bushings are brand new as well as the struts in the rear and front.

The vibration itself is more intense the harder I slow down. It varies with the amount of pressure put on the brake, and in turn how fast the car decelerates. Faster = More intense until I reach that magical 40MPH point. Maybe it is a brake problem? I mean it could be a bad drum that's just a bit off...(old ones were bad, I might have gotten bad ones as replacements as well...it happens!).

[jeffcoslacker]

See, on a FWD car, the only time the rear tires are under any real tread belt stress is under braking, other than that they just follow.

Usually on the rear, the only time you'll feel a belt separation is under braking...

I'd rotate them and see what it feels like after, just to rule it out. Easy and free...

[ptcfast2]

Good idea. I'll do that tomorrow when I'm changing the oil and get back with the results.

[jeffcoslacker]

It's possible it could have a bent stub or flange back there too...watch the gap between drum and backing plate for any weird runout while you spin the wheels...

[maxwedge]

"Bell mouthed" drums could do that also.

[Bearwulf]

Did you have the drums turned before installing them on the car? What method did you use to bleed the aair out of the system?