MacGyver

A couple of weeks back I noticed an intermittent shudder from the rear wheels... it would typically start a few miles into a trip, but disappear after a handful of miles. It's not a tooth-jarring shake, but it's very noticeable, so something is going on. It's speed related in the sense that faster speeds mean faster vibrations, but it could just as easily appear/disappear at 40mph as it could at 70mph.

This past weekend I swapped the inner CV cups and repacked them with Redline CV-2, but I have noticed no change. Even though my car was lowered a bit for about 2 years, the cups appeared to have practically zero wear on the drive surfaces. They were out, so I swapped them anyway.

What should I be looking at next? Would failing wheel/hub bearings show this kind of symptom? What about the diff itself? I noticed zero play in the diff while under the car, so I don't believe that's the issue.

Thanks!

jguerdat

Got another set of wheels/tires? Try swapping those in. Could be balance, wobble, etc. FWIW, my original S02s were wearing out so I had them flipped. Even though I couldn't see anything unusual, the tires created a nasty vibration above 70. We even tried balancing them on a machine that preloads the tires - it helped but not by much...

MacGyver

I'll be swapping to my summer rims later this evening (time permitting), but I don't believe it to be a balance issue. It it was tire balance, I would expect the vibration to always be there at specific speeds, but as I mentioned in my original post, it can come and go at various speeds/times.

MacGyver

I believe I have found the problem (or at least one of them), but I won't be able to verify until this evening.

After coming home from work yesterday (highway driving), I decided to check the wheel temps in the hopes a failing bearing would show up as a warmer rim. All four wheels felt cool, but on a lark I went back and tried the rotors... practically burned my fingerprint off when I got to the passenger front.

So, looks like a seized caliper, though I won't be able to verify that until this evening. I already placed an order for 5 rebuild kits (I intended to rebuild four extras I have on hand for a swap, so this just came at a bad time). This is the second caliper I've had seize on me. I wonder if the piston grease is just going bad...

MacGyver

Finally repaired the caliper... big-time rust collector Though that's what 5-6 years in salty road winters will do to a car, I suppose. It took me forever to scrape enough rust out of the dust boot lip so the boot would fit, but the blackness of the fluid was downright amazing. I'm actually surprised since the entire system was flushed two years ago. I need to bleed it all tomorrow (ran out of time today), but the wheel turns free again. Gee, I can't wait to find out what will fail next

Supra-holic

So did it help? I have the rear vibs too at around 42-72 on certain roads or with slight bumps it loses composure. This is an 06 with 40K miles.

I got my tires balanced and it didn't help. Anti-seize on the brake pad sliders too. I'm going to grease the sway bar to see if that helps.

There is a mode of vibrations that happens on motorcycles and trailers call weave mode. Basically a frequency at certain speeds that is usually dampened by suspension setup, frame stiffness, tire construction, etc. Maybe the car is experiencing these and lacking that ability to dampen those frequencies. I'm also going to play around with different tire pressures. You say it goes away after a couple of miles when the tires warm up.

Luckily it doesn't happen all the time.

MacGyver

Worked like a charm... the vibration has disappeared. It probably started vibrating once the rotor heated up after a few miles.

Supra-holic

Hmm, tomorrow I'm going to jack up the car and do some more trouble shooting and check out the front brakes also.

I'm a mechanical engineer, so this is driving me nutz. Even if it disappeared on its own, I need to know whats causing it. Freakin closure.

:ponder: