Short Version:

This is for a 1998 S70 base model, automatic transmission

After driving my car at relatively high speed for 15-20 minutes, there is a nonspecific rumble coming from the rear of the car followed by progressively increasing resistance to motion (creating a wobble in the steering wheel and a bit of bucking-forward and backward motion-which prematurely slows the car).

Could this be some sort of heat-induced warping of the rotors? Any other ideas?


Long version:


After driving at relatively high speed (about 45-50mph) for at least 15-20 minutes, a resistance to motion develops. It begins with a nonspecific low rumble coming from the rear of the car. Once this develops, I also notice increasing resistance to motion; that is, the car slows down prematurely. I notice that this is independent of the gear I am in (i.e. is equally present in both “drive” and neutral)

As I said before, the resistance slows the car down (like an unwanted braking effect), getting worse and worse until the car begins to “buck” a little and I notice increased vibration and wobbling in the steering wheel. I have also noticed that this symptom is not directly related to speed; that is, once the noise and concomitant resistance develop, the pitch does not vary with speed, leading me to believe this is not a presentation of a worn-out wheel bearing.

Also, after this “ bucking” pattern develops, I notice a smell of “hot metal” coming from the left rear wheel well. This smell ONLY comes from the left wheel well; to me it's like a smell of metal-on-metal friction ( I am certain this is NOT burning rubber which smells very different)

Finally, just wanted to mention that short trips at low speeds are perfectly fine. No significant changes/symptoms are noticeable on a quick 10 min trip to the store and back. It’s only when I have to drive a bit further that I get scared I’m not going to make it home.

I lost my trustworthy mechanic and am hoping you guys can provide some sound advice for me before I take my car in for repairs (or fix it myself if it's a simple fix)

Any help is much appreciated, thanks!

james

 

I'd start by jacking it up and spinning the wheel.
Just remembered - a few years ago I stopped on the highway for some reason (OK, I had to take a leak really bad) and hooped back in, dropped her in gear, and took off (being shy and embarrassed). Several minute later I developed similar symptoms to yours, but when I got out I smelled cooking brakes, not metal. Yep, left the e-braked partially on.

 

Sounds like you have a brake dragging. Either the parking brake is out of adjustment and dragging on the rotor, or the caliper is not allowing the brakes to retract fully, and then when you drive at high speed it's getting things hot and making it worse.