Car is a 1995 Miata, setup for STR
Brake hardware is original, with 74k miles
Pads/rotors are cheapy junk stuff up front, HP+ rear (stupid brake bias!)
Symptoms:
1) After driving a >10 mins or so at high speed (>45mph sustained), I get a vibration in the steering wheel.... like the wheel is out of balance. The longer I drive, the worse it gets until it feels like I'm running over a very exaggerated rumble strip with only one side of the car.
2) After driving >10mins or so, the car develops a pull to the left.
I rarely drive more than 10 mins at >45mph, so its not often replicated. I thought I smelled brake fluid once. I tried to check if the brakes were warmer on that side, but being on 15x9s and pretty low, its hard to get in there to figure it out. I pulled apart brakes and lubed the slider pins, but nothing appeared to be terribly stuck. Problem still persists afteward.
When cold, the car drives absolutely fine. The only other mechanical issue I am aware of with this car is the motor mounts are totally shot.
If it's a brake caliper, the wheel will get hot. Although I'd be more interested in the condition of your wheel bearing on that side.
It could be shot, but if I jack up that side and try and wiggle it, I'm not getting play. Should I just do bearings as well as a precaution?
Are you trying to wiggle by hand or have you used leverage with a crow bar? (may as well check all the stuff down there while you're at it is what I'm saying)
By hand. What other stuff? Not sure on the ball-joint condition - original I suspect, but all bushings have maybe 5K miles on them tops.
Also, my first post should say smelled "hot brakes" not brake fluid. I'll see if I can take a bit longer drive on the way home and see if things get hot.
Miatas are hard on their front wheel bearings on the track.
I wouldn't expect ball joints, they usually only make noise when they're moving, such as steering loads or bumps. Never a rumble.
Just for fun, rotate your tires.
Check brake hoses... if original... check that they allow fluid transfer in both directions.
I had a 1980 Capri (Fox body) one of the front brake hoses collapsed on the inside with no exterior signs of damage or cracking. I finally figured it out.. replaced both hoses and was good to go....
I would expect though, that a difference in brake pressure would trigger the light (as would a stuck caliper) an a tire problem would cause a speed relative vibration. I'd still check, but I'm with Keith's first suggestion. Just brainstorming out loud...
The Miata's brake system doesn't measure brake pressures side to side. You could take a caliper off the car, and you wouldn't get a light under you'd pumped all the fluid out.
Brake hoses are original. I will check.
Keith, the car has never seen track time, although has probably ~250+ autocross runs on the STR setup. I will look more closely at the bearing, and also rotate tires.
The thing that makes my gut say this is brake related is that the vibration only appears after enough time/speed. Do wheel bearings fail in a similar manner - only have play when hot?
I have noticed a E36 M3ty thing the last few times I have put pads on a few cars.
The pads need to be able to move a little bit in a sliding caliper type brake. The new pads I got at the parts stores all have burrs or nicks or some other defect which is not allowing the pad to move freely.
My wifes mazda6 kept going through the outside rear brake pad. I finally figured out it was the pad getting stuck against the rotor.
I ground all the sharp edges off the pads and make sure they can wiggle a little bit.
Problem solved.
I woud suggest checking that out before replacing a caliper. I thought it was the caliper at first.
Rob R.
Wheel bearings tend to fail normally, they'll make noise all the time. But unless you've just changed something (rule: always go back to what you just did), I wouldn't expect the brakes to spontaneously develop a problem like this. But I would still check temps when the problem is occurring. You could also get it to manifest, then jack up the problem corner and try spinning the wheel while everything's still hot.
Do your investigation in the state where the car has trouble.
