BigE

iTrader: (2)

I bought a 98 Formula second week in January. It had ~41k miles on it. I noticed a slight vibration when applying the brakes when I bought it. I drove it 520 miles home and noticed a slight but noticable constant vibration. I figured it was the rotors as well. I got it home and found that one of the caliper pins had seized. This is my only car right now, so I pounded out the seized pin, cleaned it and reinstalled with synthetic caliper lube. I also replaced the front rotors and pads. A test drive revealed that the vibration when applying the brakes was gone, but the highway vibration remained. I bought a new caliper pin to replace the formerly seized one (just in case) and installed it later that week. Again, highway vibration remains.
After driving the car daily for a while, I have also noticed a low speed 'lurch'. When applying the brakes and coming to a very slow stop (like rolling up to a redlight you expect to change but doesn't), the car lurches forward like there's a low spot on the rotor. By that I mean the braking force changes noticably.
And now for the final consideration. The tires on the car are Dunlop Sport 5000's. They have A LOT of tread left, but as you can tell by the mileage, the previous owner let this car sit a lot. There is slight dry-cracking between the treads. For what it's worth, the vibration is all over the car, but feels like it is biased towards the rear (can feel it in the seat more than the steering wheel).

So with all of that information, what do you think the problem is? Flat-spotted tires causing the vibration as well as the low speed lurching? Rear rotors warped, too causing both problems? Sticking caliper? Something else?

BTW, the car is bone stock (for now).

Thanks all

ArcticZ28

iTrader: (14)

Could be a bunch of things. The vibration as you are driving fast on the highway could be that you need new tie-rod ends. Those are usually what tend to cause that. The lurching while braking is most likely warped rotors, but could possibly be something else. I would have all the rotors turned (or get new ones) and work from there. The tires with dry cracking are definitely a no-no. You're gonna want to get some new tires pretty soon and get an alignment as well. New tires, alignment, and possibly new tie-rod ends (if they are a problem) would most likely clear up all highway vibrations. Good luck.

2002blackZ

iTrader: (4)

Do some searching on drive shafts. I think I read somewhere on here that you would notice it at certain rpm's. (possibly the speed you are at on the highway.)
The rotors shouldn't really cause it without applying the brakes, unless they are really bad. At least that is my experience on several other vehicles.
Good luck finding it!

BigE

iTrader: (2)

Thanks! I think I have tracked the problem (the lurching under braking at least) to the rear rotors. It feels so weird because it is causing irregular braking force but without affecting the steering wheel. I'm going to pull the wheels this weekend and check the runout. I think the rest of my problem is dry-rotted/out of balance tires. If I can get them safe to run on, I'd like to keep these tires for a little while until I've figured out which ones I want (perhaps even DR's). I'll take a picture of the tire/dry-rotting and post it up next week. That way I can get some feedback from firsthand experience.

Mr Yak

iTrader: (4)

It is very odd that the rear rotor would do that, another reason you may be getting that vibration is if your tires are that old and dry rotted they steel belts could be seperating. if your tires are more than about 3 years you should probably replace them. the way you tell how old your tires are is the last 2 numbers will be the year and the 2 numbers before that will be the week on the DOT number you will see DOT mcbe 8974 0105
that is just an example but this tire would have been made in the 01st week of 05 something i didn't learn until a couple months ago. if it has only 3 numbers at the end 019 it would have been in the first week of 99
if you can catch it early you can get your rotors turned all you have to do is a visual and maybe a phyical inspection, wait til your rotors are cool, then just run your finger across the rotor if it feels like a mountian range your pretty much S.O.L. but if you have one or two little lines you need to replace your rotor and pads peferably. you can also look for cracking like mine has.