Finding the Warped Rotor

[NeoMishMoo]

Car is shaking pretty good when braking, it still brakes fine but I'm thinking I may have a warped rotor? All brake pads are fine, so how do I figure out which rotor is warped? I'm thinking its a front one because the steering wheel shakes so much when braking, but is there a better way? I've got 4 good rotors off a junk car so I guess I'll just swap one then test it, then swap another until all are replaced or the shaking stops?

Or would it just be easier to take it to a brake shop and get the rotors turned?

Oh yeah while I've got it apart I've been told to go with ceramic pads? I'm guess it'd probably be better to just search about specific pads on the forum.

[Holland]

Turning the rotors should fix the problem, unless they have been turned too much already.

[StereoInstaller1]

What control arm bushings you got?

[619E30]

Jack up the car and get someone to brake softly and turn each wheel by hand and see which one isn't braking smooth enough

[jlevie]

While it is possible to have a warped brake rotor, that is extremely unlikely to be your problem. Uneven pad deposits on the rotors, worn suspension, worn wheel bearings, bad tires, or bent wheels are the more likely causes.

[E30Nova]

Have you pulled the wheels to see the rotors? I have the same problem and my rotors are hot spotted to hell. That's more likely than actually warping rotors.

Matt

[AndrewBird]

Rent a dial indicator with a magnetic or clamp style base from the auto parts store. You can use this to measure the runout of each rotor and see which is warped. See here:

http://www.clubcivic.com/board/showthread.php?t=41467

Having them turned might not be enough to remove the warp, and as cheap as new Brembo blanks are, I would just go new.

[NeoMishMoo]

Pads are fine, rotors look fine, everything is stock, I'm pretty sure I replaced the wheel bearings about 5 years ago. Worn suspension is very likely, as I recently replaced a few parts and noticed that everything looked as if it should be replaced.

I've got junk parts so I'd like to use those first, maybe it would be best to just pay a mechanic a couple hundred dollars to have complete diagnostics done so that I know where to start.

[jlevie]

You can do the diagnostics yourself. Get the front end up in the air and use a pry bar to pry on each of the control arm ball joints. Then use a large (24") pair of channel locks to squeeze each all joint. And motion in the ball joints is cause for replacement of the control arms. Examine the control arm bushings for cracks or tears and replace if present.

Grab each wheel at the the 12 & 6 o'clock position and check for motion. Do the same at the 9 & 3 o'clock positions. If the control arm ball joints aren't shot, motion along the vertical axis will be wheel bearings and motion along the horizontal axis will be tie rods.

Shocks are as important as the rest of the suspension components. OE shocks are good for no more than 60k. Bilsteins, about 100k. Koni SA shocks are good for a really long time if you start with them set for 1 to 1-1/2 turns from full soft and adjust them for increased rebound as they wear. If the shocks have enough mileage to be worn, just replace them and the upper strut bearings.

[StereoInstaller1]

You can do new urethane CABs in about an hour for under $100

[NeoMishMoo]

wow yeah I think most of the suspension parts were made in west germany back when there was a west germany, so I'm guessing I probably ought to replace most of it eh? I couldn't think of a better way to spend my tax returns.

[dsobering47]

vibration in steering wheel only when you brake = front rotors

vibration in your seat only when you brake = rear rotors

drive about 15 mph and tap the brakes...if the front end "clunks" then your CAB's are worn out....also inspect your ball joints, but you'd feel that more often than just braking.

[jlevie]

vibration in steering wheel only when you brake = front rotors

vibration in your seat only when you brake = rear rotors

drive about 15 mph and tap the brakes...if the front end "clunks" then your CAB's are worn out....also inspect your ball joints, but you'd feel that more often than just braking.

Close, but...

Vibration that you feel in the steering wheel is from the front wheels/suspension.

Vibration that you feel in the seat is from the rear wheels/suspension.

Vibration that you feel in the brake pedal is from the front or rear brakes.

[DJB]

A modern ventilated rotor warped from heat? Not likely. Look elsewhere.

I had an ATE rotor manufactured with an out-of-plane inner hat surface -- the one that touches the wheel hub.

It took me about two years to find it, as it would wear tires out-of-round and then the vibration would move when I rotated and re-balanced the wheels.

I finally figured it out when I heard uneven brake pad contact while casually spinning the wheel wheel doing an unrelated project. The dial caliper confirmed it, but it was the rubbing noise that provided the real diagnostic clue.

That said, vibration only while braking is usually loose suspension components. On the e30, that's often the CAB or outer ball joint, in that order.

A new, stiff CAB will even hide a little ball joint looseness, but you might as well replace a bad control arm because you have only about a 50% chance of the CAB remaining intact when you pull it off. (Unless you have your own press and do it as a hobby, replacing the just the off-angle ball joint will cost more in labor than just replacing the whole control arm.)

[dsobering47]

What? So youre saying a single worn-out outer right ball joint could cause the same vibration in the steering wheel as a warped front right brake rotor? I dont think so.