Test your diagnosis skills, whats wrong now?

[bigbird]

Ok so first let me list the things i know are wrong and are being replaced soon (already have parts).

bad halfshafts
OLD calipers which i think are sticking
steering rack bushings
lower control arm bushings

SO, heres the symptoms.

Vibrations: Only after making several long moderatly hard stops at highway speeds. feel liek a warped rotor. once this has started it gets worse as brake frequency is continued. at low speeds, sub 10mph, the car acts like the brake rotors are warped, catching and releasing ever so slightly as the car rolls. both of these vibrations are relitive to speed. faster i go, the harder and more frequent i feel them.

Pedal feel: i feel slight vibrations through the gass pedal and steering wheel, but nothing that leads me to believe it is tied to either of these areas directly. the most feel is when lightly depressing teh brakes.

Braking: consistant and firm, the car brakes fine. vibrations are only present when brakes are used frequently. performs 100% under heavy braking, no swaying or noise. just a vibration the lessens with pedal pressure. OH i forgot to add. at low speeds, if i brake to a near stop, then release. there is a sound and feeling as if the calipers are sticking.

Noise: none except at low speeds. the brake upgrade made a humming sound under light braking since the upgrade was performed. sometimes, in these conditions, the sound will occure with no pedal pressure while coasting at slow speeds. but it feels liek teh car isnt coasting naturaly, as if the brakes are applied slightly.

Weird crap: the vibrations can be eliminated by driving at 60ish mph+ for a short while. after the first time this happens, it is harder to duplicate afterwords.



so, what do yall think?

[jtex2717]

I would go with warped rotors dude...that sounds like one of the only things it could be...noise at low speeds could be things like wheel bearings, backing plate is touching, warped rotors, frozen caliper, bad axles....these are the main things that could make noise when moving which are relative to the brakes.....but you have weeded out, caliper/axles I am sure ur backing plate isnt touching, and unless you have bad wheel bearings then I would say go with the rotors and change the pads...

Edit...now that I think about it...this could also give you the pedal vibration ur talking about...unless u have a bad mount...

[bigbird]

my only reason for not suspecting the rotors is because if it is, that means they warp when they are hot but not when cool. my previous experiance with warped rotrs has them vibrating when the brakes were applied reguardless of temp of the rotors.

OH i forgot to add. at low speeds, if i brake to a near stop, then release. there is a sound and feeling as if the calipers are sticking. they release making a slight clunking sound.

[jtex2717]

Change ur calipers and then see whats happening....I think once you start changing components then you can do a process of elimination...other than that I would def say its one of the two....and depending on how bad they are warped you could get various symptoms...

[bigbird]

well thats my intention. I even have a set of new new supra rotors wating for the day these cheap ones warp, if they arent already. I just wanted to see what people thought.

[Solid_Koolaid]

Hard one, maybe not only one problem... dunno.

Before beginning with the parts replacement ritual, I'd check the easy ones.

Stuck calipers ? (check if they do really move freely : remove them from the car )

While you're at it, check the bearings and any loose in the steering/suspension.

[zppeacock]

I would pull it apart, look at the pads, check the caliper and see if the piston moves back in, check the slides on the bracket and go from there.

[jtex2717]

Yeah I would def say check the pads....i did a brake job last week and the pads were cracked in half...the metal separated from the actual pad and became 2 pieces.....lmao

[RningOnFumes]

What puzzles me is how you describe the vibrations starting after you've done some braking. If you have warped rotors, you should feel them from the get-go, no? The other thing is why would you feel it in in the accelerator? The braking is consistent. The problem disappears somewhat when you hit over 60?

How cheap are the rotors if they warp and "re-shape" for the next drive?

I'm going to go for the long shot and say to look into the vacuum assist lines and/or the master. This is because of the 60+ thing, high reeves, more vacuum; less reeves: braking that is on and off from the assist which might resemble warping.

I know of a possible test. Find the vacuum assist line, I believe it's the same as the one everyone uses for Seafoam. The next time this happens park, remove that line and go down a deserted road. Do a few runs and see what happens.

Just one man's opinion.

[fenixus]

yeah i was about to suggest checking brake booster and master cylinder perhaps as above. low engine revs has something to do with it, not only speed i think.

and sticky calipers "might" cause that thing too! i would remove pads and measure all of them with a digital caliper at same spot and compare. it will point to what exactly is sticking meaning either pins or the piston (usually it's pins, so clean them and re-grease).

if the inner pads are worn more than outer then it means the piston is not being retracted, so it's seal might be bad, piston corroded, etc. if so replace calipers with remanuf ones.
if the outer pads are worn more than inner then it means the anchor pins are sticking, so remove them, clean with brake cleaner, dry and re-grease with e.g. Permatex Ultra Disc Brake Lube.

flush the brake fluid maybe too? and check brake booster and vacuum lines for leaks. hope the master cylinder piston seals are good.

[Chris Crash]

I personally think a sticky caliper is causing the rotors to heat up, and thats when you notice the vibration.

Check it out.

[bigbird]

all sound reasonable. the parts are already purchased for a good deal and to replace old or worn parts so process of elimination is what i'm doing. didnt think about the master. i had ruled that out since the car stopped just the same, just with an added vibration. but a vaccum issue might cause issues. something to look into.

[SexieWASD]

I'm not sure if you've got drums on the back, but mine did that to me. When they would get hot they would warp into an oval shape and rub the shoes. It would happen everyday on my way home from work after I got off the off ramp, then stop after they cooled back down.

[Mister_Perkins]

make sure the rubber line that runs to your caliper isn't collapsed. This will also make your calipers stick. Have you physically touched your hubs / rim to see if they are overly hot?

That's the best way to check for a sticking caliper. Its not very common for two calipers to go bad at one given time. After a trip, touch your hand to the rim around the hub assembly area on both front. If you notice a temp difference between either side, the hotter side is more than likely your problem.

[fenixus]

also another idea. do you have ABS?
might be worth putting it into speed sensor diagnostic mode as it may be causing one of brakes to engage.