Front end vibration.

[Thunder-71]

When I hit the brake on my 1984 944 NA, I have a vibration on the front end, worse at higher speed. Replaced the rotors and it is still there so it is not the rotors. Front end seems tight. Any ideas as to what it is?

[mytrplseven]

Wheel bearings, bent wheel, alignment, tire bubble or cord delamination? I'd take it to a reputable tire, wheel and alignment shop.

[Thunder-71]

Originally Posted by mytrplseven

Wheel bearings, bent wheel, alignment, tire bubble or cord delamination? I'd take it to a reputable tire, wheel and alignment shop.

If it is any of the things you mention the vibration should be there all the time. It happens only when I brake.

[John_AZ]

Originally Posted by Thunder-71

If it is any of the things you mention the vibration should be there all the time. It happens only when I brake.

Have you ever rebuilt the front brake rotors?

J_AZ

[edredas]

Had a vibration like that once and a bolt had come out of the control arm. Under braking the arm was violently shaking... so be sure to check all the suspension components for anything loose. I hope that helps!

[IdahoDoug]

Former vehicle developer here for both GM and Lexus. I've experienced loose front wheel bearings that don't wobble except under braking. One easy test is if its most obvious under the light braking you'd experience as you exit a freeway ramp, but under heavier braking you don't feel it.

I have not removed my front rotors yet to know if with your new rotors you have to put new wheel bearings on. If the answer is no and the wheel bearings are untouched then I'd put them at the head of the list as a suspect.

I'd also check your tie rods and all other front end bits by laying on the ground and gripping each tie rod one at a time while someone wobbles the steering wheel quickly back and forth. You'll "feel" the tiny thump or click of a bit of slack this way long before you'd hear it. Easy check for tire/wheel is to jack each tire barely off the ground in turn and have someone spin them. Your eye should easily tell you if either has a wobble by watching the tiny gap from tire to ground. There is normally some - no tire or wheel are perfect - and if there is "some" plus you have slightly loose wheel bearings on a sporty car without overdamped power steering you will feel it. If so, try swapping front to rear tires and see if one of them is "rounder" and diminishes it.

Another random comment is that if a car is supposed to have a slight toe-in on the fronts and instead its perfectly straight ahead then it is easy to get what you describe. Just a faint tension on the tire patches toward one another will damp that slight wobble from a nonperfect rim, or wheel bearings that are on the loose end, or other real life variations, etc. That's probably why someone mentioned alignment. I don't know the 944's specs but I am taking mine in next week as I recently put new struts in and new tires on, so this is the right time. Good luck and post up what you find.

[flash968]

braking vibrations are usually due to contamination or poor break in of the pads and rotors.

you cannot reuse pads on new rotors, and have a mixed chance of success even with a pad slap on old rotors. pads and rotors need to be changed together, and then bedded properly. see the stoptech site for the proper procedure.

failing that, i would be willing to bet that it is lower control arm bushings. i have had this happen before. they are almost always neglected, and at this age, almost certainly shot.

[Thunder-71]

Originally Posted by flash968

braking vibrations are usually due to contamination or poor break in of the pads and rotors.

you cannot reuse pads on new rotors, and have a mixed chance of success even with a pad slap on old rotors. pads and rotors need to be changed together, and then bedded properly. see the stoptech site for the proper procedure.

failing that, i would be willing to bet that it is lower control arm bushings. i have had this happen before. they are almost always neglected, and at this age, almost certainly shot.

Thank you to all of you guys, you all make sense. Doug's comment about "more noticeable on light braking and not so noticeable at hard braking" kind of matches my car's behavior. I will check the front end, tie rods control arm bushings first before I replace the bearings. I will keep you posted as to what I will find for possible future similar situations to fellow Pelicans.
Thanks again and have a Happy and Safe Memorial weekend.

[Thunder-71]

Originally Posted by flash968

braking vibrations are usually due to contamination or poor break in of the pads and rotors.

you cannot reuse pads on new rotors, and have a mixed chance of success even with a pad slap on old rotors. pads and rotors need to be changed together, and then bedded properly. see the stoptech site for the proper procedure.

failing that, i would be willing to bet that it is lower control arm bushings. i have had this happen before. they are almost always neglected, and at this age, almost certainly shot.

How do I check them?

[Spring44]

Idaho Doug is exactly right. All of those places in a front end (wheel bearings, ball joints, struts inner/outer tiered ends and steering rack) wear over time and cause a cumulative looseness that can cause instability during braking or acceleration if you have no or too little toe in. Toe in provides a lateral stability to the front tires and wheels that you don't have in wheels looking straight ahead and free to move in either direction with the road irregularities.

I once built an old Ford hot rod and just set the toe-in initially by eyeball. Took it out on the highway for a test spin and when I decelerated to turn around, both front wheels started flapping violently from side to side. The culprit turned out to be zero toe-in. Set the proper amount of toe and never had anymore trouble with vibration.

[flash968]

first, rule out that pads were reused on new rotors. used pads, even for a short period, will have deposits on them, and will likely cause vibration under braking, especially light braking. see the stoptech site for a full explanation.

second, was a proper bedding in done? if not, then again you are dealing with deposits.

if you installed new rotors on old pads, you can try surfacing the rotors and then installing new pads.

if you installed new and new, then in addition to surfacing the rotors, you can try sanding the pads and then hashing the pads with a knife and putting a cross-hatch pattern on them

as for the control arm bushings, you have to have the car up in the air. then you can see the bushings, and look for cracked rubber. the castor blocks (rear) are pretty easy to tell if they are shot. the front bushings not so much.

[djnolan]

How does the wheel feel when you spin it by hand? Does it have even resistance for the full turn? If not maybe the rotor is not seated flat on the hub.

[IdahoDoug]

I wouldn't chase the "old pads" thing too much. One 10 minute bedding procedure as described on various websites will properly distribute pad material to rotor and vice versa. In addition is the statistical unlikelihood that areas of grip/less grip as you go around a rotor (the only thing of concern there) would randomly line up with each other on the two front brakes to cause a shimmy. It is just as statistically likely that these grip variations would either cancel each other out, or be close enough that their frequencies are within the resonant frequency of the wheel/tire. In other words, you can't wobble a heavy assembly like a wheel/tire if the forces are too close together in time. Knowing this, to the OP - if you're feeling the frequency of the wobble changes quite a bit then let us know. However, the "grip/no grip" issues regarding pad/rotor interface would more likely manifest as "pulsing" type feelings at many speeds and be more obvious/noticeable at slower speeds. I'd focus on the other stuff first and certainly don't mess with pads by cutting them etc at this stage in the diagnosis. Creates too many variables for a low probability solution. HTH....

[flash968]

there is no procedure for "fixing" used pads. it is a chemical bonding that occurs between the pad and rotor. that cannot be scrubbed off with any assurance of success. in over 30 years of doing this, i have seen less than a 50% rate of success. it is worth a try, as you have nothing to lose, but likely to fail.

at my shop i made a fair amount of money fixing this on cars that people had done "pad slaps" on, or failed to properly bed pads. once you have uneven deposits, you are basically screwed. these are essentially "hot spots", which do not react to the coeeficient of friction evenly. essentially the pads are "skipping" across the rotors, as they encounter the areas of higher and lower coeeficients of friction. i cannot count the number of bets i have one with guys who were "sure" that they could do it halfway "because a buddy told them they could, and he never had a problem".

again, consult the stoptech site on this.

start with a good baseline. new pads and rotors, bedded properly. if any of those are not in the equation, the result will almost certainly be less than desired.

and before anybody says it, no, the rotors are not warped. rotors almost never warp. that is an urban myth. i have seen exactly 1 warped rotor in my life, and it was from a frozen caliper.

[IdahoDoug]

I don't want to derail this thread as the OP has a problem he's trying to figure out. Pads and rotors are both consumable items that are designed to wear down. A pad is the same material its entire depth. So there is not a logical reason to say "don't use old pads on new rotors" if the reasoning is some type of material incompatibility. Nor is there a reason to say "don't use old rotors on new pads".

Yes, break in is a good idea. Yes there is a right and wrong way to do it. But discouraging people from re-using perfectly good parts may not be the best for people on a budget. I disagree the only way to refresh brakes is to replace pads AND rotors every time. That's not what the people who design and build cars advise. However it would not be a surprise that people like Stoptech who sell brake components would have us do.

I'd be more than happy to participate in a separate thread to discuss positions on whether it's OK to re-use pads, re-used rotors, or re-use both.

[OK-944]

Generally agree with the above...but - be certain that if you are wanting to use old rotors with new pads that the rotors have not been ridged in any way within the area of pad contact, and that any outer rotor ridges (as are sometimes present on the outer circumference due to wear) don't interfere with the new pads....unless the rotors in question still have enough meat left to be machined.

[flash968]

there is a chemical bonding that happens between the rotor and the pad. when it happens, it goes all the way through the pad. i find it amazing at how many people resist the physics. i saw it all the time at my shop, and continue to see it on boards like this, where so often somebody is trying to do something "on the cheap". it is almost always bad advice. i get that not everybody can afford everything, but there are some things that just should not be done half way.

stoptech is a very reputable company. yes, they sell brake stuff. that does not change the reality. they are not making this stuff up.

used parts are not necessarily "perfectly good parts". i have successfully done pad slaps, but the rate of success is low. it frequently results in pulsing or vibration. in order for rotors to be reused, at a bare minimum, they must be free of deposits, of any "blueing" or hot spots, and absolutely smooth, with no grooves or wear. they should absolutely be surfaced prior to use. if you are going to reuse rotors, you have to use the same compound of pad as before. that means the same brand and model. you cannot mix and match pads. you definitely should not reuse pads.

brakes are the only thing stopping your car. they are not to be messed with. it's just not worth it. it's like the guys who buy cheap tires, and then wonder why they lost traction and hit a tree.

i understand about budgets. everybody is on one to one degree or another. however, if you can't afford to properly maintain a car, then you should park it until you can. been there done that. that's exactly why i don't own a ferrari.

as for the OP and the issue, unless i missed something, we still don't know if he reused the parts or not. if not, then it is more likely that the problem is elsewhere, like the control arm bushings.

[Thunder-71]

Originally Posted by flash968

there is a chemical bonding that happens between the rotor and the pad. when it happens, it goes all the way through the pad. i find it amazing at how many people resist the physics. i saw it all the time at my shop, and continue to see it on boards like this, where so often somebody is trying to do something "on the cheap". it is almost always bad advice. i get that not everybody can afford everything, but there are some things that just should not be done half way.

stoptech is a very reputable company. yes, they sell brake stuff. that does not change the reality. they are not making this stuff up.

used parts are not necessarily "perfectly good parts". i have successfully done pad slaps, but the rate of success is low. it frequently results in pulsing or vibration. in order for rotors to be reused, at a bare minimum, they must be free of deposits, of any "blueing" or hot spots, and absolutely smooth, with no grooves or wear. they should absolutely be surfaced prior to use. if you are going to reuse rotors, you have to use the same compound of pad as before. that means the same brand and model. you cannot mix and match pads. you definitely should not reuse pads.

brakes are the only thing stopping your car. they are not to be messed with. it's just not worth it. it's like the guys who buy cheap tires, and then wonder why they lost traction and hit a tree.

i understand about budgets. everybody is on one to one degree or another. however, if you can't afford to properly maintain a car, then you should park it until you can. been there done that. that's exactly why i don't own a ferrari.

as for the OP and the issue, unless i missed something, we still don't know if he reused the parts or not. if not, then it is more likely that the problem is elsewhere, like the control arm bushings.

When this issue appeared I figured it was a warped rotor and bought new ones. The pads were thick and did not change them. I had no chance to check the car I should do it by the end of the week. I will keep you posted.
PS: I hope it is the pads but I am not holding my breath.

[flash968]

yeah - i hear this one a lot. shops tell customers that their rotors are warped, so as to sell them new rotors. in the real world, rotors don't warp. it takes something catasrophic to warp a rotor on a car (like a frozen caliper). i've done a few thousand brake jobs, and seen exactly 1 warped rotor. i have seen a bunch of rotors with deposits and/or hot spots though.

more than likely you just developed deposits on the pads. i have had to toss brand new pads, due entirely to an inadequate break in procedure. it happens.

hopefully you can replace the pads, and just surface the new rotors. it will really depend on how long you have been running the old pads on the new rotors. however, do NOT merely replace the pads. make sure you surface the rotors. they guy at the shop will tell you they are fully thick, but if you tell him you are trying to remove the deposits to cure a vibration problem, he will do it.

do yourself a favor though, and before doing any of that, just to rule out the suspension, get the car up in the air and inspect the lower control arm bushings. it will cost you nothing, and if that is the problem, it will save you a more costly and then pointless process on the brakes.

[Thunder-71]

Originally Posted by flash968

yeah - i hear this one a lot. shops tell customers that their rotors are warped, so as to sell them new rotors. in the real world, rotors don't warp. it takes something catasrophic to warp a rotor on a car (like a frozen caliper). i've done a few thousand brake jobs, and seen exactly 1 warped rotor. i have seen a bunch of rotors with deposits and/or hot spots though.

more than likely you just developed deposits on the pads. i have had to toss brand new pads, due entirely to an inadequate break in procedure. it happens.

hopefully you can replace the pads, and just surface the new rotors. it will really depend on how long you have been running the old pads on the new rotors. however, do NOT merely replace the pads. make sure you surface the rotors. they guy at the shop will tell you they are fully thick, but if you tell him you are trying to remove the deposits to cure a vibration problem, he will do it.

do yourself a favor though, and before doing any of that, just to rule out the suspension, get the car up in the air and inspect the lower control arm bushings. it will cost you nothing, and if that is the problem, it will save you a more costly and then pointless process on the brakes.

I had a chance to get under the car today. Tie rods/ball joints are clean and tight on both sides, lower control arms look visually good, no visual issues on the bushings, they look good. Since I had the wheels off I checked the rotors and pads. Before removing the pads I span the rotors by hand (no wheels on them) left rotor spins smoothly but the right was biting a little on a couple spots about 6 inches from one another. I removed the pads and span that rotor, seems visually good with no wobbly signs but is it bad? both sides pads are clean, no deposits, both rotors have nice and smooth surfaces. Should I replace the pads on both sides tomorrow and see what happens and if problem still present replace the rotors? I also noticed slightly leaky struts that I plan to replace the inserts. What do you recommend on those?