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Vibration from Brakes and squeaking

Discussion in 'A4/S4 forum(B5 Chassis)' started by aragorn, Oct 29, 2008.

  1. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Ok i changed the calipers, disks, pads, bearings and ABS rings on the rear of the car quite a few months ago now (think it was before easter), but this problem seems to have been there since then, and i'd like to try and fix it!

    When your driving along at normal speeds, anything from 5mph to 40mph say, theres a constant chirping noise coming from the nearside rear wheel, that increases in frequency with the speed.

    I've jacked that corner up not long after i first noticed it, and when you spin the wheel the caliper seems to "grab" the disk at a certain point in its rotation. My mate and i thaught that perhaps the stub axle was slightly bent and decided it wasnt really worth pursuing any more as the brakes worked fine. I've since thaught about it and i dont think it is the stub axle, because if it was, the "high spot" wouldnt move as the disk spun, it would just permenantly run crooked, and the pads and tyres would likely wear funny.

    Now the odd bit, ive already retightened that bearing once not long after fitting it, as i'd noticed a little play in it, now at the MOT, the tester says there is slight play in that same wheel again. I've also noticed then when you brake hard in the car, at speed - say 70mph, theres a vibration thats felt thru the entire car, but not so much thru the steering wheel like you would expect with warped fronts.

    So any ideas what could be wrong here? is it possible the disk itself is actually bent? Or more likely that theres something odd going on with the bearing? I doubt its the stubaxle as ive said above.

    I've got some 312mm TT carriers to do the front brakes after i get paid and i want to sort this rear one at the same time. Just not sure wether i should replace the disk or the bearing or something else...

    Kevin
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  2. Blue_Thunder
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    Blue_Thunder Active Member

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    If you bought the discs 2nd hand there's every chance it could be warped.

    If that is the case, you should be able to see which part of the disc is hitting the pad as it will be shinier than the rest of the disc. You can get them skimmed fairly cheaply.
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Everything was new, which is why i was leaning in the direction of a bearing fault rather than the disk itself...

    Also, the disks cost about £15, so if it was infact warped i'd simply be replacing it instead of messing with getting it skimmed!
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  4. ALPINE
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    ALPINE Yes its diesel, now cry u lost

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    my car used to shake like **** under breaking. i changed all the front arms and it stopped.
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  5. NHN
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    NHN Modmetractor

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    I mean all things seem to point to bearings, but warped disc seems more logical as thats usual vibration in breaking & the little chirp which would be pad on discs at warped area, a skim would fix that easily.
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    remember the bearings on the rear of a FWD are taper bearings. Which i'd imagine are a bit more prone to wear than the roller bearings in the front.

    The other thing i'm considering is that the bearing race isnt quite seated perfectly inside the disk causing it to run squiff...

    Another symptom has appeared though, it seems that i'm getting a vibration thru the car at certain speeds regardless of braking. i could feel it thru the car, but not the steering wheel while on the motorway at normal speeds last night, and increasing speed a little made it far more pronounced. The missus has also admitted that she drove over a kerb in a carpark with the NSR wheel a few weeks ago (the same one with the dodgy brake/bearing), so i'm hoping she hasnt bent the damn alloy!
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  7. PW-Motorsport
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    PW-Motorsport Member

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    When you tightend the rear wheel bearing how tight did you go?
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    a bit more than finger tight?

    istr your supposed to tighten it until you can just move the thrust washer with a screwdriver which is what i did.
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  9. PW-Motorsport
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    PW-Motorsport Member

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    Yep, you do get some who tighten them up with a long bar !

    I think it may be wise to check this bearing, strip is off inspect and replace if any of the chrome plating on the roller bearings has failed.
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  10. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Got onto it today after work to see what was going on.

    I'd ordered up a new bearing thinking thats what it would be, took it apart and noticed that the "high spot" of the disk wasnt shiney like the rest of it, clearly the pads havent been touching properly...

    Pulled the bearings out and the grease looked very black, then noticed something very peculiar. The inner bearing race (the larger one) was loose in the disk, i could spin it round with my finger! I tried fitting the new bearing race to the disk and found it was just as loose, so got onto the motorfactors and got another disk from them. Looks like they'll take the old one back as a warranty replacement too when i described the fault to them.

    Fitted it all back together, New disk and new bearing, original pads, and its now running true when you spin the disk unlike before. Missus says the brakes feel a bit better, i suspect theres a bit less travel in the pedal now, as before the runout would have kept knocking the calipers pistons back.

    Got some 312mm's to fit to the front now, but unfortunately i didnt manage to get them done due to having to run off to get a new disk.
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