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Warped New Discs/ Graunching


japscrap
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hello all.

boring background bit :D - if you have some knowledge, i could really use your opinion.

a few thousand miles ago i got all discs and pads changed as a result of warped old discs. got spurious new discs and pads all round and had my brother fit them. the car was ultra smooth and quiet for a few days but slowly it started getting wobbly when driving again. it also pulled to the left under braking and the wobble goes crazy. it also developed a graunching noise from the o/s/f. the noise can only be compared to the creaking noise you get from the pedals of an old bike and it is definitely cyclical as the noise slows down as the car slows down.

my brother diagnosed the car as having warped new discs. he demonsrated this by removing the wheel, removing the pads and tightening the discs back on with the wheel nuts. as the discs rotated, you could not only see them wobble, you could see that the 'walls' of the disc were actually thicker and thinner in places. rang motor factors and they agreed to take the discs back.

however, he also diagnosed the cause of the graunch as being related to worn brake pad carriers and/ or their bolts. he re-assembled the car but left the carrier bolts loose. only slight wobble in steering, no more graunching and no more pulling to the left/ wobbling. he was happy with his diagnosis so he tightened the carrier bolts and the car returned to 'normal'.

now the question,

chicken and egg- did the carriers cause the discs to warp or did the warped discs wear out the carriers? carriers are a big pile of doh-re-mi and if i don't fit them, will i warp my brand new discs? if the discs were actually at fault and now i have another new set, will worn carriers be ok?

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At a guess I would say that if the discs were fitted to clean rust free surfaces and ran perfectly true ie; runout within spec. at least, then maybe the brake cylinder/s are partly seized on one or both sides.

One brake piston pressing harder than the other???

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i'm not sure. we picked through the braking a bit, greasing as we went. we actually had trouble with the n/s caliper and expected trouble from that side if any.

i think the damage is done to the carrier now and its just a question of whether i have to replace the carriers as well or if the graunchin goes away when the new discs get fitted.

if i do need new carriers, i'd appreciate any suggestions as to where i can source them without having to go to the main stealer

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Before you go down that road, why not remove the calipers and check for seizing?

The carriers and calipers are pretty substantial stuff, I think distortion on these is your last resort.....

just my two pennorth....... :duh:

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From the symptoms u describe i think it will be one of the following "common" probs:

1) tighten wheel nuts in following order 1,3,5,2,4 to 103Nm torque to hold disc squarley on wheel hub or the dics will warp - i had a brand new disc ruined (= new front discs and pads) by a back street tyre place where i had my wheels balanced and they didn't tighten nuts properly.

2) seized caliper piston - either remove clean and recon (with kit) and replace or fork out for a reconned one.

3) worn wheel bearing - causing disc to wobble on hub - replace wheel hub/bearing.

the solution to all this is to replace both front discs and all front pads aswell as resolving root of problem.

hope this helps.

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if the discs are that susceptable to wheel nut torquing i suppose it's possible that they probably weren't given the attention they need. ps should they be torqued from loose or should i give them all a small squeeze first?

i am reasonably happy that the calipers are working fine. but do you think the wear/ play in the carriers might be the root problem? or is that just a symptom of warped discs? does this play automatically mean they must now be replaced or is a little wear okay?

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when the car is jacked up - tighten the wheel nuts by hand in the order given until they are hand tight - make sure the wheel is squarely on the hub. give them all a little "pinch" in order. then drop thecar and tighten in order to correct torque.

bottom line is, if you want it perfect, tighten each nut, in order, 1/4 turn, until all nuts are at correct torque. But u dont have to be this strict...

if discs are warped - juddering when braking - it is best to just replace them + pads.

try www.brakeparts.co.uk - cheapest in the UK and good quality from my experience.

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