Wheel Judder on Braking

Z

Z4 Coupe

Member
I've been trying to fix a wheel judder and I need some advice before I blow any more money.

It started after the Z4 track day at Cadwell Park. During the last session the brake disk warning came on which was to be expected as they were due to be replaced. On the way back the steering juddered under braking but I thought that was the shot rear brakes so wasn't too bothered. I mentioned it to the garage to have a look at when they were changing the brakes who said it looked like the bushes but to see what it was like. Unfortunately is was exactly the same so I booked it in for the rear bushes which was Monday this week.

Since then its better but still not fixed but I'm not sure what to do next. I will ring the garage tomorrow as I trust them but I respect the views of people on the forum so want to we what you guys suggest.

It only happens when braking hard from high speed and is worse when downhill. I also get a slight wobble at high speed driving.

It doesn't feel like tracking or balancing but more to do with the brakes but I would doubt if I've warped them on a track day (I wasn't that good)
 
They could have warped if they're low thickness or you could simply have glazed them which may wear off. Or are you saying all discs have been replaced? Steering wobble would be front discs IMHO.
 
Have you checked your springs? I had the same, steering judder under braking, and pumping through the pedal. Transpired a rear spring had been snapped for a while and then went completely. Had not a single judder since replacing the springs. It must have been upsetting the balance /stability / abs.

Sent from my Galaxy Nexus using Tapatalk 2
 
I'd start by eliminating the classic of pad deposits on the discs.

Warm the brakes then on a long straight road brake from 60 to near zero without stopping. Repeat 3 times then drive until the brakes cool.

If not then given the use perhaps warped discs (which is actually rare), but frankly all sorts can do it on Zeds with their snsitive suspension from bushes to tracking to shock to bent rims. Bit of diagnosis and elimination
 
Thanks for the quick replies.

Just the rears were replaced after the track day but the fronts weren't done that long ago.

I will go for a few laps of the dual carriageway braking almost to zero and report back.

It sounds like I need to get it booked back in to get it checked again but I have a sinking feeling its going to be either new front brakes or rear springs :-(

How do I check the springs? What should I be looking for or will it be really obvious.
 
Grr taptalk isn't letting me upload my photos for some reason today. Either look through the alloy or if that's not possible jack the car up. In mist cases if you look closely at the seat where the spring rests on you'll see a lower coil snapped. In my case this had been the case for a while but I didn't know. Only because about three coils in one go went bang did I then look and see.

Sent from my Galaxy Nexus using Tapatalk 2
 
cj10jeeper said:
I'd start by eliminating the classic of pad deposits on the discs.
Click to expand...

Spot on - if you google the subject 95% of wheel judder is due to deposits on discs - ie you've got them super hot then come into the pits & kept your foot on the brake - this transfers a lump onto the discs casing unevenness wen braking & very difficult to remove.

I had similar issues that started out with a sticking sticking caliper which super heated the disc causing frightening wheel wobble.

Upgraded to 325mm rotors & shortly afterwards after an italien tune up session to really test them had some wheel wobble back again - then I found this http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

I didn't get them skimmed, just rebed them in again. On heavy use, I always apply the parking brake ASAP when stationary, never leave foot on brake & never had the problem return since

Best of luck
 
Funny enough Jembo the stop tech link is where I often point people.

Mentioned it to an XF owner last week who was adamant he had warped discs, but tried the braking cycle cure and bingo. Problem fixed.
 
might try this to see if i stops my rear brake whurring and slight judder in my thread (missed this with tapatalk in a 3g signal light area ).
 
I've been struggling to find a quiet road where I can bed the brakes in. I think I'll need to out in the middle of the night.

I've checked the rear springs and they seem ok.

Drivers
tamytuta.jpg


Passenger
ube2a2ud.jpg
 
Whist you are at it, do check that all your wheel bolts are properly torqued, because one of them a tad out of spec can also cause wheels to judder.
 
Z4 Coupe said:
I've been struggling to find a quiet road where I can bed the brakes in. I think I'll need to out in the middle of the night.

I've checked the rear springs and they seem ok.

Drivers
tamytuta.jpg


Passenger
ube2a2ud.jpg
Click to expand...

Try driving on the Aston Expressway at rush hour. 3 cysle of 60 to 0 then the road clears up
 
I drove a few hundred miles yesterday and it looks like it's a constant wheel wobble that is made worse by braking. :cry:

I'm booking it in today but would still like to know if this could be caused by brake deposits?
 
I've not chipped in until now, but for what it's worth I had a severe judder under braking from high speed and it turned out to be one of the bushes on the front, completely buggered. It had also somehow damaged my brake pads and - dare I say it in light of the above, though this is what I was told - buggered up the discs. I think I'd be checking all the bushes next - being crap at mechanical stuff that would involve a trip to my local indy.
 
Z4 Coupe said:
I drove a few hundred miles yesterday and it looks like it's a constant wheel wobble that is made worse by braking. :cry:

I'm booking it in today but would still like to know if this could be caused by brake deposits?
Click to expand...

'Could be' yes, but is be looking at wheels out of balance, buckled. Bushes worn, wheel bolt torque clean mating faces, etc.
 
Heavy braking and ABS can sometimes cause discs to warp. Replace them with new pads and problem is fixed.
If your going to continue enjoying track days then an upgrade would be best
 
cj10jeeper said:
Z4 Coupe said:
I drove a few hundred miles yesterday and it looks like it's a constant wheel wobble that is made worse by braking. :cry:

I'm booking it in today but would still like to know if this could be caused by brake deposits?
Click to expand...

'Could be' yes, but is be looking at wheels out of balance, buckled. Bushes worn, wheel bolt torque clean mating faces, etc.
Click to expand...

Have you checked you haven't got a sticking caliper - jack each front wheel and spin. If they both move freely, no issue, if there's resistance... it's a caliper & it's something that does happen. This will super heat the discs & cause the problems you describe. Those who attended Silverstone in 2012 may remember I had the RAC out infront of the world... bit embarassing, hey ho.
 
Thanks for the replies as it will make me look as if I half know what I'm talking about.

I've got it booked in for Wednesday. Fingers crossed its something cheap as its been an expensive month!
 
I've now had the car fully checked over and they say its pad deposits on the disks which is good news.

I've not managed to do the 6 stops from 60 but I've done about 500 miles of normal driving and its pretty much gone. I will do the bedding in procedure but its finding the right time and right road.

Thanks for all your help guys!
 
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