Diagnosing brake disc/hub not spinning 'true'/wobbly...

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TeddyRuxpin

MB Enthusiast
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Joined
Jan 10, 2019
Messages
2,369
Location
Cardiff / London
Car
2x E350 CDI Sport W212s... for a bit
Hi all,

Recently did a lot of work on the car:

- Gearbox service & map
- New rear ARB drop links
- All front control arms (both sets) and ball joints replaced
- Front tie rod ends
- 4 wheel hunter alignment
- Brake fluid flush & MOT (no advisories) @ MB specialist/indie
- Fitted 17 Winter wheels

All Lemforder parts. No wheel balancing issues.

Problem: the front right wheel/disc does not spin freely when lifted off the ground - it ‘catches’ at a certain point, and then is easier to rotate for half the turn. Problem persists with 2x different wheels. I discovered today that the brake disc has a 'wobble' to it.

Real world side effects are subtle - very slight judder in the steering wheel at 65+mph and a very very quiet ‘whoosh’ of the sticky point as the wheel the wheel spins once per rotation at slow speeds. I don’t have judder when actually braking. Also for years, the car's brakes would 'jam' when the car's been wet and left for a long time and you'd need to accelerate hard to break it free, so I think this issue predates the work I've been doing.

The W212 had just sat for about 6+ weeks - please don't mind the rust on the discs, I moved it a little but ultimately it needs a good drive to clear the discs and pads. Today I discovered that:

1) The slider pins are really seized. I could hit them with a hammer and move them about but they both don't move freely.

2) I couldn't remove the actual pins/sliders inside the rubber boots so that I can re-lube them as I'm unsure how to get them out without destroying the rubber boots. No obvious cracks in the rubber. I will have to simply be more forceful. Hard to do when the caliper is hanging in mid air from a hook, though.

3) Spinning the brake disk with the caliper and pads removed, there is a bit of wobble on rotation of the disk. I've recorded a video showing this below. Is this an acceptable level or should it be completely 'true'? There is no play in the hub/bearings when I try to shake it from side to side.

My questions are:

1) Any tips on removing the seized slider pins?
2) Is the 'wobble' acceptable/normal and could the issue be caused solely by the seized slider pins? I assume not, I am thinking that there are two issues.
3) What do you think would be the most likely cause of this 'wobble'?

When swapping out the control arms, I removed the brake disk and hub from the strut. Could I perhaps have incorrectly torqued the two main bolts that hold the hub to the strut? I will double check this of course...

Any other thoughts would be welcome, thank you!

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There is very likely a small particle of grot between the disc and hub. Remove the disc and scrupulously clean the mating surfaces, and I mean scrupulously. Accept nothing less than operating theatre clean.

The sliding pins are a different problem which will need addressing immediately.
 
I will be removing the disc soon and checking that it's true, as well as checking for rust behind it, between it and the hub. An MB indie fitted these a couple of years ago, they are OEM discs and pads.

@Stratman - I hope that's the issue - thank you!

I am guessing though that running like this since they were installed is probably not going to be good for the pads/discs. The pads weren't noticeably different thicknesses.
 
With a runout like you have you would have definitely felt it when breaking ,if it was like that before carrying out the work.

A piece of debris behind the disc on re-assembly would be my guess.

If i am honest they look as if they are not far off needing replaced , so if you are going to remove them anyway then if funds permit i would be replacing them.

K
 
That’s far far too much runout. You usually would be measuring for a fraction of a mm using a DTI to check the play on wheel bearings and runout on the discs, you can see a good amount of runout just with a naked eye.

Most likely debris/rust between the hub and disc, which as said you might as well replace if you’re going to that trouble. Needs cleaning up to be 100% spotless and flat before reassembly this time :thumb:
 
They look worse for wear because they sat for so long and then I moved the car back and forth a bit, but they aren't bad.

Just to be clear, I did not remove the disc with recent work. I removed the entire hub 'unit' from the strut. The disc hasn't been off since the indie put it on. You can see here:

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Before I did all the work listed in the original post, the car didn't noticeably judder, but then there will have been so much play in the tie rod ends and control arm rubber that I'm guessing that vibrations were more 'hidden' and are now revealing themselves. Either that or I buggered up reassembly!

The pads have always 'stuck' when wet and left for a few days, though.

I would've taken the disc off today but I couldn't get the caliper bracket bolts off without turning the wheel but I only had one wheel in the air today... oh and another cold snap is coming... great!
 
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I think you need to pop the disc off and check for runout in the hub then 👍

It doesn’t look right, far too much runout in the first video.
 
Just checked and the pads and discs are 3 years or ~30,000 miles old, fitted @ TM Motors in SW London (MB indie)
 
Finally found time to get the disc off. Lots of mini ‘mountains’ of rust everywhere. You can see it especially around the edge of the hub. Don’t think anybody who’s changed the discs has ever bothered cleaning anything. Spent some time with wire brushes (chipping away with a screwdriver on the big bits on the rear inside of the disc) and attached pics of before/after. I’ll probably be giving it another once over tomorrow and reinstalling everything, both surfaces can probably be 5% better.

The hub itself seemed to spin true, although not the easiest to tell. The disc itself seems to lie flat on a flat surface.

I’m hoping to clean and reuse the disc and pads (wear superficially looks even on pads), grease everything, along with new slide pins and boots. Bit annoying that I at least have to do the other side too, just for the sake of completeness. Should be quicker next time.

Fingers crossed….
 

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Finally found time to get the disc off. Lots of mini ‘mountains’ of rust everywhere. You can see it especially around the edge of the hub. Don’t think anybody who’s changed the discs has ever bothered cleaning anything. Spent some time with wire brushes (chipping away with a screwdriver on the big bits on the rear inside of the disc) and attached pics of before/after. I’ll probably be giving it another once over tomorrow and reinstalling everything, both surfaces can probably be 5% better.

The hub itself seemed to spin true, although not the easiest to tell. The disc itself seems to lie flat on a flat surface.

I’m hoping to clean and reuse the disc and pads (wear superficially looks even on pads), grease everything, along with new slide pins and boots. Bit annoying that I at least have to do the other side too, just for the sake of completeness. Should be quicker next time.

Fingers crossed….
What ? Those discs are scrap .
 
As an aside . I log on pretty much every few days but this is the first time I have seen this thread that was posted over16 days ago .

Where has it been all that time ?

My first instinct when logging on is to click on 'new posts' just to see whats going on.

Since this thread started I have probably clicked there a 100 times. Why do I only see it for the first time today ?

Just asking
 
I will be removing the disc soon and checking that it's true, as well as checking for rust behind it, between it and the hub. An MB indie fitted these a couple of years ago, they are OEM discs and pads.

@Stratman - I hope that's the issue - thank you!

I am guessing though that running like this since they were installed is probably not going to be good for the pads/discs. The pads weren't noticeably different thicknesses.
" A couple of years ago" means not a lot. How many miles have they done, and it what circumstances is the real question
 
As an aside . I log on pretty much every few days but this is the first time I have seen this thread that was posted over16 days ago .

Where has it been all that time ?

My first instinct when logging on is to click on 'new posts' just to see whats going on.

Since this thread started I have probably clicked there a 100 times. Why do I only see it for the first time today ?

Just asking
Cause he just updated the thread today
 
I know what you saying Jase , but I should still have been 'aware' of this thread without having to wait for the OP to updated it .

I have seen this 'trend' a few times on here . For example , I will see a thread completely new to me pop up that turns out to be weeks old ?? 🤷‍♂️
 
The reason the discs look a bit worse for wear is because the car sat for 2+ months and there was a superficial rust build up on the surface. I then only moved the car a few feet and the pads didn't take off all the surface rust, and I've had my dirty hands and dust all over them, so they look worse than they really are. It's on my table right now and looks fine to me. They've done about 30k miles, as I said above.

There is very little lip 0.66mm per side, measured with a vernier gauge.

My aim is to clean the mating surface of the disc and hub and put everything back - if there is an issue, I will replace the disc and pads. However the issue I had in the first place was not with the braking action of the car, it was the fact that the disc was not sitting flush on the hub and causing a a vibration at about 70mph. There was no issue with braking and in fact the car did not judder under braking.

I don't know why you haven't seen this thread before... I don't use the 'new posts' feature, I generally pop into specific forums.... helps me stay away from the 'off topic' forum...
 
Those discs look pretty much toast. Not the lip on the edge but they look badly scored, coupled with the fact that they’ve been run out of true on the car and that they’re already well used I would just replace them :thumb:
 

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