Warped Hub?

HelpThisDude

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When I bought the car, I knew the front discs were not right, I assumed warped.
I left it as it was, because I wanted to do the AMG caliper conversion.

Once fitted, I thought my cheap discs were warped again, as I had a very obvious judder braking from 40 mph and above.
With the wheel and pads removed, watching the disc against the fixed point of the caliper, while spinning by hand it was obvious the disc was not spinning true.

So I bought brand new MB discs and totally scraped the hub face clean. The New disc was offered up and secured on the torx screw. However, when spun in the same way, the same things happens.

With ONE pad in the caliper, it is even more obvious, as the disc rotates it bends hard up against the pad. Once rotated past the 'tight spot' the disc bends away and turns free. By eye, I would say the run out is > 1mm, which I believe is huge!
The Drives side is the same.

I also noticed that the pins that hold the brake pad spring in place had come loose, the passenger side pins had totally dislocated, and the pad spring had been catching the wheel ballancing weights!

Back to the issue... Can the Hubs be distorted?
 

Alex Crow

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in short it is unlikely. you really need a couple of bolts in to check the float, relying on that little bolt to hold the disk tight to the hub is not enough...
 
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HelpThisDude

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I like the location, 'super suffolk' :)
I understand what you mean about needing the disc firm against the hub face for 'end float' which is somthing like 0.02mm. Or to detect a disc a fraction out of true. But as I stated above, this is so obvoiusly out you can see it with your eye, without a DTI.
Anyway, something is obviously is bent. If not the Hub, then what would be likely? Head scratching now...
 

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Like Alexander said,, Just screw in two wheel bolts with a large nut or something to act as washers or packing,and I bet it will be OK
 

Alex Crow

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....or take the disc off and check float at the hub, then you will know for sure. if it is still looking warped it can only be the hub then, but i have never seen this on any mercedes.
 

Number_Cruncher

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If that corner of the car has had a whack, you might find a deformed hub, but, I would say that a bent spindle would be much more likely.

A good hub should not contribute more than about 0.1mm of run out at the outer edge of the disc, and, as we all know :), bearing end float should be about a factor of ten smaller still.
 

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and how would one go about setting up bearing end float george??

also, how can a bent spindle give disc run out? think about it, the spindle doesn't turn...
 
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OK, thank you all for your advice :)
Guess the chances of both hubs being bent is not likely!

I will let you know what I find, cheers all.
 
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I did the end float with a dial gauge when I changed the wheel bearing. The DTI magnetic base sits on the Hub face, and the dial piont is centered on the middled of the spindle. Bearing End float is read while pulling the hub and reading the deflection.

The spindle does not turn, but it is the axis for the hub to rotate on, so I guess it would have a factor...
 

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>>also, how can a bent spindle give disc run out? think about it, the spindle doesn't turn...

Calm yourself!, I didn't actually say that it did give disc run out.

What I was thinking was that the spindle is much much weaker than the hub, and, if the hub were deformed, then, you would also expect to see a bent spindle.
 
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I better check my credit limit..... :(
 

Alex Crow

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>>also, how can a bent spindle give disc run out? think about it, the spindle doesn't turn...

Calm yourself!, I didn't actually say that it did give disc run out.

What I was thinking was that the spindle is much much weaker than the hub, and, if the hub were deformed, then, you would also expect to see a bent spindle.

fair enough, i was surprised that YOU had made this mistake, turns out i had jumped to the wrong conclusion :Oops:
 

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I did the end float with a dial gauge when I changed the wheel bearing.

could it be then that the bearing cups are out of true? or not seated correctly?

my question about the end float measuring was directed at number cruncher, bit of a contentious subject around these parts. as is greasing wheel bolts, but forget i said that, mums the word ;)
 
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Had a Simpson moment....Just re reading the post and the penny dropped why a bent spindle would not cause run out.

Had a dial gauge on the HUB today, after cleaning it for about half hour with fine emery and scraper again. The hight spot is always in the same place, and the deflection on the gauge reads 0.15mm. I think that is OK?

I will throw on some New discs tomorrow and bolt them in with the wheel bolts as suggested, and then try the dial gauge.
Im assuming I will see the same amount or run out?
 

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Number_Cruncher

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0.15mm at the hub is about 5 times more than the permissible maximum values.

See;

http://forums.mercedesclub.org.uk/showpost.php?p=404006&postcount=17

This will, approximately, double up to be about 0.3mm of contribution from the hub, PLUS, any extra caused by the disc.

I'm sure you don't need me to tell you, but, be careful to make sure the probe of your dial gauge is reading on the flat of the hub, and isn't riding onto the chamfer on the circumference.
 
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HelpThisDude

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Number cruncher thank you for that buddy, I will re check and ensure the probe is not sat in a dip and riding off into the chamfer.... excellent point.
The Hub face is very pitted, and some of the pits are really deep. Im amazed how much surface rust came off..... never seen a hub face like it.
I'll give it another go.
Thanks again.
 
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Limited time today as I'm working tonight...
Decided I could not get a good reading off the hub and gave up.
Fitted the new disc and clamped it in place with 3 wheel bolts.
DTI fixed to two different fixed points, both time it reads 0.02mm, which is ok I believe.

I'm too Confused to be happy.

Gentle braking from 50/60&70mph proved there are no more vibrations.
I can only assume, that the rusted face on the hub caused the initial run-out, and vibration. The old cheap discs then distorted a fraction adding to the total run-out.
(I guess that the run-out result I got when checking the Hub was flawed, but I do love a good learning curve)

Thank you all again.
 

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Number_Cruncher

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>>it reads 0.02mm, which is ok I believe.

Yes, 0.02mm is very good.
 

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Too confused to be happy :D:D as number cruncher that is good
 

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ive seen many discs ruined because the hub face was not cleaned off properly, if at all. thats the garages bonus scheme for the mechanics for you. jobs done quickly but badly!
 


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