Deep goove on rear disk brake

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Player#3

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Hi,

I am slowly going over all parts of this new to me bike I have removed the rear disk as it has a deep groove on one side. It was quite rusty and very stiff to turn so I wanted to clean it up.

Here is a pictue of the bad side.
Deep goove on rear disk brake
https://www.dropbox.com/s/ycupr0lzifu9o ... 03_003.jpg
The other side is good and smooth.

Would you say that this goove is acceptable or should be be skimmed out ? The groove is right in the middle of the contact area for the breaking pad.

What is the opinion of my peers ?

Regards,
Sean
 
Hi,

I have no experiences with MK3 rear discs, but I can't imagine what can cause this damage. Looks very deep. Skimming is what I would do at least.
In case of doubt find a new or good used one.

Ralf
 
Do consider that about no matter what you do with it - it can't be as bad a risk as it is now with a good many miles evidence on it working good enough. Point being could just have it flattened, ie: hi areas removed and go with it as really truly rear brake is more a back up needed when going rather slow or in slicks not racing around, then it should lock up on a stab to save a hi side or supermotard slide turn. The thinner it gets the more prone to heat wrapage and maybe even cracking but again really truly just hot are ya going get rear brake unless switch backs in the Alps. Most reasonable cause of groove was not replacing pads in time, but also maybe something was throwing grit at that level and side or something got tangled around so pad dragged it into rotor. Spiral ordinary milling ain't as good of friction as the dual stone sideways milling but then again could ya even tell on the rear. Price a few rotors and ebay to help sway decision.
 
Replace it to be safe, your front brakes do all the work but still need good brakes on the back as working both brakes is the way to go, safety is alway the most important thing than trying to save a few $$$ and good brakes should never be a issue.

Ashley
 
Im sure there is a "Spec" on this site for minimun thickness of rear discs... ..Measure what you got (may have previously been skimmed).. Guesstimate the depth of groove (feeler gauge and steel rule) plus a bit more (.020).. If your within minimum thickness/width, then get it ground down, if not it will make a nice base for a standard lamp...
IMO, Brakes have to be as good as you can make them and on a stock MK3. Perfect brakes on a MK3 are just "adequate"....
 
Was thinking a stone stuck in the pad , then saw the picture .You could get a prize for a groove like that .

If you ride at 5.000.000 miles an hour & get it red hot , scrap it .

If you think 60 mph is really challengeing and occasionally manadge it , a light skim would improve things .

But useing it hard & heat soaked means suddenly , some day , when you least expect it , somethings going to happen , and it will probably be unpleasant . :(

So if youre not stuck for a buck , grab something better . May as well throw something fancy back there & cut down the weight . :D
 
It looks deep, a skim would just make the disc thinner so its either a new disc or leave it as it is and wait for the pad to bed in, once its bedded in it won't be long for a new set of pads ;)
 
That disk is junk in my opinion. You can't resurface the disk and still be in spec because that looks very deep.

Get a new one or look for good used one on Ebay.
 
I've had some experience with having my front disc Blanchard ground way back in the 70's and as I remember there is precious little meat to remove before you get to the minimum thickness listed in the manual. I agree that you'll need a new one with that deep a groove. Also there has to be a reason for the groove and I'd make sure that is fixed before ruining a new disc. (Mine had a stone imbedded in the pads.)
 
it seems to me that the cause of this, if you have opposed pistons in your brake calliper, one of your pistons is sticking, you might be able to skim the disc but the cause will remain.
 
Bernhard said:
it seems to me that the cause of this, if you have opposed pistons in your brake calliper, one of your pistons is sticking, you might be able to skim the disc but the cause will remain.
Click to expand...

Not sure that a stuck piston would cause this type of damage...they also are pretty easy to find since the bike will be very difficult to move (rolling). This looks like something got in there or the pad was completely gone and it was metal against metal...but the rest of the disc looks okay...so foreign object seems the most logical.
 
Hi Guys,

Just one day and a massive response to my question.
Thanks for all these quality replies.

I found several disc rotors on e-bay from 5 to 75 pounds. I was quoted 50 to get the old one skimmed and I am not sure the old one would be thick enough after skimming .

So it is clear I should go for a new one.

Thanks again.
Sean
 
L.A.B. said:
Towner said:
I can't imagine what can cause this damage.
Click to expand...

The damage was caused by somebody fitting an over-length caliper-to-carrier plate mounting bolt (the one nearest the wheel axle/spindle).
Click to expand...


Good hint !! He should check the bolts as well ....
 
Hi,

You were spot on. The end of the bolt was nice and shiny too and fitted perfectly in the groove it had made on the rotor disc.

Problem solved !

Many thanks.
Sean
 
Good call L.A.B. You must have seen that one before...wonder why they didn't hear the screeching grinding noise this would make?
 
Did the bolt keep coming loose , and he kept winding it it . :shock:
No wonder it seemed a bit hard pushing the Bike Around .
" Why is my rear brake sticking " . :x :oops:
 
I think it's fair to assume that the groove was cut in for clearance. At least that 's how it appears to me. :roll: :shock: :lol: :oops:
The word "damage" is relative in this regard. :?
But, being a MKIII thing, I will never assume. :x
Damn MKIII's! :evil:
 
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