ST1100 Rear Brake Disc Run Out

tim welsh

Joined
Aug 4, 2016
Messages
23
Location
wales
Hello all,
Some advice please. There is a judder noticeable on applying the rear brake on my 2000 abs/tcs st1100. I measured the rear disc run out (in situ, with a dti) and got 0.7mm. I believe the spec is 0.4mm maximum, so its pretty bad!. So I removed the disc from the wheel and checked it on a surface plate, didn't seem too bad , certainly not 0.7mm. I then checked the wheel surface that the disc is bolted to, again in situ with a DTI (dial test indicator). and got 0.4mm, i.e more than the spec! So the wheel disc bearing surface is out, and causing the disc to distort when bolted to it. Anybody else had this, and found a solution (apart from buying a new wheel!) . I wonder if there is a way of bolting a lathe tool to the swinging arm, and skimming the disc bearing surface on the wheel? Many thanks. Tim
 
If you can determine the high, or low spot on the wheel, could you not shim the disc (under the bolt holes) in that area to prevent the distortion?

Never heard of this problem before though. Usually just a warped disc.
 
Could you not rotate and bolt up the disc with the runout 180 degrees opposite of the hub runout, thereby offsetting the effect
 
Assuming that the wheel bearings are in good shape and the wheel is not bent my first suggestion before spending a lot of money and/or effort is to have a look at your calipers to make sure that they are not sticking at all and are moving freely on all of the slider bolts/pins. If the caliper is not free to move in and out then it cannot follow the variances in the disc as it rotates through the pads. If this is the case then the pistons have to move in and out to absorb these variances. This causes the shudder that is felt in the brake pedal/handle. The calipers are designed to follow the movement of the disc and absorb these variances. You might still have something out of spec. but it might not be noticeable in the pedal/handle if the brake calipers are moving freely. Easy to check and it costs nothing to do. If the calipers are fine then try offsetting as suggested above.
 
Tim,
How long have you had the bike, has this come on suddenly?
The disc mating surface will not have changed unless there's corrosion on the surface.
I think we need a bit more information but 0.7 is enough to notice on the pedal for sure.
Upt'North.
 
tim welsh said:
I wonder if there is a way of bolting a lathe tool to the swinging arm, and skimming the disc bearing surface on the wheel?
Click to expand...
That seem very unlikely to me although in a perfect world it might be the most accurate solution. If you ignore the fact that in a perfect world there would be zero runout.

Maybe both the disc and wheel bearing surfaces could be trued on a mill. I didn't realize warping is also referred to runount as in lateral runout. It does sound better that 'warpage'.
 
Last edited:
Bush said:
If you can determine the high, or low spot on the wheel, could you not shim the disc (under the bolt holes) in that area to prevent the distortion?

Never heard of this problem before though. Usually just a warped disc.
Click to expand...
Thanks for reply. Shimming seems a good idea, i've ordered some brass shim and think i'll try this first. Doesn't involve removing metal I cant replace!!
 
Bmacleod said:
Could you not rotate and bolt up the disc with the runout 180 degrees opposite of the hub runout, thereby offsetting the effect
Click to expand...
The disc tends to warp in a different place and conform to the disc flange on the wheel (which isn't "true") when its bolted down, so two wrongs don't make a right!
 
Upt' North said:
Tim,
How long have you had the bike, has this come on suddenly?
The disc mating surface will not have changed unless there's corrosion on the surface.
I think we need a bit more information but 0.7 is enough to notice on the pedal for sure.
Upt'North.
Click to expand...
Thanks for reply.About 8 years. Its done about 80,000m. It just got worse gradually. Theres no corrosion on the mating surfaces. My readings show that the mating surface HAS changed and varies by 0.4mm. There are a series of variations to this maximum, each "section" of the 6 segments (with a bolt hole in each) varies by up to that maximum. In other words its not just one min/max in 360 degrees rotation. I think the wheel hub casting distorts eventually with age/ heat.
Its going to be impossible to get the runout with in the 0.3mm spec, if the wheel is out by 0.4mm, even if I use a new disc.
 
ST Gui said:
That seem very unlikely to me although in a perfect world it might be the most accurate solution. If you ignore the fact that in a perfect world there would be zero runout.

Maybe both the disc and wheel bearing surfaces could be trued on a mill. I didn't realize warping is also referred to runount as in lateral runout. It does sound better that 'warpage'.
Click to expand...
Milling seems an option. Might try the shims first (see above).
Isnt Warpage something to do with ropes?!!!
 
Strange about the wheel but you know its history and dial gauges don't lie. I suppose the wheel might have always been out but now the disc is out as well you can feel it at the pedal.
I think the shims, although they might try your patience could work as long as the disc is still snugged up.
Nothing ventured, nothing gained. Or some nonsense like that.
I think unless you have access to cheap milling a new disc/wheel could be easier and cheaper. Obviously new/used.
Good luck.
Upt'North.
 
Andrew mentioned Wheel Bearings which could cause the problem.
Perhaps that is where to start. I doubt the casting is warped from age.
 
Slydynbye said:
Andrew mentioned Wheel Bearings which could cause the problem.
Perhaps that is where to start. I doubt the casting is warped from age.
Click to expand...
I replaced the wheel bearings last year, and they are as new. No "play" detectable at wheel rim. Caliper is regularly checked and serviced, all sliding pins etc ok.
 
Hi,
Thanks to all who replied.
Thought I'd bring things up to date. What I ended up doing was putting the wheel in place without the disc, marking all the high spots on the disc mating face, then whilst checking with a dti, and using a sanding disc in an angle grinder, sanding the alloy down until I got a reading of runout of nearly 0 all the way round the mating face (was 0.4mm max). I then bolted the disc back on and checked the runout on the disc outer edge. It was now 0.3mm!! (Just about on spec, and a lot better than the 0,7mm I had before).The disc is used, but is still 6.8mm thick , so still a bit of life in it.
So I can only say to those who have a large runout figure on their discs, check the wheel first before buying a new disc?
 
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