Slight brake issues

newbuild100 · May 24, 2017

Folks. Bike is a 58 plate GS 1200 (with ABS)
On braking at fairly low speeds on the front brake, im getting symptoms of a warped disc, (ie, feeling a slight pulse thru the brake lever for instance)
Not being sure if its one of the callipers or the actual wheel, ive swapped the wheel from a pals bike, and the problem isnt there. Therefore, its my wheel, not the calliper.

With my wheel back in, ive taken off the right calliper (hung it up out of the way, but still connected up etc), ridden the bike over a few yards and the problem is still there. Ive done the same with the left calliper and the problem goes away. Therefore its either the left disc causing the problem or its mountings or dare I say it, the "trigger" mech for the ABS. Whilst I havent had a DTI on the disc, a quick view with the naked eye suggests there doesnt seem to be any "warpage" (ill get a DTI on it tomorrow).
I guess a small amount of warping may be taken up by the discs bobbins anyway, which seem fine by the way !

Any other clues anyone ? (Apart from stealing my mates wheel back !!)

Alan R · May 24, 2017

It seems to me that you are methodically narrowing it down to either the left disc being warped or one or more of the pistons in the left caliper sticking which can produce symptoms similar to those felt with a warped disc. A dti will tell you the state of the disc: a visual examination of the pistons after a good clean may reveal corrosion. Have you recently had a tyre changed by a hamfisted tyre fitter who warped the disc? Have you recently fitted new pads and pushed corroded pistons back and damaged the dust seal?
Alan R

newbuild100 · May 24, 2017

Ive had several tyre changes over the years BUT this slight problem has always been there (Yes, only just getting round to looking at it !!)

If it was a sticking calliper/pad, then surely it would have done it with the other wheel in !!

Back to you folks !!

Pukmeister · May 24, 2017

It could be corrosion of the wheel beneath the disk mounting bobbins.

It could also also be an uneven build up of brake material on the disk face.

Try using some fine emery and brake cleaner to key up and clean the disk faces, then repeat your test.

newbuild100 · May 26, 2017

Folks. Right, I have access to a DTI now. On the right disc (Not the suspect one), the run out is 0.05mm . . . . . .according to Mr Haynes, thats within the service limit

On the left disc though (the suspect one), the run out is 0.15mm. ie 50% more than the suggestion by Haynes.
I think im looking a new disc.

However, given that (I think) there is some sort of "wave" washer behind the disc retaining bolt (and its possible to very slightly move the disc side to side, ie parallel with the wheel spindle if that makes sense), shouldnt those washers and that movement, take up any minimal runout of the disc ???

newbuild100 · May 26, 2017

Anyone ??

Pukmeister · May 26, 2017

You could try rotating and remounting the disk around the wheel to put the high disk points on the low mounting bobbins, then recheck with the dti. You might improve things enough. You could also clean up the mounting bobbins and wheel mounting faces.

Alan R · May 26, 2017

newbuild100 said:
However, given that (I think) there is some sort of "wave" washer behind the disc retaining bolt (and its possible to very slightly move the disc side to side, ie parallel with the wheel spindle if that makes sense), shouldnt those washers and that movement, take up any minimal runout of the disc ???

It doesn't sound as though they are doing. To think through what is happening, imagine what the movement of the disk if it were extremely warped: its more likely that the disk will move the pistons back than the pistons will force the disk to rock on the mounting bolts.
New disks and normal service will be resumed.
Alan R

DrFarkoff · May 27, 2017

N.B. Do not "abrade" the disc mount pillars Just a wire brush to clean the surfaces

Use plenty of heat to loosen the Thread Lock If you are unscrewing the disc mount bolts

It might actually be worth Undoing the disc and cable tying it back to the wheel spokes and measuring the height of the disc mount pillars in comparison to the Fork leg for example

My bike did this when I got it, a Calliper rebuild both sides and a good scuffing with 80 grit on discs has cured it thus far

Sgt Bilco · May 27, 2017

Pukmeister said:
You could try rotating and remounting the disk around the wheel to put the high disk points on the low mounting bobbins, then recheck with the dti. You might improve things enough. You could also clean up the mounting bobbins and wheel mounting faces.

Thats where the problem will be I suspect. I had this on and off for a couple of years and eventually narrowed it down to teh pillars which have corroded. I put on a new (to me) wheel and bingo, problem gone. Bear in mind my wheels had 140,000 pretty hard miles on them.

newbuild100 · May 27, 2017

I appreciate all the comments guys and will endeavour to look further into the isuue. However, still no real answer to my last question . . . .

"However, given that (I think) there is some sort of "wave" washer behind the disc retaining bolt (and its possible to very slightly move the disc side to side, ie parallel with the wheel spindle if that makes sense), shouldnt those washers and that movement, take up any minimal runout of the disc ??? "

Kenny Rodkiss · May 27, 2017

Swap your discs over and see if your problem swaps sides?

Santa-2512 · May 27, 2017

dont know if its possible,

could you take your discs off and place on a sheet of glass, use feelers at varing positions to see if you have a warp

newbuild100 · May 27, 2017

Yes could try all of the above. Thanks so far folks

DrFarkoff · May 27, 2017

Roxsters used very thin stainless shims between the disc bobbin and the Pillar

I have found that the pillars corrode as Chris says above and then the wave washer pushes the disc at the lower corroded bit

Search this BRA70217

newbuild100 · May 29, 2017

Well folks. I took the disc from the wheel and I have to say the wheel/pillars look perfect. The pistons/callipers seem spot on too.
I put the disc back on the wheel 180 degrees to its original position and the DTI showed the problem to be worse. I guess the only thing left now is to swap the discs over (as someone above suggested) and see if the problem switches sides !

I will have to get another T30 "socket" first though, the one im using is shite !

PS . .do you guys use the same bolts on rebuild or replace them after every time ????

Slight brake issues

newbuild100

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Alan R

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newbuild100

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Pukmeister

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newbuild100

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newbuild100

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Pukmeister

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Alan R

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DrFarkoff

Grumpy Ole Git!!!

Sgt Bilco

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newbuild100

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Kenny Rodkiss

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Santa-2512

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newbuild100

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DrFarkoff

Grumpy Ole Git!!!

newbuild100

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