Braking problem

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jbraz7

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I have a 1990 Yamaha Vmax and it used to not do this but recently, the front wheel as started like bouncing almost when I brake and the slower I get the slower the bounce gets. Also if I brake and it bounces and if I let off and then brake again it stops doing it for a little bit then starts again. It only does it on the front brake and front wheel. Does anyone have any suggestions on what it might be? I checked my rotor width and it was still in tolerance I believe.

Thanks!
 
Hi 7,

Could be material transfer from the brake pad to the rotor. Give the pads and the rotor a good sanding and wash down with brake cleaner. Check for a lost wheel weight??
Lew
 
Last edited:
I was thinking a warped rotor too. can I check that with a straight edge? or how would you go about checking that?

The wheel weight was still on in the correct spot.

I think im gonna give the sanding and a good cleaning a try.

Thanks.
 
I was thinking a warped rotor too. can I check that with a straight edge? or how would you go about checking that?

The wheel weight was still on in the correct spot.

Before checking the disk confirm the following:

  • The wheel balance is still correct (and yes, I know you say the wheel weight is still in place)
  • The fork oil volume is correct and has been replaced since Sinatra was at #1.
  • Head bearings are correctly torqued.
If it is a disk related issues there are four things you need to consider:

1) Have the disk's glazed? Unlikely to cause judder, more likely noise.
2) Are they sitting square on the wheel flange. Unlikely to be the issue unless you have recently taken them off or replaced them.
3) Disk run-out.
4) Disk thickness variation.

3 & 4 can cause juddering. With 3) The calliper pistons get pushed in on one side but the opposite pistons come out. Therefore you need a (relatively) large distortion to cause an issue.
Conversely, with 4) both pistons are pushed out thus less variation will give rise to judder.

On that basis I would check both.

For a quick run-out check lift the front wheel and arrange a pointer so it I within (say) 1 mm of the wheel.
Spin the wheel and any warping will show as a variation in the gap between your pointer and disk face.
Accurate check: use a Dial Test Indicator (DTI) to measure any run-out.

For variation a micrometer is needed (vernier callipers are best avoided in all but a brand new disk because as the pads wear the disk it will leave a lip which most callipers can't bridge. It is the swept area of the disk you are measuring).

Maximum run-out is 0.15 mm (vented type ) and 0.3 mm (solid)
For thickness variation <0.008mm

If you want to become a brake Guru then you could do worse than committing this to memory. Pages 30 & 31 are particularly relevant.
 
The disk's were glazed pretty badly, and the calipers were full of brake dust. I cleaned the rotors then hit them with some 2000 grit and cleaned them again, and I cleaned out the calipers. It has mostly gone away but I can still feel it a tiny tiny bit so I feel theres probably some disk variation now like you said Steve. I'll go measure them today. Thanks guys!
 

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