brake judder

[(RIP) pastyman]

Out on the RT yesterday, great ride on a wide selection of roads. have to say what a great bike. unfortunately I noticed a slight judder on the front brake. not bad but just sort of spoilt the feel. I did a bit of a check on the discs but could not find any sign of warping but my check was pretty rough.
could a sticking piston cause any judder? or is there a better way of checking the discs.
The bike has twin brembo discs. the pads are almost new. any ideas?

 

[fayeslane]

ABS cutting in?

 

[newbuild100]

You could check the wheel and the discs with a DTI. (check discs to see if they are warped and for even thickness across and around their surface)

What about tyre pressures and wheel balance. ?????

Wheel out of true. ????

What model is it exactly

 

[Beemerboff]

Give the disks a good clean with a SS scouring pad before you spent too much money

 

[Kritou]

This may be of interest ....... http://www.ebbo.org/front_brake_fix.php

 

[Redboots]

Head bearings need adjustment

John

 

[(RIP) pastyman]

You could check the wheel and the discs with a DTI. (check discs to see if they are warped and for even thickness across and around their surface)

What about tyre pressures and wheel balance. ?????

Wheel out of true. ????

What model is it exactly

THANKS. iT IS A 1990 r100rt, and a very nice well kept one to. Jabba had it before I twistd his arm. The tyre pressures were checked before the ride so ok. no sign of judder at any speed with the brakes off and even when cornering hard, so I think the wheel balance and condition is good. brakes work well and are quite powerful, much better than the GS. the judder can be felt from slow to moderate speed with gentle pressure applied.
I am also pretty sure the head bearings are fine. So what is a DTI.
dont really want to buy two new discs so it sounds as if I will have to give them a clean and have another look at them, maybe check that all the pistons are free and working.
Thanks for the suggestions.

 

[brassmonkey001]

THANKS. iT IS A 1990 r100rt, and a very nice well kept one to. Jabba had it before I twistd his arm. The tyre pressures were checked before the ride so ok. no sign of judder at any speed with the brakes off and even when cornering hard, so I think the wheel balance and condition is good. brakes work well and are quite powerful, much better than the GS. the judder can be felt from slow to moderate speed with gentle pressure applied.
I am also pretty sure the head bearings are fine. So what is a DTI.
dont really want to buy two new discs so it sounds as if I will have to give them a clean and have another look at them, maybe check that all the pistons are free and working.
Thanks for the suggestions.

DTI Dial Test Indicator. Useful bit of kit.

Here's one googled at random:
ebay

Not a bad price at all, I might get one myself.

Very useful for determining TDC and suchlike.

 

[(RIP) pastyman]

That looks OK and I wouldnt mind getting one but how easy is to use. Ive never even seen one.

 

[brassmonkey001]

That looks OK and I wouldnt mind getting one but how easy is to use. Ive never even seen one.

Piece of wee-wee.
Attach the magnetic base to your fork leg, adjust the arm so that the spring-loaded pin of the DTI is touching the side of your disc and is under pressure, set the dial to zero then turn your wheel and watch the dial. The needle will wave back and forth and tell you how warped your disc is and where the worst warp is.

Here you go:

<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/H_1ySs7liS4?fs=1&hl=en_GB"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/H_1ySs7liS4?fs=1&hl=en_GB" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>

 

[steveo]

have you had the bike long, or has it been standing a while? run it every day for a week,using the brakes hard when you can, thats sorted similar probs on bikes ive had, good cheap option

 

[John Roberts]

Have the discs been repalaced with cast iron ones? They rust after a run in the rain but this thin layer soon gets wiped off by using the brakes on the next run. On the other hand if the bike is left unused for a while this layer gets a firmer hold and if the process is repeated due to infrequent use you can get a build-up of this rust which eventually produces brake judder such as you describe. I got rid of this layer with emery cloth and then used the brakes harder for a while to fully clean it off.

To be honest I'm not sure if it was absolutely necessary to emery it off initially, but I think I'd read somewhere that if you try to get rid of it by just braking hard then the rust layer (which is simply one type of oxide of iron) is converted to another type of oxide by the high temperature generated by the hard use of the brakes and instead of getting wiped off it just forms a harder layer. Myself I'm not at all sure that you would reach sufficently high temperature on the road for this to happen but rather than risk ending up with these harder patches of oxide I used emery to clean them up before things got too bad.

Having said all that I won't be changing back to the original stainless steel discs, pretty though they were; the cast ones work so much better. Nor do they crack between the drillings or develop grooves between the drillings.

 

[Flipfly]

Got no judder on Bertha

Mind you, there's no brakes either

Hope you get it sorted pops

 

[(RIP) pastyman]

The judder I get is not baqd enough to be a worry but just a feel that sort of spoils an otherwise great ride. I took the pads out today and cleaned things up and made sure all the pistons were working. Just by a visual check there did seem to be the very slightest wobble on the offside disc but whether that is enough to make a difference I dont know. Guess I will just haveto try the old girl out again.