Disc run out

Hi,
I have been puzzled by the amount of ineffective travel in my J's front brake lever. it seem to take up about 1/3 of the lever movement before the pads bite.

All the seals have been replaced both in the MC and slaves and new braided lines fitted. Still there is excess travel. No air in system. Even the local brake shop is mystified.

Someone suggested the rotors could be warped pushing the pads back too far. Is this likely and if so whats the remedy? One rotor is .13mm out of true,the other .25mm. Can these rotors be machined flat straightenedor are they scrap?

You would need to have the rotors ground if you want to get them back flat, I would suspect you still have some air in the system, I have played hell in getting brakes bled all the way

If your rotors were warped you should feel a pulsation in then lever as you come to a stop, the hotter the rotor gets the more it should pulsate. Also try checking the end of the lever that contacts the piston on the mc, is it worn down? Does the lever move back and forth as if there is a gap somewhere? I doubt if it is air in the system, try "pumping" the lever and see if it gets better. If it does there is air. Has this problem always been there or did it start after the work you did?

No pulsation on discs when braking. My measurement of run out was done with the dial gauge mounted on the floor. This may have introduced some inaccuracies.

So far I have:

had MC bore checked and fitted an new MC kit. With the MC hose outlet blocked off the MC is rock solid when the lever applied. So my conclusion was MC A OK.

All lines replaced with stainless braided. Both Calipers have had seals and pistons renewed.

System bled and bled and bled (reverse) Air unlikley!

Not much left?? All I notice is there seems to be a lot of caliper movement before the pads bite

However one curious factor. When I tried to remove the two sliding pins which hold the caliper in place (and allow a single piston operation) I had enormous difficulty getting them out of what is a blank hole. This was particularily true with the ones which seem to have an anti rattle plastic sleeve over them. Previously I had greased these pins.

Any possibility that greasing these pins creates a vacuum behind them, pulling the caliper away from the pads. Nothing in any of the manuals refers to them needing lubrication and I may have created a problem so doing?

One thing I aways do after I bleed brakes is to compress the lever and strap it down overnight. This makes the reamining bubbles in the lines rise to the top and when the strap is removed, they escape through the master cylinder (usually).

Another thing to check is to make sure that the holes in the bottom of the master cylinder (where the fluid enters and returns from the lines) are higher than where the top brake line bolts to. Air can get trapped in between the holes and the line if the top line is higher.
On bikes where the line is lower then the holes (clip on bars, clubman, etc, some LTD style bars.), I usually have to take the mastercylinder off (the bars) and mount it to a spare handlebar to get the holes in the bottom of the reservoir higher than the line. Sometimes you can get the holes higher than the line by turning the bars all the way to the left.

On the sliding pin, it is very easy to get the rubber seal pinched, causing the caliper to bind. They dont need alot of lube to work properly.

Fish

Fish,
thanks for you comments.

I have cleaned out the slider holes and removed the plastic sleeves which fit over the lower sliders. As usual these lower ones were a devil to remove as they seemed to bind in the holes.

Having removed these sleeves the brake action seems much more solid, with an immediate bite. I feel this confirms my view that somehow they were binding on these plastic sleeves as the caliper moved back and forth.

Now to find out whay I have a mystery click click click coming from the brakes.

Kiwiz wrote:

Now to find out whay I have a mystery click click click coming from the brakes.

Remove both calipers and spin the wheel( or just remove the speedo cable 1st). Sometimes the speedo drive clicks on its own (grease the speedo drive and cable, the cable is usually the culprit). Or you may have something in the tread of the tire tapping against the fender.

Replace each caliper, one at a time to isolate the clicking sound. This should get you looking in for the mystery click the right direction, instead of looking at the whole front end and wondering What? Where? Why?

Good luck,
Fish

Fish,
once again your comments 100% on target.

I dropped off the calipers but the noise was still there. Dropped the axel and regreased the speedo drive, reassembled and wow the noise was gone. I had obviously not correctly assembled something, perhaps electronic speedo drive lugs, but it still worked. Anyway noise is gone.

Still a little mystified what the little plastic sleeves over the sliders are. My Clymer says "friction boot". I have remove both of these so there is now no friction. Who knows how important these things are but I don't think having these removed will prove fatal. I have a feeling these boots were just cut off pieces of plastic hose not the original parts and maybe my friction was more like binding!

On my 76 KZ 900, It has 4 little rubber boots on the sliders for the calipers (2 on each side of the caliper mounting bracket sliders things). I think that they are more for sealing the slider from the elements. I would replace them with the correct parts to keep them from getting dirt, water, etc. in the sliding area and keeping the caliper from moving properly.

Fish

Fish,
I have the rubber boots on mine also which are used to keep water /grime from getting on the sliders. I have 4 on mine as well. However these sleeves I refer to are on the lower slider shafts only . The lower slider shafts are a different diamenter than the upper and are waisted on the section which fits inside the hole. It this waisted section where these plastic sleeves are. Maybe this is peculiar to a J as they do not show up on the parts book for earlier Z1's

Perhaps the sleeves have swelled? I'm not familiar with the J models, but if it was there from the factory, then there is a reason for it to be there.
Maybe others can chime in.
Fish

Kiwiz wrote:

Fish,
thanks for you comments.

I have cleaned out the slider holes and removed the plastic sleeves which fit over the lower sliders. As usual these lower ones were a devil to remove as they seemed to bind in the holes.

Having removed these sleeves the brake action seems much more solid, with an immediate bite. I feel this confirms my view that somehow they were binding on these plastic sleeves as the caliper moved back and forth.

Now to find out whay I have a mystery click click click coming from the brakes.

I think you might have internal friction on your pins. . .and the calipers are hanging up on them. . .

see if this thread:

link here

offers any assistance. . .