Front Wheel Spindle

[BoxerCup R]

What a bloody nightmare you are having Humbug, I feel for ya Mate. Fair play to ya for keep changing discs etc time and again. I hope you get to the bottom of the problem soon and can once again enjoy riding your bike without any pulsating/juddering from the brakes :thumb left:

'Thrupence Ha'penny', as much as that

[boxerscott]

Interestingly, Simon from this forum mentioned to me that he experienced a similar slight pulsation from the front brakes and the cause of his issue was that the hub posts that the discs mate against were worn. On fitting new discs it may not have been an obvious to look for. So if new disc was torqued up against a worn hub post then this would cause disc warp. I believe Simon told me he fitted some fine ss washers to smooth things out. ??

It sounds plausible to me.

Chris

[simon]

Interestingly, Simon from this forum mentioned to me that he experienced a similar slight pulsation from the front brakes and the cause of his issue was that the hub posts that the discs mate against were worn. On fitting new discs it may not have been an obvious to look for. So if new disc was torqued up against a worn hub post then this would cause disc warp. I believe Simon told me he fitted some fine ss washers to smooth things out. ??

It sounds plausible to me.

Chris

What fixed it for me was a new(er) wheel with unworn posts and good bearings. Old wheel had 40k miles and could see that disks had worn an oval on the posts and the disks rattled. Tried putting old spring washers on top of the posts which helped a bit until they moved. Motorworks do washers to go between posts and disks (possibly standard on later models).
Given you appear to have replaced most of everything, what about the fork legs... the mounts for calipers maybe?

[Humbug]

I had thought about the fork legs but the cost of them would push the repair bill beyond economical. You are right about the mounting posts which is why I changed the original wheel. They seemed corroded past the point of being flat so that was the second move after the calliper overhaul. We will see what happens to the replacement discs when fitted with all the other changes. I can't detect any play in the bottom ball joint so fingers crossed. The braking is normally fine for a few hundred miles with new discs which suggests binding, heat build up followed by warping so I am hoping the replacement callipers with new discs will do the trick. I'm at a loss as to anything else that doesn't break the bank or my fragile spirit.

[Humbug]

Just had a suggestion from someone that might warrant some of your thought on this issue. He mentioned that on some bikes he had worked on, the issue was the master cylinder. Seems that the master cylinder was faulty preventing all of the fluid returning which in turn stopped the pistons in the callipers releasing causing the disc to heat up and warp.
Thoughts welcomed

[dave the german]

I suppose that would cause the problem. It doesn't appear that a rebuild kit is available for the master cylinder. Are the discs hot to touch after a ride? or maybe brake hard and ride for a short while and see if they're still hot?

[Humbug]

Just fitted new discs and with the wheel suspended its tighter to rotate than I would want it. I imagine it would get hot if I rode it now like this. Would it make any difference if the brakes were bled with the pistons pushed completely back in rather than out a bit? Can't see that it would but read somewhere that the pistons should be right in when bled. Surely there would not be so much fluid that the system was pressurised at all times? The reservoir is not completely full. My brain hurts at the moment.

[GerryB]

I had a similar problem , but mine was easy to fix. It appeared about 100 miles after fitting new brake pads ... (EBC)

Dumped them and fitted Goldfren ( I'm partial to them from racing days) and problem disappeared .

[dave the german]

Just reminded me that I had a similar problem with my mountain bike (avid brakes - usually cause some problems if not bled right). Solution was to crack a bleed valve open and push the pads all the way back then nip the valve up and that was it. But I suppose this really just points to too much fluid which yours doesn't appear to have

[Humbug]

Just ordered a replacement master cylinder which I'll get fitted when it arrives. I can see the logic in the pads staying in contact if the fluid cant return to the cylinder properly. As a little test, I pumped the brakes a few times, left them a minute and then cracked each bleed valve on the callipers. Fluid came out under a bit of pressure, enough to make bubbles at the end of the tube which would indicate that the fluid is remaining under pressure rather than returning properly to the master cylinder. Tried EBC, Brembo and Goldfren pads with the same result over this trying and worrying time. Just reluctant to give up and let the bas***d beat me.

[dave the german]

Just a thought but you say you replaced callipers. I was looking for a set to get refurbished for when I get a paint job on my 12s and thought I’d found a pair - looked identical to mine but were for an RT. Could there be the slightest chance you have the wrong callipers?

[boxerscott]

Re the master reservoir piston. if this has corrosion on it then it may not move as freely as it should. If the wheel spins freely when you have physically pushed the caliper pistons back then it does not having applied the brakes and released then there may be some logic in that theory. I am thinking that if it were the case you would notice re the bikes handling before damage was done to warp the discs? WAPITA!

Chris

[Humbug]

Just a thought but you say you replaced callipers. I was looking for a set to get refurbished for when I get a paint job on my 12s and thought I’d found a pair - looked identical to mine but were for an RT. Could there be the slightest chance you have the wrong callipers?

I suppose that is a possibility although this is the second pair of replacement callipers. These were from James Sherlock and apparently came directly off of a 12S. Both sets had the same issue but I am going to check against the originals.
The wheel spins beautifully with the pistons pushed back, but then once the brake is applied, there is more friction than is normal. The wheel will not move freely at all and when rotated stops as soon as you let go with absolutely no free movement.
I think the next move will be to route straight from the master cylinder to the lower fork brace doing away with the ABS to see if that has an effect if the master cylinder doesn't solve the issue straight away.
Does anyone lube their calliper pistons at all? If so, with what? Heard that most things will degrade the seals except brake fluid.

[dave the german]

you can use brake fluid or red grease - it doesn't take much. If you need some let me know. Got a big tub of the stuff. It is starting to point to somewhere further up the system though. Mine hasn't got ABS so I can rule that output do you not need a GS911 forABS bikes?

[Humbug]

Thanks for that, I have just checked them and they are nice and free. New master cylinder fitted and original levers fitted as some after market ones can cause issues. Bled through ok with cable tie on overnight to release air. I have never had an issue with bleeding through without GS 911 although opinion is divided on the net. Jason of JDS (Race mechanic for Dan Hegarty prior to his tragic accident) has also changed the fluid on the bike with no issues. Never exactly found out what the GS 911 does in relation to the ABS, presume it must activate valves to allow all fluid to be flushed from the ABS pump. Just need to test once the rain starts to see what is going on. Also got to clean the coating off of the new discs. Not used Brembo this time.