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Front brake binding


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#1 muddy

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Posted 05 December 2007 - 02:14 pm

I'd be grateful for any advice at all on this as it's doing my nut in.

A couple of weeks ago I gave the front callipers a clean, as my brakes had been binding. I cleaned gunk of 2/3 of each piston, but did not take the pistons fully out as I didn't have new seals to put in should I damage them. The pistons moved reasonably freely, so I put everything back together and then bled both discs in turn.

I used a Mityvac type vacuum pump to pull the fluid through, but found there were a lot of air bubbles and the vacuum didn't hold. So I took the nipples out, put plumber's tape on and a bit of grease. This seemed to seal the nipples and I got a constant vacuum reading. On the nearside I managed to pull clear fluid through, but on the offside I got a constant stream of tiny, pinhead size bubbles. I kept on topping up the reservoir and pulling fluid through, but still the stream of bubbles came through.

Fed up, I stopped bleeding them and tested the brakes. They felt good, and just running around the block they were fine, with no binding. But next day, the brakes were rock solid after a short run and the disc red hot, so I had to nurse the bike back home. I've now done this a few times with the same results. As well as that, I tied the lever up over night to encourage any bubbles to rise up and out of the lines, but to no good effect.

Any ideas at all would be well received. I've put so many hours into this, superficially, simple job and it's getting me down sad.gif

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#2 bcristian

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Posted 05 December 2007 - 02:30 pm

Did you see any signs of fluid leaking anywhere along the hoses, the joints (e.g. at the union above the front wheel - if you have one), or the calipers?

#3 TonyDevil

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Posted 05 December 2007 - 02:40 pm

QUOTE(muddy @ Wed 5th Dec 2007, 01:59 PM) <{POST_SNAPBACK}>
but on the offside I got a constant stream of tiny, pinhead size bubbles. I kept on topping up the reservoir and pulling fluid through, but still the stream of bubbles came through.

mine did this while bleeding them, it was air trapped in the double banjo bolt thing at the M/C
took me 4or5 litres of brake fluid before i worked that one out

ps. do you have standard calipers or bluespots? standard lines or braided?
where abouts are you located as i have 2or3 sets of spare original calipers sitting in my shed (dont fancy messing around posting them but could deliver/collect)

"Never argue with an idiot. They just bring you down to their level and beat you with experience"
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Black 1991 850 MK1, 160k+ miles(ish, best guess really, gave up trying to keep count after 3rd set of clocks and 3rd engine), PilotRoad2 tyres, custom stubby exhaust system, bluespot calipers & goodridge braided hoses with dunlopads, maxton forks, Ohlins shock, kedo handguards, stainless TDM grill, Scottoiler with lubetube & dual nozzle thingy, Givi Wingrack2 with E45 & 2xE36s, renntec crash bars, Autocom with blueteeth & PMR radio, TomTom Rider2, Optimate IIIsp, Bagster tank cover, anti-dazzle coating
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to fit : led brake light strip, replacement heated grips

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#4 muddy

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Posted 05 December 2007 - 03:04 pm

No fluid leaking as far as I can tell.

I've got blue spots and standard lines Tony.

Bloody hell, 5 litres of brake fluid, must've cost a bomb.

As far as the double banjo's concerned I'll have to nip down and have a look. What had happened, was there air trapped in the banjo's and how did you resolve it?

Thanks for the offer of the calipers, that's kind of you, but lets see, I hope it don't get that far.

Edited by muddy, 05 December 2007 - 03:19 pm.

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#5 TonyDevil

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Posted 05 December 2007 - 03:16 pm

QUOTE(muddy @ Wed 5th Dec 2007, 02:49 PM) <{POST_SNAPBACK}>
No fluid leaking as far as I can tell.

I've got blue spots and standard lines Tony.

Bloody hell, 5 litres of brake fluid, must've cost a bomb.

As far as the double banjo's concerned I'll have to nip down and have a look. What had happened, was there air trapped in the banjo's and how did you resolve it?

loosened em, i gave em a wiggle, just watch out for fluid drips sad.gif

luckily, most of that was just me recycling what i'd bled
not bad considering that was my first ever attempt at bleeding brakes

"Never argue with an idiot. They just bring you down to their level and beat you with experience"
My TDM :
Black 1991 850 MK1, 160k+ miles(ish, best guess really, gave up trying to keep count after 3rd set of clocks and 3rd engine), PilotRoad2 tyres, custom stubby exhaust system, bluespot calipers & goodridge braided hoses with dunlopads, maxton forks, Ohlins shock, kedo handguards, stainless TDM grill, Scottoiler with lubetube & dual nozzle thingy, Givi Wingrack2 with E45 & 2xE36s, renntec crash bars, Autocom with blueteeth & PMR radio, TomTom Rider2, Optimate IIIsp, Bagster tank cover, anti-dazzle coating
to fit : led spotlights, heated grips, new braided lines and rear caliper that actually has bleed nipples
Silver-ish 2003 900, 70k miles, PilotRoad3 front tyre (new@65k) & PR2 rear(new at 69k), Renthal 755 bars with KTM handguards, oxford unheated grips, power commander 3usb, scorpion titanium exhausts, standard screen with vario winglet thingy, stainless grill, oem centre stand, bagster tank cover, givi monokey topplate mounted on grabrail with V46 topbox, Givi PL pannier rails with E21s, crash bungs, mirror extender thingys, Halfords Advanced Laser Blue brillance bulbs, 21w led spotlights, touring scottoiler with leehenty dual nozzle, Autocom with blueteeth & PMR radio, TomTom Rider3 Urban, winter style anti-dazzle coating
to fit : led brake light strip, replacement heated grips

current rides : TDM850 3vd/mk1=tourer&scratcher, TRX850=weekend twisty toy, 2003 TDM900=commuter, 2005 
TDM900=unmolested.  Gone but not forgotton : XTZ750=overland touring toy, GS500e, GS125
If a strange looking truck driver honks at you & gives you the thumbs up, its could be me  :good:


#6 Sparky

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Posted 05 December 2007 - 04:59 pm

For the binding problem, if the pistons are nice and free, then I would suggest removing the pads and cleaning the caliper bracket out, then grease the rear faces & backplate edges of each pad and replace. I just replaced my rear pads and although they weren't binding, there was quite a lot of corrosion inside the caliper bracket, causing the pads to stick fast - maybe you have the same problem?

One other cause of binding is hoses which have perished internally - a flap of rubber peels away inside the hose and acts as a non-return valve. Having said that, I'm extremely doubtful that that is your problem since we're talking about a bike that's only 3 years old.

Edited by Sparky, 05 December 2007 - 05:04 pm.

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#7 dandywarhol

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Posted 05 December 2007 - 06:07 pm

Are you sure the gunk hasn't reacted with the seals?
I used Jizer to clean out calipers a while back and it softened and swelled the seals causing the piston to jamb.

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#8 muddy

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Posted 05 December 2007 - 06:44 pm

I polished the retaining bolts with very fine emery and then greased the bolts before putting the pad back in. And I feel pretty sure it's not the pistons sticking because they'd tend to be consistent and I'd expect one disc to be worse than the other. Also how would sticking parts account for the lever going rock hard on me? That's what makes me think it's an airlock that's shifting around and causing intermittent 'squeezing' in the lines.

Too cold and wet to do anymore today. I'll go down tomorrow and loosen a few banjos before I bleed them again.

On edit: I used Halford's brake cleaning spray to clean around the pistons. I would hope that they've concocted a solution that won't swell the seals unsure.gif

Edited by muddy, 05 December 2007 - 06:48 pm.

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#9 Guest_GuyGraham_*

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Posted 05 December 2007 - 06:54 pm

QUOTE(muddy @ Wed 5th Dec 2007, 06:29 PM) <{POST_SNAPBACK}>
I polished the retaining bolts with very fine emery and then greased the bolts before putting the pad back in. And I feel pretty sure it's not the pistons sticking because they'd tend to be consistent and I'd expect one disc to be worse than the other. Also how would sticking parts account for the lever going rock hard on me? That's what makes me think it's an airlock that's shifting around and causing intermittent 'squeezing' in the lines.

Too cold and wet to do anymore today. I'll go down tomorrow and loosen a few banjos before I bleed them again.

On edit: I used Halford's brake cleaning spray to clean around the pistons. I would hope that they've concocted a solution that won't swell the seals unsure.gif



If you've got an airlock, no matter where it is located, you'll get a spongey lever

I think Dandy has prob got it correct - possible re-action between seal and gunk

Normally. cleaning just the pistons doesn't have much affect on binding brakes, as alot of crud (technical term) builds up behind the seal causing much higher friction between the seal and piston which stops the piston from being sucked back when you let go of the lever

Only answer is to get the pistons out, clean the groves in the claiper bodies where the seal ans dust seal sit, re-assemble and re-bleed
That should sort you out
Failing that, and kind surface imperfection on the piston can cause excess friction betwee the seal and piston and rsult in binding brakes. There should be no rust, pits, dents or any other kind of surface blemish on the nickel plating of the piston
New pistons are the only cure if this has happened.


#10 muddy

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Posted 05 December 2007 - 07:07 pm

QUOTE(GuyGraham @ Wed 5th Dec 2007, 06:39 PM) <{POST_SNAPBACK}>
If you've got an airlock, no matter where it is located, you'll get a spongey lever

I think Dandy has prob got it correct - possible re-action between seal and gunk

Normally. cleaning just the pistons doesn't have much affect on binding brakes, as alot of crud (technical term) builds up behind the seal causing much higher friction between the seal and piston which stops the piston from being sucked back when you let go of the lever

Only answer is to get the pistons out, clean the groves in the claiper bodies where the seal ans dust seal sit, re-assemble and re-bleed
That should sort you out
Failing that, and kind surface imperfection on the piston can cause excess friction betwee the seal and piston and rsult in binding brakes. There should be no rust, pits, dents or any other kind of surface blemish on the nickel plating of the piston
New pistons are the only cure if this has happened.


Damn. I was hoping that nobody would say that. But these questions still remain:

Why am I getting the constant stream of tiny air bubbles?

Why does the front brake work perfectly for a little while and then firm up so there's almost no play in the lever?

I would have thought if the pistons are sticking then there would be a light binding where the pistons are failing to return and not a the solid clamping that's occurring. And how are the pistons clamping without me having applied the brake? Just don't quite make sense to me that's all.

Edited by muddy, 05 December 2007 - 07:11 pm.

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#11 Guest_GuyGraham_*

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Posted 05 December 2007 - 09:09 pm

QUOTE(muddy @ Wed 5th Dec 2007, 06:52 PM) <{POST_SNAPBACK}>
Damn. I was hoping that nobody would say that. But these questions still remain:

Why am I getting the constant stream of tiny air bubbles?


Youv'e still got air in the system - try leaving the bike overnight with a ty-rap around the lever. This will allow any air to rise and escape into the the reservior


QUOTE(muddy @ Wed 5th Dec 2007, 06:52 PM) <{POST_SNAPBACK}>
Why does the front brake work perfectly for a little while and then firm up so there's almost no play in the lever?


The only time I have known this was when the pistion in the master cylinder wasn't returning due to no free play between the lever and the master cyl piston (because I had lengthened the adjuster screw which wasn't allowing full return of the master cylinder piston).
Have you done anything the to master cyl?
Is there free play between the lever and the master cyl piston?


QUOTE(muddy @ Wed 5th Dec 2007, 06:52 PM) <{POST_SNAPBACK}>
I would have thought if the pistons are sticking then there would be a light binding where the pistons are failing to return and not a the solid clamping that's occurring. And how are the pistons clamping without me having applied the brake? Just don't quite make sense to me that's all.


depends on just how stuck they are.
Can vary from light binding to full pressure remaining after lever released


#12 dandywarhol

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Posted 05 December 2007 - 11:19 pm

It's the square section of the caliper seal which retracts the piston and therefore the pads from the disc.
When you apply the brakes the square section becomes a parallelogram shape and when you release the pressure the seal returns to a square shape bringing the piston with it.
If the seals are at all damaged/soft they won't do their job and the pad could stay in contact with the disc causing heat build up and binding.

Sparky's theory about the "flap" inside the brake hose can be caused by someone using mole grips to stop the fluid from escaping when you remove the caliper - this damages the inside of the rubber hose membrane.

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#13 robelst

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Posted 05 December 2007 - 11:46 pm

Sounds like sticky pistons, this would also explain the bleeding difficulties; I am not 100% sure why, but bleeding brakes with free moving pistons is always a whole lot easier. I noticed on my Sumitomos that the the thin (vulnerable!) outer lip of some dust seals had partly torn off and blocked the movement on some of the pistons. Replacing the seals fixed all and bleeding them was a doddle. The price of new seals is so outrageously high that it might be interesting to inquire what new pistons would cost (they come with the seals included): they are relatively good value and would give you virtually new brakes.

Another tip to fix difficult bleeding: Sometimes the thread on the bleedvalve leaks air, letting you bleed until hell freezes over. Opening them only a little bit (quarter of a turn) can help, otherwise renew or replace with coated Speedbleeder valves.

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#14 muddy

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Posted 06 December 2007 - 12:29 am

QUOTE(dandywarhol @ Wed 5th Dec 2007, 11:04 PM) <{POST_SNAPBACK}>
It's the square section of the caliper seal which retracts the piston and therefore the pads from the disc.
When you apply the brakes the square section becomes a parallelogram shape and when you release the pressure the seal returns to a square shape bringing the piston with it.
If the seals are at all damaged/soft they won't do their job and the pad could stay in contact with the disc causing heat build up and binding.


So piston travel is just a few mm then. I didn't realise that they worked to such small tolerances. That explains a lot. Thanks.

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#15 Guest_GuyGraham_*

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Posted 06 December 2007 - 12:55 pm

QUOTE(dandywarhol @ Wed 5th Dec 2007, 11:04 PM) <{POST_SNAPBACK}>
It's the square section of the caliper seal which retracts the piston and therefore the pads from the disc.
When you apply the brakes the square section becomes a parallelogram shape and when you release the pressure the seal returns to a square shape bringing the piston with it.


I didn't know that - always thought it was the spring in the master cyl pulling the master cyl piston back which creted a lower pressure so sucked the pistons back
Sounds feasible





#16 dandywarhol

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Posted 06 December 2007 - 04:58 pm

More than feasable GG cool.gif - I gotta teach this kind o' shoite! laugh.gif

The piston travel is probably about 1mm muddy - the pads are constantly in touch with the disc (slightly) so it doesn't take much movement to apply the brakes.

Edited by dandywarhol, 06 December 2007 - 05:00 pm.

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#17 muddy

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Posted 06 December 2007 - 08:35 pm

I haven't had a chance to do the work today as it's been raining most of the day and I don't have a garage or cover.

Thinking about what Guy said, I feel pretty sure that one or two of the pistons were blemished. I had the same on my TA and that had incurable binding brakes. This is really going to piss me off as the bikes only 3 years old and a piston and seal set is about £70 mad.gif

Dandy
Thanks for explaining how the piston operates, that really is helpful to know and clear up a lot of my questions tup.gif

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#18 muddy

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Posted 18 December 2007 - 03:57 pm

UPDATE.

I took both calipers of the bike and brought them indoors to dismantle before I froze to death. I took out the pistons, unfortunately leaving a bit of plier rash in the process. I then took the seals out and they were all intact. I gave the piston a polish, and used some abrasion to take of the plier rash. They were all smooth and polished. I cleaned out the seals groove with matches and put back the seals and pistons. Before putting the calipers back on the bike I made sure the bleed nipples were well sealed.

Put the calipers back on the bike and connected the banjos. I attached my Sealy vacuum pump to the nearside bleed nipple, topped up the reservoir, pumped up a vacuum to 15-20 and cracked the bleed nipple. Now all I seemed to do was pull air through the system, no end of it. The reservoir was always topped up, in fact considering the vacuum I applied over the duration, hardly any fluid got sucked through, just spurts followed by lots of air bubbles, then nothing for a while, followed by more of the same.

It absolutely cannot of been drawn through the bleed nipples, they were well sealed. So I can't think where the air was coming from and why so little fluid was coming though (less than a cups worth).

I'm close the point of surrender. Reading all the various threads from different forums, brakes are indeed a black art isurrender.gif

Edited by muddy, 18 December 2007 - 04:00 pm.

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#19 Sparky

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Posted 18 December 2007 - 04:17 pm

QUOTE(muddy @ Tue 18th Dec 2007, 03:42 PM) <{POST_SNAPBACK}>
UPDATE.

I took both calipers of the bike and brought them indoors to dismantle before I froze to death. I took out the pistons, unfortunately leaving a bit of plier rash in the process. I then took the seals out and they were all intact. I gave the piston a polish, and used some abrasion to take of the plier rash. They were all smooth and polished. I cleaned out the seals groove with matches and put back the seals and pistons. Before putting the calipers back on the bike I made sure the bleed nipples were well sealed.

Put the calipers back on the bike and connected the banjos. I attached my Sealy vacuum pump to the nearside bleed nipple, topped up the reservoir, pumped up a vacuum to 15-20 and cracked the bleed nipple. Now all I seemed to do was pull air through the system, no end of it. The reservoir was always topped up, in fact considering the vacuum I applied over the duration, hardly any fluid got sucked through, just spurts followed by lots of air bubbles, then nothing for a while, followed by more of the same.

It absolutely cannot of been drawn through the bleed nipples, they were well sealed. So I can't think where the air was coming from and why so little fluid was coming though (less than a cups worth).

I'm close the point of surrender. Reading all the various threads from different forums, brakes are indeed a black art isurrender.gif


Aaaaarrgh! Dunno specifically about the Yamaha calipers, but most brake pistons are nickel plated to prevent corrosion and should never, ever have abrasives used on them! Pliers are definitely a no-no - air from a footpump is the way to remove them, or simply pump them out and lose some fluid.

Enough criticising ( sorry.gif ) - I also use the Sealey vac pump. I find that the air is drawn through via the threads of the bleed nipple. The answer is to keep smearing thick grease around the threads to seal out the air. I use vacuum grease, although I might suggest vaseline as an alternative, since it is very similar. Get it right, and you'll be able to pump down the vacuum and the gauge will hardly sink at all when you open the bleed nipple. cool.gif

Good luck and hope you succeed soon!
Ex-TDM owner. Now riding a Sprint ST 1050

#20 brihol

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Posted 18 December 2007 - 04:44 pm

I didn't have much luck bleeding my brakes with a vacuum pump so I got a large syringe and screwed it into the bleed nipple holes and forced the air out of the system by injecting the fluid into each and up into the main cylinder.

Are you sure the original problem was not caused by a too tight adjustment at the handlebar lever? With new pads and fluid etc the wheel could be free to spin when cold but when everything heats up the expansion could force the master cylinder piston against the adjuster and apply the brake. I'll probably be shot down by the eggspurts but it makes sense to me.

Brian


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