Dragging brakes.

[King Herald]

1997 R1100R, 123,000 miles, stainless brake hoses, fluid flushed a year or two ago.

 

The front brakes start to drag a bit after a couple thousand miles. The wheel won’t spin freely when it’s on the centre stand, and the brake lever has a bit of ‘give’ like there’s air in the system.

 

I pull the calipers off, whip the pads out, do a good clean all around the pistons, with brake cleaner and a brass wire brush. I pump each piston out about 1/4” to clean it, and then put them back on the bike. And after that they are great for a while, really good feel, no sponginess. 

And then they’ll gradually go back to the dragging with a ‘loose’ feel to the lever. 
 

Any suggestions what could cause it? Maybe the original seals are getting old and tired/hard? 
 

Is it much of a job to pump each piston out and put a new seal on it? 

[dirtrider]

1 hour ago, King Herald said:

1997 R1100R, 123,000 miles, stainless brake hoses, fluid flushed a year or two ago.

 

The front brakes start to drag a bit after a couple thousand miles. The wheel won’t spin freely when it’s on the centre stand, and the brake lever has a bit of ‘give’ like there’s air in the system.

 

I pull the calipers off, whip the pads out, do a good clean all around the pistons, with brake cleaner and a brass wire brush. I pump each piston out about 1/4” to clean it, and then put them back on the bike. And after that they are great for a while, really good feel, no sponginess. 

And then they’ll gradually go back to the dragging with a ‘loose’ feel to the lever. 
 

Any suggestions what could cause it? Maybe the original seals are getting old and tired/hard? 
 

Is it much of a job to pump each piston out and put a new seal on it? 

Afternoon  King Herald

 

Can you tell if both side calipers are tight or just one side causing the rotor drag?  

 

With the hand lever feeling a little loose or having a little extra free-play it sort of sounds like a lightly sticking piston in the master cylinder. 

 

The master cylinder bore can get a bit gunked up just behind the piston so possibly that is causing the piston to not return far enough to uncover the little port in the bottom of the reservoir.

 

If that little take-up port hole in the bottom of the reservoir doesn't open at lever release then it can retain a little fluid pressure in the front brake system at lever release. (usually gets worse as the brakes heat up)

 

[cambio]

I think all older calipers do this, I've found it's aluminium oxide build up in the seal groove bores which deforms the seal and causes them to always grab so it stops the pistons fully retracting when you come off the brakes. The seals are square section which means when you apply the brakes the pistons deform the squares into a parallelogram shape before the piston slides through the seal. This deformation tension in the square seal means then when you release fluid pressure, the seals pull the pistons back a tiny amount, freeing the discs and pads to rotate with minimal drag and putting a small amount of pressure in the fluid, which gives you a ice sharp feel when you next touch the lever. If this doesn't happen it also creates an initial spongy feel as the pistons are being held out. To sort it's a pistons and seals out job and gently work the oxide out of the seal grooves. I'd advise against metal tools and you need to be gentle, if you score the groove you will get leaks. Fine grade red scotch brite can be used as well. Once cleaned, a load of red rubber grease in the grooves, then refit the seals, clean off any excess and refit pistons. The grease will keep the seal grooves oxide free for a good few years, then you just need to pop pistons out a bit and clean with a tooth brush and brake cleaner (don't use a wire brush, you'll scratch the pistons) and then a thin smear of rubber grease and push the pistons back in, wipe clean and away you go for another year. I've found a pair of piston pliers is handy to rotate and work the pistons allowing a thorough clean.

[King Herald]

15 hours ago, dirtrider said:

Afternoon  King Herald

 

Can you tell if both side calipers are tight or just one side causing the rotor drag?  

 

With the hand lever feeling a little loose or having a little extra free-play it sort of sounds like a lightly sticking piston in the master cylinder. 

 

The master cylinder bore can get a bit gunked up just behind the piston so possibly that is causing the piston to not return far enough to uncover the little port in the bottom of the reservoir.

 

If that little take-up port hole in the bottom of the reservoir doesn't open at lever release then it can retain a little fluid pressure in the front brake system at lever release. (usually gets worse as the brakes heat up)

 

Morning DR, it never occurred to me it could be in the MC actually. After cleaning the calipers/pistons the brake lever always feels normal again, but the amount of pumping the MC gets while sorting the calipers out could well free it up, temporarily. 

 

I shall investigate it next time it happens. 

Oddly enough, the bike came with a spare MC piston and seal when I first bought it. It’s still in the parts box in the shed.

[King Herald]

13 hours ago, cambio said:

I think all older calipers do this, I've found it's aluminium oxide build up in the seal groove bores which deforms the seal and causes them to always grab so it stops the pistons fully retracting when you come off the brakes. The seals are square section which means when you apply the brakes the pistons deform the squares into a parallelogram shape before the piston slides through the seal. This deformation tension in the square seal means then when you release fluid pressure, the seals pull the pistons back a tiny amount, freeing the discs and pads to rotate with minimal drag and putting a small amount of pressure in the fluid, which gives you a ice sharp feel when you next touch the lever. If this doesn't happen it also creates an initial spongy feel as the pistons are being held out. To sort it's a pistons and seals out job and gently work the oxide out of the seal grooves. I'd advise against metal tools and you need to be gentle, if you score the groove you will get leaks. Fine grade red scotch brite can be used as well. Once cleaned, a load of red rubber grease in the grooves, then refit the seals, clean off any excess and refit pistons. The grease will keep the seal grooves oxide free for a good few years, then you just need to pop pistons out a bit and clean with a tooth brush and brake cleaner (don't use a wire brush, you'll scratch the pistons) and then a thin smear of rubber grease and push the pistons back in, wipe clean and away you go for another year. I've found a pair of piston pliers is handy to rotate and work the pistons allowing a thorough clean.

I would have thought the feel of the brake lever would be firm, if the pads are being held against the discs, rather than sprung back a little as normal. 
 

Next time it happens I shall go ride a few miles and refrain from using the front brake, then pull up using just the back brake, and see if either, or both calipers are warm, which should indicate if one, or both calipers are dragging. And I’ll investigate from there. 

[cambio]

2 hours ago, King Herald said:

I would have thought the feel of the brake lever would be firm, if the pads are being held against the discs, rather than sprung back a little as normal. 
 

Next time it happens I shall go ride a few miles and refrain from using the front brake, then pull up using just the back brake, and see if either, or both calipers are warm, which should indicate if one, or both calipers are dragging. And I’ll investigate from there. 

trouble is they dont usually drag enough to get hot. i think when they dont retract they get knocked back by the discs as well, i chased this issue on another bike for a while and only really solve the sloppy lever on first application by cleaning the seal bores and greasing and new seals, they had a load of oxide. they went from intial lever pull 'oh feck loads of travel' to one finger responsiveness and seem to have stayed there with a regular clean and grease for about 4 years now, ridden in all conditions.

[dirtrider]

4 hours ago, King Herald said:

I would have thought the feel of the brake lever would be firm, if the pads are being held against the discs, rather than sprung back a little as normal. 
 

Next time it happens I shall go ride a few miles and refrain from using the front brake, then pull up using just the back brake, and see if either, or both calipers are warm, which should indicate if one, or both calipers are dragging. And I’ll investigate from there. 

Morning King Herald

 

I theory that is how it should work as there is no (very/very little) travel left at the caliper pistons. 

 

When the hand lever is released ALL the hydraulic pressure should be released on the front braking system when the master cylinder piston retracts all the way to the piston retaining ring & opens the take-up port in the bottom of the reservoir. Once that hole is opened there is a direct un-impeded path between the fluid reservoir & the calipers. 

 

But things don't always works as they seem, like possibly only one piston is sticking allowing the others to retract slightly. 

 

The place to start is to see if both side calipers are effecting the drag, or if one side rotor is getting hotter than the other side after riding a ways AFTER a brake apply but without re-using the front lever.  If both sides are dragging the same then you could have both sides sticking the same (unlikely but possible). Or you have a common source for both sides not fully releasing & that would most likely be in the master cylinder area. 

 

 

[King Herald]

Thanks guys, it’s given me something to go by. I may buy a set of caliper seals and do a front brake overhaul if and when the time comes. And I’ll see if the spare MC seal is in good shape. I’m assuming no special tools needed, and I shan’t be splitting the calipers, I’ve been warned off about doing that before. 
 

Winter is closing in here, and though I ride all year round I won’t go out in snow, so if we get a good layer of that it would the ideal brake overhaul time. 

[cambio]

I rebuilt mine a few months back and reused seals, mainly because i didnt want to spend any money on the bike as i was reviving it from a complete basket case that hadnt been used in several years, so didnt know if it would even run, think its about £80 per side from motorworks for new pistons and seals. The pistons are coated or anodized, but having spent time on the seal bores and refitted the seals the brake lever is great, but several of the pistons were showing light surface damage so will need replacing in due course. 2 tools needed to disassemble were piston pliers and a grease gun, as a couple of pistons were seized solid so i had to pump grease into it to pop it out. But if your bike is running fine theyll probably all be ok - but expect one or more per caliper to be sticky like DR says. Piston pliers are less than £10 for cheap chinese versions on fleabay, bare in mind they arent indestructible but theyre the tool to use to work the pistons out - gently rotate them first and then work them out once they are moving. If theyre seized such that they wont move then compressed air or a grease gun is your friend (a standard grease gun outlet has an m10x1 thread which just screwed straight into the caliper), its messier but much safer than compressed air - watch your fingers!- as you have to scrape and flush the grease out. You might need a vice and g clamps and bits of wood to hold any free pistons in while you work seized ones out. A satisfying job on a winters day for sure!.