ABS Issue R1100RT

[Matts_12GS]

I replaced a set of rear pads and adjusted the bracke actuating lever a bit too tightly and wound up dragging my rear brakes a good bit, enough to have a nice brick red disk!

 

Anyways, I loosened up the actuating rod, the caliper backed off without issue. I didn't take the time to let it all cool off before I put the rod back in place and went to try and adjust the rear brake, but it didn't feel like it was doing anything at all.

 

I let it be and rode the rest of the way in to work, and gave it a good bit of time for it all to cool off enough and it seems that I was getting some rear brakes back. So, if I get my brakes back after everything cools off, should I bleed the ABS circuit, just from the ABS to the wheel?

[Joe Frickin' Friday]

I replaced a set of rear pads and adjusted the bracke actuating lever a bit too tightly and wound up dragging my rear brakes a good bit, enough to have a nice brick red disk!

 

This happened to a friend a couple of years ago. He had adjusted the rear brake pedal to remove some of the deadband (deadband = initial range of lever motion that doesn't cause any braking action), and inadvertently moved the master cylinder's at-rest position to the point where it covered the bleed port, sealing the caliper and line off from the reservoir. Traveling at speed generated a small amount of heat in the caliper, which warmed/expanded the fluid; since the fluid couldn't return to the reservoir, it pushed the caliper pistons out, which generated more heat, which warmed the fluid even more...anyway, it kept going until there was so much heat the final drive pivot boot caught on fire.

 

So, if I get my brakes back after everything cools off, should I bleed the ABS circuit, just from the ABS to the wheel?

 

Easy enough to bleed the whole thing on an 1100. There are not separate "wheel" and "control" circuits per se; you can put fluid in the reservoir, bleed from the caliper, and flush the whole thing this way. It may or may not help, but it definitely wouldn't hurt.

[Clive Liddell]

I would also change the final drive oil. I think more final drives have been damaged by dragging rear brakes than anything else.

[Tom P]

He had adjusted the rear brake pedal to remove some of the deadband (deadband = initial range of lever motion that doesn't cause any braking action)

Mitch,

I would like to remove some of the deadband on my '98 RT.

 

Know of any write up instructions?

[Joe Frickin' Friday]

He had adjusted the rear brake pedal to remove some of the deadband (deadband = initial range of lever motion that doesn't cause any braking action)

Mitch,

I would like to remove some of the deadband on my '98 RT.

 

Know of any write up instructions?

 

I posted this last year for the front brakes; the procedure will be similar for the rear brake, though I think it may be difficult to see the geyser in the rear brake reservoir (you'll know what I'm talking about as you read on). Where the writeup talks about the giant setscrew on the front lever, for the rear you're dealing with shortening/lengthening the link at the far rear end of the pedal arm.

 

this procedure DOES NOT APPLY to any BMW bike with servo-assisted brakes.

 

Read on:

 

===========================

Sponginess (a nonlinear relationship between lever position/force) is either air in the lines, or elasticity of the brake lines themselves. If the lever produces a very large mechanical advantage, then you'll readily feel even very slight elasticity in the lines. Deadband is different; it's the first portion of lever movement where absolutely no brake effort is produced, and comes from a couple of things.

 

One part of the deadband may be due to the pistons retracting into the calipers after a long period of brake-free riding. If you have a lot of deadband on the first pull after a long cruise, and then small deadband when you pull the lever again immediately after the first pull, then this is probably it. I think TADT if you go for a few miles without braking, but if you get large deadband relatively soon after the previous lever-pull, then maybe you've got warped rotors that are quickly causing the pistons to retract into their calipers. Not a problem if you can deal with it (e.g. lever setting #4), but if it's really making you miserable, you might try replacing the rotors.

 

OTOH, if you've got large deadband on every lever pull - even when parked - then it's something different, and you can fix it with a screwdriver. I'll tell you what I did on my RT, but let me start with a warning: if you screw up on this procedure, the brakes may lock up at speed; you'll crash, burn and die, and that's not good. So don't screw up.

 

When the lever is unpressed, the piston in the master cylinder is far enough up in its bore so that a bleed port connects the brake line to the reservoir. That allows fluid to leave the brake line (as the fluid in the calipers warms/expands during the course of a ride) or enter it (as the pads wear or the fluid cools/contracts after a spirited ride).

 

When you pull on the brake lever, the first part of the piston's travel squeezes some fluid out of the bleed port and back up into the reservoir; if you use Speedbleeders or a traditional brake-bleed method, you've probably seen this little geyser of brake fluid in the reservoir when you first pulled the lever. Anyway, this backsquirt continues until the piston actually covers the bleed port; after this point it can only push fluid down to the the caliper, applying the brakes. If you've got a lot of deadband, the piston's at-rest position is too far from the bleed port; it's got a long ways to move before it covers that bleed port and starts working the brakes.

 

There is a very large setscrew in the lever, near the base, that presses on the piston in the master cylinder. On my bike it was secured with some extremely viscous syrupy red stuff. I was able to turn it with a very large flat-blade screwdriver held very firmly. I turned the screw to eliminate the deadband in the lever as far as I dared, while making sure that the first little bit of lever pull still caused that geyser of fluid in the reservoir; if you don't see at least a little geyser when you first pull the lever, then you know that the piston in its at-rest position has sealed off the brake line from the reservoir, and on your first ride you may lock up the front wheel when the fluid in the calipers heats/expands and can't relieve line pressure. Another rider here went a bit too far with this procedure on the rear brake last year, and the resulting heat started the final drive boot on fire.

 

So that's it. Look for that big monster setscrew, and crank it in until you've got a small, short-lived geyser in the reservoir when you first pull the lever (PROTECT YOUR PAINT!!!!!!). Go for a test ride, but keep speeds low and stop periodically to check rotor temps for the first few miles.

=====================

[Tom P]

Thanks Mitch

[Matts_12GS]

This happened to a friend a couple of years ago. He had adjusted the rear brake pedal to remove some of the deadband (deadband = initial range of lever motion that doesn't cause any braking action), and inadvertently moved the master cylinder's at-rest position to the point where it covered the bleed port, sealing the caliper and line off from the reservoir. Traveling at speed generated a small amount of heat in the caliper, which warmed/expanded the fluid; since the fluid couldn't return to the reservoir, it pushed the caliper pistons out, which generated more heat, which warmed the fluid even more...anyway, it kept going until there was so much heat the final drive pivot boot caught on fire.

 

Yep, happened to me today.

New boot, rotor and pads on order as soon as I get a chance tonight. Thanks again Mitch!