Sanity check, rear brake edition

But my brakes do work, nothing locks up or spins freely when it shouldn't. I might try to block off the rear abs portion and run a line straight from the master to the caliper.
No they dont work

you have a pad not backing off from the disc ... its not right

going forward

if going direct master to caliper restores normal operation

that would suggest the ABS unit is having an influence

if not you need to eliminate

master cylinder
Brake line
Caliper

You need to think about how the circuit works

Master cylinder - ABS unit - caliper not master cylinder - caliper & add ABS when needed

The ABS unit is monitoring the rotation speeds of the wheels constantly A) for ABS & B) to provide your road speed in the Kombi

if the ABS unit detects lock up when braking it modulates the brake pressure to give cadence braking on/off/on/off/on/off very rapidly to slow you and give steering control

So as long as you have your brake applied enough to trigger the ABS module - its doing the braking not you

once you come off the brakes, and wheel rotation is restored the ABS stops modulation

so if you have an internal fault in the ABS unit the pressure might not be released enough, and the symptom of a sticky caliper

Thats similar to what had on the front, we initially thought sticky caliper

6 months later - it was the ABS unit gone south

As i said

Eliminate the other parts

Rear master cylinder

rear brake line

rear caliper

if one of those clears the fault :) job done, i was wrong

if not, it can only be the ABS unit

One thing you havn't mentioned ,or if you did i missed it

What year of bike hexhead or twincam
mileage
service history (brake fluid changes)
 
No they dont work

you have a pad not backing off from the disc ... its not right

going forward

if going direct master to caliper restores normal operation

that would suggest the ABS unit is having an influence

if not you need to eliminate

master cylinder
Brake line
Caliper

You need to think about how the circuit works

Master cylinder - ABS unit - caliper not master cylinder - caliper & add ABS when needed

The ABS unit is monitoring the rotation speeds of the wheels constantly A) for ABS & B) to provide your road speed in the Kombi

if the ABS unit detects lock up when braking it modulates the brake pressure to give cadence braking on/off/on/off/on/off very rapidly to slow you and give steering control

So as long as you have your brake applied enough to trigger the ABS module - its doing the braking not you

once you come off the brakes, and wheel rotation is restored the ABS stops modulation

so if you have an internal fault in the ABS unit the pressure might not be released enough, and the symptom of a sticky caliper

Thats similar to what had on the front, we initially thought sticky caliper

6 months later - it was the ABS unit gone south

As i said

Eliminate the other parts

Rear master cylinder

rear brake line

rear caliper

if one of those clears the fault :) job done, i was wrong

if not, it can only be the ABS unit

One thing you havn't mentioned ,or if you did i missed it

What year of bike hexhead or twincam
mileage
service history (brake fluid changes)
Thanks for the comprehensive write up!

It's a 2010 model, twincam. About 45000 miles. Brake fluid changed as soon as I got it last year, fluid that came out looked fresh. Changed the fluid again earlier this week when I rebuilt the caliper. The slide pin rubbers where not allowing sliding as they should. I cleaned them with the wrong cleaning agent earlier this year when changing pads. So last week I replaced all the seal, rubbers parts, stainless steel pad springs and pad pin. Besides that the disc was replaced with a new one and new OEM pads where installed. I'm still thinking the pads and disc need to be bedded more.

The pressures I'm reading in motoscan are alarming, also the pressure drops as soon as I let of the pedal.

The pads do come of the disc, original question was do they come off far enough? And it's hard to make a precise assessment by friction in the rear wheel or by noise. As soon as I let go of the pedal the rear rotates again. Last nights ride of about 20 miles made the brake caliper like warm. Disc slightly warmer than that. Mind you, I did all my braking on the rear.

If it was really binding wouldn't it have been hotter/scolding hot? How warm should the rear be after a ride?

Just for fun I'm going to a local shop this afternoon that has a few gs'es of this vintage, just to feel listen and compare
 
So ive just had a new rear disc on mine literally yesterday

Just been down to the garage - rotating the rear wheel you can hear slight pad/ disc contact - the pad is resting on the disc no pressure applied just resting

it sounds the same as if you rotate a wheel on a car - a light contact noise

you dont want clearance as in a measureable gap, as this has to be taken up before the pad bites

yours sound as if there is still residual pressure on the pad, so its applying the brake ever so slightly

Have you confirmed the caliper is sliding on the guides?
 
Just a thought,

you said your replaced the sliders, did you confirm the caliper was sliding on the slider?


This is going to sound really stupid or contraversial depending on how approacheable you are

You have assembeld the pads the right way round and not on metal to metal ?

if you can, pop the pads out and get a photo up & the disc,

might give a few more pointers
 
if you can, pop the pads out and get a photo up & the disc,
i was going to suggest that (photo) earlier, but the OP isn’t a member - I didn’t think “registered users” had privileges to upload photos?
 
Just a thought,

you said your replaced the sliders, did you confirm the caliper was sliding on the slider?


This is going to sound really stupid or contraversial depending on how approacheable you are

You have assembeld the pads the right way round and not on metal to metal ?

if you can, pop the pads out and get a photo up & the disc,

might give a few more pointers
I'm really approachable, all pointers are welcome!

In the rebuilt caliper the sliders slide freely, when pushed fully in they spread ng back after that. Before rebuilding that didn't happen.

Pads are right way around.

Just came back from the shop I was talking about earlier. I am no longer welcome there because allegedly I have a "wheel rotation fetish"... (Joking obviously). But there were 4 GS's, 2 RT's, 1 R and one R nine T. Touched them all (appropriately), some rotate smoother than others, some make more noise from pads than others.

Their mechanic (who only works in BMW's and Ducati's) took at look at mine and said nothing was out of the ordinary. Brake functions, pads retract far enough after releasing pedal.
 


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