RE: What a saga, binding rear brake - 3

The oddness continues. The rear pads eventually bedded in after changing just about everything, pistons, seals, rubber boots and fluid. I was back to being happy and I've done about 3k miles maximum since this saga. Yesterday I noticed a rust witness mark on the left hand side of the rear wheel. Now this isn't the wheel rusting of course as its alloy. It doesn't seem to want to clean off. It seems to be coming from the rear calliper and there is rust/red debris around the piston side pad.

Today I took the calliper apart to check and both pads are completely shot in about 3,000 miles or less. The OEMs lasted over 30,000 miles. The piston side pad looks like it's been overheating and spalling off material onto the wheel. Braking has been normal, the calliper seems fine and the disk hasn't been binding when I checked by spinning the rear wheel with my boot.

I guess there are two possible issues.

1. Possibly dodgy pads? I've just ordered a replacement set from Lloyds Motorrad in Carlisle in the hope that the OEM ones will be the answer to the problem. The knackered ones are Ferodo and bought from Motorworks in the UK. Perhaps they are cheap 'knock offs'?

2. Somehow the rear brake is coming on while I'm riding and I don't notice when I check after a ride. I ride with my toes on the footpegs most of the time and there is a distinct clearance between the lever and the master cylinder.

All these issues started when I changed pads to the Ferodo ones. Motorworks say that they have had no reported issues. It could be that now the rear disk needs examining closely and measuring with a micrometer (that I don't have).

I'll clean the calliper, grease the pins and fit the new pads when they arrive. I'll update. The staining to the rear rim seems permanent.

I'm not entirely sure that there's not an underlying cause I haven't identified. When I replaced the OEM pads the wear was mainly on the fixed calliper pad which is unusual. This time it's more even with the piston side getting marginally more wear.

IMG_1684 copy.jpg - Bild entfernt (keine Rechte)

I missed this thread first time around, but am interested as it seems to be very similar to my own experience on my current RS a couple of years ago, detailed here:

Overheating rear brake?

I can't claim to have all the answers to your problem as in my case BMW took the bike back under warranty and replaced the whole rear brake assembly which resolved the issue. They didn't ever say specifically what was wrong, just that 'whatever it was, everything's been renewed so the issue is gone now.' Wasn't a wholly satisfactory response but 12,000 miles later the bike hasn't missed a beat.

It's be nice to know what the issue was FF. I'm not planning on spending 1000's of £'s fixing my 6 year old 34,000 mile bike however much I love it.

I'm wondering if the rear linked pump is coming on when it shouldn't. Maybe it can be isolated electrically to test?

I've been reading around rear brake issues on the internet. GS's have their share of problems (mainly the loss of brake) even without 'linked' brakes. There is 'talk' of defective master cylinders or seals on earlier bikes and of BMW replacing them. I do know that when I have bled my rear brake the pedal resistance position can change noticeably.

A 2nd hand master cylinder can be had for about £60. A new one is £140. I've decided that a new one is the next step in resolving this problem and the price is less than I expected. The rear disc doesn't look so bad so that can wait. I do notice that the pad material is starting to block the disc holes and that surprises me.

Make sure that the brake lever is able to fully return/retract to the "off" position.

In a hydraulic brake system there is a vent hole within the master cylinder. When a brake is actuated and the master cylinder moves, the first thing that happens is master cylinder piston moves to cover the vent hole and then the piston moves further creating system pressure and this causes the slave cylinders to move and etc etc. When the brake actuating lever is retracted to the "off"position the pressure is reduced and the slave cylinders retract as the slave cylinder piston seals "pull" the slave cylinder pistons back (just a nidges). The vent hole is again open which allows any residual pressure to diminish and for the fluid to equalize as it expands or contracts due to temperature changes.

If a brake lever has not returned to the fully "off" position the vent hole could remain closed. There could be a small amount of pressure in the system which could prevent the slave cylinder rubbers from moving the pistons back.

However.....

if the vent is open on the rear bake when the foot lever is in the "off position", how does the integrated brake system additionally apply pressure to the rear brake when the front brake only is applied?

Yes the rear brake lever is allowing the master cylinder to return to it's rest position fully with a clearance. A proud Aerial 3 owner? There weren't many back in the day

There must be a control valve that isolates the master cylinder and reservoir when the electrical pump is pressurising the rear circuit.

Zitat von Sanemancured im Beitrag #38

---

Yes the rear brake lever is allowing the master cylinder to return to it's rest position fully with a clearance. A proud Aerial 3 owner? There weren't many back in the day

There must be a control valve that isolates the master cylinder and reservoir when the electrical pump is pressurising the rear circuit.

---

Well, BMW OEM pads went it. It was immediately apparent that everything was good. No dragging or binding at all with new pads, unlike when I fitted the Ferodo's. I've been out for 40 miles today and everything is just as it should be. I cancelled the order for the master cylinder and I'll monitor the wear rate.

The OEM pads are far more 'sintered' looking and less 'organic'.

Fingers crossed.

Zitat von Sanemancured im Beitrag #40

---

Well, BMW OEM pads went it. It was immediately apparent that everything was good. No dragging or binding at all with new pads, unlike when I fitted the Ferodo's. I've been out for 40 miles today and everything is just as it should be. I cancelled the order for the master cylinder and I'll monitor the wear rate.

The OEM pads are far more 'sintered' looking and less 'organic'.

Fingers crossed.

---

Zitat von Sanemancured im Beitrag #40

---

Well, BMW OEM pads went it. It was immediately apparent that everything was good. No dragging or binding at all with new pads, unlike when I fitted the Ferodo's. I've been out for 40 miles today and everything is just as it should be. I cancelled the order for the master cylinder and I'll monitor the wear rate.

The OEM pads are far more 'sintered' looking and less 'organic'.

Fingers crossed.

---

Zitat von wessie im Beitrag #43

---

Zitat von Sanemancured im Beitrag #40

---

Well, BMW OEM pads went it. It was immediately apparent that everything was good. No dragging or binding at all with new pads, unlike when I fitted the Ferodo's. I've been out for 40 miles today and everything is just as it should be. I cancelled the order for the master cylinder and I'll monitor the wear rate.

The OEM pads are far more 'sintered' looking and less 'organic'.

Fingers crossed.

---

which Ferodo compound? I ordered a set of Ferodo pads when M&P had an offer for 3 for 2 i.e. the rear pads for free. They had my favoured ST compound (gold pack, HH sintered) for the front but only the black, Eco Friction for the rear https://www.ferodo.co.uk/blog/eco-fricti...er-braking.html

do you think there was something different in the dimensions or that the compound was causing drag? I know some compounds can contaminate disk rotors that can give the impression of warped rotors

---