Rear Brake Caliper Seal Orientation R1250RT

[Tony Fyson]

My 2019 R 1250RT has had a sticking rear brake from new. My dealer could not find anything wrong with the brake, despite the fact that it had worn out two sets of rear pads in 6000 miles, and the rear disc was hot even when I had not applied any rear brake.
The rear disc has worn below the minimum thickness in less than 24,000 miles. See link below for details of this issue.

viewtopic.php?p=54045&hilit=sticking+rear+brake#p54045

As the bike is now out of warranty, I have purchased replacement Brembo pads, caliper seals and disc. I fitted the replacement parts today.
Unfortunately I did not check to see if the seals were tapered, and required fitting in a particular orientation.

From what I have found on the website, the taper needs to be towards the hydraulic side (facing towards the base of the piston recess). Please can anyone confirm if the seals are tapered, and if so, how should they be orientated. Is it possible the seals could have been fitted the wrong way round when the bike was manufactured?

Thanks
Tony

[David.]

Have a look at this thread, it's for a Camhead but may well apply to a Shifthead too, viewtopic.php?p=49715&hilit=seal#p49715 hope that helps.

[David.]

My 2019 R1250RT has had a sticking rear brake from new. My dealer could not find anything wrong with the brake, despite the fact that it had worn out two sets of rear pads in 6,000 miles and the rear disc was hot even when I had not applied any rear brake. The rear disc has worn below the minimum thickness in less than 24,000 miles.

The dealer should have replaced the rear caliper. I had both the front calipers replaced under an insured warranty because they were binding. They also replaced the pads as "consequential damage", (damage caused by another covered part, the calipers).

As the bike is now out of warranty, I have purchased replacement Brembo pads, caliper seals and disc. I fitted the replacement parts today.

Has this solved the problem of the sticking rear brake, if so, I'd be going back to BMW to recover the costs.

[Tony Fyson]

Hi David
The rear brake is still binding on the disc. Hence the enquiry regarding caliper seal orientation.
I will remove the brake pistons and check to see if there is a raised edge on the caliper side of the seal, not the pad side.

Frustratingly, I have complained to my dealer about this problem, and they claim that they could not find anything wrong.
Could there be an issue with the rear master cylinder not allowing fluid to return to the reservoir?
When I push the pistons back into the caliper, the fluid level in the reservoir rises - as expected.
Thanks
Tony

[exportman]

Hi

Did the pads wear evenly or just one? Common issue is the pad nearest the wheel ( the side without the pistons) wears more than the other side due to the calliper not sliding freely on the pins. It happens on many makes with the same issue. Regular maintenance of the slide is required.

[60Aviator]

I know maybe too late for you but this video shows how to service the rear brake caliper to keep it working great.

[David.]

This isn't a BMW caliper but very similar, no mention of the seals being directional.



Have spoken to Motorworks who sell this seal kit, https://www.motorworks.co.uk/rear-brake ... 607-2.html
It's the same one as was fitted to my Camhead and Motorworks have confirmed that the seals are not directional.
Their recommendation was to ensure that the pistons are well lubricated with the silicone oil provided in the kit.

Paul at The WorkShop, https://www.theworkshopyork.com/ has also confirmed the above is true.
He described the fluid seal as having fins but being U shaped. Careful not to get them twisted during installation.

[David.]

When I push the pistons back into the caliper, the fluid level in the reservoir rises - as expected.

Same as in this video by The Old Mechanic, FF to 13:15.



IMO, if the pistons can be pushed back by hand, they are free enough not to bind the brake.

[David.]

This video shows a Brembo/BMW front caliper being overhauled.



At 3:00, it mentions the first (outer) narrower seal having a "double ridge".
If this is the same design as the rear, perhaps it confirms that the seals cannot be inserted incorrectly & are therefore not directional.

[Tony Fyson]

Hi All

Many thanks for the help and advice.
As I suspected, the piston seals do not have a taper, so can be fitted either way round.

Exportman noted that the pad opposite the pistons tends to wear more quickly, if the caliper does not slide freely on the pins.
All three sets of my pads have worn excessively on the pad closest to the piston. This indicates that the caliper slides freely, and the pistons are not retracting enough to allow the pad to move back slightly from the disc.

I have fitted new seals, and the brake is still dragging. I removed the caliper from the mounting, and took out the pads. I depressed the rear brake pedal to observe the pistons moving out. However, when the brake pedal was released, the pistons barely retracted.

When I fitted the new seals, the pistons slipped easily into their locations. But since they do not retract, could a piston be slightly oversize (at the top end of its specification)?

[David.]

I removed the caliper from the mounting, and took out the pads. I depressed the rear brake pedal to observe the pistons moving out. However, when the brake pedal was released, the pistons barely retracted.

This video shows how to test for brake caliper piston retraction. The pistons are moved out until they apply some pressure before they are observed to be retracting, FF to 4:00.

[David.]

Has the rear brake pedal freeplay been checked.

[Tony Fyson]

Ummm... How do I check brake pedal free play?
There is some movement in the rear brake pedal, when depressed, before the pistons start to move. How much movement do I need?
Thanks

[David.]

Sorry, don't know how to check the brake pedal free play on a Shifthead.

If there is some pedal movement before the pistons move, you'd like to think it's ok.

Found this generic video, it's probably a similar set up on a Shifthead.





More info. here but it's for an R1200GS, https://www.advrider.com/f/threads/r120 ... nt.673961/