F800 Rear brake lock up

A question from a visiting K rider.
I recently took a F800ST out for a test ride. As I approached the traffic light at the end of an off ramp following a 12 mile ride on the interstate the bike seemed to slow very quickly and I noted a burning smell. I pulled onto the nearest side street to investigate and found the rear brake to be engaged and the rear disk looking darkened. There were no warning indicators for the ABS, or any other warnings. Since the bike would move with some reluctance and I was within a couple miles of the dealer, I forced myself to rev it high enough to get moving and by the time I arrived at the dealers the bike was operating normally. Have any of you experienced a similar problem? Are there any braking problems associated with the F800's equipped with ABS?

No such experience with my '07 F8ST.
That had to be a little spooky for you, yes?

Yeah, spooky in more ways than one. It's not a good feeling to have problems with someone elses bike and I'm left wondering if I missed something that would have told me there was a problem?

I really liked the bike; light weight, quicker and more responsive than my K.

You were on an unfamiliar bike. Are you sure you weren't maybe resting your foot on the brake pedal?

After you noticed the brake dragging you said the problem went away on the ride back to the shop. Could of just been you accidently dragging the brake until you consciously avoided it.

lostandwandering said:

<snip> Are there any braking problems associated with the F800's equipped with ABS?

Click to expand...

I don't own an F800S or ST but I have been monitoring F800 related message boards, thinking I might want to swap my K75 for an F800. A few F800's seem to have a rather serious ABS problem where in the computer will sometimes release all braking pressure even though the rider really does want to stop. That's one of the reasons I still have my K75.....

Well, it has happened to a few people including myself. I took a used 2007 F800ST with about 10K on it for a test ride from the local dealer. About 10 miles into the ride I noticed that I was having to add more and more throttle input to maintain speed. As soon as I pulled the clutch the bike wanted to stop pretty quickly. So back on the throttled and pulled into the first parking lot I could find. As soon as I pulled the clutch in, the rear completely locked up. You could not move the bike at all. The rear brake caliper was literally on fire. A bit of smoke, cracked paint and a bit of brake fluid oozing out of the bleed nipple.

The bike got picked up by BMW Roadside service and the next day I went to the dealer to see what the deal was. The tech at first, not knowing who was the rider it messed up on yesterday, said it was user error. After politely explaining that I was the rider and no I did not ride with my foot on the rear brake, in fact I even tried to pull it up after it started acting up with no luck and it had happened to others as well. He stated they it looks to be like a seized piston and something to do with the caliper pin.

Needless to say that I did not buy that bike but took a new 2009 of the floor as I really liked the bike

Similar problem with my F800ST

I had a similar problem with my Bike a few months back, it was shortly after Dealer maintenance. I took it to another (non-BMW) dealer whose shop manager is trained on BMW's. He determined that the rear brake reservoir had been over filled by the dealership. Since I found that out I have seen one other F800ST with a similar problem, and warned the rider to have it checked. When filling that reservior you need to keep the level about half way up, and not to the full line. Otherwise, with hard braking the fluid gets hot and cooks, first locking the rear brake and then providing no braking at all.

Tom Pemberton

Very interesting indeed: Being a brake system Geek, Question when was the fluid last flushed out completly ?, what type of riding boots were you wearing ?, due you know exactly what type and brand brake fluid was in the bikes mentioned above, I understand the overfill and the riding of the rear brake even if it was just a block or two, Just looking for information thats all....Matthew

I have a 2008 ST with about 13k miles and have never experienced any rear brake problems as described or otherwise. Have only once had the ABS engage and that was during a 'controlled' panic stop during an experienced rider refresher course. Assuming the "resting the right foot on the brake pedal" wasn't the cause, I think the suggestions about the brake fluid are the most likely explanations. I have talked with one rider personally and seen a few posts on the F800riders forum about some fluid issues including more than one case where the fluid seemed contaminated in that it was very dark. In those cases it was flushed by the dealer and no problems or darkening recurred.

F800ST rear caliper rust caused outer pad to drag

The outer pad on my rear brake wore down on a recent trip. After tearing down the brake caliper I found that the 2 rods that it slides in and out on were frozen. One of them had rust on it. The bike spends most of its life in my garage. It is only outside for rides, but I do ride in the rain some. The rubber cover over that rode had a very small hole in it. I assume that is how the water got in. I cleaned the rust off and greased the rod. I can only find the whole caliper assemble for sale new for $450.00. I guess I will look around for a used one. I just need the small rubber cover that goes over the rode.
Anyone else experience this with the rear brake?

DavidMTX said:

The outer pad on my rear brake wore down on a recent trip. After tearing down the brake caliper I found that the 2 rods that it slides in and out on were frozen. One of them had rust on it. The bike spends most of its life in my garage. It is only outside for rides, but I do ride in the rain some. The rubber cover over that rode had a very small hole in it. I assume that is how the water got in. I cleaned the rust off and greased the rod. I can only find the whole caliper assemble for sale new for $450.00. I guess I will look around for a used one. I just need the small rubber cover that goes over the rode.
Anyone else experience this with the rear brake?

Click to expand...

OK, I am answering my own question
I got some info from someone on the f800riders.org site forum.

Same problem on 17 R12GS/improper brake adjustement

I had the same problem on my 2017 R12GS. I had adjusted the rear brake pedal backlash a little too tight, though it seemed to still have significant distance between the relaxed pedal and initiation of braking when cold.) I loosened the linkage a bit, and let the rear brake cool, and have not had that problem since.