I was just out for a ride on my 1991 900ss and the bike appeared to be loosing power, then it felt more like the rear was dragging, went to pull in and the back wheel locked up, rear disc now a fetching shade of purple! (ref photo) rear brake lever solid, waited about 10 mins and the brake freed off completely and movement returned to the brake lever, just tried the rear brake as I pulled into my road and there’s not much braking and lots of travel on the lever, has anyone experienced similar?.
This is usually because there is no free play at the master cylinder pushrod to allow the piston to fully return and uncover the bleed hole that allows the fluid to return to the reservoir. Once the brake gets hot the fluid expands pushing the brake on harder until it locks. When it cools down it is free to move again. Check for free play at the pushrod.
Sometimes even with free play in the lever the plunger doesn't fully return, remove the rubber boot from the master cylinder and you can see if the plunger has fully returned back to the circlip , I have successfully removed the plunger and carefully cleaned the inside of the master cylinder with very fine wet and dry wrapped around a piece of wood to ease the free play of the plunger and solved this problem. Steve
Thanks for the replies, I’ll have a look tomorrow, the master cylinder was new about a year ago, only done about 3k miles, faultless until now, anyway I’ll have a look tomorrow evening and report back.
Yup, no free play, I blame the idiot that fitted the new master cylinder, me!, pistons and seals seem OK, new pads on order, the terrific fun of rear brake bleeding to come, what a donkey, just call me Dominic!
Yeah, I’m trying to figure out why it didn’t happen much sooner?, still got away with it lightly considering what the consequences could have been I suppose:0
Changed pads? Maybe air gets in over time and takes out any play. May be worth checking every now and then now you know it’s likely, as you may done a percent job: circumstances have just changed over time
Yup, happened to me with a BMW R80/7 Only time I was ever grateful for the brakes being truly awful. Dread to think what would happen with really powerful front brakes...
How long since you last used it? Partial seizing of slave/master due to standing can be enough to cause this and might explain how you got away with it for so long despite master cylinder pushrod not having correct freeplay.
Had the same on my 916. At the first service dealer adjusted the brake pedal and on the ride home it started to feel sluggish until it eventually stopped me (a 916 with working rear brake??). The pads were actually on fire and the disc all sorts of rainbow colours. Dealer collected it, changed the pads, adjusted the freeplay and it was OK again but a year or so later the rear caliper was found to be leaking - possibly because of the overheat?
almost certainly because of the overheat as body and/or piston can warp, had the same on a 'car' after a first speed test, worst bit is the heatsoak when slow moving or even moreso stationery, nearly lost the whole car and I can still remember the sound of the tyre ticking.
Happened to me on my M600 rear and resulted in new disc, caliper and master cylinder. Suspected free play, but it was actually blocked return hole in M/C.
Hi Chris I’m out on the bike every weekend so it’s not a lack of use thing, I had just gone over a series of 4 mini islands in quite a spirited fashion including heavy braking so I’m wondering if the bleed hole was only partially blocked due to the maladjustment and in the past single use of the brake coming up to a junction etc allowed the fluid to drain back and the brake to free off before to much heat was generated, whereas the rapid reapplication of the brake with the islands all within 300 yards up each other led to the fluid not draining back and the fluid becoming seriously overheated expanding and exacerbating the issue, maybe?, anyway I’ve adjusted the master cylinder correctly now and when the new pads are in I’ll bleed it and then keep a close eye on it.
Had it on mine at motorway speeds.Felt a little sluggish,so gave it a bit more.It seemed to sort it self out.When I got home it had eaten both pads and melted both pistons,then thrown the fluid over everything.Probably my fault for trying to get the back brake to work.Doh!Wont bother next time.
