1150 Brake problem

[(RIP) Dennis]

My 2000 1150 with 50K miles has developed a gentle pulsing through the brake lever when applying the font brake. It feels as though the discs are warped ( a fairly common BMW problem I believe) so I replaced the discs with two nice new cast ones from Motorworks. Problem still there just as bad.

The bike has ABS which sets OK, but won't switch off as it should. Whether this is part of the same problem or something different I simply don't know.

Whilst the pulsing is fairly gentle it make heavy braking quite uncomfortable.

Any suggestions ?????

 

[Greg Masters]

I think that I'd be getting my micrometer and my dial guage out. Check for both consistency of thickness around the disc and then check for run-out. I would have though that any more than about 5 thou out on either would start to cause problems like the vibration you describe or pad knock-off (long lever travel).

Greg

 

[(RIP) Kaister]

Are the mounting bolts and washers ok and does the disc still 'float' on the wavy spring washer.
If not, id suggest the disc carrier is warped and forcing the disc out of true when its bolted down.
Did you buy brand spankers new discs or used ?

Phil

 

[(RIP) Dennis]

Phill, Yes brand spanking new, but I've now changed back to the original disc as they had made no difference. Also changed the bolts wavy washers and bobins, and all brand new.

Just checked again that the discs do "float" on the washers, seem to be fine. Someone suggested that the brake bolts wear and that the calipers should move on the bolts, but that does not appear to be the case on mine !!!

 

[(RIP) Kaister]

i'm a bit stumped - new discs should sort it, then.

The calipers have to be solid to the forks - no float AT ALL

The discs can actually be slightly warped - as in 'bent' and you wouldn't notice it as long as the thickness was the same.
As one piston went in - relative to the caliper body - the other would go out by the same amount - pressure being equal eveywhere.

i had a guzzi that had a very bent disc and you could only tell by looking at it - it braked fine - no pulsing.

The pulsing can only be generated by pressure undulations - which are caused by the pistons moving out of synch - ie towards or away from each other - which would indicate a thinner or thicker area of a disc.

The only way is to check with a micrometer.
You could get your old discs surface ground for flatness by a m/c shop - if you still had pulsing - then i dont know - i'd have to see the bike

Phil

 

[(RIP) Dennis]

Is it possible that it could be a fault with the ABS System? Hope not though cause that sounds expensive even to think about !!!

 

[Keith Chapman]

Did you match new pads to the new discs???

 

[(RIP) Dennis]

Yep! new allround. When I changed the discs back I changed the pads a second time.

 

[Rob Farmer]

You need to make sure the pistons are not stuck in the caliper. I had a K1 that did exactly the same thing. It turned out to be one piston sticking causing the other to slightly distorte the disk when braking, resulting in a judder.

 

[(RIP) Dennis]

I feel a caliper strip down coming on me.......It's sure worth a look Rob, thanks for that, will keep you posted

 

[(RIP) Dennis]

Rob,
I Think you have solved the problem. Checked left caliper last night: Bingo,2 seized pistons, in fact both of the outside pistons were siezed.

Managed to get them moving to a degree which has improved the situation. Tonight I will take the caliper right off and give it a full strip/rebuild (didn't have enough brake fluid last night).

Many thanks to all who replied with suggestions & thoughts

 

[(RIP) Dennis]

Job done. Now all I've got to do is get all the air out of the system.

Left caliper has normal bleed nipple, right one has some other gizzmo that doesn't want to budge ( and I don't quite know what to do with it if it does)

 

[Greg Masters]

The little bar-steward on the right-hand caliper is a filling valve. On mine I took it out and replaced it with a regular bleed nipple. If you go that route, be warned, it's well Loctite'd in!!

I think that you can just unscrew and remove the grubscrew in the top and use a regular bleed nipple to bleed, then replace the grubscrew.



Greg

 

[jpisace]

Caliper

You might be referring to the factory fit adapter that is used to backfill the system. It resembles a round 'pedestal' that stands up above the caliper, on the right hand side, with a hex head 'grub screw' in the top. Just take out the whole thing (the hex head rounds off easily - so be careful, otherwise mole grips required etc to turn the main body) and replace with a bleed nipple.

If push comes to shove you can attempt to bleed the front brakes through the left hand nipple - but only if absolutely necessary as there would still be a significant doubt that all air had been removed from the system.

Best bet is order/buy another nipple and fit that when it arrives.

Johnieeeeeeeeeeeeeeeeeeeee

 

[Greg Masters]

Re: Caliper

Best bet is order/buy another nipple and fit that when it arrives.

It's a regular 10mm nipple that can be had from most motorists' shops. About 99p for two (why two???!)

Greg

 

[(RIP) Dennis]

Thanks for the info guys, I was a bit worried that it was something to do with the ABS (although I couldn't see how).

Sorted