Need help with brakes please - K-Bikes.com - Excellence in Motion
 
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post #1 of 6 (permalink) Old Jun 2nd, 2013, 3:59 pm Thread Starter
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Need help with brakes please

Hello Guys!

I am having a little trouble with my rear brake on my 97' k12rs. I hade front pads changed yesterday, and the rear checked. the rear wasnt changed as the pads are still good. On the way home from the garage after few miles the rear brake started to apply itself and I hardly managed to pull over to a service station. By the time I stopped, the rear wheel locked up completly. Phone call to the mechanic, he was there in about 20 mins, and by the time he got there the pads and rotor cooled down and all was fine, however he adjusted the brake. Managed to get home without any problems.
Today same problem, about 3 miles of ride and comlete wheel lock up. Any idea what might be the problem?

I saw another thread about changing the pads, nice tutorial, but in there the caliper was not removed in order to change the pads. Mine was taken off, pads checked and then back again.

I appreciate any help/suggestions.
thank you!
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post #2 of 6 (permalink) Old Jun 3rd, 2013, 3:08 am
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Look on 'the other site' where I explained a problem and suggested your mechanic had taken the specified free play out of the rear brake master cylinder push rod adjustment.

When you rode off from the garage (because they did not test ride the bike) the rear brake master cylinder became a one way valve unable to release the pressure. He fooled you with the 20 minute call out, because he probably knew he had altered the adjustment and still may not have it right even now or your calipers got so badly overheated you have secondary faults caused by his maladjustment in the first place.

Potential problems may now be warped/blued rear rotor, burned and glazed over pads, sticking caliper pistons and excessive brake drag.

In my opinion at this stage you should pass over comments about rear brake line hoses, air in lines and just get on with checking the rear brake adjustment because your problem caused by the garage may now cost you a lot of money.

I only rode a mile with a locked rear brake. Fortunately, I was town riding and felt the drag when slowing. If I had been on the freeway I would not have felt the drag and the consequences could have been a rear end fire!!



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post #3 of 6 (permalink) Old Jun 3rd, 2013, 11:39 am
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In addition Vox's recommendations, you might as well pull that caliper and remove the pads. Clean it all up with simple green or similar, ensuring the pistons are in fact extending and retracting properly and that there is no debris in there or incorrectly assembled pieces. Once you get it all back together properly, you can use those brake pads to test whether the rotor is now warped by spinning the wheel and observing whether it hangs up in any location or if it rotates smoothly.
Best of luck on this!

Jim Douglas
'00 K1200RS >135,000 mi, '09 K1300S sold @ 22,232 mi
'93 K1100RS traded up @ 78,000 mi, '85 K100RS sold @44,000 mi, Kawi 650 track bike - sold
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post #4 of 6 (permalink) Old Jun 4th, 2013, 3:19 pm
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As voxmagna says, I inadvertently did this myself on my old R1100S, rear brake pedal adjustment is critical and from memory involves feeler gauges, well it did on the boxer.

Tim
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post #5 of 6 (permalink) Old Jun 4th, 2013, 8:39 pm
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Brake fluid..

Wondering if you also had the brake lines bled? If yes, possible air in system? Unlikely though. I have seen rear brakes lock up on a friends bike from having moisture in the brake fluid. If the system does have water in it (doesn't take much!) when braking, the heat build up will expand and will sometimes inadvertently cause brake pressure. Just saying....
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post #6 of 6 (permalink) Old Jun 14th, 2013, 11:53 am
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The only problem is the rear brake free play adjustment!

You take off the rear master cylinder like I did. Then see what happens on the fluid side when the push rod is moved back and forth and how small the distance is for the piston to sit forwards and block the fluid return hole, you (I) realise that the existence of free play is absolutely critical to stopping the master cylinder locking up. Even corrosion crud internally that causes the piston to stick and not return to the correct back stop can 'offset' the free play too far forwards.

That is the story I posted, because just measuring free play is insufficient. You have to be 100% sure that the piston rod and piston has returned fully back to the casing stop position BEFORE measuring the free play and adjusting it. When the master cylinder boot is fitted you see nothing so you must pull it back. Their circlip is plain steel and it can rust changing the critical distance setup too.

The issue is all to do with their design of the m/c. They made it so small and short that to get the required stroke length from the pedal and with the minimum of dead zone (initial pedal movement but no pressure), they put the fluid return hole really close to the piston stop position.



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