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1Back to top Go down   Rear brake issues Empty Rear brake issues Sat Jun 30, 2018 5:30 am

AL-58

AL-58
Life time member
Life time member
I use the rear brake a lot on the sidecar, it helps with the steering a bit.  Recently it hasn't worked all that good.

If I stand on the brake pedal, I get some retardation but not much.
Syptoms: rear master cyl has no signs of leakage, brake pads show evidence of getting very hot at some stage, caliper pistons move freely.

I stripped the master cyl, stripped the rear caliper and cleaned everything(ultrasonic cleaner). 
The master cyl seals appear fine and like I said no leaks - reassemble
Cleaned and replaced all seals in the caliper, internal seals were not leaking, pistons moving freely.  Outside seals were bad.
Replaced the hose from the reservoir just in case.

Once reassembled, it's no different.  I have pedal pressure but no braking power at all.

I'm thinking that even though the master cyl is not leaking its obviously not doing much.  I know I can put a seal kit in the master cyl (the bore is good) at a cost.  There are some inexpensive master cyls available online but I cant find one that tells me the piston diameter which is the important thing.

Has anyone used one of the cheapie M/Cyls with any success?  Have a link?
Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Rear brake issues K-dogs10
    

2Back to top Go down   Rear brake issues Empty Re: Rear brake issues Sat Jun 30, 2018 6:07 am

Laitch

Laitch
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If the pistons are freely moving, there are no leaks and resistance at the brake pedal is appropriate, the master cylinder seems ok. Have you replaced the brake fluid within the last two years? Have you de-glazed the rotor? Doing that and scuffing the pads might change the outcome.

There are successful, less costly substitutes for oem. Here's a thread describing one of them.


__________________________________________________
1995 K75 81,000 miles
Rear brake issues Usa-lo10
    

3Back to top Go down   Rear brake issues Empty Re: Rear brake issues Sat Jun 30, 2018 6:27 am

AL-58

AL-58
Life time member
Life time member
All new fluid flushed through today.

Softer pads are in order to begin with, the current pads have lots of metal.  Hard wearing pads are not a requirement.

Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Rear brake issues K-dogs10
    

4Back to top Go down   Rear brake issues Empty Re: Rear brake issues Sat Jun 30, 2018 7:01 am

MarcS

MarcS
Silver member
Silver member
Try hitting the rotor with 80 grit sand paper on an electric sander. You may have glazed the disk, sanding will rejuvenate it by removing the glaze.


__________________________________________________
K100rt ex plod bike 5/1990.



I have no problem with authority. Just some of the morons that are paid to enforce it.
    

5Back to top Go down   Rear brake issues Empty Re: Rear brake issues Sat Jun 30, 2018 7:02 am

Dai

Dai
Life time member
Life time member
n/m. I should read the entire thread first!


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

6Back to top Go down   Rear brake issues Empty Re: Rear brake issues Mon Jul 02, 2018 7:19 am

K75cster

K75cster
Life time member
Life time member
Al I believe an  XL600 Honda brake master is a good 13mm replacement for the rear master. Cant remember the years that fit though. In a pinch that may give you back the pressure you need, the master on your bike may have grit in the fine hole just in bore past where the piston sits its an equalisation hole and if blocked would probably drop the pressure you don't have. Maybe pull it apart and double check that little hole.

Maybe the rubber thingy that the threaded adjuster pushes is starting to perish and is squashing down instead of doing its job.


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

7Back to top Go down   Rear brake issues Empty Re: Rear brake issues Mon Jul 02, 2018 8:56 am

charlie99

charlie99
VIP
VIP
keith may be on the right thoughts Al

if memory serves me correctly rossko had a very similar issue
eventually he found the equalizer tube and freed it up ...but I think that was after he ditched the master cylinder for a newer version


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%ORear brake issues Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

8Back to top Go down   Rear brake issues Empty Re: Rear brake issues Mon Jul 02, 2018 10:41 am

duck

duck
Life time member
Life time member
Have you considered trying a smaller diameter master cylinder to increase the pressure? K bike rear master cylinders come in both 13mm and 12mm. Switching from 13 to 12 should yield about a 15% increase in line pressure.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

9Back to top Go down   Rear brake issues Empty Re: Rear brake issues Mon Jul 02, 2018 10:58 am

sidecar paul

sidecar paul
Life time member
Life time member


__________________________________________________
'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

10Back to top Go down   Rear brake issues Empty Re: Rear brake issues Mon Jul 02, 2018 11:16 am

92KK 84WW Olaf

avatar
Life time member
Life time member
I had an issue with my rear brake and discovered inside the boot/gaiter there is a little pad/[in to go between the brake pedal and the piston on the master cylinder. This was misaligned so it was contacting the master cylinder instead of pushing down on the piston and I got plenty pedal pressure and little braking. Peel back the boot and have a look to see its all correctly aligned.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

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