BMW K bikes (Bricks)

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1Back to top Go down   K100 rear brakes Empty K100 rear brakes Wed Jun 01 2016, 09:07

gunsports

gunsports
Silver member
Silver member
Need some help from the experts:

'83 K100 8v, no ABS. Never had rear brakes. replaced the brake disk (Motobins), the brake pads and the master cylinder (second hand unit off a K75). The master cylinder has good pressure and there is no flow back under pressure that I can see. No corrosion in the cylinder bore. I also replaced the bleed nipple.

Bleeding these brakes are a pain! Eventually, I used a big syringe attached to the bleed nipple to suck the brake fluid through the system till it was clear and without air.

Brakes worked well. Did not lock up under hard breaking, but very effective.

Next morning: No brakes, no pressure, nothing. No leaks and no flow back as far as I can see.

Please help

    

2Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 09:50

92KK 84WW Olaf

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I was cleaning the underneath of the bike last weekend and found something that may be of interest. Its only one of a possible number of issues.

I noticed the gaiter on the rear brake master cylinder was a bit distorted and had come off. I decided to investigate as I had found been finding a not good rear brake. Pulled the gaiter to one side and saw that the pedal was not acting on the piston. There is a plastic plug which has a recess on it for the brake pedal push point and this sits into a recess on top of the piston. Or should sit in because it wasn't. All the brake pedal was doing was pushing the plastic plug to one side but having nil effect on the brakes. I reset it all and put it back together and hey presto a working rear brake. It's an easy check but fixing it does probably mean pulling off the brake pedal.

In my case it happened recently when I changed the rear brake light switch.


__________________________________________________
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
    

3Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 09:50

RicK G

RicK G
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Sounds like the second bleed hole in the bore of the MC is blocked. looking in the open end there will be one hole about 2-3mm in diameter and a much smaller hole directly behind it. That small hole is probably blocked so that when you let the plunger return to the rest position fluid isn't drawn into the MC to replace what has been bled out. It is not easy to see or clean out. I have used a bristle from a wire brush held in a pair of long nose pliers to get to it clear.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki
    

4Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 13:12

Dai

Dai
Life time member
Life time member
Front or rear? Olaf has assumed rear, Rick seems to have assumed front (unless I've mis-read him). I read it as rear, because you mention replacing a disc (singular).


__________________________________________________
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
    

5Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 13:25

92KK 84WW Olaf

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Life time member
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@Dai wrote:Front or rear? Olaf has assumed rear, Rick seems to have assumed front (unless I've mis-read him). I read it as rear, because you mention replacing a disc (singular).
Just goes to prove there's always two sides to every argument.....even better both might be correct Korrect.


__________________________________________________
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
    

6Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 13:29

gunsports

gunsports
Silver member
Silver member
It is the rear brakes.

    

7Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Wed Jun 01 2016, 14:41

Dai

Dai
Life time member
Life time member
I should have read the title... sorry to both you and Rick. To add to Rick's comment, you will need to dismantle the rear brake assembly so that the master cylinder is on the bench. To see the two holes I'm pretty sure you'll need to remove the inlet pipe on top. Be sure to get a new one (and its O-ring) before starting because you can almost guarantee that it will break during removal.


__________________________________________________
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
    

8Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Mon Jun 06 2016, 02:48

gunsports

gunsports
Silver member
Silver member
Thanks for the advice. Will check it out. In bed with the flu and its damn cold down here. Brakes will have to wait a while.

    

9Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Mon Jun 06 2016, 19:40

Point-Seven-five

Point-Seven-five
Life time member
Life time member
@Dai wrote:I should have read the title... sorry to both you and Rick. To add to Rick's comment, you will need to dismantle the rear brake assembly so that the master cylinder is on the bench. To see the two holes I'm pretty sure you'll need to remove the inlet pipe on top. Be sure to get a new one (and its O-ring) before starting because you can almost guarantee that it will break during removal.
Do you know where I can get one of these inlet pipes?  It isn't shown on any parts lists I have seen. 

I had my master cylinder sleeved last year and the shop damaged the inlet pipe when they removed it.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

10Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Mon Jun 06 2016, 19:48

RicK G

RicK G
admin
admin
It is almost impossible to get the pipe out without breaking it. I believe Mazda have a suitable replacement in their parts list but as yet have been unable to find it. I was told this by a person I met that used to work for a brake resleeving place, he said it had the Mazda logo but he only knew that much because his boss treated it like a state secret.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki
    

11Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Tue Jun 07 2016, 05:43

Dai

Dai
Life time member
Life time member
Brembo. It's common across a lot of their motorcycle master cylinder range. The problem is that you'll need to locate a genuine Brembo supplier and talk to them because the company don't deal direct.


__________________________________________________
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
    

12Back to top Go down   K100 rear brakes Empty Re: K100 rear brakes Tue Jun 07 2016, 11:16

Dai

Dai
Life time member
Life time member
Motorworks (www.motorworks.co.uk) at a £10 each. I just called them to ask about it - the part isn't listed on the website.


__________________________________________________
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
    

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