BMW K bikes (Bricks)

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1Back to top Go down   Rear brake amplifier Empty Rear brake amplifier Wed Jul 28, 2021 10:01 am

Kjell.Martinn

Kjell.Martinn
active member
active member
Hey! Its leaking from the rear brake amplifier, any troubleshooting tips and tricks, or just some tightning?

Rear brake amplifier 986df510  

Thanks guys!

    

2Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 12:30 pm

Ringfad

Ringfad
Life time member
Life time member
You probably need a rebuild kit available from Motorworks and I am sure other places also but the link shows the components.

Motorworks BMW Motorcycle Specialists - Shop - Spares and Accessories


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Rear brake amplifier Ir-log10

   ;BMW; K100RS Style Black 1987 105K Km     ;BMW; K1 Black 1993 60K Km     ;BMW;  K1100RS Blue 1994       ;BMW; K1 Blue 1990 25K Miles
    

3Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 1:43 pm

Laitch

Laitch
Life time member
Life time member
@Kjell.Martinn wrote:Its leaking from the rear brake amplifier, any troubleshooting tips and tricks, or just some tightning?
Around here that part is called a rear brake master cylinder. Tightening it is not an option. A repair kit might work if the cylinder is not worn out. You could consider replacing it with an inexpensive master cylinder that some riders here have done successfully. Here is a link to a thread about that.


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1995 K75 81,000 miles
Rear brake amplifier Usa-lo10
    

4Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 2:19 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member

I've never had any luck rebuild kits. The only fix that ever worked was to replace the original master cylinder with a Communist one for $13. It's in the thread that Laitch linked to.

The problem I have seen in these master cylinders is that water collects in them and corrodes the bore. Because the casting is so porous the corrosion goes deep and is almost impossible to correct. The communist master cylinders are so cheap it doesn't make sense to try to repair the old ones.


__________________________________________________
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
    

5Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 6:08 pm

MartinW

MartinW
Life time member
Life time member
You can extend the life of your master cylinder by packing silicone grease into the boot. It will reduce the chance of water and road crap ingress.
Regards Martin.


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K75s Hybrid
    

6Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 8:56 pm

Laitch

Laitch
Life time member
Life time member
@MartinW wrote:You can extend the life of your master cylinder by packing silicone grease into the boot. 
I did that following Martin's suggestion. It gets renewed every couple of years. I wring out my moto on the worst municipal gravel roads in Vermont for six months out of the year—rills, ruts, moonscapes and mud. It's all so adorably rustic. The rear master cylinder hasn't been bothered by any of it for years.  cheers


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1995 K75 81,000 miles
Rear brake amplifier Usa-lo10
    

7Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Wed Jul 28, 2021 9:12 pm

MartinW

MartinW
Life time member
Life time member
I love silicone grease it saves a lot of headaches. I haven't changed  fork seals in over 20+ years, just I pack silicone grease between the fork seal and the dust cover and change it every couple of years. I would change it more often if riding in dusty conditions. I also pack a bit in around the piston entry point on the front master cylinder.
Regards Martin.


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K75s Hybrid
    

8Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Thu Jul 29, 2021 8:36 am

yamaguzzi

yamaguzzi
Life time member
Life time member
I use the silicon grease in the forks ,never tried it in the brakes but what I do in the brakes is flush out the fluid every season .I had good luck with the rebuild kits.What I did there was really clean the bore then lightly hone it with 1500 wet /dry paper  and then cleaned it again with brake cleaning solvent a couple times .Gonna try the grease in the boots now.Never heard of using it there before .


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://motoguzzi850t.blogspot.com/
    

9Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Thu Jul 29, 2021 8:51 am

Laitch

Laitch
Life time member
Life time member
@yamaguzzi wrote:. . . what I do in the brakes is flush out the fluid every season . What I did there was really clean the bore then lightly hone it with 1500 wet /dry paper
Rear brake amplifier 112350
When I salvaged the rear master cylinder on my moto, I used a Scotchbrite pad for polishing the bore. It worked well, too.


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

10Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Thu Jul 29, 2021 3:11 pm

brickrider2

brickrider2
Life time member
Life time member
"...and then cleaned it again with brake cleaning solvent a couple times"


What is this brake cleaning solvent of which you speak?


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1996 K1100LT
    

11Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Thu Jul 29, 2021 4:59 pm

Kjell.Martinn

Kjell.Martinn
active member
active member
Thank u guys! Thanks again Laitch for some very good help! I'll try to diasemble the master cylinder and maybe consider a repair kit, or follow the thread u showed me :-) Also great with som advice for maitance and making longer life of the Rear Master, great people with good advices! Thanks!

    

12Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Thu Jul 29, 2021 6:03 pm

yamaguzzi

yamaguzzi
Life time member
Life time member
@brickrider2 wrote:"...and then cleaned it again with brake cleaning solvent a couple times"


What is this brake cleaning solvent of which you speak?
I use this stuff pictured hereRear brake amplifier Img_5311


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://motoguzzi850t.blogspot.com/
    

13Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 9:45 am

Kjell.Martinn

Kjell.Martinn
active member
active member
Another thing! The Rear Brake master cylinder started leaking after removing the caliper and gave air to the system? It will not fix itself when i assembel the caliper again and letting the air out again?

    

14Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 10:20 am

yamaguzzi

yamaguzzi
Life time member
Life time member
The master failed .It failed when you were in there messing around but that is not why it failed.It was shot before you ever messed around in there. it may not have been leaking at that point but it would have very soon and disturbing it just made it happen a little sooner .Looking for reasons for it's failure is like a dog chasing it's tail.The fact is you have two choices here.You can rebuild it or you can replace it.Getting the air out had nothing to do with the failure ,it just wore out.


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://motoguzzi850t.blogspot.com/
    

15Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 12:47 pm

brickrider2

brickrider2
Life time member
Life time member
I once used that very brake cleaner on a bike with a hydraulic clutch system.  Soon after the cleaning of the slave cylinder it started to cause problems. The brake lever would not return after using the brake.  I limped home and replaced the slave cylinder o-ring, which had swollen, preventing preventing the piston's return. The second time I had the cylinder apart I only used brake fluid to flush it.  The problem never returned.  
I urge caution when using brake cleaner.  It may well be that it is best restricted to use on drum brakes.


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1996 K1100LT
    

16Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 2:53 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Another caution about using CRC brake cleaner is that if you have repainted anything on your bike with rattle can paint it may make a mess of the finish. No need to ask how I know this.


__________________________________________________
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
    

17Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 6:28 pm

yamaguzzi

yamaguzzi
Life time member
Life time member
This product is for cleaning brake parts  like brake pads or shoes, metal parts like caliper pistons or wheel cylinder pistons , internal metal parts of wheel cylinders and calipers and master cylinders like the bores after a hone before coating them lightly with brake fluid for assembly.Just about any solvent will eat rattle can paint and lots of stuff will cause rubber to get flabby and swell. Carb cleaner will do the same thing.Using these chemicals requires caution and common sense .They have a specific use and are very good for their intended purpose .You can't just spray away you need to remove parts to work with this stuff or protect the surrounding  area somehow. As for the product,it's not the product that causes problems like bubbling paint or failing rubber it's the user


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://motoguzzi850t.blogspot.com/
    

18Back to top Go down   Rear brake amplifier Empty Re: Rear brake amplifier Fri Jul 30, 2021 8:44 pm

RicK G

RicK G
admin
admin
I have found and others here also mentioned it that when you are bleeding you use the full stroke of the master cylinder and gunk that has collected at the lower part has stuck to the wall and when the piston seal passes over it the seal is damaged. I always now clean the master cylinder before bleeding and so far (fingers crossed) I have not had a failure after bleeding.


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"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 2004 K1200GT 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki
    

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