BMW K bikes (Bricks)

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StefanMajonez

StefanMajonez
active member
active member
Hi!

Recently, my rear brake stopped working, and I figured it was due to the master cylinder. I found this thread that said you can replace the rear master with a Chinese one with great success, and with many people saying it's a very good option.

But, there were no step-by-step guides with photos, so here I am making mine. If you know something I don't, or want to correct something I've written, feel absolutely welcome to do so.

Before anyone scolds me, yes, I did pressure wash my entire bike right after doing this mod.

Disclaimer: This was done on a 1994 K1100LT. Other models should work, but some details may be different.

First off, here's my rear cylinder. Apparently I'm a very 'lucky' person with a master cylinder that is non-servicable, which, in addition to no cheap genuine used parts, is the reason I'm doing this.

Replacing rear master cylinder with a Chineese one LxejvT4
Replacing rear master cylinder with a Chineese one Zzm89bf
Replacing rear master cylinder with a Chineese one OKaPDxg

First thing I did was unscrew it from the brake line, and then remove the entire unit+reservoir from the bike.
Replacing rear master cylinder with a Chineese one KoFRQoa

Then I took the side panel (with the brake pedal) off the bike. Took that opportunity to disassemble the entire brake pedal pivot assembly and put some grease on it, because why not. I removed the bolt that pressed in the old master cylinder, and threaded the new Chineese master cylinder into it until the holes in the cylinder lined up with the threaded holes of the side cover. Then I screwed the master cylinder to the side cover.
Replacing rear master cylinder with a Chineese one FVI1GFM
At this point the brake pedal, when pushed, couldn't bottom out the cylinder because it was binding. With the cylinder screwed into the side panel, I unscrewed the threaded rod from the pedal until it started binding at the beginning of its travel, and then backed up two turns or so.

Removed the excess thread with a hacksaw
Replacing rear master cylinder with a Chineese one WTuDvkn

The next thing I did was try to fit it to the bike, and find a nice location for the new reservoir. There was actually a perfect place for it - an unused hole in a piece of metal that was behind the side cover.
Replacing rear master cylinder with a Chineese one UcFAnia
Replacing rear master cylinder with a Chineese one 0bA7Q5V
Replacing rear master cylinder with a Chineese one WttZ7Xq
Unbelievably perfect placement.

Then, I unscrewed the solid brake line from the ABS II unit, and placed an M12x1 to M10x1 adapter into it.
Replacing rear master cylinder with a Chineese one IyWv1LJ
Replacing rear master cylinder with a Chineese one UzDM8cP

I then pulled out the old, metal brake line form the bike (which wasn't easy and took a fair bit of bending it) and put in a new line - an 80cm line with a right angle on one side and a slight bend on the other.
Replacing rear master cylinder with a Chineese one J2i43Zj
Replacing rear master cylinder with a Chineese one A5MmpqM

So, everything is assembled, now to put fluid into it... But how to do it, if the input to the cylinder is from the bottom?

What I did is to flip the entire thing upside down!
Replacing rear master cylinder with a Chineese one EOdBaSk

I pumped the brake until no bubbles emerged in the reservoir. That means that there's no (or very little) air between it and the cylinder.

After that, I put the side panel back on. First I put a hose on the ABS bleeder, and put a big 50ml syringe on the hose. Unscrewing the bleeder and pulling a vacuum meant that the entire length of the new hose had air sucked form it fast. Pumping the brake all the time so new fluid is put inside the new brake line.

After that, standard bleeding procedure. What I did was bleed the ABS until no air bubbles emerged, then I bled the caliper, I went back to the ABS unit and then back again to the caliper. It probably could be done smarter and with less waste brake fluid, but I wanted to ensure no air in the system.



And, that's it! Here are some additional photos:
Replacing rear master cylinder with a Chineese one TC9JTfv
Replacing rear master cylinder with a Chineese one Sier0tH

I tested this setup out very briefly on a few hundred metres of asphalt, The brake works very nicely, feels sharp. On some light sand or gravel, I can more easily lock up the brakes and activate the ABS than with the original cylinder.

If you want more photos, feel free to ask! I'll get up tomorrow and take them. Also, I'll be test-driving the bike tomorrow afternoon, so I'll report on that as well.



Last edited by StefanMajonez on Sat Apr 20, 2019 1:39 am; edited 1 time in total


__________________________________________________
1994 - BMW K1100LT
Dyno results 2017


Previous bike:
1989 Honda CB450S
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Nice job!  Welcome to the Chicom master cylinder club.  Take the $260 you saved and use it for fuel to take a nice trip. 

Screw BMW and their stupidly priced master cylinders.


__________________________________________________
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
    

MartinW

MartinW
Life time member
Life time member
Welcome to the Chicom club. A couple of Brickers using the method you used without the articulation of the cut down bolt have experienced binding. See link http://www.motobrick.com/index.php/topic,9364.msg76252.html#msg76252
Regards Martin.


__________________________________________________
K75s Hybrid
    

StefanMajonez

StefanMajonez
active member
active member
@MartinW wrote:A couple of Brickers using the method you used without the articulation of the cut down bolt have experienced binding.

I've experienced binding as well, what I did was unscrew the master cylinder rod until it started binding at the beginning of its travel, then backed up a turn or two. That way I could bottom the master cylinder without issue.

Is there a better way to do it? My initial plan was to use a joint of some kind, but there's very little space between the new cylinder and the brake pedal.


__________________________________________________
1994 - BMW K1100LT
Dyno results 2017


Previous bike:
1989 Honda CB450S
    

MartinW

MartinW
Life time member
Life time member
See the link I posted there are two slightly alternate methods. With either method you can just counter sink the head of the bolt using a vice and a suitable size drill as per .75 (Gryph]. Once done you wont look back. I will shortly have to buy another one as I am out of stock people keep on pinching my spare.
Regards Martin.


__________________________________________________
K75s Hybrid
    

Woodie

Woodie
Life time member
Life time member
Thanks for taking the time to document the process StefanMajonez.  For all of us that have made the change to this MC we must have a very sizable number of kms/miles now with this alternate part.  I know that I am pushing 20k kms since I made the change.  It hasn't done anything other than what it is supposed to do since it got installed.


__________________________________________________
1985 K100RT
52667
"Keep your stick on the ice.  We're all in this together."  Red Green
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Countersinking the end of the ChiCom shaft to accept the pin on the pedal has worked perfectly on two different bikes for about 20,000 miles now.  The spring centered pivot on the master cylinder does a very nice job of accommodating the arc the pedal swings through.

With the money saved by using this master cylinder, get stainless brake lines and new pads and you'll have the best rear brakes you can buy.  Absolutely amazing feel and stopping power.


__________________________________________________
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
    

tinyspuds

tinyspuds
Platinum member
Platinum member
My new Chinese m/c has arrived and my thanks to Stefan for this guide and great photos. I’m not rushing to make the swap so I have plenty of time to get the remaining parts in. Just spent over an hour reading the development history of this solution, which is a reminder of how much work the hard core put in so that us newbies can just swan up and go “oh yeah, you just use the universal Chinese master cylinder swap”. So thanks all from the young engineer onwards. 
S


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

Woodie

Woodie
Life time member
Life time member
I was on my home from work yesterday afternoon and on a whim I decided to make a sudden slow down and quick turn and go down a road less traveled.  My lovely non OEM M/C locked up the rear wheel and blessed me with a little chirp.  Very Happy  The previous OEM M/C had been long past its ability to do this.  15 bucks - hell yah!


__________________________________________________
1985 K100RT
52667
"Keep your stick on the ice.  We're all in this together."  Red Green
    

tinyspuds

tinyspuds
Platinum member
Platinum member
@Woodie wrote: The previous OEM M/C had been long past its ability to do this.  15 bucks - hell yah!
When my unbraked chair is fully loaded for a trip I need a rear brake that can make itself heard so yes: 15 bucks - hell yah! mech


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Like you guys, BMW had totally erased from my memory banks the absolutely heavenly sensation of a working rear brake. 

Then the Young Engineer introduced me to the cheapy from the ChiComs.  Hell, Yeah!


__________________________________________________
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
    

tinyspuds

tinyspuds
Platinum member
Platinum member
The two methods of articulation explained previously are to either drill a detente into the end of the new push rod or; burr the end off the new push rod and create a larger detente in the head of an 8mm bolt which replaces the existing adjustor bolt in the pedal.

Both of these methods are intended to replicate the articulation available in the OEM nipple and detente arrangement.

I was planning to take the first approach as I have neither lathe or drill press but it occurred to me that, rather than drill the detente, I could just leave a push rod nut a couple of threads proud of the rod (maybe loctite in place) and let the nut ‘capture’ the nipple... I have a strong track record in drilling bolts and studs but none survive the experience.


Photo: Dry run with a single nut sitting a couple of threads above the rod:

Replacing rear master cylinder with a Chineese one D8d5ff10
Replacing rear master cylinder with a Chineese one 08f4d510

This approach looked like a runner but rather than loctite I added a second locking nut (there is room on the rod for two and still have full compression) which feels like a very secure cage for the adjustor nipple. I also like this as it retains the brass to brass friction surface.

Replacing rear master cylinder with a Chineese one 6609e510

You can just make out the nipple almost completely buried inside the nut and the nut is set just low enough that the flange around the nipple clears the nut at full articulation of the rod.

For shorter rods a half width locker or one nut with loctite could be used.


“If I have seen further it is by standing on the shoulders of giants”


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
That looks pretty good.  Nice job!


__________________________________________________
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
    

MartinW

MartinW
Life time member
Life time member
Replacing rear master cylinder with a Chineese one 112350 Replacing rear master cylinder with a Chineese one 112350 Another way to skin a Roo.


__________________________________________________
K75s Hybrid
    

tinyspuds

tinyspuds
Platinum member
Platinum member
“Pride goes before a fall” section.

When I put everything back together I over did the pedal adjustment and the brakes were everything I hoped for. Except the over adjustment resulted in the m/c piston being unable to return fully. In turn this meant that the caliper pistons couldn’t retract properly.
In turn this meant that after a 10 mile ride I experienced a loss of forward movement then stall.
Rear brake was locked on and smoking like a damp bonfire. 

Caliper dismantled, plastic cover discarded, melted seals replaced, everything cleaned, greased and re assembled. Now I cannot get back pressure into the system which is the problem I had before - which is why I over compensated on the adjustment (without thinking it
 through) in the first place.

I’ve flushed all the boiled fluid, can get good pressure at the m/c outlet, and at the caliper end of the stainless steel line but can’t make it carry through to the caliper.

Both pistons move, both pistons retract when pushed, both pistons will lock on when pumped but there is a barely noticeable increase in resistance at the pedal and the pad grip isn’t exactly snapping turtle.

I have used both the hand pedal pump method and the vacuum assisted. Run through litre and a half of fluid and spent 6 hours without progress.

Any thoughts?


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

Laitch

Laitch
Life time member
Life time member
Do you have the reservoir cover screwed on tightly when checking the brake pressure? Sometimes the mind wanders. Replacing rear master cylinder with a Chineese one 652573


__________________________________________________
1995 K75 73,000 miles
Replacing rear master cylinder with a Chineese one Usa-lo10
    

tinyspuds

tinyspuds
Platinum member
Platinum member
@Laitch wrote:Do you have the reservoir cover screwed on tightly when checking the brake pressure? Sometimes the mind wanders. Replacing rear master cylinder with a Chineese one 652573
More of an aimless shuffle really. 
When I tested at the cylinder with my thumb over the banjo outlet I couldn’t resist the pressure, so am assuming that reservoir to banjo is aok. Likewise testing at the caliper end of the brake line, not as conclusive as the olive was leaky when the swivel was unscrewed, but nonetheless, certainly a good flow coming out between the olive and the line.
Writing that makes me wonder if the olive should be leaky when unscrewed, but all the joints stay dry when everything is buttoned back up.


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

tinyspuds

tinyspuds
Platinum member
Platinum member
I’ve moved this to a new thread ‘cannot bleed rear brake’ as it is not a ‘how to’ (yet Replacing rear master cylinder with a Chineese one 44271).


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106. (Not blind to the irony of an April 1 production date).
2007 HD883 Sportster. Bobbed and bettered.
1954 Royal Enfield 350 Bullet. Original.
    

19Back to top Go down   Replacing rear master cylinder with a Chineese one Empty Chicom master cylinder on Tue Aug 06, 2019 1:39 pm

Chewbacker

Chewbacker
active member
active member
Hi, does any one have a link where i can buy one please?

    

John A

John A
active member
active member



Last edited by John A on Wed Aug 07, 2019 4:42 am; edited 1 time in total (Reason for editing : put in wrong link)


__________________________________________________
1985 BMW K100RT Vin: 0051738 (old style tank)
1982 Suzuki GS650GL
    

21Back to top Go down   Replacing rear master cylinder with a Chineese one Empty master cylinder on Tue Aug 06, 2019 2:22 pm

Chewbacker

Chewbacker
active member
active member
Hi John, that takes me to a fuel pump. Maybe I should clear my cache.

    

John A

John A
active member
active member
@Chewbacker wrote:Hi John, that takes me to a fuel pump. Maybe I should clear my cache.
Sorry, I was reading the thread about the fuel pump before switching to this one and posted the wrong link. I have updated the link to the master cylinder that I bought. I am sure that many other master cylinders on fleabay do the job just as well.


__________________________________________________
1985 BMW K100RT Vin: 0051738 (old style tank)
1982 Suzuki GS650GL
    

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