Author Topic: Aftermarket Rear Master Cylinder Replacement Guide $10-$25  (Read 35748 times)

Offline wmax351

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #75 on: March 11, 2017, 11:06:28 AM »
This might be the Magura repair kit for a K75S (ABS 12mm non 13mm) but the page won't display.  :nono Magura isn't talkin'.

Good find.



http://webcache.googleusercontent.com/search?q=cache:aod0tXf829wJ:www.magura.com/en/components/powersports/originalspareparts/productdetailpage/%3Fp%3D21710+&cd=1&hl=en&ct=clnk&gl=us

Try google's cache.

Here's a place to order it. https://www.louis.eu/artikel/magura-repair-set-for-bmw-288-brake-lever-assembly/10019379
Looks like the part is a magura 288 master cylinder. Rebuild kit is (I Think) magura part 10019379. That might be the part for the louis cycles, though.





https://cdn1.louis.de/content/catalogue/articles/zusatz/anl/10019379_MAGURA_Anleitung.pdf?_ga=1.50803680.873073721.1489248398


Here's the manual to install.


  • Ann Arbor, MI on the way to ABQ, NM
  • 1991 BMW K75 Standard, Refreshed '94 engine
Bikes:
Current:1991 BMW K75 Standard, 1998 Moto Guzzi California EV11
Past: '83 BMW R65LS, '75 Honda CB550F, '69 Honda CB175, 1999 Royal Enfield Bullet 500, 1973 Triumph Tiger TR7V, 1971 BMW R75/5 in Toaster outfit, 1979 Harley Davidson XLS-1000 Sportster Roadster

Offline Laitch

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #76 on: March 11, 2017, 11:17:58 AM »
Good find.
Here's the manual to install.
I just used that site to find a dealer, not that I need these components. The only dealer was Onion River Sports—a high quality outdoor gear dealer in Montpelier VT whose motto is Muscles, Not Motors. They must be supplying disc brake components made by Magura for bicycles.



  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline lmiklosy

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #77 on: March 11, 2017, 01:45:49 PM »
Didn't mean to mislead anybody, as wmax351 found the Magura Repair-Kit does not fit the K75S, see the applicability under TECHNISCHE DETAILS on the Google Cache page. With no test history the Chinese replacement MC is unknown but I'm happy to begin testing, mine is on the way from Zhejang.  For those who wish to rebuild cylinders with new parts I'll report back with any sources I find. As a matter of fact a variation of the EPDM rubber used for MC plastic bits is used in the thermal liner for US fleet ballistic missiles and the NASA Space Shuttle, Ariete offers those bits. The material science it would appear supports rocket science.
  • Laguna Beach, CA
  • 1993 K75S-Mystic, 1981 R100RS-RedBaron, 1991 K75S-Marrakesh

Offline milq

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #78 on: March 11, 2017, 07:56:14 PM »
Good stuff! I've used a very similar MC as well as a caliper to rebuild the rear brake system on my son's Yammy Blaster a couple years back. Everything worked well and just required a couple of brackets that I made in the shop.
  • Southern IL
  • 1988 K75S

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #79 on: March 12, 2017, 01:07:28 AM »

Made up the 6mm to 8mm adapter learnt by my mistake on the first one. Placed the adapter behind the foot peg plate, I ended up cutting 25mm of the OEM reservoir line and cut the new hose down so that it curved up to meet the OEM line. I was expecting problems with the bleeding but my home made Nescafe bleeder coped well. As I pushed down on the pedal with the bleed nipple open and connected to the bleed jar, I pulled the trigger on the suction gun, I kept doing this until no air was being drawn out of the caliper , it did take a little bit longer than usual. I am happy with the ease of the conversion and it doesn't even look dodgey looks pretty much OEM. Not to sure if I could of shortened the hose to the caliper but I think I'll leave it. I put the boot on that I scored for nothing, I could have put the OEM boot on with a slight modification but I am going to try and track down the supplier of boots and M/Cyl cups. I put a dab of marine grease on the end of the stop where it meets the push rod.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #80 on: March 12, 2017, 01:23:30 AM »
Looks pretty nice, Martin.   :clap:
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #81 on: March 12, 2017, 01:39:50 AM »

Thanks Gryph I'm very happy with it. However all up it took about 5-6 hours to make the two reducers.  :dunno  The first one sheered just as I was finishing the last couple of passes, the centre hole made it too weak. The second one I just drilled a 3mm pilot hole through it which when I tried to drill it bigger the bit jammed could not free it up. I eventually broke off the bit, the only way I could eventually get it out was to cut off the lump at the end and drive it out with more 3mm drill bits. At $50.00 and hour that means it cost $250.00.
I don't think I'll get a job making 6mm to 8mm adapters.  :hehehe :hehehe
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #82 on: March 12, 2017, 08:56:53 AM »
Hey, $250 is the same price as a rear master cylinder.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline wmax351

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #83 on: March 12, 2017, 10:14:35 AM »
It would be helpful if someone with the master cylinder disassembled could measure the cup seals and all other associated parts, front and rear. Trying to find an alternate source of these would be excellent. I can talk to some engineering friends about where to source them.

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  • Ann Arbor, MI on the way to ABQ, NM
  • 1991 BMW K75 Standard, Refreshed '94 engine
Bikes:
Current:1991 BMW K75 Standard, 1998 Moto Guzzi California EV11
Past: '83 BMW R65LS, '75 Honda CB550F, '69 Honda CB175, 1999 Royal Enfield Bullet 500, 1973 Triumph Tiger TR7V, 1971 BMW R75/5 in Toaster outfit, 1979 Harley Davidson XLS-1000 Sportster Roadster

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #84 on: March 12, 2017, 06:36:22 PM »

Gryph master cylinders in OZ are $300.00 so I saved $50.00. :hehehe If I'd been patient I could have ordered one of EBay for $5.00. :dunno  Max I am going out today to see if I can find the local supplier of cups and boots. I don't think finding a supplier of cups and boots is a problem, the problem is fitting them. As previously posted a special tool that slides over the piston and is tapered allowing the cup to be slid up and into the groove needs to be made or sourced. With the supply of rear master cylinders now solved for some of us, I am now just trying to solve the front master cylinder problem. I have thought about making a tool for the front cylinder cup replacement, but I need measurements, piston diameter and how far the tool needs to slide onto the piston. The other problem is a source of material for the tool, I have aluminium but I think polished stainless steel may be better. I am going to talk to a mate who has lathe tools capable of cutting stainless steel and might have a scrap piece to work with.
Regards Martin.

  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #85 on: March 12, 2017, 06:57:58 PM »
Martin, If  I recall, the tools I remember were machined out of aluminum or brass.  I think the tool needs to be softer than the aluminum of the piston you are putting the seal on.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #86 on: March 12, 2017, 10:57:55 PM »

Just got back from chasing up a cup and boot supplier. I a good talk to Glen the guy that owns the business, he seems to be one of two places in OZ the other is in Adelaide SA. He is a really nice guy and was very helpful. He sleeves the old cylinders in imperial stainless and the OEM pistons do not fit, so he makes new pistons out of brass. He does not like doing the rear OEM cylinders as the plastic piece for the reservoir is extremely hard to get out and it invariably breaks he then has to make a new one out of brass with an "O" ring   seal. He was reluctant to give a price on doing these and when I told him about the Chinese ones he said good. Cylinder sleeving costs $200.00 and under a two week turn around he gets cylinders from all over and will ship. He does guarantee and test them, but you need to tell him if they are not going to be used. Because if left sitting the brake fluid dries out and forms crystals which will cause the cylinder to leak. Replacement cups for his cylinders are $10.00 replacement boots are $4.00 picture attached. I asked him about the special tool to get the cups back on to the pistons. What he uses is a couple of well linished screw drivers with no sharp edges and plenty of rubber grease. I also dropped in on a mate and he is willing to make up a special tool out of stainless if needs be, if I can supply the measurements. I also got a bit more aluminium stock but I am concerned about the wall thickness required when placed over the piston. Before I can proceed I need someone to supply accurate measurements of the front master cylinder piston.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #87 on: March 13, 2017, 01:03:46 AM »
Does your buddy have a replacement for that friggin' clutch boot that tears if you let the arm slip and costs $40(probably $70 next year)? 
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #88 on: March 13, 2017, 03:51:54 AM »

Good question Gryph, I will see if my mate has an old one to do a comparison. If not do you have the measurements. If they can be had cheap I will post you one or two.They used to be $20.00 on EBay, just had a look, now $30.00. The EBay guy is sort of local south of Brisbane. I thought $4.00 was pretty reasonable for the master cylinder boot so I bought two. Apparently my boot never went over the brake pedal stop as yours did, I will rectify that situation with one of the new boots. I know you had a bad experience with sleeving but after talking to this guy and his very reasonable pricing I would give it a go if needed.
Regards a satisfied  Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline wmax351

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #89 on: March 13, 2017, 10:14:40 AM »
Does your buddy have a replacement for that friggin' clutch boot that tears if you let the arm slip and costs $40(probably $70 next year)?


You can do some searching, you might be able to find something. But I doubt it will save that much. BMW parts, as expensive as they are, are not that bad on the scale of things: They are also readily available. Try getting some rubber stuff for a honda from the 80s.

If you get the dimensions, you could look here.

This is just a random small one I found. http://www.rubberstore.com/catalog/neoprene-multi-convoluted-rubber-bellow-20mm-connector-p-8054.html


Or just get one here: 29 bucks. http://www.boxer2valve.com/motorcycle/2313731.html
Seems like they sourced one somewhere. Cheaper if you buy in bulk, so they might have ordered a few dozen.
  • Ann Arbor, MI on the way to ABQ, NM
  • 1991 BMW K75 Standard, Refreshed '94 engine
Bikes:
Current:1991 BMW K75 Standard, 1998 Moto Guzzi California EV11
Past: '83 BMW R65LS, '75 Honda CB550F, '69 Honda CB175, 1999 Royal Enfield Bullet 500, 1973 Triumph Tiger TR7V, 1971 BMW R75/5 in Toaster outfit, 1979 Harley Davidson XLS-1000 Sportster Roadster

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #90 on: March 25, 2017, 07:47:00 PM »

Finally fitted the new $4.00 boot. I had to relocate the brake pedal stop bolt lock nut to the back of the pedal, this required grinding a bit of the pedal to allow the nut to rotate. I can live with that as I can still go back to OEM even with this modification. I also had to cut a slot in the end of the bolt to allow adjustment with a screwdriver. This boot now totally seals it against road scum and water ingress. Instead of using a cable tie I found a non worm drive S/S hose clamp of the correct diameter and I also painted the reservoir hose clip black. My Brick owning mate, originally did not like the thought of modifying the Brick with a Chinese master cylinder. However after seeing the ease of the modifications, has now got me to order two for him. So I have placed an order for three, two for him and one that I might pull apart and have a look at or just put into stock. It has now been on the road for a while and I don't have any problems with tendencies to lock up it does however present a firmer pedal compared to the OEM.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #91 on: March 27, 2017, 11:58:11 PM »

Received the three Chinese master cylinders today cost $40.00 AU for three or $13.33 Au each. To pull them apart you need push the boot off the nut and screw the nut up out of the way, then gently pull the boot out of the recess in the master cylinder, it is just pushed in and does not sit in a groove. Next using circlip  pliers remove the circlip. The piston is then free to be removed. Looked at the bore and it looked fine no imperfections, the piston also looked well made. A set of cups locally for the Chinese one $10.00 AU, but not worth the trouble.


The second picture shows the OEM piston below the Chinese one, the Chinese piston is larger than the OEM one, and therefore unless you want to rebore the OEM cylinder and try and line up the ports is not a substitute kit. But who would want to do that anyway, with the ease and cost of the Chinese replacement.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline arnonymous

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #92 on: October 29, 2017, 02:52:43 PM »
Soooo, after discovering this thread, i thought i'd try the same with my leaky rear master cylinder.
I got the same chinese cylinder, and proceeded with the first approach as YoungEngineer shows in the OP. But i noticed that the brake wouldn't move smoothly due to the excessive sideloading, it just didn't feel good, and wouldn't push deep enough.
So today i cut the shaft shorter following Gryphon's approach, drilled a "cup" into it and using the original ball-end push-rod on the brake lever, the whole thing just moved smoothly :clap: [size=78%].[/size]
I then tried to refill and bleed the system, but for some reason this is where i failed.
I have (K75RT) ABS, and the original FAG banjo(quite fat one) coming from the ABS pump seems to fit the new MC, only with the new bolt, as others described.
To remove air from the reservoir hose, i used pliers until no bubbles come out of the reservoir.
I then used my normal bleeding procedure, without a vacuum, which always went quite fast for me. Now, though, nothing happened so i connected a vacuum, but no matter how much i pump on the brake lever and the vacuum,  i can't get the brake fluid moving... the level in the reservoir never drops. Does this mean i just have an air bubble at the MC entrance?


Any tips on getting the system pressurized, why is this failing?!?


ps. Quite disappointed to discover,  the ABS system passes the startup test with and unpressurized system. Apparently it just tests the brake light switch.

Offline YoungEngineer

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #93 on: October 29, 2017, 03:16:20 PM »
You are quite right about following Gryphon's  approach. I soon followed as I noticed the brake sticking on. I've not had any problems since. It may be worth updating my original post.
  • London
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Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #94 on: October 29, 2017, 03:25:01 PM »
I assume you are opening the bleeder at the input to the ABS modulator, is that correct? 

Are you getting anything coming out of the bleeder?  Do you see air bubbles coming from the bleeder when the vacuum is applied?

Is the pedal allowing the rod on the master cylinder to fully extend?  This is important because the orifice that allows fluid into the cylinder only opens at almost full extension of the rod.

I had used a vacuum pump to bleed my brakes in the past, but stopped because it seemed to suck air into the system at the master cylinder because the orifice to the reservoir was so small in the master cylinder. 

I would suggest cracking the bolt on the banjo fitting on the master cylinder and trying to bleed by pumping the pedal until you see fluid coming out, then go to the ABS module input connection and do the same, followed by the ABS module bleeder. 

As far as ABS self test, I think all that is checked is the brain, power(12v), that the wheel sensors both work and register the wheel speed, and that the motors in the modulators are connected.  The other test when pulling the brakes is for the brake light bulb monitor and the brakes switches.  That test is not part of the ABS startup and is also found on non-ABS bikes.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline lmiklosy

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #95 on: October 29, 2017, 04:30:29 PM »
Everything Mighty Gryphon said but I'll stress two points.

First if the brake pedal adjusting screw is tightened against the master cylinder plunger too far, the fluid supply hole will be blocked and no brake fluid can enter the master cylinder from the reservoir to displace the air.  Second, as you pump the brake pedal the MC piston does not sweep the entire volume of the MC. If there is an air bubble in there it will remain there laughing at you whilst you pump away at the brake.  :hehehe To help rid the MC of bubbles loosen the banjo bolt on the MC outlet side and work the break pedal again, you will see bubbles leave the system at the banjo bolt.  Tighten the bolt and move downstream to the next fitting (ABS pump if so equipped). The ABS pump has a bleeding fitting, connect a clear vinyl hose there and repeat pump the brake pedal. Watch for air bubbles leaving the system in the hose.

Hope that helps.
  • Laguna Beach, CA
  • 1993 K75S-Mystic, 1981 R100RS-RedBaron, 1991 K75S-Marrakesh

Offline Andrew2

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #96 on: October 29, 2017, 06:26:39 PM »
You are quite right about following Gryphon's  approach. I soon followed as I noticed the brake sticking on. I've not had any problems since. It may be worth updating my original post.


 Hey YoungEngineer, thanks for starting this thread, it's been invaluable :2thumbup: .


  Cheers
  Andrew
  • Wollongong, Australia
  • 1987 K100RS
It is no measure of one's health to be well adjusted to a profoundly sick society

Offline arnonymous

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #97 on: October 29, 2017, 07:30:13 PM »
Thanks for the replies, it does seem to make most sense that its probably set too tight, and basically never fully retracts to allow fluid in.
I'll try again, and report soon.

Offline YoungEngineer

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #98 on: October 29, 2017, 08:02:31 PM »

 Hey YoungEngineer, thanks for starting this thread, it's been invaluable :2thumbup: .


  Cheers
  Andrew




Not a problem.at all. I'm glad that it's been useful to others. I will amend my post at some point to make sure new viewers do not make the same mistake I did.


It's quite obvious now why BMW engineers put that pivot point in where they did.
  • London
  • K1100LT

Offline jdaley

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #99 on: January 30, 2019, 06:46:01 PM »
Thanks for this onfo, its gr8. I am building a K100 into a racing sidecar
  • Australia
  • K100
John Daley, Bendigo, Australia
K100 1983 as a racing sidecar along the lines of
UK BEARS sidecars and
Thunder sidecars in Australia

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