Author Topic: Aftermarket Rear Master Cylinder Replacement Guide $10-$25  (Read 25108 times)

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #25 on: February 10, 2017, 09:59:10 AM »
I don't have a problem with the reservoir hose location.  What I am addressing is my desire to keep the original screw on the pedal and the articulated joint between the pedal and the master cylinder.

I still don't have the new cylinder so I can't say for sure, but I think I will be doing a slight modification to the mounting holes on the new cylinder, a simple bracket to allow mounting the cylinder a couple cm further from the pedal, and some way to provide a bit of a socket on the actuator shaft similar to what is on the original master cylinder to allow for some articulation.

The idea is that if, for some reason, I need to go back to original, it will be as easy as possible since I will avoid any permanent changes to the bike itself to accommodate the new 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 Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #26 on: February 10, 2017, 02:59:04 PM »

I'm just trying to offer alternatives and trying to find something as close as possible to the OEM. The only problem I can see with the reservoir hose on the bottom is that it could be more vulnerable to damage and snagging.  I am waiting to see what TMG says about the articulation, as I to don't want the mod to be irreversible. The closer to OEM and the less mods the better, especially for the less mechanically inclined.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Scud

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #27 on: February 10, 2017, 04:15:47 PM »
I bought some caliper rebuild kits from MG Cycle, because Moto Guzzi and BMW used many of the same Brembo parts - and the Moto Guzzi parts were less expensive. MG Cycle currently shows many rebuild kits and complete master cylinders available. I haven't looked into compatibility myself, but here's a link.


http://www.mgcycle.com/index.php?main_page=index&cPath=110_112

  • Carlsbad, CA
  • 1992 K75s. 2002 Moto Guzzi V11 Scura, 2003 Moto Guzzi V11 LeMans. 2007 Husqvarna TE450

Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #28 on: February 10, 2017, 04:47:16 PM »
I tried the local Ducati and Guzzi dealers to try and get alternate kit replacement for the OEM. They weren't interested in even looking, too much trouble to go looking, was told to go OEM. :dunno
  • 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 #29 on: February 10, 2017, 06:07:33 PM »
The cheap master cylinder arrived today.  Haven't had much time to look at it, but at first glance it makes me wonder how BMW can justify the additional $245 for their master cylinder. 

The slotted mounting holes look like they will accommodate the spacing of the mounting bolts on the footpeg plate without modification.

The push rod pivots through something like 10-15 degrees and is solidly returned to a centered position.  The boot looks kind of cheezy, but the boot from the old master cylinder fits in it's place.

Installation will involve removing the reservoir from the new unit and connecting the hose to the hose on the original master cylinder.  Will need a hose barb and a couple clamps.

The mounting tabs are thicker than the original, so it looks like I'll need a longer screws and a pair of flat washers.

There is a tang on the end of the body that looks like it might interfere with the brake line banjo fitting.  Might have to cut it off. 

The plan for the push rod is to cut it off at about the same length as the original.  I will install one of the nuts on the push rod and will counterbore the end to form a cup for the rounded end of the rod attached to the brake pedal to ride in. 

Right now, I am not too concerned about the hose connecting to the bottom of the cylinder.  It looks like it doesn't hang down any more than the center stand.  I suppose it could get knocked off, but it would take one heck of a bump on the center stand and the rest of the stuff down there to get to it.

I hope to get some work in on it this weekend.
  • 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 Filmcamera

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #30 on: February 10, 2017, 06:11:53 PM »
Sounds good, I am watching this with great interest and look forward to your reports, as I am sure do many others, when it is done lots of photos please!
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Laitch

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #31 on: February 10, 2017, 06:12:26 PM »
The cheap master cylinder arrived today. 
Can we please have a photo of it in its virgin state?
  • 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.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #32 on: February 10, 2017, 07:10:15 PM »
Here's a photo showing the new master cylinder with an original.  I have put the boot from the original master cylinder on the new one to see how it fits.  Looks like a good fit. 

The reservoir has been removed.  The new hose is a larger i.d. than the original.  Looks like I will need to get an adapter 1/4" to 5/16" to match them up. 

You can just see the nut on the push rod at the point where I plan on cutting it.  So far, without spending any time in the shop, I am thinking this could be as easy as the Spal fan retrofit.  Outside of cutting off the push rod and drilling a slight counterbore there is no real metalwork in this job.  Basically, it's just bolting things up.

  • 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 Laitch

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #33 on: February 10, 2017, 07:18:54 PM »
Here's a photo showing the new master cylinder with an original.
Thanks.
  • 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.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #34 on: February 11, 2017, 05:46:02 PM »
In between painting tragkorbs and a mirror I started in on the new master cylinder.

First snag I hit was finding a reducer coupling to get from the 8mm(5/16") hose for the new to the 6mm(1/4") hose for the old so I could keep the original reservoir.  Spent two hours this morning going around to auto parts and hardware stores with no luck.  Had to order one on line for $10.  :mbird

Prepped and painted the new master cylinder black.  The gold just didn't do it for me.

Cut off the push rod to about one thread more than 1/2" extended from the body.  This puts the end of the rod about where the end of the piston on the original is.  I didn't want to mess up the geometry of the original with the pedal.

Then I drilled a 3/16" hole about 1/8" deep in the end of the rod to receive the rounded tip of the adjuster on the pedal.   The hole is to prevent the rod from sliding off the end of the adjuster when there is any side load.  The rod pivots about 10 degrees and will slide off easily with any side load on it.

Since I want to use the original boot to help hold the adjuster in the end of the push rod I cut two slots in the ribs on the master cylinder to help hold the boot in place.  When I am done mounting the cylinder and know the action is okay I'll put a black cable tie around the boot to further hold it in place.

Tomorrow I hope to get the cylinder installed and pedal adjusted.
  • 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 #35 on: February 11, 2017, 09:33:15 PM »

Looking good, looks like a pretty easy conversion could you please include pics when mounted on the foot peg plate. I looked at your conversion and was going to follow it with a few minor changes. However I borrowed a M/Cyl, pedal and plate from my mate, and at the moment I am pursuing the M/Cyl with the top reservoir mount, just to see if it is possible and what it involves. The more choices the better.If it doesn't look doable without a lot of trouble I will follow your path. How are you going to fit the hydraulic hose, new hose or an adapter.
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 #36 on: February 12, 2017, 10:12:48 AM »
Martin, just fired up the heater and I'm waiting for the garage to warm up a bit this morning.  It would be nice if you guys could send a tiny bit of your heat up here, we would be glad to take it off your hands.

The hardest part so far was centering the hole in the push rod.  Fortunately, I had a centering jig to use.  Once I had a pilot hole started, I put two nuts on the shaft, locked them together and clamped my Vise Grips on them to hold the rod while I drilled the final hole.  This is a job where you definitely want to use new bits and some cutting oil.  The sharper the better.

I plan to use both the old and the new hoses.  Neither is long enough to do the job.  I have an 8mm to 6mm reducer on order to connect them.  I hope it arrives this week. 
  • 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 #37 on: February 12, 2017, 01:27:06 PM »

OZ is in the middle of a heat wave, I'll redirect my three garage fans to blow some heat in your direction. I broke my own cardinal rule on Friday and rode back from my weekly dump day without my Kevlar jeans and jacket, rode home in shorts and a polo shirt. I think at this stage the M/Cyl that you have chosen is the better choice due to the slotted mounting holes. However I am proceeding with my choice, at this stage. However that may change today. I'm going to try and print a picture of the M/Cyl to scale if I can remember how to do it. I will definitely have to slightly slot the holes, I will probably know more by the end of the day. I was hoping to order one by Tuesday. About to go out now for my 4.30 am walk.
Regards a hot 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 #38 on: February 12, 2017, 01:47:36 PM »
Master cylinder is mounted on bike.  Took about an hour total including a bit shimming the footpeg plate out a bit to accommodate the bend that was put into it last summer when It went down on the right side.

With the 1/2" extension on the push rod the link to the pedal appears to be perfect.  Pedal action is pretty much the same as it was with the original master cylinder.  Bolting up was easy as the hole spacing and layout are nearly identical to the original.   So far I haven't even had to readjust the pedal. 

One thing, I put a dab of assembly paste in the counterbore of the push rod to insure that there will be no unusual wear there.  All that is left is to connect the hoses.  As of now I am going to use a right angle connector for the job.  Will be off this afternoon to get one and finish the job.  So far, I have only about two hours invested in this job.

So far I am very pleased at how easy and neat this is working out.  I was concerned about clearance with the center stand, but the photos show that is clearly not an issue.

 
  • 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 The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #39 on: February 12, 2017, 04:00:09 PM »
DONE!!!

Jury rigged a 1/4" elbow to connect the hoses, bled, adjusted brake light switch, and the damn thing works like a champ.  Nice firm pedal with a good feel.   :clap: :2thumbup:
  • 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 #40 on: February 12, 2017, 04:10:57 PM »

TMG I just need clarification what mods did you have to do to connect the caliper line to the M/Cyl. Pic would be nice.
Regards Martin.
  • 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 #41 on: February 12, 2017, 06:22:52 PM »

Printed out a couple of scale drawings of the intended M/Cyl with the top mount reservoir and measured everything up. While it could be possible, it would be tight due to the right angle bend for the reservoir. And due to the extra length in front of the mounting hole by the time you get it fitted no adjustment would be possible. You could make up a bracket to move the M/Cyl back enough to get the adjustment but that would require more work.
When I set out to try and do this I was after a quick cheap and simple way of doing it. As it stands Gryph's M/Cyl fulfills that criteria so I will use the same with a few mods.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Elipten

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Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #42 on: February 12, 2017, 08:11:57 PM »
Hat damn!  Screw BMW and their over priced parts!


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  • San Antonio, TX
  • 1990 K75RT

Offline Filmcamera

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #43 on: February 12, 2017, 08:22:09 PM »
I seemed to have trouble with the link that was posted but eventually found it - at least I think I did


https://ducati-gowanloch.com/shop/brakes/brembo-ps11b-rear-brake-master-cylinder-str-black/





  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #44 on: February 12, 2017, 09:09:20 PM »

Filmcamera that link was just for the rubber boot on the end of the M/Cyl. I Don't think that M/cyl will fit.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline PaulP

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #45 on: February 12, 2017, 10:25:21 PM »
If a field-test/ report is of any use to anyone, I used one of these el-cheapo master cylinders last summer in the restoration of my K100. I'd used them before on a couple of other projects.

The original BMW one and the rear caliper had been given to a friend circa 1999, and when I looked at the price of a new one I first squinted at the screen, then I winced, followed by a sharp intake of breath, and finally a right good chuckle.

A wee bit of footering with a bracket to get it mounted (since I don't use the original footpeg mounts) and the action was champion.

I've put about 1000 miles on it now and the operation has been perfectly fine. I only really 'trail' the rear brake in either heavy stop, or complete stop scenarios, so I couldn't say that it's had much in the way of abuse, but it works as it should.

I can't really comment on the long term efficacy of the gadget, as I can't presume that it's made from highest-grade unobtanium, but it hasn't crumbled into pieces yet.
  • Scotland, UK.
  • '91 K100 LT. Ex-Polizei.

Offline The Mighty Gryphon

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Re: Aftermarket Rear Master Cylinder Replacement Guide $10-$25
« Reply #46 on: February 13, 2017, 12:37:50 AM »
Martin, I went to the local auto parts emporium and bought a right angle 1/4" vacuum line elbow.  The line from the old reservoir connected ok, and the 8mm line from the new master cylinder seems to work when it's clamped tight with a fuel line hose clamp.  For some reason, reducers from 5/16(8mm) to 1/4(6mm) are impossible to find, so you have to go for 1/4 to 1/4.   If worse comes to worse, and it leaks, I think I can build up the leg for the 8mm line with some marine shrink tube, the stuff with the hot melt glue inside.  Two layers should be more than enough.

The line from the master cylinder is cut to about 3 inches long.  The original line was kept at original length.  I'll post a photo of the finished installation tomorrow.

One other thing, the banjo bolt on the cheapo master cylinder is not the same thread pitch as the original, so I'm not sure how easy it would be to find replacements if you ever needed one.

The reservoir line exiting at the bottom of the cylinder makes getting all the air out a little more difficult.  Took me half an hour of tapping and working the pedal to get all the bubbles out.

Haven't had it out for a road test as it snowed today and the roads are full of salt, but the pedal has an amazing firm feel compared to the old cylinder.  It's so firm that I had to adjust the pedal slightly to get the brake light to work.
  • 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 #47 on: February 13, 2017, 12:58:22 AM »


Gryph just ordered one much the same as yours. The reservoir adapter not a problem I've got a 60 year old metal lathe and some alloy stock. Air in the system not a problem I've got a homemade vacuum bleeder made out of relish jar and a vacuum sprayer hooks to my compressor.


However I am curious on how you have connected from the master cylinder to the caliper. I've posted for help on obtaining a cheap substitute kit for the front master cylinder I've had no cooperation from Ducati or Guzzi locally thought you guys might be able to have a crack at it. Looking forward to the final pics.
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 #48 on: February 13, 2017, 01:37:31 AM »
The connection to the brake line to the caliper is done with a Banjo fitting that comes with the master cylinder.  I just unbolted the line from the old cylinder and connected it to the new one.  The fitting works with the brake line, it just has a different thread pitch from the original, so they aren't interchangeable.  Or do you have the non-ABS rear brake where the line screws into the end of the master cylinder?  If you do, you will need a line with a banjo fitting if the threads on the line don't match. 

Do you have a photo of your existing master cylinder and brake line?

I used a vacuum bleeder as well, but it did not do that good of a job pulling the air out of the cylinder because of the connection being at the bottom.  Seemed that a lot of air stayed in the hose.  That's what I had to fiddle with.   The vacuum got me most of the way, but I still had to manually get a bunch of bubbles up to the reservoir. 
  • 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 #49 on: February 13, 2017, 02:17:11 AM »

Gryph mine is non ABS, screws straight into the master cylinder. But the guy across the road operates a mobile hydraulic and brake business. But I'll wait until the master cylinder arrives in a month or two and see what I have in my box of bits. Thanks for the information now it's just a matter of waiting.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

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