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Old 10-03-2014, 10:30 AM   #1
caponerd OP
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rebuild kit for R100 handlebar mount master cylinder?

The search function appears to be broken, so I don't know if this has already been brought up.

Does anyone sell a kit to renew the piston seals in the 1981 and later front master cylinder?
Mine's leaking. I've taken it apart and cleaned it up (that cured it several years ago), but cleaning it up didn't help this time around.
The bore is still smooth and shiny after cleaning the crud out of it, no pitting that I can see in the area where the seals go, so I presume new seals should cure it rather than putting out $350 for a complete replacement.
Don't see an advantage to a used one, it will be just as old as mine, and possibly in worse shape.
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Old 10-03-2014, 10:41 AM   #2
JStancampiano
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Look at Max BMW parts list: http://www.maxbmwmotorcycles.com/fic...3&rnd=04282014
under steering section.

You need to know diameter of master cylinder..15 or 16mm.

Not cheap at $83.06

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Old 10-03-2014, 10:45 AM   #3
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FYI, motobins in the UK has complete MS's for waay less than here in the US.

Think the same is the case for rebuild kits as well
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Old 10-03-2014, 10:45 AM   #4
caponerd OP
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Quote:
Originally Posted by JStancampiano View Post
Look at Max BMW parts list: http://www.maxbmwmotorcycles.com/fic...3&rnd=04282014
under steering section.

You need to know diameter of master cylinder..15 or 16mm.

Not cheap at $83.06

Joe

Thanks, now I guess I better take a real good look at the cylinder to make sure it's really in good shape. I'd hate to spend nearly $85 only to find out I'm going to have to replace it anyway.
If it's 15 mm and turns out to have some pitting I didn't spot before, can I get it honed to 16mm and buy that kit?
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Old 10-03-2014, 01:32 PM   #5
caponerd OP
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Quote:
Originally Posted by SOLO LOBO View Post
FYI, motobins in the UK has complete MS's for waay less than here in the US.

Think the same is the case for rebuild kits as well


The motobins price for the entire master cylinder assembly is about 1/3 less than the cost in the US, but the kit looks like it will come out about the same after shipping.

They list sizes for the kits and complete cylinders running from 12mm to 16mm and a 20mm size. Why so many different sizes? Are they interchangeable on the brake lever mount, or does each one require a different mount?
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Old 10-03-2014, 07:15 PM   #6
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The 12 and 13mm cylinders were mostly used on single disc bikes (with the exception of early monolever bikes). 14mm and larger were used on dual disc. 20mm is very different and is used with 4-piston calipers. I think the varying sizes can be explained by BMW tinkering with lever feel.
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Old 10-03-2014, 08:06 PM   #7
manic mechanic
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Look on the bottom of the master cylinder and you should find a number stamped there telling what the diameter is. I recently replaced the piston and seal assembly on an '83 RS, ~$70 from the dealer.
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Old 10-03-2014, 09:39 PM   #8
Beemerboff
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Unless someone has already honed a 14mm out to a 16 mm, as happened to me.

My local brake guy has the right machine with a capstan head set up and can re sleeve with a SS liner for less than the cost of a repair kit so I haven't done a hone / seal kit for years, but I don't remember them ever lasting as long as a new cylinder.

A 12 mm MC will give you much better braking power and feel and is worth the price for that alone .
It doesn't change the length of pull as much as some would have you believe - the majority of the lever movement takes place before the bleed hole in the MC is closed , and it is only the lever movement after that point that is changed, after a couple of applications you wont notice the difference.

But you will always notice the extra power
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Beemerboff screwed with this post 10-04-2014 at 06:17 AM
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Old 10-03-2014, 09:58 PM   #9
Rob Farmer
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The replacement master cylinders are now made by Grimeca, identical in appearance to the Brembo unit.

I rebuilt a master cylinder last year before a trip to France. It was fine for weeks prior to the trip and for most of the trip but let rip cutting the trip short by two days. I ended up buying a new master cylinder effectively wasting the rebuild kit.

Sometimes it's as well to spend the extra on a new cylinder and forget about it for the next 20 years or so.
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Old 10-04-2014, 07:13 AM   #10
Darryl's bmw
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I have a master cylinder for $150 + shipping in excellent shape.
Came off a 1984 R100RS.
dt.cainey@gmail.com
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