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Discussion Starter #1
I have a 2013 Bonneville and I love her to bits. However, I do find one or two things a wee bit ugly looking. One of these things is the gurty big plastic urine sample container that is the master cylinder.

I know there are replacements out there..I have my eye on the direct mount made by Britisb Customs. However, when I look at various T100 models, they have the low profile and much sleeker looking oblong master cylinder.

I saw one of these on Ebay (not sure the year as the listing didn't say) but according to the seller's reply to my message, it will need fit onto my 2013 Bonnie.

Is there any year T100 master cylinder that I can do a straight swap with or will I have to go with the direct mount one from British Customs?

Please note, I am still a newbie with basic tools and knowledge, so please take that into account when responding. Thanks?
 

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Basic rule of thumb is that alloy wheel Bonnevilles have 7/8'' bars and spoke wheel Bonnevilles have 1'' bars.
Scramblers have 7/8'', Thruxtons with clip-ons have 7/8'', Thruxtons with full bars have 1''.
 

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You'll need to be able to bleed the brake, which is as much an art as a science, and very frustrating the first couple times you do it. We all have tricks and favored techniques for accomplishing this, which you can read about all day if you search this forum.
 

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Discussion Starter #4
Thanks guys, but neither comment actually addressed my question about the master cylinder itself.

Basic rule of thumb is that alloy wheel Bonnevilles have 7/8'' bars and spoke wheel Bonnevilles have 1'' bars.
Scramblers have 7/8'', Thruxtons with clip-ons have 7/8'', Thruxtons with full bars have 1''.
I have bought a Renthal ultra low super bar to replace the stock one, and I already made sure it was 7/8".

You'll need to be able to bleed the brake, which is as much an art as a science, and very frustrating the first couple times you do it. We all have tricks and favored techniques for accomplishing this, which you can read about all day if you search this forum.
I don't necessarily think I will have to. Johnny Cactus and a few others didn't need to bleed the brakes when they put the BC direct mount master cylinder on. If I can get the oblong one that I mentioned in my post, then yes, I may need to bleed the brakes. But, there's a great video on Delboy's Garage how to do this, so should be fine if that is a requirement.
 

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Thanks guys, but neither comment actually addressed my question about the master cylinder itself.


I have bought a Renthal ultra low super bar to replace the stock one, and I already made sure it was 7/8".


I don't necessarily think I will have to. Johnny Cactus and a few others didn't need to bleed the brakes when they put the BC direct mount master cylinder on. If I can get the oblong one that I mentioned in my post, then yes, I may need to bleed the brakes. But, there's a great video on Delboy's Garage how to do this, so should be fine if that is a requirement.
There are loads of after market master cylinders on the market to fit 7/8th's bars. You will need to bleed the system when changing one though, I can't see any other way of doing so without getting air in the line, it can be a pig of a job to do mind you.
 

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Discussion Starter #6
There are loads of after market master cylinders on the market to fit 7/8th's bars. You will need to bleed the system when changing one though, I can't see any other way of doing so without getting air in the line, it can be a pig of a job to do mind you.
Thanks. I have seen many aftermarket master cylinders available. But, do you know if it's possible to put the oblong one from a T100 onto my Mag wheel Bonnie? That's what I really want to know. If it's not possible I will just get the BC direct mount master cylinder.
 

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Thanks. I have seen many aftermarket master cylinders available. But, do you know if it's possible to put the oblong one from a T100 onto my Mag wheel Bonnie? That's what I really want to know. If it's not possible I will just get the BC direct mount master cylinder.
Are you talking about just changing the plastic pot or the whole master cylinder assembly?
 

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The answer is NO. You have 7/8'' bars, T100 has 1'' bars. T100 Reservoir/master-cylinder assy only fits 1'' bars.
 

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Discussion Starter #9
Are you talking about just changing the plastic pot or the whole master cylinder assembly?
Either or. I know I can change the plastic cup with an aftermarket one, but I really like low profile nature of the oblong one on the T100. It seems like that would entail an assembly swap and not just the pot. Which I'm fine with, IF it's possible.

The answer is NO. You have 7/8'' bars, T100 has 1'' bars. T100 Reservoir/master-cylinder assy only fits 1'' bars.
Ah! Thank you. At least I know that now. BC direct mount it is. Cheers!?
 

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Be sure the M/C you get has an 11mm bore, any bigger and you won't like the results. If you could get a good deal on a T100 M/C you could make it work with handlebar shims. I haven't tried it but see no reason why it wouldn't work.
 

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Discussion Starter #11
Be sure the M/C you get has an 11mm bore, any bigger and you won't like the results. If you could get a good deal on a T100 M/C you could make it work with handlebar shims. I haven't tried it but see no reason why it wouldn't work.
The BC direct mount is designed for the Bonnie. Saw a videp Johnny Cactus did replacing his. Took about 15 mins start to finish. Definitely going to go with that option as it's the same size as the plastic cup, low profile and looks great on the bike.
 

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You might be able to get away with not bleeding, especially since you're only replacing the reservoir. What I describe below might be overkill for this job, I'm not sure, because I have the integrated unit that you want but can't use. Here's how I would do it if it comes to that point:

Remove the caliper, but don't disconnect the line at that end. Do NOT squeeze the brake lever after this. Clean the sides of the pistons with a bit of brake fluid, and carefully let the caliper hang there.

At the top end, protect the surrounding area from brake fluid. Do what you have to do, being sure to keep the brake line vertical so as to not lose any fluid in it.

Put a small amount of fluid in the new reservoir. Loosely cover the reservoir with the cap or a rag. Gently and SLOWLY push the brake pistons into the caliper a little bit at a time until you see some fluid come up into the reservoir. You should be able to do this with your fingers. (If the pistons don't move easily, this is your opportunity to clean them and replace the seals, which is a whole other project.) Give the assembly some sharp taps to encourage any air to bubble up and out.

Now re-mount the caliper, fill the reservoir with fluid, cover it, and pump the lever until the pistons seat against the rotor, making sure to keep sufficient fluid in the reservoir. You'll know then if you need to bleed it.
 

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To save a whole lot of hassle I would be tempted to try and get hold of a custom billet aluminium reservoir to replace the plastic one, this way you definitely wouldn't need to bleed the system.
 

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am I missing the obvious? why is that
Because your caliper, pipe and master cylinder would already have fluid in them, you would only be (very carefully) replacing the reservoir and it's contents..
 

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Discussion Starter #16
For those of you who have posted about bleeding the brakes after replacing the master cylinder, here is the Johnny Cactus video I have mentioned a couple of times featuring the British Customs direct mount reservoir I will be getting.
 

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This is were the confusion is. In the video that you have shown young Mr Cactus is only changing the brake fluid reservoir and not the brake master cylinder, although the reservoir is part of the hydraulic system it is not the actual master cylinder itself. You can change the reservoir quite easily without having to bleed the brake because the reservoir is on the non pressure side of the system so it wouldn't hurt to introduce a little air during the process, any air would be dispelled when topping the reservoir up with fresh fluid. If you were to change the master cylinder assembly then yes you would have to bleed the brake, because you would be working on the 'pressure' side of the brake system and when air gets into the brake line it will have to be 'bled' out, otherwise at best you would end up with a 'squidgy' front brake that would need to be pumped to get it to work any sense or at worst no front brake at all. If I remove brake master cylinder's or calipers then I bleed them every time for safety's sake.
From what I could understand from your discussion starter you wanted to fit a master cylinder with an integrated fluid reservoir. You could only fit one of these by removing the hydraulic brake pipe at the master cylinder end, in this case you would definitely need to bleed the system because you would be working on the 'pressure' side of the hydraulic system.
 

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Just watched the video, a word of advice: Be careful with the circlip tool. The clip will go flying to places unknown before you know what happened.
 

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Discussion Starter #20 (Edited)
Apologies if my explanation was worded incorrectly. I did say I was a newbie. Still learning the correct terminology.

However, gron my research it seemed liked any replacement reservoirs I could find were all round. If possible, I wanted an oblong one like on the T100. But it looked like that was integrated into the bracket that connects to the handlebar. When I looked this up on the internet everywhere was calling it a master cylinder. My back-up wax always going to be the BC direct mount reservoir.

That being said, braided steel brake hoses are one of the mods I plan on adding in due course. And due to my lack of knowledge/confidence that would be something I would get the guys ag my local motorcycle garage to do for me. They are a local business with a grwsg reputation and charge ridiculously low prices (sometimes they will do quick and simple things for free).
 
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