Xs750 master cylinder

Xs7501978

Active Member
I’m looking to buy a xs750 master cylinder...preferably aftermarket and not to expensive....I’m not really sure what are the requirements when picking because eBay says that the aftermarket ones I’m looking at will work but I want to be safe...will these work? Which will work best? Or at all...I’m not really looking to spend more than $40-$50
https://www.ebay.com/i/301845800563
https://www.ebay.com/i/301894577798
https://www.ebay.com/i/321937169024


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If you're not stuck on OEM factory spec, numbers-matching, concourse restoration, check your local online classified ads or bike salvage yards for a take-off piece from a more modern bike (think R1, CBR 600, GSXR, Ninja etc.). Then you can be assured of quality, and typically they're priced cheaply.
The CBR has a very tidy looking integral master cylinder, if you want to keep your cockpit clean.

I put a master from a 2003 GSXR 1000 on my '81 CB750C for $50 CDN (less than the cost of a rebuild kit) and the guy tossed in the clutch lever to match it. Works a treat!
 
The piston diameter is the important thing you need to know to find a suitable replacement. If you are keeping the same caliper(s) as stock, then any MC with the same piston dia as stock will be fine. If you are altering the brakes, then you will need to calculate the stock MC piston the caliper piston(s) ratio and select your new MC accordingly. Very often you can swap master cylinders with different piston sizes and have a functioning system - a higher ratio will make for more brake power vs. hand power with more lever travel for instance. Manufacturers select components to obtain a balance of these things. You can run into trouble using too small a MC piston size on large piston caliper brakes for instance as you can run out of lever travel before sufficiently squeezing the rotor(s) for example. Most MC's have the bore dia cast into them - 5/8 or 16 for 5/8" or 16mm bores for example. If you don't like the action, you can replace the MC with a different size piston to get the performance you want.
 
Okay I’m planning on keeping it stock, so any of the ones I linked should be okay? I’m assuming the stock mc is 16mm because that’s what mikesxs.net sells for the duel rotors...am I correct?


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I think its 1/2" actually,(even though its japanese) 16mm would not make a noticeable difference from stock.
 
Okay cool I ordered one, will I need to renew the brake lines for the bolt(idk what it’s called exactly but the bolt that has holes in it from the mc to the first brake line), I tried to but my bros Harley on but the bolt was too big


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No idea what the stock size of your MC is/was, but if it was 1/2", the piston is about 508 mm2. A 16mm piston is about 804mm2. That is a substantial difference and you will definitely notice it. I would suspect the 1/2" MC is for a single disc and the 16mm is for a double disc setup. Regardless, if you did indeed have a 1/2" MC before, and are replacing it with a 16mm MC and keeping all the other parts the same (the lines have no impact on how powerful the brake is) you will have to pull the lever a LOT harder to get the same braking action. Make sure you are using the correct hardware in all cases. The bolt with holes drilled into it for the brake fluid to flow through is called a banjo bolt (because it holds on the banjo fitting which of course looks like a banjo). You must have the correct one. There are only a few common sizes, but you have to have the correct diameter and thread (obviously), and also the correct length and configuration for single or double lines. And don't forget the copper washers which serve as gaskets - one on each side of the banjo fitting.
 
jpmobius said:
No idea what the stock size of your MC is/was, but if it was 1/2", the piston is about 508 mm2. A 16mm piston is about 804mm2. That is a substantial difference and you will definitely notice it. I would suspect the 1/2" MC is for a single disc and the 16mm is for a double disc setup. Regardless, if you did indeed have a 1/2" MC before, and are replacing it with a 16mm MC and keeping all the other parts the same (the lines have no impact on how powerful the brake is) you will have to pull the lever a LOT harder to get the same braking action. Make sure you are using the correct hardware in all cases. The bolt with holes drilled into it for the brake fluid to flow through is called a banjo bolt (because it holds on the banjo fitting which of course looks like a banjo). You must have the correct one. There are only a few common sizes, but you have to have the correct diameter and thread (obviously), and also the correct length and configuration for single or double lines. And don't forget the copper washers which serve as gaskets - one on each side of the banjo fitting.
Pretty sure my stock pump is 1/2" even if its strange coming from japan and all.. and its dual discs on it. Now that you mention it it feels kind of underwhelming and wooden.. if its that big a difference i might look for a 16mm pump myself..
 
datadavid said:
Pretty sure my stock pump is 1/2" even if its strange coming from japan and all.. and its dual discs on it. Now that you mention it it feels kind of underwhelming and wooden.. if its that big a difference i might look for a 16mm pump myself..
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16mm feels great, $36 on eBay ! Not to bad


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Re: Xs750 master cylinder

Checked it now, my stock pump is 11/16", whatever that is in mm..
Edit: 17.4mm apparently.
 
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