Author Topic: Rear Master Cylinder Keeps becoming unseated + bonus question!  (Read 520 times)

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Offline spmc

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Hey guys, just brought out the bike and already having trouble to shoot! The one nagging thing that seems to happen frequently enough to be annoying is my rear master cylinder keeps coming unseated and effectively rendering my rear brake useless. I believe what's happening is the inside of the cylinder has rusted inside enough that even though I seat the circlip in the inner groove, it always seams to become unseated and then everything loses pressure. It's a brand news rebuild kit as well so I'm ruling out those pieces as culprits. I can't really sand in there all that well. Anyone know where I might be able to buy a new one or what years are compatible with the 77 Supersport F2.

The other thing is I bought some replacement shocks from vintage750.com and they're just generic ones but I got them a bit longer because of a handful of reasons. I got them on okay but there were a couple issues. One the wide of the top EYE is narrower than the stock, so the new ones leave a bit of a game on the peg. I feel like I should fill that but I've read not to stack washers against each other and I was just wondering why that was the case. Or if you think it wouldn't be an issue? Also the clevis had a small gap as well but sort of bent to fit maybe by a mm or two. Is that others experience with these kind of shocks?

Offline seanbarney41

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Re: Rear Master Cylinder Keeps becoming unseated + bonus question!
« Reply #1 on: April 14, 2019, 05:41:28 pm »
You can use a rear master from an 75-79(ish, not sure what year there may have been a change) gl1000 Gold Wing,  It bolts right on and functions but you will need a brake line adapter or a custom brake line, as the Gold Wing uses a hard line there instead of a banjo bolt.

I don't know why some aftermarket shocks are built that way.  I do know it is a pain in the ass.  You need to shim the top and/or the bottom so the shocks remain parallel and straight up and down...this is very important.  If not done correctly they will just bind up and it will be like riding a hardtail.  Also the shocks will probably get damaged.
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Offline scottly

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Re: Rear Master Cylinder Keeps becoming unseated + bonus question!
« Reply #2 on: April 14, 2019, 07:27:16 pm »
Try cleaning out the groove for the circlip with a dental pick. Do you still have the original circlip to compare to the new one? Also, if the circlip has one side with rounded edges and one side with sharp edges, the sharp edge side should be facing out.
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Offline Bankerdanny

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Re: Rear Master Cylinder Keeps becoming unseated + bonus question!
« Reply #3 on: April 15, 2019, 12:37:12 pm »
I picked up a very inexpensive master from eBay for my F1. I had to make a small adapter bracket for it, but it was simple and your stock F2 brake line will work.

https://www.ebay.com/itm/FOOT-REAR-BRAKE-MASTER-CYLINDER-WITH-FLUID-RESERVOIR-FOR-SUZUKI-GSXR-600-750-/311760520557?hash=item489660056d

I'll post a photo in a moment
« Last Edit: April 15, 2019, 01:08:16 pm by Bankerdanny »
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200