CB360 Master Cylinder - 16mm piston too big?

[Matnetik]

Hey all,

I have a 1974 CB360 and when I bought it, it had a master cylinder from what I believe is a goldwing. I recently replaced the caliper assembly along with a new stainless steel brake line. After hours of bleeding and running a 12oz bottle of fluid through, the brakes still felt soft and I had to squeeze them so much just to engage. I assumed it was the master cylinder to I replaced it with the same one. After going through the same rigorous process again with the new master cylinder, I’ve had no luck. Brakes feel the same. I also tried the zip-tie over night, tried it for a few days and nada. Also tefloned the bleeder and banjo bolts and still...soft brake.

Few things I have noticed, I don’t have a disc brake cover, now I have done some research and found some others had an issue with this and how it angled the caliper on the disc causing uneven wear and pressure. Could this be the cause of the lack of braking power? I’ve tried to look up the diagram for assembly but can’t find much on that, maybe a washer could do the trick? Not sure where it goes, on the inside of the fork in between the privet arm of the caliper?

Or could it be that a CB360 uses a 14mm master cylinder and I have a 16mm? Although I thought the bigger the piston the less travel the lever has to do, so in theory wouldn’t it start applying pressure sooner than if I used a smaller piston?

I am 1 billion % sure there is no air in the line, bleed brakes a million times on so many bikes before but I just can’t just this one right. Any help would be beyond appreciative!! Here are a few pictures below -

 

[Matnetik]

Well after further inspection after taking these pictures I think my new caliper front is dripping from the banjo bolt. I bought it on eBay, who knows. I think at this point I am just going to order a set of levers from 4into1 with a 5/8” piston, a new caliper front and a new brake hose adapter. Still curious if a 16mm piston is too big or not

 

[Sderbyshire]

If the piston in the mc is too big in relation to the caliper then the brake lever will be too hard not too soft.

on these old honda single piston calipers it is vital that the pads are correctly aligned with the disk, yours are not

in pic 3 above is the pad touching the disk at the bottom and not at the top?, you can adjust the angle of the caliper with shims/washers on the top bolts

a leaky banjo wont help either !

hth

steve

 

[Matnetik]

If the piston in the mc is too big in relation to the caliper then the brake lever will be too hard not too soft.

on these old honda single piston calipers it is vital that the pads are correctly aligned with the disk, yours are not

in pic 3 above is the pad touching the disk at the bottom and not at the top?, you can adjust the angle of the caliper with shims/washers on the top bolts

a leaky banjo wont help either !

hth

steve

Yeah I think that might be the issue is the pad not aligning with the disc properly, either way I went ahead and ordered some new parts, great advice on the washers on the top bolts to level it out, will report back once everything arrives!

 

[Sderbyshire]

Here’s a photo of the twin disk setup on my old 360, you can see i had to space the calipers out to get the alignment right

 

[Matnetik]

Here’s a photo of the twin disk setup on my old 360, you can see i had to space the calipers out to get the alignment right

ayyyeee this is super helpful!

 

[doc_rot]

Another thing to consider on the MC is the ratio of lever length to lever pivot offset. This has a significant effect on the feel of the lever. Thats why race style MCs have adjustable pivot points to dial in the "feel" you can move from a 16m MC with 25mm pivot to a 16mm MC with 18mm offset and they would feel completely different. even if they were identical in every other way, the less offset the pivot has to the center of the bore the more leverage the you will have making it feel soft. 25mm offset will feel firmer with less lever travel than 18mm with more lever travel, all other things being equal.

 

[Matnetik]

Another thing to consider on the MC is the ratio of lever length to lever pivot offset. This has a significant effect on the feel of the lever. Thats why race style MCs have adjustable pivot points to dial in the "feel" you can move from a 16m MC with 25mm pivot to a 16mm MC with 18mm offset and they would feel completely different. even if they were identical in every other way, the less offset the pivot has to the center of the bore the more leverage the you will have making it feel soft. 25mm offset will feel firmer with less lever travel than 18mm with more lever travel, all other things being equal.

I ordered these since it has the brake switch built in, don't it's adjustable though?

https://4into1.com/80s-style-master-cylinder-w-clutch-lever-set/

 

[doc_rot]

I ordered these since it has the brake switch built in, don't it's adjustable though?

https://4into1.com/80s-style-master-cylinder-w-clutch-lever-set/

Those are the generic Chinese MC you see everywhere on eBay, Amazon etc. Ive used them they work ok, but quality is low. Adjustable MC are usually only available in top tier race parts. Compare the pivot offset to stock to see if that’s your issue.

 

[doc_rot]

You can also determine if your MC is sized correctly by calculating the area of the MC piston (16mm) then dividing that by the area of the active caliper pistons. A good ratio for unopposed caliper pistons is around 1/13, opposing caliper pistons like to be around 1/27

 

[Matnetik]

You can also determine if your MC is sized correctly by calculating the area of the MC piston (16mm) then dividing that by the area of the active caliper pistons. A good ratio for unopposed caliper pistons is around 1/13, opposing caliper pistons like to be around 1/27

Brilliant info here, everything is arriving today at some point so I will report back once I give it a try, if the lever is still causing issues after I have installed the new caliper and made sure the pads are even on the disc I will definitely be looking at a higher end lever! Feel free to throw a couple out there if you know any! Thanks again for all the help everyone, the forum always comes through!

 

[doc_rot]

A higher end lever will not solve your problem if your hydraulic and mechanical leverage ratios are inadequate. I like Brembo master cylinders, their standard MCs arent too expensive and very high quality. I went back and re-read your post. I thought you had gold-wing brakes. if you have the stock 360 caliper 16mm is probably too big. I'm not sure what the stock 360 MC size is, but usually single calipers need a 13mm or 14mm MC.

 

[Matnetik]

A higher end lever will not solve your problem if your hydraulic and mechanical leverage ratios are inadequate. I like Brembo master cylinders, their standard MCs arent too expensive and very high quality. I went back and re-read your post. I thought you had gold-wing brakes. if you have the stock 360 caliper 16mm is probably too big. I'm not sure what the stock 360 MC size is, but usually single calipers need a 13mm or 14mm MC.

Ah I meant lever/mc combo. Yeah stock uses a 14mm piston so originally I wasn’t sure if 16mm was too big since that’s what seems to be sold everywhere for her 360, other than common motors, they sell a 14mm lever/mc combo

 

[Matnetik]

Alrighty so here’s the update! Looks like it was a few issues. I ended up sticking with the master cylinder/lever I bought from eBay (the 16mm one from the goldwing) because the one from 4into1 was wayyyy to big, I also don’t need mirror screw holes so going to return them.

I added some washers in between the pivot mount for that holds the caliper but only on the top two bolts - after looking at my pads they were worn at an angle so this should fix that issue, Once the top wears a bit they should wear evenly.

I liked that the 4into1 caliper came in pieces and I got the stainless steel non-hallow piston. Was nice to rebuild it myself knowing the seal was in correctly and the brake line bolt/bleeder were set right. Aligned the back brake pad properly to the disc (need to order a new bolt for the adjuster screw since the end of mine is slightly broken off). Used anti-seize on the screws and proper grease for the pads to eliminate squealing issues.

Bled the brakes until there was no air in the line and it is fixed! SOLID resistance and pressure, feels like the brakes on my CBR, super pumped!! Barely have to squeeze the lever for it to engage. Thank you all so much for the help and advice, this is by far my favorite forum to post on. Now off to figure out why my left spark plug as oil on it.

Once again, thanks and hope this post helps someone else in the future!

 

[Sderbyshire]

Excellent news, glad you got it sorted !