9/16" or 14.3MM CB750 MC to replace Brembo PS15 dice roll

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gpzkat

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Mission Viejo, California
I was researching a fix to the wooden brake feel for my '74 3C, and 14mm seems to be the consensus here. I looked for the commonly recommended Brembo PS14, but they seem scarce used & are far too expensive new for me. Plus they aren't the stock look I'm after. I also want to keep the lovely levers, if possible, and match the fit & form. The way my bars are set up (upwards), It's a bit of a tight squeeze vs. the instrument housing.

I noticed that the PS15 looks very Honda CB750-like, having owned a few of those bikes. Yes, the CB's brakes are wooden too, but I have rigged them up to work better than the 3C's, tolerably so. I found a CB750 9/16" (14.3mm) reproduction. It seemed worth a try, and if it doesn't work, I have another bike I can use it on. The PS15 cap screws right on, but the new copy isn't faded anodized, so I probably won't use it. The Laverda lever's pivot hole is a bit too small, but milling down the pin on the new one will fix that. The last issue would be the brake travel stop eccentric screw. They are different, but I think I can modify the new MC to make things work. Hope so, as that would keep the look I'm after. If not, I'll just use the lever it came with, but that would be a bit of a disappointment.

I've dealt with this issue on other bikes (Norton N15CS with Commando brake and a Yamaha scooter's Nissin MC, Suzuki with grafted CBR900RR setup) and ended up with very good performers; I hope I can do so here. I figure 14.3mm should be a decent improvement, not perfect, but improved. Has anyone gone down this trail?

CB750MC.JPG
 
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The Brembo PS14, you can't get rebuild kits for anymore, so not a good choice. The PS14 does make the brakes fell a little better but not a huge improvement. The best thing you can do is to use four pot calipers and they need a PS15.

Also, what brake pads are you using? The factory Brembo ones are crap.
 
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I suppose you could try that Honda MC, but I purchased a newer rectangular style Brembo MC from Bevel Heaven, along with new direct lines and EBC pads which transformed the brakes that now actually work
 
1200ts said:
The Brembo PS14, you can't get rebuild kits for anymore, so not a good choice. The PS14 does make the brakes fell a little better but not a huge improvement. The best thing you can do is to use four pot calipers and they need a PS15.

Also, what brake pads are you using? The factory Brembo ones are crap.
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I use Ferodo organic pads. Their stopping power and feel have been fine on my other bikes, which have proper MC ratios. The ultimate stopping power of the Laverda is good, I just want the feel improved.
 
I think the lever geometry has something to do with the wooden feel as well. The relationship between the lever pivot and the piston is probably quite different on other m/cyls. Clearly demonstrated with radial type.
 
Worst part of old Brembo MC's (even when new) is that they rely on a sliding contact between two aluminium surfaces - the radiused lever blob on the flat piston end. When new and still with their correct somewhat hard anodised surfaces it works *okay*, but when worn it is a source of mega-friction and contributes enormously to the terrible feel. The newer 1990's type Brembo mc's have a pushrod mechanism which eliminates much of the friction, which is a large part of why they feel/work so much better, even for the same piston size.
 
If I had known that it would have saved me a bucket load of money. The issue mine had was that it had worn a step in the end that resulted in a jerky application that was horrible, especially in the rain. 2 minutes with a file would have improved its application to the point where it worked pretty well. In my case, I bought a set of custom-made 4-piston callipers, then the 4-piston callipers, and then a radial master. The brakes ended up way better than standard, but I could have lived well enough with rebuilt std parts minus that warn in step.
 
breganzane said:
Worst part of old Brembo MC's (even when new) is that they rely on a sliding contact between two aluminium surfaces - the radiused lever blob on the flat piston end. When new and still with their correct somewhat hard anodised surfaces it works *okay*, but when worn it is a source of mega-friction and contributes enormously to the terrible feel. The newer 1990's type Brembo mc's have a pushrod mechanism which eliminates much of the friction, which is a large part of why they feel/work so much better, even for the same piston size.
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Little known fact.. OE clutch PS15 had a little plastic pad inserted into the lever-engaging end of the piston to eliminate friction, sadly no longer available from Brembo.

Shouldn't be too much of a problem machining the end of a replacement piston to accept a little PTFE button. Not so sure if it's such a good idea to incorporate one on the brake side, having it fail may lead to an undesirable situation, aka, Murphys' Law.

Another alternative would be to modify the lever to accept a little roller or a ball bearing as thrust component.

Otherwise, a little blob of grease now and then can be a friend.

piet
 
OP...

Suzuki 12.7mm (half inch) for me. Gives me just the feel I like. Looks kinda right, despite the reservoir being square. It's from an 80s/90s GSF400 I seem to remember.

Anyway, my point is don't be too worried about reducing the master cylinder by quite a lot. When I tried 14.x mm I found the improvements were not enough for me. It's all personal and subjective of course.

The callipers themselves are extremely capable when given the right fluid pressure.

Good luck.
 
I use a Nissin Triumph 900 Sprint one as recommended by Clem. Cheap, works well, nice adjustable lever which makes a big difference to me but unfortunately it's square and not round as required by the original poster.
 
Haggis said:
OP...

Suzuki 12.7mm (half inch) for me. Gives me just the feel I like. Looks kinda right, despite the reservoir being square. It's from an 80s/90s GSF400 I seem to remember.

Anyway, my point is don't be too worried about reducing the master cylinder by quite a lot. When I tried 14.x mm I found the improvements were not enough for me. It's all personal and subjective of course.

The callipers themselves are extremely capable when given the right fluid pressure.

Good luck.
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I once fitted a 1/2" M/C from a 250 Yamaha paired to Brembo P08s. Lever geometry combined with the hydraulic ratio made for excellent feel without excessive travel. quickly learned that most 1/2" or 12.7mm M/Cs have rather small reservoirs, after a week of hooning over alpine passes I was caught out halfway down the Grossglockner with an empty reservoir! Brake pad wear on twin disc set-ups can become critcal with small M/C reservoirs.

piet
 
Hi Piet. Yep, totally agree with the fluid capacity thing. The Suzuki M/C I use has quite a large reservoir. From memory I'm running EBC-HH pads and the wear rate seems pretty low with them. They might be Lucas pads (?) as I remember buying some on your recommendation many years ago.

The only time I have exceeded a braking system's capacity recently was also on the grossglockner! There must be something in the Austrian air! I was heading home from Breganze on Jane's V-Strom. I knew the bike pretty well by then and had discovered that, even though it handles really well, tipping into a corner with a tad of back brake made it turn-in superbly. Anyway three quarters of the way down the back brake gave out and much boiling occurred. A fantastic days riding. Happy days.
 
Good info, thanks for the tips. I'll put a dab of grease on the lever's contact point to the piston and check the business end carefully for a flat spot. Worth a quick try & see. I am not in love with brake bleeding, so if that helps enough, great. All the action on the 3C is moderately high effort, and I can live with it for the time being, but arthritis is setting in.

On my Suzuki 1100Es, one has stock twin-pot brakes, and the other has '92-'97 CBR900RR Nissin four-pot calipers grafted on. Somehow the stockers are better, but that is probably the CBR caliper's pads, as I haven't put new ones on yet. Or the MC. Brakes on my bikes are keeping me busy!

I saw a nice round reservoir MC on the Bevel Heaven site, but it's $900, and that's out of my budget. I'm not 100% committed to keeping the round original look, or Brembo in general, but I figured it's worth a shot to try this Honda one out. I hope to get to it in the next week or so, and will report back.
 
Not the best picture quality, but here's my Suzuki jobbie.
Mirror mount, dog leg, adjustable span, decent reservoir size, outlet port in roughly the right direction = all I wanted. Have used it for thousands of miles and will never go back.
1000066592.jpg
 
Be interesting to compare that Suzi m/cyl with a Lav Brembo with respect to the position of the lever pivot relative to the point of contact with the piston. If I'm right, the Suzi one pictured above would give a better leverage ration than the Brembo. It looks like it would be closer to the piston.
 
Haggis said:
Not the best picture quality, but here's my Suzuki jobbie.
Mirror mount, dog leg, adjustable span, decent reservoir size, outlet port in roughly the right direction = all I wanted. Have used it for thousands of miles and will never go back.
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It seems overly tricky to find out the bore size of MCs online. I looked up the US market '91 'Bandit' GSF400, the PN is 59600-45C10. I tried some UK/Euro sites and didn't find much, just rebuild kits, so Partzilla was my reference for the PN. I asked Google what the bore diameter for that unit is, and it said 14mm. Is that right? Who knows. Many sellers don't know what they have either.

I have a similar-looking 14mm Suzuki MC on my GS1100E with the mid 90's CBR900RR Nissin 4-pots. My other GS1100E, which is stock except pads and brake hoses, is very good, much better than the CBR brakes. Go figure. Maybe it's the pads.

Anyway, question for you: How do you know it's 12.7mm? Going down the rabbit hole on Wemoto, there are GSF's with single and others with dual discs, depending on the market. Do you know which yours came from, year and model? How did you confirm the bore size is 12.7mm, did you open it up?
 
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gpzkat said:
Anyway, question for you: How do you know it's 12.7mm? Going down the rabbit hole on Wemoto, there are GSF's with single and others with dual discs, depending on the market. Do you know which yours came from, year and model? How did you confirm the bore size is 12.7mm, did you open it up?
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'Cos it says so on the underside... :rolleyes:

Almost all motorcycle M/Cs carry a cast marking denoting piston size, at least all Nissin and Tokico products, which covers about 99.9% of all Japanese motorcycles. Most Brembo stuff is stamped.

Hydraulics are traditionally measured in imperial units. Brembo stuff that is marked 13mm is actually 12.7mm or 1/2", 14 is pretty exactly 9/16" and 15 actually turns out to be 15.8mm which is 5/8". Haven't yet measured 12mm Brembo pistons, but I'd risk a bet they're actually 7/16".

Most single disc set-ups will use a 1/2" M/C. Dual discs will usually have a 9/16" M/C in conjunction with 2-pot calipers. 4- and 6-pot calipers will generally have 5/8" M/Cs. All pretty irrelevant in the times of radial M/Cs, piston sizes and lever geometries completely different.

piet
 
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piranha-bro2 said:
Be interesting to compare that Suzi m/cyl with a Lav Brembo with respect to the position of the lever pivot relative to the point of contact with the piston. If I'm right, the Suzi one pictured above would give a better leverage ration than the Brembo. It looks like it would be closer to the piston.
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Quentin,

Seems pivot/piston distance is universally around 24-25mm these days on axial M/Cs. The Yamaha M/C I mentioned previously was more like 28mm which compensated a great part of the longer travel of the 1/2" piston when paired with dual discs. The donor bike would have had a single disc with a single pot caliper, RD250LC iIrc.

piet
 
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