Help identifying a vintage Brembo master

[Rusnak_322]

Anyone know how to tell what I have on my bike? The bike is a 850T but it is a Frankenstein bike with stuff added from other bikes.

There are no numbers on the master, only the Brembo cast into the metal Reservoir.

I have not had any luck searching online. There is a weeping coming from the piston area and I want to get a rebuild kit, but with out pulling it apart and measuring it, is there anyway to tell if it is a 12mm or 15mm or ??

http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_112&products_id=753










Also, the brakes work, but they are pretty wooden and requires a pretty heavy pull to stop the bike.

It looks like I am running a pair of Brembo F08 Calipers. I have new stainless steel hoses with cast iron brembo disks, the brakes are not linked with the rear.

[canuck750]

It is an original period correct for the 850T as well as the dual disc V7 Sport, 750S and I know it was used on the 74 Laverda SF2 with dual disc brakes and probably many other Italian bikes of the early 70's.  As for the diameter, I can't recall for certain but I think it was 15mm.

these master cylinders are getting very hard to find and they can go for silly money on Ebay when in good shape.

[Rusnak_322]

I think i found it -

https://store.bevelheaven.com/Brake-Related-Parts/Brembo-15mm-LRD-Brake-M%7CC-Kit-fits-round-reservoir-70s-80s-front-rear-MCs/


you are right - these are spendy.
https://store.bevelheaven.com/Brake-Related-Parts/Early-BREMBO-15mm-Brake-Master-Cylinder-RESTORED/#

[canuck750]

you are right - these are spendy.
https://store.bevelheaven.com/Brake-Related-Parts/Early-BREMBO-15mm-Brake-Master-Cylinder-RESTORED/#
[/quote]

$429.50 for a rebuilt master / brake lever ???  add Ducati to the part listing and the price goes stupid quick.

I found a new CEV light switch for my Morini 500 on Italian Ebay for around $130.00, the exact same switch (also new) on Ebay described as a Ducati switch was around $300.00

And to think I just bought a Ducati 860, maybe I do need my head examined.

[Frenchfrog]

Re pops are now available at much better prices

[Rusnak_322]

Re pops are now available at much better prices

I am hoping a $20 to $30 rebuild kit from Brembo will do the trick. I like saving and repair over replacing.

[Roebling3]

For those of us with a lesser skill set (me), or w/out proper tools. Quality Remanufacturing Paterson, NJ 07513.
Marion Szotak 873-523-8800. 969 Market St.
Calipers, MC -clutch, brake, starters, alternators, - - -  R3~

[Ronkom]

This is the front brake MC that came on my single disc '74 Police Eldo. The black  Brembo finish was badly faded when I got the bike, so I polished  the assembly when I did the first restoration (many moons ago). When I added the second disc to the front wheel,  the lever pull got very hard & "wooden". After living with that for several years I broke down & bought a MC from a two disc bike (Ducati I think). I will have the MC pictured for sale at the Mid Ohio swap meet in July.
ronkom

 

[Rusnak_322]

This is the front brake MC that came on my single disc '74 Police Eldo. The black  Brembo finish was badly faded when I got the bike, so I polished  the assembly when I did the first restoration (many moons ago). When I added the second disc to the front wheel,  the lever pull got very hard & "wooden". After living with that for several years I broke down & bought a MC from a two disc bike (Ducati I think). I will have the MC pictured for sale at the Mid Ohio swap meet in July.
ronkom

What was the difference between the two MC that made the brakes feel better. I am just about to order the rebuild kit and it looks like I have a 15mm piston. that is the largest that they made, there was a 12mm but not for that round style and I would assume that one was for the single disk.

[Tom H]

Give this a read over:
https://www.vintagebrake.com/mastercylinder.htm

Tom

[Perazzimx14]

If you are running the stock single disc DO NOT buy a new or rebuild the stock 15mm master cylinder. It is grossly oversized and is to be used on dual disc setups. Guzzi really fudged this sizing up 40+ years ago.

A $16 10mm generic master cylinder off Amazon will give you much better breaking and feel.

https://www.amazon.com/Front-Hydraulic-Brake-Master-Cylinder/dp/B0176TAF8Y

While not period correct it'll work 100x better.

[Rusnak_322]

Give this a read over:
https://www.vintagebrake.com/mastercylinder.htm

Tom

per that chart at the bottom, i should be good.

"For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1. I think ratios lower than 23:1 produce a lever feel so "wooden" as to have little, if any feel."

I have a pair of the Brembo F08 calipers, they are 38mm dual piston. So 4 pistons [38mm (4)].

With a 15mm MC, that gives me a ratio of 25.67:1

I don't know the diameter of the disks.

[Rusnak_322]

If you are running the stock single disc DO NOT buy a new or rebuild the stock 15mm master cylinder. It is grossly oversized and is to be used on dual disc setups. Guzzi really fudged this sizing up 40+ years ago.

A $16 10mm generic master cylinder off Amazon will give you much better breaking and feel.

https://www.amazon.com/Front-Hydraulic-Brake-Master-Cylinder/dp/B0176TAF8Y

While not period correct it'll work 100x better.

I am running dual disks and really want to keep a vintage look above all else. I don’t want to throw a modern looking MC on it.

[Perazzimx14]

If you running dual disc you'll be fine with the 15mm MC. MG Cycles has all the parts to rebuild from the reservoir, cap & diaphragm, piston and seal kits.

Trust me if you were running single disc you'd quickly get over the "vintage" look for a front brake that actually works.

[canuck750]

I am running dual disks and really want to keep a vintage look above all else. I don’t want to throw a modern looking MC on it.

Damn nice looking Guzzi you have!

[Antietam Classic Cycle]

If you running dual disc you'll be fine with the 15mm MC. MG Cycles has all the parts to rebuild from the reservoir, cap & diaphragm, piston and seal kits.

Trust me if you were running single disc you'd quickly get over the "vintage" look for a front brake that actually works.

Single F09 and the 15 mm master cylinder works acceptably well.

[Perazzimx14]

Single F09 and the 15 mm master cylinder works acceptably well.

With F08's might as well have the little rascals set up with with an old shoe on a stick rubbing against the tire

[wirespokes]

It's funny all the different responses you're getting on this.

I've found that chart to be worthless. My personal experience has been different.

I've ridden the older airheads since 1990 and they've got F08s (when not the earlier swinging ATE) just like these older Tontis.

Back in the 70s (and even the 80s) disc brakes were a new thing and the engineers spec'd Masters with bores too large. I've found that three or four steps down was usually best. If a 15 or 17 was spec'd, somewhere around a 12 or 13 worked best.

Guys say you've got to have stainless lines for the brakes to work best. I've got both (rubber and SS) and they both feel fine. Perhaps on the track it would make a difference, but on the street it feels the same to me.

My 87 LM came to me de-linked. The front master was changed to the larger one customary for dual discs. The old smaller original (a 12mm as I recall) was in the parts box so put it on and the brakes, good before, were even better. 

So to answer your question, unequivocally I'd say dropping to a 12 would give much better braking. Here's something to think with:

Picking the right master is a game of leverage versus lever movement. The farther the lever moves, the greater the leverage and the more feel you'll have.

A bore too large will give minimal lever movement and the least leverage. You'll feel like you're pushing on a brick wall.

A bore too small, and the lever will come all the way back to the bars without fully clamping the calipers.

Some of the airheads came with a 17mm master, and wow - there was hardly any lever movement. Horrible! A 15 is better, but a 13 or 14 made a huge difference.

As it is, with the 12mm on the 87 LM, the lever can be pulled half way to the bar, but in actuality the brakes are fully engaged before then. So perhaps an 11 or 10mm master will work. I've never tried.

I've heard complaints that the 12 doesn't work - the lever comes back too far and the brakes are mushy. That's not the problem of the master's size, but air in the lines. Been there, done that.

That chart comes up every time with this discussion and might be a good rule of thumb, but for sure, real world experience trumps it every time. Listen to those who have been there. Good brake pads, clean discs, calipers that work properly, and the right size master go a long ways to having excellent braking. I've had to stop suddenly a few times and haven't found them lacking.

[John Croucher]

It's funny all the different responses you're getting on this.

I've found that chart to be worthless. My personal experience has been different.

I've ridden the older airheads since 1990 and they've got F08s (when not the earlier swinging ATE) just like these older Tontis.

Back in the 70s (and even the 80s) disc brakes were a new thing and the engineers spec'd Masters with bores too large. I've found that three or four steps down was usually best. If a 15 or 17 was spec'd, somewhere around a 12 or 13 worked best.

Guys say you've got to have stainless lines for the brakes to work best. I've got both (rubber and SS) and they both feel fine. Perhaps on the track it would make a difference, but on the street it feels the same to me.

My 87 LM came to me de-linked. The front master was changed to the larger one customary for dual discs. The old smaller original (a 12mm as I recall) was in the parts box so put it on and the brakes, good before, were even better. 

So to answer your question, unequivocally I'd say dropping to a 12 would give much better braking. Here's something to think with:

Picking the right master is a game of leverage versus lever movement. The farther the lever moves, the greater the leverage and the more feel you'll have.

A bore too large will give minimal lever movement and the least leverage. You'll feel like you're pushing on a brick wall.

A bore too small, and the lever will come all the way back to the bars without fully clamping the calipers.

Some of the airheads came with a 17mm master, and wow - there was hardly any lever movement. Horrible! A 15 is better, but a 13 or 14 made a huge difference.

As it is, with the 12mm on the 87 LM, the lever can be pulled half way to the bar, but in actuality the brakes are fully engaged before then. So perhaps an 11 or 10mm master will work. I've never tried.

I've heard complaints that the 12 doesn't work - the lever comes back too far and the brakes are mushy. That's not the problem of the master's size, but air in the lines. Been there, done that.

That chart comes up every time with this discussion and might be a good rule of thumb, but for sure, real world experience trumps it every time. Listen to those who have been there. Good brake pads, clean discs, calipers that work properly, and the right size master go a long ways to having excellent braking. I've had to stop suddenly a few times and haven't found them lacking.

This is the correct answer.  Do you want a bike that looks good on the side stand or stops good while riding? 

The correct ratio make for two finger braking, good modulation and brake bleeding.  Braided s.s. lines are the best choice over rubber.  Loosing brake energy thru expanding lines reduces braking power.  I have seen a small I.D. master cylinder balloon a rubber brake line. 

[Rusnak_322]

This is the correct answer.  Do you want a bike that looks good on the side stand or stops good while riding? 

The correct ratio make for two finger braking, good modulation and brake bleeding.  Braided s.s. lines are the best choice over rubber.  Loosing brake energy thru expanding lines reduces braking power.  I have seen a small I.D. master cylinder balloon a rubber brake line.

I don’t think it is a either / or. I think that what I have can be made to work.

I was emailing back and forth with MG Cycle and he thinks that this is a 15 mm MC that was originally used on a single caliper brake system. He said he has several bikes with the same MC and has added a second caliper and they work.

I have a rebuild kit on order, if this doesn’t fix the feel I will look at rebuilding the calipers. I have new stainless steel lines on the bike.

[wirespokes]

[John said: The correct ratio make for two finger braking, good modulation and brake bleeding.  Braided s.s. lines are the best choice over rubber.  Loosing brake energy thru expanding lines reduces braking power.  I have seen a small I.D. master cylinder balloon a rubber brake line.] 

I'll have to take your word for the ballooning rubber lines. I have heard they can expand a little, but I'm easy on brakes so don't normally have an issue with losing braking energy. And, yes, with the smaller master, two finger braking is normal. Four piston and six piston calipers might be better, especially at high speeds, but these old 2 piston Brembos are plenty sufficient for me. I'm sure they'll skid the tires if I wanted to.

[F-22]

Biggest advantage of stainless lines is that they do not degrade with time. A new rubber line is quite fine, but a lot of manufacturers recommend replacement every 10 years, which is practically always neglected. Old rubber lines are a lot more flexible and can be dangerous.

I don't know exactly why, but most airhead BMW brakes were very bad, at least compared to most Guzzis I've ridden. Possibly, the stainless discs BMW used do not offer the same friction as the cast/steel discs Guzzi used.

[wirespokes]

My airheads have stopped really well, but agree the Guzzis are better. BMW used master cylinders too large for the application just like Guzzi, something I've rectified with my bikes. Guzzi started using 2 Piston F08 Brembos from the very start in 74, while BMW used the 1 piston ATEs. With a smaller master, the ATEs can work very well, but be sure the calipers are adjusted and free to swing. In 81 BMW finally went with the F08 Brembos which eliminated adjusting and setting of the caliper. So at that time, BMW and Guzzi both used the same brake components, except, as you say, the discs. Yes, the Guzzi cast iron discs have a better friction coefficient and work better. But I wouldn't call the airhead brakes lousy, just the particular bikes you rode most likely needed attention.

[Tusayan]

In 81 BMW finally went with the F08 Brembos which eliminated adjusting and setting of the caliper. So at that time, BMW and Guzzi both used the same brake components, except, as you say, the discs. Yes, the Guzzi cast iron discs have a better friction coefficient and work better. But I wouldn't call the airhead brakes lousy, just the particular bikes you rode most likely needed attention.

In addition to lower friction stainless disks, 1980s BMWs had larger front wheels and smaller discs than was typical for Italian bike of that era.  This has a direct effect on their relative braking power.

On my R100GS, I've installed a later model 4-piston caliper and higher friction pads to increase braking power to safe levels with the single disk, but disk life is now relatively short.  I stick a new disk on it every now and again, it's a 15 minute job.  I do love the ultra simple design of the GS brakes (the rear drum has never needed anything over 100K miles) but it's just adequate in performance as modified.

Confirming what was written by others, the Brembo master cylinder pictured works fine with dual calipers, but is too large for a single disk/caliper.  My memory says those fitted to 850Ts etc were 5/8 inch diameter but given that everybody else mentions 15-mm, I'm guessing my memory may be incorrect.

[wirespokes]

I think you're right about the BMW disc diameter being smaller but never really compared the two.

Another factor is height of the bike. The taller the bike the more it wants to rotate around the front contact patch. Guzzis tend to be slung lower than the beemers, so that makes a difference as well.

I've got a four piston caliper ready to go on my GSPD but haven't installed it yet. Too busy riding the 87 LM these days.

Yeah, the 15mm master will work, but it's not the best choice. And you're probably right Tusayan - 5/8" could be it. Even though those European bikes list their brake parts in metric sizes, they're really all imperial. Measure the bores and see for yourself.

[Antietam Classic Cycle]

The "15 mm" Brembo master cylinders have a bore size closer to 16 mm actual - 15.85 mm IIRC - so yes, very close to 5/8".

[Tusayan]

The "15 mm" Brembo master cylinders have a bore size closer to 16 mm actual - 15.85 mm IIRC - so yes, very close to 5/8".

That probably means they *are* 5/8 inch, which is 15.875 mm.  At least my memory is not failing too badly.  The Japanese size their master cylinders in inches too, like wheels.

Way too big for most single calipers regardless.

[Antietam Classic Cycle]

That probably means they *are* 5/8 inch, which is 15.875 mm.  At least my memory is not failing too badly.  The Japanese size their master cylinders in inches too, like wheels.

Way too big for most single calipers regardless.

Like I posted earlier, it works *okay* with a single F09, but still not optimum.

[Rusnak_322]

OK, anyone have an idea on how to get the piston out?

I got a rebuild kit - http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_112&products_id=753


I found a few tutorials and they all talk about a C-ring or snap ring that needs to come out. Even the instructions with the rebuild kit show it, but they only show the rear master.

I pulled the rubber boot and there isn't a C-ring under there. and there isn't a new one in the rebuild kit. There is a silver washer, I cant get it to move with a pick. I cant get the piston to pull out either.

any ideas??? 

[Frenchfrog]

very thin punch or nail through the exit hole and then a small tap should do it