Optimizing the second series "Super Freni" drum brakes

arancia

arancia

Senior member
Location
Arizona, USA
I'm taking a side track from the discussion about relining at "relining thread"

While the SF2 with its 2 front disks is imho a huge step up from the drums on the SF and GTL, I do like to ride the SF and GTL and am looking to get the best out of their "brakes" (aka "gentle retarders").
I did a recent long trip on my GTL after doing the best I could to get the existing brake shoe contact points balanced (same as late SF and the rear on SF2 and 3C) with a friend on his significantly updated Norton Commando, a replica of the 76 prototype as in the Birmingham museum, with cast wheels, 3 disks, etc - all the improvements that would have been possible if Norton management had decided they really wanted to compete. There were several occasions on that trip where I was following where he decided to turn at a junction and I just went sailing though the junction - no way to slow at his deceleration rate!!
Reflecting that I was lucky that road situations did not need a real emergency stop and accepting now that it's time to optimize those brakes before such an event occurs, I'm planning a full renovation of the GTL's 2 late Laverda drums.
I'm interested to see that in Andy Wagner's book, he suggests that we should return to the circlip retained shoe linkages (instead of split pins) and the heavier shoe-to-shoe springs instead of the later weaker springs from shoes to backplate - in effect returning to the the early series SuperFreni internals instead of the later setup.
Looks like this requires only the 4 pins with circlip grooves, 4 circlips, and a pair of springs. When looking at the investment in shoe relining and arcing to drum that seems a minor additional expense so I'm asking is everyone doing this with their later drum brakes - experiences?
Any other thoughts on getting the best out of the second series SF brakes?
 
The shoe material has a big effect; no more ASbestos is a good thing, except for getting the best out of brakes, so they say. What's available now?
 
First of all you need to eliminate as much slop within the linkages as you possibly can. This basically means new backplate bushings and actuating levers/shafts to suit, pins and plates and brake shoes with tight clearances, not to forget the external levers with their pins and clevis. Never seen any advantage between circlips and split pins other than the circlips are easier to fit. I have resorted to reaming out all plate bores and making new pins to suit. The shafts can be re-ground, under-sized bushes are then needed. The internal link plate pairs need to be the exact same length!

The small springs are not meant to work as return springs, they only steady the shoes when not in use and prevent them from clattering around. The true return spring is the one on the link rod in the back plate. For a firmer feel at the hand or foot lever, 1 or 2 springs of the Serie 1 brake can be fitted. I use these in my rear brake only.

With all this done, attention can be focused on the brake linings, keeping lever geometry in mind. The shoes are fitted to the back plate and centred as well as possible. The actuating lever needs to be positively located in a position that will later allow the fitting of the cable. For this I use a threaded rod solidly connecting the lever to the cable adjuster boss. For safety reasons, the shoes are tied together with a cable tie or wire. The linings are then machined to the true diameter of the drum. The leading edges of all linings must be chamfered.

The result should be a brake that works well immediately. Sometimes the brake actually ends up working too well, in this case the leading edges of the linings need a longer chamfer at a flatter angle.

All this does require a drum that is truely circular, not worn conical and shows no deep gouging.

It’s a lot of effort, and cost if you can’t do it all yourself, but well worth it. What remains to do is regular maintenance, so sadly lacking in the past that it got you where you are now!

piet
 
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A good while back there was a site that sold various Ferado lining types for brake shoes, designated by colours for various applications. One early mistake I made was using race, in my case, front disc pads, as race MUST be better. Later, I found they needed a lot of heat to work well, and my piddling pace wasnt enough. Piet, do you need to centre rear shoes by applying the brake hard as you tighten the axle nuts like front drums?
Quote.

The small springs are not meant to work as return springs, they only steady the shoes when not in use and prevent them from clattering around. The true return spring is the one on the link rod in the back plate. For a firmer feel at the hand or foot lever, 1 or 2 springs of the Serie 1 brake can be fitted. I use these in my rear brake only.

That must have been what what done to soften my brake, 20 years later it was repeated on my modern Husky dirtbike, They used stronger 2 stroke exhaust mounting springs on the rear brake to stop uncontroled locking. Old school race mechanics at work.
 
Very little to add to Piet’s info other than yes, centering the anchor plate by applying the brake is of importance before tightening the wheel spindle.

Another advantage of using two long springs between the shoes is that you can leave out those short springs. On two occasions such a spring broke without me noticing it, until I opened the drum and found a big mess inside..

Marnix
 
I used to see pics of extensively drilled hubs done by very brave people to dissipate heat and extended front-facing air scoops for the same reason. Spent some time on moutain roads in old cars, heat soked brake fade is a scary thing. You see modern vehicles with brake lights lit up heading down mountain roads for hours at a time. Even modern brakes get hot.
 
Almost all drum brakes require centering. Some makes have self-centering brake spindles, Norton Commando rear or Kreidler Florett come to mind, but it's not a waste to centre these by the same method.

piet
 
I have wasted many days of my life trying to get the early Grimeca front brakes on a 750 to stop the bike. After trying many types of lining material that were arced in and every mechanical adjustment I could try, they still can not stop a 500lb bike from speed. After one stop the lever comes all they way back to the grip and now no brakes at all. So I don't think the linings or linkage makes much difference, the problem at least with Grimeca, is the drum grows way to much when it is hot.

So I tried the Laverda front brake, it is better but you still can't stop.

Best of luck with trying to get the brakes to work, I gave up.

I can't imagine trying to stop a Laverda triple with drum brakes!
 
I had the shoes on the front Grimeca on my S relined by the local car shop.
It's a very powerful brake and needs caution at normal riding speeds.
Something's wrong with yours.
Paul
 
My 3c doesn't stop using only the rear brake and rolling backward, the Bonnie I had with a Conic twin leader front was the same. At one point I added an early Honda Twin leader that came std on one of the early Honda MX bikes before Dics on my highly modified XT 500 Yamaha, and it was the same, scary trying to hold a spot on big hills. I very fast added dics to just about every bike I had for a very good reson.
 
1200ts said:
I have wasted many days of my life trying to get the early Grimeca front brakes on a 750 to stop the bike. After trying many types of lining material that were arced in and every mechanical adjustment I could try, they still can not stop a 500lb bike from speed. After one stop the lever comes all they way back to the grip and now no brakes at all. So I don't think the linings or linkage makes much difference, the problem at least with Grimeca, is the drum grows way to much when it is hot.

So I tried the Laverda front brake, it is better but you still can't stop.

Best of luck with trying to get the brakes to work, I gave up.

I can't imagine trying to stop a Laverda triple with drum brakes!
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The front brake (and the suspension) was the reason I sold my carefully restored SF (0). It tried to kill me 3 times... Front did almost nothing, rear was blocking by the slightest touch. I decided I am a disk brake man and sold it on. So did the new owner after just one season afaik.
 
Lothar,

You spent a lot of time and effort to restore the SF, pretty sure the brakes could have been made to work as intended.
Piet and Marnix have pointed out what it takes to optimize the drum brakes.

My SF(C) replica type 750 with series one brakes had me do an emergency braking at 150 km/h ( Sigma Speedo) on the Autobahn a few years ago.
The brakes saved me from rear ending a cage.

Front suspension is a different issue.....

Gerald
 
One can make almost anything work. However, as Piet also pointed out, it takes a lot of money and efford to get it right and I was just fed up after 3 times almost being thrown off the bike in less than 200km. I had similar events with the Jota when I had it new and it took me 20 years, tons of cash and a change of almost ANYTHING related to suspension and brakes to get it where I wanted it. Life is just to short and to valuable to make things work so you are not being killed by it I decided for me and sold the bike on.

It was a beauty to look at though, the engine was smooth as silk and started any time on the first push on the button instandly (tributes to Piet/OCT!! Even Roger was impressed how well it was running, and that means something, as he has seen hundreds if not thousands of it!) and the sound was just making even the most critical neighbour smile like a kid in front of the christmas tree. But if you get scared every time you want to go for a ride, it's the wrong thing to have. Still miss the sound and the riding position though...
 
Laverdalothar said:
The front brake (and the suspension) was the reason I sold my carefully restored SF (0). It tried to kill me 3 times... Front did almost nothing, rear was blocking by the slightest touch. I decided I am a disk brake man and sold it on. So did the new owner after just one season afaik.
Click to expand...
obviously not carefully restored
 
Tippie said:
Isn't it also a feature of these brakes that they were virtually useless to stop you rolling back on a steep hill? Was that a set-up issue?
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Got 2 trailing shoes, next to no rearward stopping performance!

The self-servo effect of a leading edge is not present, makes them pretty useless backwards, but that's not what motorcycles were built for. :unsure:

piet
 
v2ventiler said:
obviously not carefully restored
Click to expand...
not to the level Piet mentioned (which in my eyes is WAY beyond the term "restoration", it is more likely to be an "optimization", but who am I to judge... 😇 😂)

But even if i had, the fork would remain the weak point: way to soft, not corresponding AT ALL with the rear cerianis etc..

What ever. It's sold long ago and other bikes will follow. I will part with most of my bikes, maybe even all of them. My shoulder is getting sore every time I ride them and they are not that much fun as they used to be anymore. Time for something different. As I told my wife when I bought the 2nd and 3rd and 4th Laverda: "Life is to short for just one Laverda". Life is also to short for just Laverda.
 
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