Brake Problem

"The stock 3CL set up with the long alloy lever isn't too bad at al"
disagree Piet its pathetic and so are all of them, every time I ride a non Laverda, I am imediateoly impressed with the rear brake, even a 100cc scooter for goddsake.

No Haggis Haines I ditched the P9, on the basis that bigger psitons means needing to move more fluid, which the stock master cylinder struggles to do, changed master cylinder for several different types all with varrying degree of patheticness (hey a new word!), am thinking of using a servo and master cylinder from an XJ12 that should make the bugger work! I might even ditch the mag wheel and fit a 750 swingarm (direct fit) and a spoked TLS rear drum, one tiny weld on the frame for the cable and the jobs a goodun (quote Guy Martin) the front spoked wheel and discs interchanges with the cast one, so thats easy, and a pair of said wheels are waiting for me to collect in a far off distant land several light years away.

CLEM
 
Mmmm my 1200 had a variable ratio rear brake, the rotor was damaged warped, it would lockup and release with moderate non crossover linkages ( home made system ) pressure to lever arm.... always thought the flat track racers were a special breed, my attempts of emulation were feeble as the rear came around in corners, then straightened up...

With Cam, you can make the oem work sort of, though why bother really, modern riding requires modern brakes and suspension where possible. None of the, down to last 3 Laverda here have Brembo P/F 08 up front, originality tick, dying in achieving original period, no tick. Nissin 4 pots and Tokico master ( non radial ), am here typing due to those silky smooth front brakes, no question in my mind whatsoever. j
 
sfcpiet said:
it's when these stupid rear-sets and cross-overs come into play that things go down the drain. :(
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I wouldn't have thought the cross-over linkage would have much to do with the efficiency of the rear disk brake, assuming the right brake pedal/lever is simply a mirror image of the left (probably an unsafe assumption). The caliper doesn't care which side of the bike brake pedal and master cylinder are on. The only difference is the hose route.

I agree that the rear set linkages are poorly designed. They don't give enough mechanical advantage between pedal and MC.

I reckon I have your worst nightmare on my Jota Piet. Rearsets and cross-over :)

I've got them both to work quite well though. You just have to eliminate any slack in the linkage joints and the cross over shaft bushings in the gear linkage.
Eliminate slack in the brake linkage too, but also re-arrange the lever lengths and angles to give good mechanical advantage. I had to re-position the master cylinder to get the levers, link rods and angles to work. It's stretching the memory a bit (it was years ago when I did it) but I think I also made a different bell crank for the MC with a slightly longer lever and less free play than the original.
 
Yes Cam,

It certainly is all about efficiency, and quite alarming how often this is neglected. The amount of slop I find in some set-ups is mind-boggling, not to mention the incorrect angles and the lack of lube... :rolleyes:

piet
 
The brake setup is with standard foot paged and all components are original. See photo. The petal moves less than 1 inch to hit solid resistance.
 

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dave48 said:
The brake setup is with standard foot paged and all components are original. See photo. The petal moves less than 1 inch to hit solid resistance.
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If you'd compare your brake lever with the original LH alloy lever you would find you're losing out on about 2 inches in pedal length alone.

Unfortunately, the factory didn't put much effort into their half-hearted conversions to satisfy US mandates. The original nowhere-near-excellent brake was just made a bit worse...

The actuating lever of the RH brake pedal would need to be considerably shorter to regain original overall lever ratios, simple physics.

piet
 
If you have the facilities to cut and weld stuff, you could modify the lever arm on the brake pedal. That would be cheaper than spending money on a different master cylinder. It's always cheaper to work with what you've got and make minor tweaks than chucking the whole thing out and starting from scratch.
The pivot point where the link rod attaches to the lever arm on the brake pedal needs to be about where the yellow + is marked on the photo below, or perhaps even a bit lower. The lower you go with that pivot, the more pressure you can get in the hydraulics. But you end up with more pedal travel, so it's important to get rid of any free play in the mechanical linkage.

As you can clearly see, that position of that + is off the side of the existing lever arm. The reason for that is to improve the angle between the lever arm and link rod when the pressure comes on. Ideally you want 90°. You said that you get pressure when the pedal is depressed about 1", which I guestimated to be about 7° of pedal rotation on its pivot. So I put the + closer to the pedal pivot so it'll make a 90° angle with the link arm after 7° of pedal rotation. This is all just roughly sketched here. You need to do a scale drawing to optimise the measurements.

So you'll either need to weld a tab onto the existing lever arm or cut the arm off and make an entire new one. Given that anything you do at this stage is experimental, you'll want to keep it simple and reversible, so I'd suggest welding tab onto the existing arm, maybe with 2 or 3 alternate hole positions to experiment with. Take care not to get in the way of the pedal return spring. Your modification will look like crap, but it's only a prototype at this stage. Once you get the brake working to your satisfaction, you can tidy it up with a final version.

Then of course you'll need a longer link rod. I doubt the threads on the Heim joints will be long enough to extend that far (you don't want to end up with joints hanging on by 1 or 2 threads). Cutting, drilling and tapping a new rod is simple enough if you have a lathe, but if that's not an option, you can just screw in an extension piece. Search for "Heim joint extension" on Google and you'll find heaps of options.

Once you've done all that, you'll find it won't fit together because the link rod now sits a little lower and will interfere with the rear footrest mount tube that's part of the bike's frame. There are a couple ways around that problem:

1. Move the master cylinder up a bit (there's room to drill another set of mounting holes further up the diagonal bracket. You can also move the MC out a bit by using a couple of washers as spacers on the mounting bolts.
2. Bend the link rod like a banana to clear the frame.
3. Massage a clearance groove into the upper rear footrest mount tube with a ball-pein hammer.

On my own bike I used a combination of methods 1 and 2 as you can see in the second photo below. My bike uses rearsets, but the problems and solutions are basically the same. The photo also confirms that I did in fact make a new bell crank for the master cylinder with a longer arm, and if you look closely, you can see a cut-out in the top of the bell crank with a nut in it. That's a lock nut for a long grub screw through the top section of the crank to contact the stop on the master cylinder body. That screw is used to adjust the rest position of the bell crank so as to minimise free play in the system (looks like I could have made the grub screw a couple of mm longer because there's nothing left protruding through the nut). You can also see that I added a return spring to the pedal because the rearsests don't have one.

There are probably heaps of other ways to tackle the problem. I'm just sharing the solution I used.

Laverda right side foot brake modification.jpg

Brake Laverda.jpg
 
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Bleadingly obvious but don't set it to be lacking too much Freeplay or the brake will drag get hot and start to apply itself in a loop till it's fully on. Guess how I know. It happened on my Pantah in 40c plus heat on an expressway when all I had for tools was an openender 12mm and I needed a 10mm to back the adjustment off. Luckily I had some coins and I managed to pack that 12 and released the 10mm. I now NEVER go anywhere without a small tool bag.
 
Interesting topic, my last rgs had a passable rear brake, but the current one had a piece of wood that didn't work in any way. I swapped stuff out till I had nothing left to try. I noticed the tab on the pedal was welded on by someone on its history. I had a look at Jaycen and Levi's bikes one day and hey presto they had much shorter leverage. I drill a new hole about the same as the original and hey presto am almost acceptable brake, well at least I can feel some retardation now. More how long it was compared to where it is now, it was in the longer hole. Now why on earth would one do this?IMG20220927152920.jpg
 
It looks like what I tried with my rear sets on my drum rear 3c and got the same result, no improvement in the strength of what was in earlier times VERY strong rear drum. I expected stronger leverage and got less. Thankfully fixed and constantly harped on with lubing the brake links. What is funny is why I was trying so hard to fix my rear brake. Around that time I went to Bruce's farm for one of the rallies and found doing that hard right turn and going down the steep bank onto the river was really sketchy with no rear brake, feathering the front brake on dirt while turning and descending was doable but wasn't my first choice in how to do that.
 
Dellortoman said:
As you can clearly see, that position of that + is off the side of the existing lever arm. The reason for that is to improve the angle between the lever arm and link rod when the pressure comes on. Ideally you want 90°. You said that you get pressure when the pedal is depressed about 1", which I guestimated to be about 7° of pedal rotation on its pivot. So I put the + closer to the pedal pivot so it'll make a 90° angle with the link arm after 7° of pedal rotation.
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Precisely, the angle of attack is completely wrong. Look at the angle for the gear change as well, it is also way off. As Cam has pointed out they should pass through 90 deg in operation. Have the foot-pegs been rotated forward to cause the pivot points to be dragged way out of ideal?
 
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