Front disc-brake questions

[Daddy Dom]

Hi All,
now I'm going well enough but there's a new gremlin with stopping. One front disc is shiny and the other shows signs that the pads aren't contacting properly. When I explained this to him, a local Morinista was quite confident it's the caliper seals but I can't see any sign of brake fluid weeping on the disc. Would I see that? Does anyone agree that that's the most likely scenario?
Also, just as I pulled up now, the lever went back alarmingly close to the handlebars (but still stopped me okay). There seems to be enough fluid, should I just bleed and see? Are there any tricks for a double disc set-up? I've searched the forum but nothing came up.
Any suggestions welcomed!
Thanks in advance,
DD

[3potjohn]

I've tried filling the system via the bleed screw using a syringe to drive out air in the past on "difficult" brakes.A bit worrisome if the lever suddenly pulls all the way back.I have twin discs but no splitter on my 350,the hoses run as a pair right from the master cylinder-which had new seals a while back.Can you get someone to operate the lever whilst you observe the pistons moving with the wheel out.

[EVguru]

Contrary to what many people believe and to what's written in some text books, the caliper pistons don't move in the seals except to take up brake wear (or knockback). Instead the seal 'rolls' into the groove, which has the bottom cut at an angle (typically 10 degrees). When the seal relaxes, it pulls the piston back. If you get corrosion in the base of the seal groove, it can stop the seal from rolling. The brake then often starts to drag, or give long lever travel. Pumping out the pistons, removing the seals and cleaning the groove will usually solve the problem.

NLM have been waiting for parts from Grimeca for a long time and seal kits are hard to come by at the moment. The usual advice is to always replace seals if you remove them, but as long as the seals don't have nicks or splits, then they can be re-used. A sudden failure of re-used seals is very unlikely, but you should watch closely for any sign of leakage.

I resurected an old Kawasaki for which seals weren't available. The corrosion in the caliper was horrible and just getting the caliper off the disc was a challenge! The seal had been under so much pressure that it had distorted, but after sitting in brake fluid for a few days it mostly recovered and once re-installed in the cleaned caliper worked perfectly for a couple of years until the bike was sold.

Another solution is to get rid of one disc and caliper. The bike really isn't heavy enough to need two discs, but the standard single disc setup is often considered rather wooden. The same wheel, disc and caliper when fitted to the 250 2C is just fine and the difference is a smaller bore master cylinder. NLM do have new 250 cylinders and they're something like £60.

[Daddy Dom]

Thanks Gents,
luckily I can source seals locally from http://www.britishspares.com/ for $25NZ, so guess I must knuckle down and wait for a dry day.
I hope it's a simple job, I have never split a caliper before. Is there a procedure/diagram anywhere on the net?

I also have twin hoses straight off the master cylinder - will working on one side affect the other in any way? Do I need to do anything to it while dismantling t'other side?

(A contributor to the Morini mailing list recently posted a photo of a very smart job with a single-pipe coming of the master cylinder and a splitter to the twin discs on the bottom yoke - looked great.)

Cheers,
Dom

[72degrees]

Another solution is to get rid of one disc and caliper. The bike really isn't heavy enough to need two discs, but the standard single disc setup is often considered rather wooden. The same wheel, disc and caliper when fitted to the 250 2C is just fine and the difference is a smaller bore master cylinder. NLM do have new 250 cylinders and they're something like £60.

I have the 2C cylinder on the "Forgotten Error", but made the mistake of fitting a new braided hose. It is far more wooden than it used to be with the old hose. Seeing as that was the original one from 1980 though I thought it could do with changing.

[mgill]

I use an 11mm Brembo M/c and s/s braided hose with the single disc front brake.
"Wooden" it isn't, in fact it's almost too good. One or two fingers on the lever,
and it's got consistent feal...
replaced the chrome disc with a cast iron Brembo from an Alazzurra too.

Mathew

[Daddy Dom]

Braided hoses was the first thing I did on this bike, made a huge difference. When set up, my front braking is very good so I don't need to swap to a Ducati disc.

So is splitting, cleaning and reassembling the caliper a simple job without tricks?
TIA,
DD

[72degrees]

I use an 11mm Brembo M/c and s/s braided hose with the single disc front brake.
"Wooden" it isn't, in fact it's almost too good. One or two fingers on the lever,
and it's got consistent feal...
replaced the chrome disc with a cast iron Brembo from an Alazzurra too.

Mathew

It doesn't need a great deal of pressure to work, just lacks the feel it had before. I can't remember which disk I ended up putting on the Forgotten Error It will be going back on the 2C/375 soon anyway and I'll check it out and probably fit different pads and see how it feels.

[72degrees]

Braided hoses was the first thing I did on this bike, made a huge difference. When set up, my front braking is very good so I don't need to swap to a Ducati disc.

So is splitting, cleaning and reassembling the caliper a simple job without tricks?
TIA,
DD

I've never done caliper strip on Grimecas, yet, only the sliding caliper Nissin on my YZ250. That was pretty straightforward as you don't need to split the caliper. Getting the pistons out was a bit tricky because I had already removed the master cyclinder because of issues with the seals in that. I had to persuade the pistons out using an air compressor in the end. Priming the system with new fluid is a pain on those and the experts recommend using a syringe. Re-filling the Grimeca single caliper setup was easy and only needed a cheap one-man bleeding kit to get it working well pretty quickly. I've never done a twin caliper setup with a splitter or not, so can't give any advice. Some swear by a Mityvac for more complex hose configurations.

Cleanliness is important, and cleaning the seal grooves out carefully is the most important of all.

[Steve Brown]

As said above, cleanliness and a bit of care is the main thing here-and yes they are simple enough. If the pistons are seized or sticking, use the hand lever to pump them out a fair way. Then you can get hold of them more easily. Just try not to pump them all the way out cos they won't come evenly, and one will pop out and make a big messy splash before you get the tighter ones out far enough. I normally use a flat tyre lever to lay in were the pads were, it lets them travel far enough but not all the way out. If you have compressed air that can help, but be careful, they come out with a lot of force and can do a lot of damage. If you need to use air to get a piston out of the disassembled caliper half, try facing the piston down on to a lump of rag to catch it and the old fluid lurking there.
The caliper is held together by the four bolts along the top edge, and you will already have taken one of them out as it hold the caliper to its upper mounting point on the forks.
Use EvGurus tip ref softening the seals (if you do need to re-use them) and don't force the piston back in cock-eyed, it should be a nice smooth slide into the body-it's a very close fit.
Then make sure the small seal between the two halves is in place and bolt the halves together evenly. A sensible amount of torque only-they don't need big wrenches or air guns-a standard size spanner and a firm pull is all it needs.
Once that's all done bleeding should be a doddle. You'll wonder what all the fuss is about afterwards, all it needs is cleanliness and care, just like they said above. People worry too much about doing this, if you are a half able diy-er it will be plain sailing.

[Daddy Dom]

Thanks for the good advice, Steve and others.
I will give it a shot. I'm not wavering because of lack of aptitude it's just that I have nothing other than hand-tools and no workshop. This will be done on my wife's grandmother's kitchen table. Hang on, that's a workshop, isn't it?

I needed to be sure the job was actually possible in a best-case scenario without things like the compressed air.

Fingers crossed that mine is best-case then,
DD

[tonup69]

Hello all. I am new to Morini's, but not to motorcycles, and I have some input here. I just bought a lovely little 3 1/2 (1980 model) and the front brake is AWFUL! The first thing I noticed was that the disk is chromed. For some reason, Triumph did this in the 1970s as well and the first thing I've done on my 79 Special and 73 Tiger was to get rid of the chrome by having the disk re-ground. Makes a HUGE difference in combination with new pads. I also agree that the rubber brake hose needs to go, but that's because I've had rubber hose swell on my 79 Special and freeze up the caliper! I am going with steel braid line for the brake hose, but I need a source for new pads. Where can I get those? I think the master cylinder feels pretty good, so I am just going to replace the lines, grind the disk and get new pads. Will let you know how it comes out!

Cheers,

LTR
Memphis, TN
14 bikes and counting....

[EVguru]

The Chrome discs work just fine with the correct pads (even in the wet), but quite poorly or even badly with the wrong ones.

Modern brake materials work by depositing a layer of pad material on the disc (see; http://www.stoptech.com/tech_info/wp_wa ... disk.shtml ) and if the pad/disc material is incompatible, then this doesn't happen effectively.

Getting rid of the Chrome is a good idea if the Chrome is already poor (patchy etc.), but pretty much a waste of time otherwise as the discs are pressed steel and still not compatible with some pad materials.

North Leicester Motorcycles know what pads work and have them in stock.

In common with many other 1970's or 1980's disc brakes, the master cylinder has too large a bore (16mm), but this does suit me very well with a twin disc setup. The 250 felt good to me too with its (14mm I think) cylinder, but other people prefer a lighter lever and might want to go to a still smaller cylinder.

Actually, that's something else I should mention. Some people (like me) like a really hard lever, where the braking is controlled by the pressure on the lever, whilst others prefer to control braking by the position of the lever. Fitting braided lines will spoil the feel of the brake for the latter.

The first thing I noticed was that the disk is chromed. For some reason, Triumph did this in the 1970s as well

The reason is quite simple, American dealers demanded it. They said their customers didn't want ugly rusty discs. It's the reason that sainless steel is used as a disc material too. It took a while for friction materials to catch up.

At this time of year, I'd really miss my Chrome discs and 'Mysteron afternoons'.

[mgill]

I need a source for new pads. Where can I get those?

Call Michael Morse at Vintage Brake in California he has evrything you need.

http://www.vintagebrake.com/

Regards,
Mathew

[themoudie]

My apologies for resurrecting an old thread. May I have some clear up to date answers to the questions below? Please. I have searched the 'Tre e mezzo' threads and brake pads are mentioned, but the specification and part numbers aren't.

Out for a run today on the '86 K2, bog standard, and whilst the braking hasn't ever been lacking in retarding the bike, there could have been a bit more 'feel'. However, today was the first time out in a good Scottish downpour, in cooler temperatures. All went well for the first 14 miles on open roads, no need for brakes, just use the throttle and gearbox. However, on coming into a small town the brakes were required and with heavy rain falling and wet manhole covers about I feathered the brakes. NOTHING! Sweet FA! Cadence braking brought some heat and cleared the water from the discs and I came to a halt before hitting anybody or thing. For the rest of the outing I gave the brakes a wee 'rub' afore entering any built up areas 'just in case' and fortunately all was well. Even the chromed front single disc on the old Honda 500/4 when it first came out wasn't as bad as this. Whilst the front brakes on a Honda Bros 400, Yamaha SRX 600's and a Duke 450, with Grimeca double sided drum brakes I use, all anchor up reliably under these conditions. I tend to feather brakes, rather than grab handfulls and use the throttle and gearbox to control my speed.

So 'What to do?'

Service the calipers, fit pads suited to chromed discs (sintered pads)?

Service the calipers, de-chrome the discs and fit sintered pads or a mix of sintered and organic pads in each caliper?

Service the calipers, skim the chrome off the discs (seems excessive if reversing the chroming process does the job and retains disc thickness), fit appropriate pads, and maybe reduce the bore of the master cylinder (one into two lines, with splitter on the lower steering yoke, into calipers)?

Service the calipers, buy Ducati cast iron discs (as mentioned in other threads), fit appropriate pads, reduce bore of master cylinder, fit braided stainless steel brake lines and then stand it on its nose!

Concise answers with part numbers/dimensions would be very much appreciated, thank you. I do enjoy riding the K2.

My regards, Bill