Mk.lll brake lever revisited

Previously steve_elston wrote:

Hi all

Has any member had any luck with sorting the front brake lever travel on their MK 3 Commando

recently overhauled Master cylinder and brake caliper with new seals one piece hydraulic Venhill pipe work

On bleeding the brake I'm getting bugger all pressure until I've basically touched the hand grip, also could someone please explain why when trying to bleed this system oil will freely squirt out of the master cylinder before the lever is anywhere near fully depressed

It seems to me that the master cylinder piston is slightly out of position due to wear on the piston end and lever actuating piece

I was going to place a .025"/.030"shim between piston and lever to remove some of the slack and hopefully increase the pressure

I realise that too much shimming/pre-load would make the brake lock up,because the piston would'nt be able to lose the pressure when it was in a released state

any ideas

Steve

Hello Steve,

I have just fitted a one of the new front master cylinders from Andover Norton on my 850 and had similar problems. However, I cured the problem by using a brake bleeder kit from Sealy that sucks the brake fluid throught the bleed nipple on the caliper, rather than the traditional method of pumping the fluid down from the master cylinder using the lever. I also fitted new pads which seemed to make a bit of difference after the pistons were pushed fully back into the caliper. Interestingly, if you buy the bore reducing kit for the standard master cylinder from RGM, it comes with an adjustable pusher that fits between the lever and the end of the piston which means you can adjust the span of the lever to suit your personal preference, although it is critical to make the modification correctly and postion of the new reduced bore size sleeve has to be spot on, so it's not an easy fit modification. I live in the West Midlands if your anywhere near your welcome to borrow the bleeding kit. I hope this helps.

Peter Austin

Having recently gone through the samebleedingprocess (in both senses)on front brake of both my Mk 3 and Mk 1A experiencing the same difficulty, here's my advice. It can take several complete pump throughs of the refilled master cylinder and you have to persevere with the process and be patient ,as it takes time. Eventuallyproper pressure is achieved and the lever suddenly stops travelling to the hand grip. I probably spent a goodhalf hour or moreof solid bleeding on both bikes before the pressure normalized andthe usual small amount of lever travel was achieved to lock the wheel solid.

In my case I kept the original standard Norton master cylinders with all newsealsconnectedwith new hydraulic pipeto RGM disc / caliper kit for the Mk 3 and Norvil disc / caliper kit for the Mk 1A. Front brakes on both bikes now excellent.

The Sealy bleeder kit also sounds a good idea to speed up the process.

Another tip I have seen but not had need to use yet is to tie the lever back to the grip and turn the bars so the master cylinder is at its highest and leave overnight. The air travels upwards and has free access to come out.

Holding the lever on over night or longer has worked for me on many different bikes. I use a 60ml syringe and lenght of suitable bore pipe (these can be had for few pounds on Ebay). Open the bleed nipple and use these to push the fluid up the system. Turn the bars to left to raise the master cylinder and even taking off the caliper and turning it to a better angle may also help.

If no trace of air can be removed an no improvement is made the look very closely at the caliper pistons. Pressure on the lever should make them move out and then stay against the pad when pressure is released. With new seals sometimes on releasing the pressure you will see the piston move back into the caliper very slightly. This means the next squeeze of the lever must first move the piston back to the pad wasting lever travel as it does so. This is also best cured by holding the pressure on over night or longer (5 days for my caliper) as the pressure on the seal will slowly force it to "settle" as it were in the correct shape. (Thats only way I can think to put it without writing lots more) As all your system is new and therefore in good condition no damage will be caused by holding the pressure and if any leaks are found in the joints etc. these would have happened later anyway maybe when you really need to brake hard an not safely in the garage.

Steve, brake fluid entering the reservoir, from the cylinder, is correct on a correctly rebuilt M/cylinder. The first pistontraveldoes not apply the brake but closes offa relief port connected to the reservoir.

This allows hot and expanding brake fluid to escape into the reservoir other wise the brake would come on in hot weatheror will not let off after prolonged braking evenwhen the lever is released.

I hope I read your message correctly

Roger

Sounds like the pressure release valve is not being cleared in the fully off position, this seems to happen more frequently in hot weather. You can adjust this out,

This is covered in the Old Britts write up on rebuilding the master cylinder.

http://www.oldbritts.com/14_064244r.html

Fifth, assemble the cylinder to the body. Note: there are two flats on the sides of the threads of the cylinder. You should see a mark on the flat opposite the cylinder stud where the set screw presses against the flat. I blacken this mark with a black marking pen so I can thread the cylinder into the body to the exact depth it was before. You will be able to see the mark through the set screw hole. IF YOU THREAD THE CYLINDER IN TOO FAR, IT WILL NOT LET THE BRAKE PADS RETURN TO A NEUTRAL POSITION AND LOCK UP THE BACK WHEEL. Insert the set screw and tighten.

Whilst My system does not feature any Norton components I too have a similar problem. I have a 2LS rear brake using a Leyland Mini brake plate. For years I had a Triumph Herald master cylinder fitted and it worked well. I changed it for one from a Honda CBR600 recently and it worked well, until I went to Italy and it started dragging and overheating. Releasing the hydraulic fluid at the nipple solved the problem but it has happened twice again since. The fluid pressure is increasing with heat (indicated by the brake light coming on) and it must be due to the port opening the system for expansion being covered. I need to investigate the static position of the piston relative to the port.

Have you got new hydraulic pipe to the caliper ? Had this same problem of pads not releasing properly on my front wheel brake once and replacing the old (metal) piping with a new (flexible) one cured the problem. Old pipe was gunged up not allowing free flow of fluid back to master cylinder when brake released.

also as I have done eight hundred miles surely the problem would have occurred a lot earlier had I screwed it in too far

The reports I have seen typically are linked to a hot day sometimes combined with the bike being left in the sunshine, so with the recent UK warm weather it could be the trigger. But there are other potential causes of course.