850 Mk II - front brake problems; need help!

Status
Not open for further replies.
M

marctroy

Joined
Jul 27, 2008
Messages
13
I recently refurbished my front brakes on my '74 850 Mk II with the following:
rebuilt master cylinder with 13mm modification
Goodwood stainless steel brake line
Norton rebuild kit
stainless steel "pucks"
Ferodo pads
DOT 4 fluid
full bleed (no air bubbles)
the only part that hasn't been changed is the original brake lever

Since I'm new to Nortons, I can only put my problem into automotive terms (as follows): I have a "low pedal".

My front brake isn't activating until my brake lever almost touches the hand-grip and there isn't any room to modulate the brake; it seems like it's either "on" or "off".

Any suggestions would be greatly appreciated; thanks!
 
All I can say is, "bleed it again." You must have air in there somewhere. Sometimes you need to remove the caliper and rotate it so the bleed screw is uppermost....
 
No big deal, just rebleed and get the air out of there.

Would be curious to know where you got your parts. I'm thinking of doing the same work on my '74 Roadster 850.
 
Nomad, dunno if this will be of interest but I had Fred Eaton at Old Britts redo my MC, drill and blanchard ground my rotor, and sell me new pad and a S/S line - total about $750 - and my front brake went from a "suggestion" to slow down to a one-finger stopper. Well worth the investment.

You may be able to do it cheaper and/or better but this worked quite well for me. FWIW. - BrianK
 
Brian, thanks for the response. I have an S/S line on the stock setup on my Commando now, and it requires a very "assertive" squeeze (grip a 2x4 and you will know what I mean). I was thinking of starting with better pads and then taking it from there, getting the rotor drilled eventually.

Poor brakes are one thing I really will not write off as part of the "vintage bike" experience. Looks like I will have to give Fred and Ella a call. Thanks!
 
I have pretty much the same setup with the 13mm conversion on my '72 Combat and it does work. Are you bleeding it backwards through the bleed nipple on the caliper as the instructions tell you to do? It took a while and at first there was no resistance when pumping the lever but eventually it came up OK. Try putting a heavy duty rubber band around the lever and let it sit for a while. I think this is also in the instructions.

I got the 13mm master cylinder modification (exchange basis) and the SS caliper pistons, braided hose, and caliper o-rings from Jim Noll at British Bike Connection but just about all the usual mail-order dealers carry it.
 
Thanks, all, for your input. I've bled the system from the bleed screw up and from the master cylinder down about 8 times now; the only thing I haven't done is batrider's "rubber band" method of bleeding. I always thought that when there's air in a system, a brake pedal feels "spongy" and it will go down slowly after maintaining pressure on the pedal. This is different - there's about 3 inches of "free play" in the lever and then the brake is ON. I have nothing to compare it to since I got the bike as a sort of "barn find" and it's just nearing completion.
It seems as though there's just one part that hasn't been changed and that's the lever itself and I'm beginning to wonder about that. Based on the poor reputation of the dealer who serviced the bike years ago, they probably screwed the lever up in one way or another...
 
One mechanic told me the rubber seal on the master cylinder aan "fold" back if operated without oil, this has the same results you have, no feedback and then grabs very near the end of lever travel. It would be worth it to take themaster cylinder appart and check it out.

Jean
 
I did the same brake upgrade to my 850, took some time to bleed properly but then it was a far better brake. One thing that may be a cause of your problem is the difference between Mk1-2 850 front brake lever and the Mk3. The Mk3 has a different profile, basically to bring the finger reach closer to the handlebar.
I got one to fit and it was doing just what your problem is. The lever just about came the bar when the brake came on. I went back to the Mk2 lever and all is well and my fingers now got muscles.

Mick
 
I had the similar braking issues when I first got my bike. Very hard brake handle pressure and not stopping very well at all. Tried very hard keep the bike looking original but, finally succumbed to upgrading entire brakding system including 12mm re-sleeve, stainless line, 12" Grimeca disc and pads. Made a world of difference when you can stop, even tho it no longer looks original.

850 Mk II - front brake problems; need help!


850 Mk II - front brake problems; need help!
 
gw88 said:
upgrading entire brakding system including 12mm re-sleeve
Click to expand...

Where (or how) did you get the 12mm re-sleeving done? I've only seen people doing 13mm upgrades, whereas 12mm seems to be the optimum diameter to use.
 
Hi Corona, I meant to say 12.54mm or 1/2" in your lingo. It came as a kit and I had the stainless line made to length. Cheers.
 
I had a similar problem and it turned out it was the lever. The PO had altered lever in such a fashion as to not allow the lever to fully depress the master cylinder piston. I was unable to purge the system of air completely - although I thought I had. When I replaced the lever = one good bleed and perfection! I recommend that you compare your lever to a known good one. BTW - my old lever worked fine with an unmodified master - it's when I changed to the 13mm conversion this problem appeared.
 
I have had exactly the same frustrating 'long pedal' symptom that you describe. I bled the system by sucking the caliper via a Snap-On vac pump but it still would not give me a good lever. I put PTFE tape around the bleed nipple to reduce any air suck tendencies around the nipple threads. Still no good. It was driving me crazy.
Finally I rubber banded the lever and left it over the weekend. Hey Presto! It worked fine. I guess bubbles gradually rise out under gravity but can only escape if the master cylinder is open (ie. lever pulled). Also I occasionally varied the position of the handlebars to help the bubbles escape.
 
Status
Not open for further replies.

Similar threads

Dan1950
  • Locked
Recommended Brake Fluid MK II Front Brake?
2 3 4
Replies
71
Views
5,078
cliffa
cliffa
Back
Top