The front brake is killing me (mentally)

I have a 75 MK III. The front brake MC has been sleeved and checked for functionality. If I remove the brake line and plug the outlet, it is like trying to squeeze a brick solie. The brake lines are braided stainless. The front caliper has been rebuilt with new stainless pistons and new rubbers. There are no visible leaks. I filled the system from the bottom up. I bled the system fron the top down, and have had a shop use a power bleeder to make sure. I am not getting any air out the the system at this time.

When I pull on the front brake, I have probably 2" of travel at he end of the lever before I feel any resistance. I can squeeze the brake lever until it touches the grip. As I said, I have bled the system several times and am not getting ANY air bubbles coming out at the caliper. If I use a tie wrap pulling the brake lever in about half way and let it sit for an hour or two, I have a nice firm lever that I becomes very solid and will pull to about 1 1/2 - 2" from the grip. If I let the bike sit for an hour or two without the tie wrap on the brake lever, it gets soft again.

I have tried every trick I know and a few suggested by a couple well respected mechanics. I even checked the front disc with a dial indicator and found only about .007 of warp in the disc. Although not perfect, I don't think that is enough to cause a problem.

Any theories? My frustration level is very high right now.

try shimming the lever where it touches the M/cyl piston, even temporary with some small washers. see if that cures it. if so then you are on the right track,

Although for a replacement hydraulic clutch for a 1984 Honda Shadow 700; this exact same thing happened with it. Bought it BRAND NEW from a Honda dealer too. I was pulling my hair out :twisted: Finally just let it sit for a week with the brake fluid all in it. Came back, bled it again ... and it worked just fine :shock: Really don't understand it; other than maybe the seals had to be totally "wet with fluid" ??? The master cylinder did come dry, so maybe finally soaking for awhile helped ??? That's all I can think of anyway. If I were you, leave it sit for a week and try again. If it still doesn't work, buy a nissin master cylinder and enjoy modern braking !!! I bought mine at mikesxs.net for $67.00 several years ago. There is also one that "madass140" (forum member here) that makes one, with a bracket that also allows the use of the Lucas switches even ! Now that's the business 8)



Available here http://www.mikesxs.net/product/08-0255.html

Also available from Triumph specialist "northerneagle.ca" item #MC08-0262 for $69.00

madass140 said:

try shimming the lever where it touches the M/cyl piston, even temporary with some small washers. see if that cures it. if so then you are on the right track,

Click to expand...

Could also save yourself additional grief, and just buy the replacement nissin master cylinder that Don (madass140) makes

I will look into that. I would be more eager to do that if I knew for sure it is the master. The problem is, everything is new/rebuilt. I am not sure if it is the master or the caliper. Does that maste work with MK III controls?

calbigbird said:

When I pull on the front brake, I have probably 2" of travel at he end of the lever before I feel any resistance

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Resleeves do work well. The brakes are a very simple system. If you have no leaks, then easy to diagnose.

How far does the lever travel before the piston starts to move ?

When you can get some lever firmness, does the lever move to the bar when you crack the slave bleeder ?

If you move the lever say 1" at the tip, the piston should start to move. If not, you may have an adjustment or shim to do

When you crack the slave bleeder when squeezing the lever you should get a positive squirt. Remember to close the bleeder before releasing the lever.

Let us know

Cheers

sorry, my replacement mastercylinder is for pre MK3 switchblock fitment only

Are you absolutely sure there is no air in the system? A bubble can hide [ maddeningly] trapped in a non vertical spot, try dismounting horizontal components [caliper& M/cylinder] & hang them vertically, &/or bleed the M/cylinder/line junction.The 850 Mk 3 mounts its caliper on the opposite side/fork leg position yes? Not holding air bubbles there? Or, when re-sleeved, has the M/cylinder bore [ratio to caliper] been changed?

Nortiboy said:

calbigbird said:

When I pull on the front brake, I have probably 2" of travel at he end of the lever before I feel any resistance

Click to expand...

Resleeves do work well. The brakes are a very simple system. If you have no leaks, then easy to diagnose.

How far does the lever travel before the piston starts to move ?

The lever appears to immediately engage the piston

When you can get some lever firmness, does the lever move to the bar when you crack the slave bleeder ?

Yes, the lever moves to the bar when I crack the slave bleeder

If you move the lever say 1" at the tip, the piston should start to move. If not, you may have an adjustment or shim to do

The piston moves immediately with movement of the lever

When you crack the slave bleeder when squeezing the lever you should get a positive squirt. Remember to close the bleeder before releasing the lever.

Yes, when I crack the bleeder, I get fluid being pushed from the caliper an yes close the bleeder before I release the lever.

Cheers

Click to expand...

The Master has been back to the person who did the sleeve twice. Each time he reports it is working correctly. He has been very patient and I believe him.

madass140 said:

sorry, my replacement mastercylinder is for pre MK3 switchblock fitment only

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Thanks for responding. That is what I was afraid of. I considered buying the master and switch gear from CNW, but I hate to spend the money until I can confirm this is the fault of the master. Right now, I don't believe that is the case.

How does the caliper orientation compare Mk 3 to earlier Cdo? You are not trying to fit the caliper wrong way up [up - for bleed nipple is correct]?

J.A.W. said:

How does the caliper orientation compare Mk 3 to earlier Cdo? You are not trying to fit the caliper wrong way up [up - for bleed nipple is correct]?

Click to expand...

The caliper is in it's original position on the left fork. The bleed valve is at the top of the caliper

If you look in the bottom of the master cyinder fluid reservoir, there are 2 little port holes into the master cylinder itself. Are both of these ports clear ? Absolutely clear ??

A little particle of rubber, dirt, fluff, gung blocking those ports can produce these symptoms.
I once drained and flushed the fluid several times to get rid of something similar.
(it has sat unused for a while though).

You don't say if opening the bleed nipple while under pressure produces a squirt of fluid.
If it doesn't, something is seriously wrong somewhere.
As someone said, close it again, before releasing the lever.

hopethishelps.

Def `no fluid leaks ? Tried a pressure bleed? Put your finger over those port holes [per Rohan's post] as you work the lever, feel any pulses of pressure/suction?

Went through a similar situation with a re-sleeved MC. Replacement OEM brake blade didn't allow return hole to fully open . Needed to have the blade contact point on the MC shaved to allow return hole to fully open! I went through a quart of brake fluid and warped two rotors figuring it out! :evil:

The Master has been back to the person who did the sleeve twice. Each time he reports it is working correctly. He has been very patient and I believe him.

Click to expand...

Can you take the bike to him ?. He must have experience.

Based on yr reply, it sounds like the cup seal is not seeing the piston ports fully. Drain the master and check if the pistons passes the small holes in the bottom of the reservoir.

Does the lever have a freeplay (moves a bit before it contacts the piston) ?

There are other members starting to zoom in on this. Be patient, we will get it.

Cheers

I think you still have air. You need to bleed these from the bottom up - ie pump fluid through the caliper bleed nipple. My resleeved cylinder from came with a large syringe and short clear hose to do this. Also had to bungee the lever back -- overnight -- not just a couple hours.

Russ

I've previously got a reluctant brake to bleed out by removing the brake pads and pumping the pistons down as far as is safe, then after letting the fluid settle, I've levered the pistons back into the caliper as fast as I dare without getting a fountain of fluid coming out of the reservoir.
Not only should this purge out any air trapped in the system, but it would also prove that the bleed hole in the master cylinder is clear, and not masked by the piston.

Sometimes the pipe routing prevents the air from finding its way out, but not on Nortons.

RGM insist on the cylinder being supplied with the lever so they can get this adjustment right as part of their re-sleeve process.

The inboard piston cavity is a SOB to get the air expelled from while the caliper is mounted. The usual bleed process does not circulate fluid THROUGH this cavity effectively.
Pre-filling the inner cavity before inserting the piston will help.
Alternately remove the caliper from the mounting and invert it while bleeding.
I made a little sketch of the fluid path and how the inboard cavity is fed, then the light went on in my tiny brain.
An additional bleeder port located at the top of inner cavity would help tremendously.
Best of luck.

One of the issues that can affect sleeved MCylinders is mis-alignment of the sleeve ports/MCylinder ports which can cause what you describe. It would seem that since your sleever has rechecked it, it is unlikely that that is the problem. The other problem can be bad/improper o-rings on the piston which can do that as well - I've had both happen. Again, since your guy checked it out, one would think neither of those issues could be the problem. I may have missed it but did you fill the system from the caliper as opposed to the Mcylinder using some sort of pressure device (big hypodermic works fine)? That will ensure that there are no air bubbles in the system since it will force all air out as it fills. If you didn't, give that a try. If you did, I'm out of suggestions other than the suggestion to purchase the CNW Brembo Mcylinder kit. It is superb and give much better braking and feel than a resleeved oem cylinder. The one thing I don't like about it is that it requires different switchgear. But the braking is so much better that, in this case, the performance (IMO) justifies the non-oem look.