Mk3 Rear brake Problems

L.A.B. said:
Mine doesn't.:)
Mk3 Rear brake Problems
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Looking at your photo. If you rotate the lever 20 degrees or so clockwise, the bolt head would be at its closest to the M/C boot. Does it actually contact the boot as it passes the M/c? Your kickstart lever has been rubbing on the footrest arm as well.
A most likely cause of the boot contact is the kickstarting of the bike with it on the center stand.
 
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dobba99 said:
Looking at your photo. If you rotate the lever 20 degrees or so clockwise, the bolt head would be at its closest to the M/C boot. Does it actually contact the boot as it passes the M/c?
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Yes, the bolt head* just touches the boot but doesn't hit the housing.

dobba99 said:
Your kickstart lever has been rubbing on the footrest arm as well.
A most likely cause of this contact is the kickstarting of the bike with it on the center stand.
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That rub was from the kickstart lever on there when I bought my Mk3 that had worn splines and loose enough on the shaft for it to either have been colliding with the footrest hanger on the return or just vibrating against it.

I replaced that lever many years ago. The kickstart lever on there now doesn't touch the hanger.

*The kickstart bolt should have a thinned head and the parts book doesn't show/list a washer.
With that bolt and no washer, it might not touch the boot.
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Fitted the adjusted master cylinder this morning, along with the newly rebuilt caliper but still no good.

I can't get any pressure at the brake pedal and still getting air bubbles after almost a litre of brake fluid, so I must have an air leak somewhere.

Also, only the inboard pad is moving out when I apply the pedal, the outboard one seems fixed/stuck against the disc. (Which may be why the disc is getting hot during a ride). I suspect the caliper is the problem.

Next step is to switch the front caliper with the back one to see if that solves it.
 
Could be you have more than one problem. If you haven't already, pull a bristle out of you wire brush an poke it into the tiny, tiny relief port on the floor of the MC resovoir. You might have to remove the resovoir to access the port, I don't remember. In any case you have the classic case of the port being blocked.

The other problem may be that one of the caliper pistons is sticking. The only solution to this is to dismantle the caliper, clean the bores, install new quad-rings with proper rubber lube, clean the pistons or replace if the chrome is flaking and reassemble the unit. As the caliper is above the MC, bleeding isn't usually a problem like on the front.
Could be that the MC wasn't properly assembled. Being "new" doesn't guarantee that it is all correct. Likewise the caliper.

I also have had the internally disintegrating flex hose problem on Nortons and BMWs but not with a new hose, only after sitting unused for a long time. Not only does the hose deteriorate but it can be just fine but clogged with a mix of old brake fluid and water that has solidified.
 
No one has suggested trying an oem disk to see if the girling unit is contributing to the issue.
 
Pulled everything apart again, both pistons are free but there is fluid around the edges.

Checked the master cylinder too and it seems okay with no blockage. I'm goong to try the AP Racing seals again as they seem a much better fit than the AN ones:

 
Bilko said:
Pulled everything apart again, both pistons are free but there is fluid around the edges.

Checked the master cylinder too and it seems okay with no blockage. I'm goong to try the AP Racing seals again as they seem a much better fit than the AN ones:

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I use the AN pistons and seals or the AN pistons and Wassell seals and they never have leaked except one time that I didn't properly clean out the grooves in the caliper - no longer make that PITA mistake!
 
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Bilko said:
I'm goong to try the AP Racing seals again as they seem a much better fit than the AN ones:
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The seals really need to be installed in the caliper first because that should compress them slightly.
No leaks from the two AN sets I've installed.
 
Bilko said:
I can't get any pressure at the brake pedal and still getting air bubbles after almost a litre of brake fluid, so I must have an air leak somewhere.
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As you are pressurising (or at least attempting to pressurise) the system then, logically, there should be fluid leaking out rather than air getting into the system.
Are you using the standard technique of opening the bleed nipple as you begin to press the brake pedal and then closing the bleed nipple before allowing the pedal to return?

You could re-use the fluid until you've found what the problem is and then flush the system. There's no need to continually use new fluid in my opinion.
 
L.A.B. said:
As you are pressurising (or at least attempting to pressurise) the system then, logically, there should be fluid leaking out rather than air getting into the system.
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That does make sense, but I seem to have both!
L.A.B. said:
Are you using the standard technique of opening the bleed nipple as you begin to press the brake pedal and then closing the bleed nipple before allowing the pedal to return?
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I use a MightyVac bleeder, so no pumping of the pedal. I also have Goodridge Speed Bleeder Nipples fitted.
L.A.B. said:
You could re-use the fluid until you've found what the problem is and then flush the system. There's no need to continually use new fluid in my opinion.
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Never thought of that. Great idea as I'm getting through gallons of the stuff.
 
L.A.B. said:
Maybe try bleeding it the conventional way?
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Agree. The design of the Norton (Lockheed) caliper makes the fluid go in the small hole the air is coming out of for the inside chamber. The holes for the outside and inside chambers meet at the bleed screw. It seems to me that putting a vacuum there will ensure that no fluid gets to the inside chamber - it will work fine for the outside chamber but then the brake will be too mushy to use.
 
Attempting to vacuum bleed could have the potential to draw in air past the master cylinder outer piston (secondary cup) seal that's designed to seal against internal (fluid) pressure but doesn't effectively seal against air being drawn in by the vacuum.
 
marshg246 said:
Agree. The design of the Norton (Lockheed) caliper makes the fluid go in the small hole the air is coming out of for the inside chamber. The holes for the outside and inside chambers meet at the bleed screw. It seems to me that putting a vacuum there will ensure that no fluid gets to the inside chamber - it will work fine for the outside chamber but then the brake will be too mushy to use.
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That is very interesting, and it's exactly what seems to be happening. No movement on one piston and no pressure at the pedal.
 
L.A.B. said:
Attempting to vacuum bleed could have the potential to draw in air past the master cylinder outer piston (secondary cup) seal that's designed to seal against internal (fluid) pressure but doesn't effectively seal against air being drawn in by the vacuum.
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Wow, I had no idea that vacuum bleeding cause these issues.

I'm going to try and bleed the system the conventional way and see if I can get a better result.
 
Bilko said:
That is very interesting, and it's exactly what seems to be happening. No movement on one piston and no pressure at the pedal.
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It's usually the inner piston/chamber that fails to bleed when the piston is pressed in too far as it can blank off the drilling.
I haven't known it to happen with the outer piston though.

Bilko said:
Wow, I had no idea that vacuum bleeding cause these issues.
Click to expand...

It's a theory so could perhaps explain why air seems to be drawn into the system.
 
Sorry to hear about the woes with this .
My MK111 rear bleeding went quick n' easy using the conventional method . First attempt . I did it after tossing the short stock hose for a fitted braided stainless thinner aftermarket one . The protective black coil slipped right over the line and you can't tell it was changed out .
 
Try taking out the axle and loosen the shock bolt so you can remove the caliper and bracket and then move the unit up high and have the bleed nipple at the highest point and hang or have someone hold it so you can Pump bleed it. IF you have a good fitting hose on the nipple and have it arced upwards so the air goes up and then downwards into a collection container. that is best. Try using the OEM nipple and put a little sealer on the threads. Air will ALWAYS leak by if the threads are not sealed. Once you get it flowing, you don't have to open and close the nipple, but pump it to flush air out. Then tighten the nipple and test the pedal feel. Bleed some more and test again.
 
If you have it apart there is a fast, messy, and easy way!

1) Screw in a bolt (5/16" UNF if I remember right) in the feed line hole to seal it
2) Seals in, pistons not in
3) Bleed screw removed
4) Caliper on its back
5) Put in about 1/4" of fluid in the bottom chamber
6) Put in the bottom piston (inner) and push it in just enough so the pad can go in normally
7) Screw in the bleed screw to close it off.
8) Clean up the mess
9) Put the upper (outer) piston to is normal location (to allow the pad to sit correctly
10) Put in enough fluid to just fill the back of the piston area to the cap
11) Screw in the cap
12) Mount the caliper with pads installed
13) Remove the bolt and connect the feed line
14) Bleed normally (will take very little)
 
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