72 Disc Brake issue

Just rebuilt the Master Cylinder, Caliper, (Lockheed) and replaced the brake hose.
I bleeds just fine, have a nice firm feel on the lever, and the caliper pistons do compress the brake pads against the rotor.
However, the braking is extremely weak.
Where as that last time I rode it, which was about 5 years ago, the front brake worked great.
I have changed pads in the past as well as the brake fluid and have had no problem up until now.
The reason I rebuilt the caliper and master was that after sitting for five years, I gave the brake a good squeeze, and it failed, the lever collapsed to the handle bar.

Another symptom is that the brake sending unit does not activate the brake light, even though I replaced that as well, and yes the wiring is correct.

All the components cleaned up nice, but there is obviously something still wrong.

Hi, welcome.

Chrome still on the rotor?

concours said:

Hi, welcome.

Chrome still on the rotor?

Click to expand...

Yes. How does that affect things? Another symptom is that the brake sending does not activate the brake light, even though I replaced that as well.

wbehning1 said:

Just rebuilt the Master Cylinder, Caliper, (Lockheed) and replaced the brake hose.
I bleeds just fine, have a nice firm feel on the lever, and the caliper pistons do compress the brake pads against the rotor.
However, the braking is extremely weak.
Where as that last time I rode it, which was about 5 years ago, the front brake worked great.
I have changed pads in the past as well as the brake fluid and have had no problem up until now.
The reason I rebuilt the caliber and master was that after sitting for five years, I gave the brake a good squeeze, and it failed, the lever collapsed to the handle bar.
All the components cleaned up nice, but there is obviously something still wrong.

Click to expand...

If you didn't change the pads when you rebuilt the caliper, you might need to - you're brake fluid went somewhere in those 5 years. If you did change them, maybe the rotor is glazed and if so, the pads are unlikely to "break in". If that's the case, send the rotor to: https://truedisk.net/ It's inexpensive and makes them work quite a bit better.

wbehning1 said:

Yes. How does that affect things? Another symptom is that the brake sending does not activate the brake light, even though I replaced that as well.

Click to expand...

No/low pressure! If you found the master cylinder/caliper easy to bleed and you have a firm feel right away, your master cylinder is not right and the switch not working is telling you that you have too little pressure. Blocked holes, seals on backwards, valve not working.

Standard Norton front brakes are notoriously hard to bleed!

wbehning1 said:

Yes. How does that affect things? Another symptom is that the brake sending does not activate the brake light, even though I replaced that as well.

Click to expand...

The chrome has very poor friction coefficient.

Much has been discussed about this. Search the site and read plenty.

Did you clean with a wire the master cylinder holes from the reservoir?

Does that hard lever go to the bar as expected when the bleeder is opened?
Can you make it piss two feet? (Confirming pressure & volume)

Jumper the two wires at the switch, stoplight operation confirmed? Report back.

Suggest you also check the hose as a few years ago I had one that internally collapsed.

wbehning1 said:

Just rebuilt the Master Cylinder, Caliper, (Lockheed) and replaced the brake hose.
I bleeds just fine, have a nice firm feel on the lever, and the caliper pistons do compress the brake pads against the rotor.
However, the braking is extremely weak.
Where as that last time I rode it, which was about 5 years ago, the front brake worked great.
I have changed pads in the past as well as the brake fluid and have had no problem up until now.
The reason I rebuilt the caliper and master was that after sitting for five years, I gave the brake a good squeeze, and it failed, the lever collapsed to the handle bar.

Another symptom is that the brake sending unit does not activate the brake light, even though I replaced that as well, and yes the wiring is correct.

All the components cleaned up nice, but there is obviously something still wrong.

Click to expand...

At the bottom of the reservoir there are two small holes. If you pump through some of the fluid so you have say 1/4” left, then close the nipple, do you see a spurt of fluid from the hole closest to the headlight (the compensator port) when applying the brake? (You should do).

Edit:

Put a towel or similar on the tank when trying this.

marshg246 said:

No/low pressure! If you found the master cylinder/caliper easy to bleed and you have a firm feel right away, your master cylinder is not right and the switch not working is telling you that you have too little pressure. Blocked holes, seals on backwards, valve not working.

Standard Norton front brakes are notoriously hard to bleed!

Click to expand...

concours said:

The chrome has very poor friction coefficient.

Much has been discussed about this. Search the site and read plenty.

Did you clean with a wire the master cylinder holes from the reservoir?

Does that hard lever go to the bar as expected when the bleeder is opened?
Can you make it piss two feet? (Confirming pressure & volume)

Click to expand...

concours said:

The chrome has very poor friction coefficient.

Much has been discussed about this. Search the site and read plenty.

Did you clean with a wire the master cylinder holes from the reservoir?

Does that hard lever go to the bar as expected when the bleeder is opened?
Can you make it piss two feet? (Confirming pressure & volume)

Jumper the two wires at the switch, stoplight operation confirmed? Report back.

Click to expand...

Thanks for the info.
Cleaning the mc with a wire yes. That still could be the issue, I'll try it again.
Opening the bleeder and squeezing the lever - Yes it goes back to the handlebar and passes the "piss" test.
Jumping the two wires lights up the rear brake light.

Question, There are two holes in the reservoir. The one closest to the edge is wide open, where the one towards the middle narrows down to a small diameter. I ran a wire down that hole, but was unable to get it to exit anywhere. I presumed that it couldn't make a bend around a corner. Thoughts?

When I have the reservoir cap off, and I gently activate the lever with the bleeder open, I can see a small stream of fluid exiting through that hole back into the reservoir. I believe this is normal operation, and it seems to prove the hole is not blocked, although it could still be obstructed.

Could it be a hydraulic lock happening on the back section of the piston? As hard as the lever is, that seems a likely possibility.

wbehning1 said:

Could it be a hydraulic lock happening on the back section of the piston?

Click to expand...

That has been known from pattern pistons without a recess on the edge to not allow the fluid to get behind a piston fully inserted and then to push it out. So best have pistons with the recess.

With recess



without recess

If you hold the lever against the pressure in the line, the pads should clamp the disc. When that happens the brake should work. If it doesnt, you have a blockage. If the brake works but not well enough to stop the bike, you have a friction problem. To stop a Commando race bike in full flight, a single disc is not enough.

Best thing I ever did was replace the old 50 years old front brake and brought it up to modern day system, money well spent in replacing everything, my front brake is as good as my modern Triumph, even when I brought my Norton new the front disc brakes weren't the best, but it took me to about 12 years ago before I woke up and had 2 near misses but went down from bad front brake even after major rebuild and upgrade to an old system.
At the time of recovery from the 2nd failure was when I ordered a complete new front brake system and 12 years ago was not bad for under $600 delivered from RGM to Aus, one of the best upgrades I done, my life is more important than trying to fix an old system and my Norton isn't original anyway lol.

Ashley

Following on from Kommando's post, if you remove the pads can you pump the pistons closer together?
Don't let them drop out though - I put a tyre lever between (where the disc normally sits) to prevent the pistons falling out).
I find that one piston typically comes out more easily than the other, but this will highlight if yours is stuck or not getting fluid behind it.

ashman said:

Best thing I ever did was replace the old 50 years old front brake and brought it up to modern day system, money well spent in replacing everything, my front brake is as good as my modern Triumph, even when I brought my Norton new the front disc brakes weren't the best, but it took me to about 12 years ago before I woke up and had 2 near misses but went down from bad front brake even after major rebuild and upgrade to an old system.
At the time of recovery from the 2nd failure was when I ordered a complete new front brake system and 12 years ago was not bad for under $600 delivered from RGM to Aus, one of the best upgrades I done, my life is more important than trying to fix an old system and my Norton isn't original anyway lol.

Ashley

Click to expand...

The AP Racing caliper works well, but I've found the original caliper can still be decent if in good shape (I rebuild mine with stainless pistons).
Another advantage of the AP caliper is a bigger choice in brake pad material - the ones marked 'Not for road use' being the best for, er... road use

I’ve also found that once the system is full, a great way to reverse bleed the brakes is simply to force the pistons back as far as they will go. In my experience a lot of air will be expelled. (Drain some fluid from the reservoir first though).

cliffa said:

At the bottom of the reservoir there are two small holes. If you pump through some of the fluid so you have say 1/4” left, then close the nipple, do you see a spurt of fluid from the hole closest to the headlight (the compensator port) when applying the brake? (You should do).

Edit:

Put a towel or similar on the tank when trying this.

Click to expand...

that is exactly what I am seeing.