front brake stuck closed

1973x75 · Dec 6, 2015

So I took the caliper apart, and everything came out without a struggle. It was a little murky with sludge in there, but maybe the penetrating oil caused that, I don't know. Each piston has a very small spot of corrosion, or pitting, which i suppose makes them ineligable for reuse? I knew I would need a seal kit, but I should probably get the pistons too. But should I also be looking into the master cylinder? This is a 1973 750.

Thanks in advance for any information...Dave

bluto · Dec 6, 2015

FWIW I have a '73 850 w/ a resleeved MC and it used to lock the front brake on very hot days if it was parked awhile (dousing it with cold water would unsieze it) ....posted that here awhile ago and learned that others had experienced this too w/ modified stock MC's. Rather than try to fix my MC I opted to buy a modern MC kit from "Madass", only $150 and it mates to the stock mirror, switchgear, and brake line perfectly. No more problems in hot weather now...
(BTW the adjustable lever in the photo was added by me, the kit comes with a perfectly good standard lever)

Torontonian · Dec 6, 2015

Ditch the stock caliper chromed pistons and fit the stainless ones. All stickings and rust will be gone. Fit new sectioned o-rings to them too ,the correct way around. Work spotlessly clean.

CanukNortonNut · Dec 6, 2015

Paint the old M/C silver instead of black.
T
CNN

Biscuit · Dec 7, 2015

Torontonian said:
Ditch the stock caliper chromed pistons and fit the stainless ones. All stickings and rust will be gone. Fit new sectioned o-rings to them too ,the correct way around. Work spotlessly clean.

The 'square' section caliper piston seals can not be fitted wrong. The proud sealing lip you see in the caliper groove is caused by the slanted groove floor at the bottom of the groove. This twists the square ring a bit thereby raising a 'lip'. Sealing rings that have been in service for a while will appear to have a side raised higher on one edge but this is caused by a 'set' taken over time by a square sealing compressed in a non square groove.

Nater_Potater · Dec 7, 2015

1973x75 said:
...But should I also be looking into the master cylinder?

I installed a $20 fleabay special with a 12mm bore almost two years ago, and the difference in lever force/feel was night and day! A Madass M/C is in the budget, as the $20 special looks a bit "cheesy".

1973x75 · Dec 7, 2015

I just ordered the stainless pistons and a seal kit from Old Britts. A very pleasant woman took my order over the phone. I'll rebuild the caliper, then give it a drive to feel the difference, then I'll check into the master cylinder. The master cylinder rebuild kits are pretty cheap, maybe that would be the way to go?

Biscuit · Dec 8, 2015

I've rebuilt Norton masters several times and have always had good luck. Of course bore condition is the key to a successful and lasting job and pay attention to the orientation of the thin curved washer.

grandpaul · Dec 8, 2015

A perishing brake hose can become a one-way valve and lock up a brake easily.

Torontonian · Dec 8, 2015

Thanks for that square section seals re- clarification Biscuit. Re-checked manual , under Caliper re-assembly it says " In addition , the seal groove and seal are different in section so that when bedded , the seal feels proud to the touch at the edge furthest from the bore. This is normal. " . So yes , the bottom of the aluminum seal groove must be cut with a taper to achieve this. The seal being square section , used seals developing a taper , and "memory" over time. So it looks like new seals every time the caliper comes apart for sure.

As a fisherman I spend money the start of every season on fresh line to replace line that has developed coiling memory .

nortriubuell · Dec 8, 2015

bluto said:
FWIW I have a '73 850 w/ a resleeved MC and it used to lock the front brake on very hot days if it was parked awhile (dousing it with cold water would unsieze it) ....posted that here awhile ago and learned that others had experienced this too w/ modified stock MC's. Rather than try to fix my MC I opted to buy a modern MC kit from "Madass", only $150 and it mates to the stock mirror, switchgear, and brake line perfectly. No more problems in hot weather now...
(BTW the adjustable lever in the photo was added by me, the kit comes with a perfectly good standard lever)

+1 on the "Madass" front MC ... you even get to keep the "crappy from new," Lucas switchgear. :lol:

rx7171 · Dec 8, 2015

1973x75 said:
I just ordered the stainless pistons and a seal kit from Old Britts. A very pleasant woman took my order over the phone. I'll rebuild the caliper, then give it a drive to feel the difference, then I'll check into the master cylinder. The master cylinder rebuild kits are pretty cheap, maybe that would be the way to go?

Master cylinder rebuild kits are simple, just have fingers of steel when it comes to installing that rubber cupper seal onto the end of the piston.

There have been complaints about the original disc setup not offering as much stopping power as wanted and I agree the Emgo pads I tried when I first rebuilt my bike seemed sub par.
I tried some AP Racing pads I got though CommandoSpecialties. Substantial improvement.
There are threads here that talk about pads with other recommendations so keep in mind pads are part of the hardware combo you need to get the results you are seeking.

front brake stuck closed

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