Hydraulic Brake Issue (850 Roadster)

I've rebuilt many cylinders and calipers before but this has me a little stumped. My 850 Roadster has a hydraulic brake (with the characteristic hard wooden feel) and a stainless steel line. I recently noticed that, although the brake grips and the lever is hard after an inch or so of travel, constant pressure on the brake lever will cause the lever to slowly pull in farther until it is all the way to the grip.

Knowing what I know about hydraulic brakes, I immediately flushed the system (fluid was dirty) and bled out the air (none, really) and restored the nice, hard feeling that I had before. However, the symptoms have returned, which suggests to me that I have air leaking into the system somewhere. But where? There is no visible sign of weeping fluid at the caliper or the cylinder.

Before I spend the time and money to rip apart and rebuild the system, I thought I would ask if anybody has had similar problems with their hydraulic setups. The bike is extremely clean, and everything seems to be in good order. Of course, these brakes were never particularly effective to begin with, but they definitely should not be doing this. Any help appreciated!!

nomadwarmachine said:

I recently noticed that, although the brake grips and the lever is hard after an inch or so of travel, constant pressure on the brake lever will cause the lever to slowly pull in farther until it is all the way to the grip.

Click to expand...

That can be a symptom of a damaged master cylinder primary cup, as the fluid will slowly leak back past the cup as pressure is applied to the piston by the brake lever. I had this problem on my T140V Bonneville with a new stainless master cylinder unit I fitted. The damage to the cup was no more than a tiny scratch mark.

Thanks! Should I buy a complete rebuild kit for the master, or should I just replace the primary cup? Does a primary cup normall come with a rebuild kit?

Just ordered my Motion Pro snap-ring pliers...

May as well have your master cylinder sleeved while you're at it. That improves things.

nomadwarmachine said:

Does a primary cup normall come with a rebuild kit?

Click to expand...

I don't think the primary cup is available separately, but it is certainly included in the rebuild kit.

Who do you recommend to resleeve the master? Also, any leads on Fedoro brake pads for the old Nortons?

You can get a sleeved master cylinder on an exchange basis from several dealers. Stan at Rocky Point Cycles and Jim Noll at British Bike Connection to name just two.
Ferodo pads for Nortons are available from Mercury Morse at Vintage Brake.

Since you most likely have a leaking (internal) master cylinder, getting it re-sleeved is a good choice. I believe the common choice on size is 1/2" diameter. The stock diameter being 5/8". Be forewarned: After re-sleeving your Norton now will actually have a functioning front brake.

...and a little teflon paste (or tape, but I prefer the paste) on all threads in the system when reassembling.....

...and a little teflon paste (or tape, but I prefer the paste) on all threads in the system when reassembling.....

Click to expand...

Since none of the threads are tapered (pipe) threads, this will have no effect. The sealing surface is the copper washer and the tapered seat (flare fitting). Too much tape may prevent these from seating properly.

Ron L said:

You can get a sleeved master cylinder on an exchange basis from several dealers. Stan at Rocky Point Cycles and Jim Noll at British Bike Connection to name just two.
Ferodo pads for Nortons are available from Mercury Morse at Vintage Brake.

Click to expand...

Does he play football too? :lol: :lol: :lol:
I've made the same mistake, his name is Michael. 8)

I don't know if he ever played football, but Michael (Mercury) Morse knows brakes. Follow his chart for a disk front setup and send him your rear brake and you'll end up with a very good stopping bike.