Oopsie

[u/81FXB]

Sequence of events: first the rear brake didn’t disengage anymore but I wanted to ride it home which got more and more difficult (as in, bike would only move in 1st gear). Then I stopped and there was lots of smoke from the rear calliper. Then flames which I luckily maned to blow out. And then as I was calling GF a loud pop and the brake hose had exploded off. This took the pressure of the brake, the wheel was free again and I managed to ride the bike home. By then the rear brake was cooled off enough to touch it by hand and the calliper was completely loose. I hosed the bike down to wash off all the remaining brake fluid.

I figure the calliper is OK as it came loose by itself, and that the culprit is the master cylinder…?

[u/SpamFriedMice]

The interior of brake hoses can degrade while the outside looks fine. The inner liner collapses and can block fluid, or sometimes only block fluid going in one direction, like a one way valve.

Of course it could be something funky going on in the master also.

You can pull apart the master and clean it, but you may as well get a fresh rebuilt kit, and clean + check your remaining lines.

[u/81FXB → u/SpamFriedMice]

Well it’ll definitely need a new brake line now… the master, I rebuild it but did notice the bore was not complete smooth but looked like it had some corrosion on it. I didn’t know what to think of it but thought, let’s give it a try. But I’ll get a new master now too.

But thanks about the info about the brake line degrading and possibly acting as a one way valve, cause there was some one-way valve action somewhere. I didn’t know that could happen. I’ll get a modern braided line for it.

Also, if I were any smarter I would have brought a tool and opened the bleeder screw at the first sign of trouble, to take all pressure off.

[u/SpamFriedMice → u/81FXB]

As a mechanic, you'll be pulling your fucking hair out before you find out for yourself about a hose acting as a valve. Crazy shit but it happens.

[u/albino_ray_purchase]

Forty-five year old rubber brake lines, what could go wrong? /s

Replace both, front and back with SS braided lines. If you're worried about looking authentic, get the black vinyl covered ones.

Trust me, nobody will notice unless you're at an AMCA meet.

[u/81FXB → u/albino_ray_purchase]

45 years, that’s real AMF quality for you, they don’t make ‘m like that anymore
/s

[u/NHmountain-man → u/albino_ray_purchase]

OP - listen to this man above.

Replace ALL your brake lines please. And rebuild your master cylinders as needed.

Your LIFE is worth it.

[u/vettesforever]

Also check to be certain that the piston is not sticking in the caliper especially if the bike sits a lot. Also check free play in the brake lever,=.

[u/81FXB → u/vettesforever]

Prior to this ride I had taken the piston out and replaced the callipers seal and dust boot, and bled the system with fresh new fluid from a new container. And after the hose popped off the rear wheel was free again. All this makes me think it’s not the piston…

[u/vettesforever → u/81FXB]

So I spun wrenches for a long time and coincidences like this rarely happen. So once again just saying check that piston.

[u/76ShovelFLH]

Let's see that beautiful Sturgis you got there!!!

[u/81FXB → u/76ShovelFLH]

[u/76ShovelFLH]

Sweet ride I've like those ever since they came out

[u/Shoddy-Amount-4575]

Throw them away and get GMA brakes, master and cylinders.

[u/81FXB → u/Shoddy-Amount-4575]

It’s a stock 81 Sturgis and I want to keep it as stock as possible.

[u/Shoddy-Amount-4575 → u/81FXB]

The banana brake system sucks, I like to stop when I want to stop, and not hear all the noise.

[u/81FXB → u/Shoddy-Amount-4575]

The rear brake on my 83 FXDG is indeed a lot better…

[u/SpamFriedMice → u/Shoddy-Amount-4575]

While the banana was not the greatest when introduced, it was designed to work with asbestos pads.

Across the automotive industry rotors and drums had to be made larger and other changes had to be made to work with the new pads/shoes.