When should brake hoses be replaced

Twice I have seen 911s in the shop with the rear brakes seized. The hose was so internally swollen that it acted as a one-way valve holding pressure on the rear caliper.
On removal I could not blow shop at 120psi air through the hose.
One case required completely new calipers, rotors and of course pads. In that instance the brakes had created so much heat that the backing plate of the pad looked like a potato chip.
Both of these cars were essentially garage queens, with very low mileage.

In neither case was the master cylinder at fault, though I have seen it happen on Mercedes several times where the fault was with the master cylinder.

I've got some stainless steel lines I'm putting in this winter. I do plan to use a flare wrench, but I've tried to get them off before for something else and it was impossible to crack. I plan to use a fair amount of penetrant a few times for a few days before I attempt to open them up again.

--Mike

Mike,
please be careful not to allow ANY "penetrant" to enter the caliper. It can cause failure of the caliper seals and brake failure. Any oil is a big no-no in brake systems. The correct flare nut wrench should do the job. Might have to use a length of tube added over the handle if the fittings are really stuck. Bob

Hi Guys,

Most here know this but I guess it never hurts to remind everyone that Brake Systems rust from the inside out becuase of brake fluids hydroscopic nature (absorbs moisture from the air), and need to be flushed every couple years (or even more frequently if used on a track, perhaps 2-3 times a year) to remove the rust promoting moisture. Flushing also helps remove that black looking stuff in the Fluid Resorvoirs, which is disolved rubber from the seals. This flushing doesn't negate the need for new hoses, but it does prolong the life of the rest of the Brake System pieces.

Regards, JRV