This hydraulic hose came from an MG Midget, but it is very similar to the brake hose on an MGA with front disc brakes with banjo fitting on the output end. There was lot of drag in the front brakes, so the brakes, bearing hub and wheels got too hot to touch. Jack the car up and the wheels would not turn. Open the bleed nipple to relieve pressure, and the wheels would turn freely. Cause is a clogged brake hose.

The hoses appear to be in pretty good condition on the outside, but there is a world of difference inside. For this hose I could not push a wire inside past the male threaded end fitting. So after installing new hoses I sliced the old hose open to show what is inside. The first end was cut straight across very near the metal end fitting, close the clogged area. The other end was cut at an angle to expose the internal construction materials.

Using drill bits for gauge pins we find the bore size to be 1/8-inch (3.18-mm). Next size larger drill bit would not fit inside. I tried pushing smaller drill bits through the male threaded fitting, but could not get even a 1/16-inch drill to go through this clogged part of the hose. With some pushing and prodding I finally opened the bore up to about 1/16-inch diameter at the clogged end, but could still not blow through the hose.

In the pictures you can see physical construction of the brake hose. It has a tough rubber outer jacket for abrasion resistance, multiple layers of woven fiber reinforcement for pressure containment, and the small bore rubber inner liner to carry the fluid. It is the inner rubber liner that will decompose with time and swell to obstruct passage of fluid.

Several weeks earlier we had a club tech session to rebuild a brake booster on a late model MGB. Near end of job while bleeding the brakes we found a clogged brake hose on that car. Disconnecting that hose at the caliper end and pumping very hard on the brake pedal managed to blow lots of fragmented rubber "spaghetti" out of the hose, and it cleared up enough to get the brakes working again (but of course the hose had to be replaced). Picture at right shows the deteriorated rubber liner material that was expelled from the bad hose.