|The MGA With An Attitude
BRAKES LOCK UP, OR SLOW CLUTCH RELEASE - HT-104
Y'all get extra credit for this course, because it's so important, and you should spread the word to the entire world.
A common cause of brake binding is a deteriorated hydraulic hose. This is a very common problem with hoses more than 20 years old, but almost unheard of with hoses less than 10 years old. As a hose deteriorates the rubber material can swell from absorption of brake fluid. As the inner part of the hose swells, and the outer part remains in true form, the inner wall of the hose collapses inward to block off the fluid passage. This restriction then acts like a check valve. It will pass fluid in the forward direction under high pressure when you step on the brake pedal, but when you release the pedal the fluid will not return with only the small pressure derived from the drum brake return springs or the rubber seal rings in the disk brake calipers, and the brakes will drag. I have seen cases where this drag was enough to skid the tire on a gravel road. On solid pavement the wheel will usually continue to turn, but the dragging brakes will generate so much heat that the wheel will get to hot to touch. If you open the bleed nipple and the brake releases, that's a clogged hose. At the front this commonly happens with just one wheel, but the condition will likely soon manifest itself with the other hoses as well. At the back it will cause both wheels to drag, as there is just one flex hose supplying fluid to the rear axle. Dragging brakes will also wear out the friction linings very quickly.
This problem appears in the hydraulic clutch as well. As deterioration of the clutch hose progresses with time, the pedal travel gets slower, and slower. This can sneak up on you gradually over a period of years, so you may be accustomed to the feel and speed of the pedal, and you may not even be aware that anything is wrong, for a while. Then one day you do a quick up-shift and hit the gas, and the clutch is slow to engage and slips for a couple of seconds before it gets a good grip. About that time you may think the clutch is shot, which would indeed be a laborious repair with pulling the engine. But not to despair (at least not immediately). There is a test for a restricted clutch hose. Depress the clutch pedal fully to the floor. Then pick your foot up quickly, as fast as you can move it without slipping your foot off of the pedal. The metal lines for the clutch circuit are larger bore than the metal lines for the brakes, specifically to allow this quick return of the clutch. The pedal should rise fast enough stay in contact with your foot until it hits top of stroke. If you can pull your foot up faster than the pedal will rise, you have a clogged clutch hose (or maybe a much less likely kink in the steel line). If you get lucky on this issue, a new clutch hose might cure the slow and slipping clutch, and you won't have to pull the engine.
Hydraulic hoses for clutch and brakes are rather strange critters for deterioration and inspection. These hoses have very thick wall with a very small bore. By the time they are about 20 years old they can be well into serious interior deterioration, but they may still look quite serviceable on the outside. Looks can be deceiving. Do not trust your eyes on this one. If the brake and clutch hoses are anything like 20 years old or older, or the history of the car is unknown so you don't know how old the hoses are, then order the parts and put it on the maintenance schedule to install new hoses at your earliest convenience (or even if it's not convenient).
For disk brake calipers, when the piston seal gets old it looses it's resiliency, becomes quite stiff. When this happens the piston does not retract, and the brake drags a little, sometimes just enough to prevent you from pushing the car by hand. It also causes the brake pads to drag on the rotor enough to cause excess heating of the brake parts when you're driving, and since the wasted heat represents lost energy, the fuel consumption goes up accordingly. When the caliper piston seals are in good condition the rubber is flexible. It drags on the side of the piston from friction, so when the piston moves forward it deforms the seal a bit. When you release the brake and the fluid pressure drops, the resiliency of the rubber pulls the piston back a bit to leave a small air gap between the brake pads and the rotor. If you open the bleed nipple and the caliper still drags on the rotor, it's time to rebuild the caliper.