Took our AV8 out yesterday and noticed the car seemed to "drag" coming down a long hill without applying the brakes. By the time I had gotten home the right rear drum was smoking. Obviously way overheated. Never experienced this previously. New build using new drums, master cylinders, brake lines etc. Emergency brakes disengaged so ruled that out. Ideas?
You don’t say what the brakes are, but on most drum brakes, if they are adjusted too tight as the brakes drag, they get hotter and expand making them drag more until you get what you’ve got. Let it all cool, check adjustment first, then check for any mechanical failure, incorrect installation, broken hardware, springs, etc. that may have been the cause. My guess is adjusted too tight.
Make sure there is some free play in the pedal. If there isn't you'll experience exactly what you described.
Check the pedal free play. Check to see if the cap on the master cylinder has a vent hole and make sure it's clear. Check for grease on the shoes. Any small amount can cause them to stick to the drum. Check emergency brake linkage for adjustment. Check for service brake adjustment.
Untitled by Travis Brown, on Flickr Make sure the by pass port is clear. It will do what you describe as will a pedal with no free play, as mentioned.
F-1 is correct. If inadequate free play causes the piston cup to cover the relief hole when the brakes are not in use it will build up pressure in the system which will cause total brake lockup when things get hot. Look closely at the picture and you will see how little room there is for error.
Years ago my 50 Ford Coupe started dragging and the brakes would get hot and the brake lights would come on and stay on.. I had just got the car running. The master cylinder was a faulty casting. The by pass was spotted but never drilled through. Fortunately on a Shoebox, the by pass is right below the cap. 3 seconds with a drill motor and 1/16 bit and it was fixed. I never even took it off the car.
100% frigging WRONG!!! drum brakes fade when they get hot and don't stop they do not drag more when they get hot. F-1 most likely nailed the problem and the answers are that either the push rod from the pedal to the piston is adjusted too tight and doesn't have any slack and or there is no return spring on the brake pedal letting the weight of the pedal push on the piston.
Was it only the RH brake binding, was the left wheel spinning free?? Did you jack up the car and crack open the bleeder of the problem wheel at the time?? if so did it turn freely afterwards?? I would start looking at the right rear brake area first, adjustment / faulty hose/ any linkage (hand brake) anything that would cause binding of the shoes.. If it's a single cylinder master cylinder, and the pushrod / pedal adjustment was incorrect, ALL brakes would be locked on and smoking, if it is a tandem cylinder, two would be effected..
After sorting out the issues on my 34 finally got to pull the rear brakes apart on the roadster. Found the problem instantly and frankly concerned me more than the over heated drum. Tire was still tight when attempting to turn the wheel. Pulled the drum and found the right rear wheel cylinder was wet with brake fluid and the inner piston was protruding through a torn exterior rubber cup. Piston never retracted from the rear shoe and I was probably fortunate not having lost brake pressure entirely! Brakes drums etc are new from Speedway and this isn't my first brake shoe installation so I know the problem wasn't of my accord. Now have to figure out why that happened. Buying new set of wheel cylinders But where do I buy parts made in the USA? I am considering going to a dual master cylinder as well. Further input is appreciated.
I am a believer in the safety of tandem master cylinders. The old ford master cyl is pretty reliable when well maintained, but in that rare occasion when something goes wrong, just getting something working is an advantage. The old Ford cylinder has a valve that maintains some line pressure to prevent air getting sucked back through the wheel cyl cups. Using most modern tandem cylinders will require installation a line pressure valves. I have successfully used m/cyls from a Nissan SUV which come in 1 1/16".(Common in this part of the world) Must be many options.
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