I am looking for suggestions on why my 48 Chevy Pickup is constantly loosing brake pressure. It is all stock ( unknown miles due to missing gauges when I got it ) and had the brakes redone by a professional due to the lack of break lines and now they keep on loosing pressure at speeds above 45 mph. Could anyone please help. Thanks for any advise.
Do you mean that the pedal is sinking as you step on the brakes, or are the brakes simply ineffective. I once owned a 1950 Chevrolet 1 ton pick-up (3800 series) and it took considerable force on the brakes to stop the truck. Your 1948 Chevrolet pick-up is almost the same as the 1950.
If the pedal is sinking, you have a leak in the system–possibly at a wheel cylinder or in master cylinder. If so, you will lose brake fluid. The other possibility is that the internal piston in the master cyliner is worn and the master cylinder needs to be rebuilt or replaced.
If the pedal isn’t sinking, but you need a lot of force on the brake pedal, the linings may be glazed or not completely broken in. Sometimes lightly sanding the linings may help. Another possiblility may be a leaking rear axle seal and the linings are becoming saturated with rear axle oil.
I didn’t have the problems above 45 mph with my 1950 Chevrolet pick-up because I’m not certain it would even go that fast. The speedometer was broket the entire time I had the truck. Mine was really geared low–so low that I actually used the truck to stretch fence and had the fence so tight you could play tunes on it.
Thanks for the input. I went and checked each brake cylinder and noticed that it had a slight leak. I then pulled one of the hubs off ( I hate drum brakes ) and tried a very light sanding and noticed that they seemed to work much better at higher speeds of about 55 mph. Here in a few I am going to check the rear brakes and hope there is nothing wrong with them. Thanks again Triedag. I feel safer in the beast all ready.
I am assuming you have a good solid pedal; that it does not go to the floor; and the problem is that maximum effort on the brake pedal gives only marginal stopping. I had the similar condition after I overhauled the drum brakes on a 1964 Dodge Dart and a 1956 Buick Century, both nonassisted.
One of the problems with overhaul of drum brakes is that ‘arcing’ the shoes is not longer done or allowed for health reasons. That means that the shoes do not exactly fit the drums and the self actuating feature of drum brakes is ineffective. The small contact spot of the shoe fade as it heats at high speed. Things will improve as the shoes wear into the drums. One way to speed the bedding is to have the drums turned so a rough surface is available to the shoes.
One trick I have used to keep effective braking is to not replace both front and rear shoes at the same time. Do the front’s first and once they are stopping as they should do the rears.
Hope that helps
My suggestion is consider converting it to disc brakes. Those old systems like that weren’t good when they were new much less 60 years later. We converted a 57 Chevy once and never regretted it.