kb3csw
You might have misunderstood my post. I was referring to the actual "feel" of the pedal. Ie, how far it travelled and how much foot pressure it took to apply. Your referring to the "feel" of the rate of decelleration and the operators ability to interpret gauge readings. That is exactly why air brake licensing became a big deal. Too many people were jumping behind the wheel without the ability to interpret gauge readings and mistakenly assumed that, just like in their juice brake car, as long as the pedal felt normal everything was okay. This might be the first time they drive that vehicle and don't know what it's normal stopping "feel" is. That's why the "pre-trip" adjustment checks. Those are precisely the things they teach in the air brake endorsement courses here in Canada.
Juice brake systems are pressure tested on passenger cars at over 2100 psi, compared to probably 200 for air. You can get far more stopping power from hydraulic than from air. The issue became the amount of pedal travel. It's all about ratios of piston sizes. Think about your hydraulic jack. One pump of the handle on your 2 ton jack might move the ram 1/2 inch. The same stroke on your 8 ton jack only moves it 1/8th of an inch, but with a lot more power behind it. Having said that though, single axle trucks up to 5 ton can still have an acceptable amount of pedal travel, but even fully adjusted you will never find the pedal right at the top like you do on a car. Add another axle with more fluid requirements and the amount of pedal travel starts to become marginal.
Back to the original question though, disc vs drum. It doesn't matter what I think, but here's a couple of things to think about. Disc brakes claim to fame is based on 2 things, the superior ability to dissipate heat and their cost to build. On the first point, they have to be able to get rid of the heat faster, it's concentrated in a much smaller area. Compare the square area of a disc brake pad to the area of the 2 brake shoes. Scientifically speaking, brakes work by turning rolling energy into heat. Stopping 25,000 lbs from 60 mph in a given distance creates the same amount of heat regardless of what type of brakes you've got. All of the heat in those big brakes shoes is now in that small pad. You need to be able to get rid of it faster.
The real reason car manufactureers went to disc brakes up front was cost. I counted the number of pieces in my front drum brakes on my 67 442. Excluding shoes and drums there are 21 pieces of hardware on one front brake. Compare that to 4 for a single piston floating caliper on say a 70 442. Assembly time. If you've done brakes on both those systems you know what I'm talking about. Complexity of parts. Would it be easier to make 2 flat pads or 2 curved shoes with the linings precisely ground to match the arc of the drum? Savings were huge. The reason you didn't see them on the rears is that by the time they added in a parking brake system on a disc brake the savings were minimal. Stopping distances were no better. You can lock them up on a drum brake just as easily as a disc. For extreme heat applications (racing, etc) drum cars were fitted with vented backing plates and metalic shoes.
We often mistakenly assume because it's a newer technology it's better. I almost spit my beer out when a friend told me he was looking at a kit to convert his 68 mustang to newer style McPherson strut front suspension. Here is a prime example of cost cutting vs performance. Manufacturers adopted struts because it saved them 2 ball joints, 2 control arms, 4 bushings and a lot of time. The system does not keep the wheel perpendicular to the road as well as the older unequel length double control arm, but it does it adequately for a lot less money. You never see race cars (other than stock class) or high end high performance (Corvette, Viper)vehicles with them. Now there's an industry devoted to helping people replace their superior frt suspension with a cheaper poorly functioning system and relieving them of their hard earned $ in the process.

Having said all that, Yes I know it was a lot and I apologize,If you like the sound of an air brake and that big rig feel that comes with it, that's reason enough to put air brakes in your old truck.
Steve g.