The Stovebolt Site Forums The Parking Lot Big Bolts Air-hydraulic brakes

I don't want to be insulting by asking a International Harvester question, but you guys know trucks! If its any consulation I do have a 81 GMC 6000 ramp truck named Ol'Ugly. The IHC is a 72 1700 Loadstar. It has air rear brakes and hydraulic fronts. The brake pedal is air. The system is said to be stock. I'm used to one or the other. I really like the truck, but to keep them going with a normal system is hard enough, let alone something weird. Any thoughts?

Air over hydraulic is a proven system. Essentially it is an air brake system for the control part (the pedal) and a hydraulic brake system for the actuation part, the wheel cylinders.

To make it work there is an air chamber directly mounted to a hydraulic master cylinder.
Your combination system should then have three air chambers, one for reach rear wheel, and one on the master cylinder for the front hydraulic brakes.

I have only talked to a very few people who thought air over hydraulic brakes were a good idea, and actually liked them.
The impression I get from everyone else is that hydraulic brakes are OK, but nothing special, and air brakes are great, but together they are not worth having. You have the complication of an air brake system, which by it's self is OK,over the frustration of a hydraulic system, it's a way to have good brakes when they work, and a good way to spend money and waste time when they don't.

I briefly considered air over hydraulic brakes for my project, till I did some research and found out the above. I have hydroboosted hydraulic disc brakes now, and they are great. But given the chance to switch to the new air disc brakes I will, but looks like 5 years or so before "small" air disc calipers are readily available in the US.

Grigg

I had a 1964 Chevrolet L60 LCF, that had air over hydraulic brakes, & it would literally throw you into the windshield, when doing a panic stop. Had great stopping power, but parts were not readily available.

Air over hydraulic is one of those things that had its day, but that day is long gone. I am assuming that you actually use the truck for something. If it were mine, I would look for a steering axle with air brakes and go to straight air. As far as air disc brakes, different configurations have been rolled out over the past 30 years as a new revolution in braking but they have never caught on. In fact I have bought several trucks that had disc brakes on them for well below the market. I converted them to drum brakes to use them.

There is a new generation of air disc brakes coming from Europe lately, and from all I hear they are working great, and we should expect to see more and more of them. It's these brakes I want, as they will soon be offering them to fit in a 19.5" wheel package (already do in Europe).
I have also heard that the first generation air disc brakes were not much good. But sounds like they have it figured out now.

Grigg

I have been reading about the disc brakes which have been in Europe for some time. I visit my relatives in Germany quite often and look at their trucks. They have a lot of good technology. Right now is a bad time for technology to make its debut. Every quarter sets a new record for bankruptcies in the trucking industry.

so do you still need a CDL to drive air over hydraulic brakes?

Depends on the state, usually yes.

The first power assist brakes I remember hearing about on the family's trucks were on 1934 and 35 Chevy single-drive tractors towing trailers from Milwaukee to Nashville hauling beer. They had vacuum-assisted mechanical brakes! I wish a few pictures of those rigs had survived! My grandparents' primary business was selling coal and ice, and they had a fleet of about 15 delivery trucks, but they also did over-the-road trucking of beer and dynamite.
Jerry

On that thought,
I worked on and drove (just a test drive) a 1932 Marmon car with the aluminum V16, a very fancy car.
It had vacuum assisted mechanical brakes, and they worked really well, better than I would have ever guessed.
All the linkage was mechanical, similar to a Model A ford, but on the cross shaft that then pulled the linkage for each weel it also had an arm for a vacuum diaphragm to pull on. To control it was a vacuum valve in the rod from brake pedal to the cross shaft.

The way the vacuum part was controlled and operated was similar to air assist power steering, or similar to the early Chevy PS. Otherwise all mechanical, but with a sensing valve and then a cylinder to help the mechanical stuff.

Grigg

Nothing really new in the world, Grigg, they just change the names to confuse the newcomers!
Jerry

For what It's worth, I don't believe that GM ever offered an air over hydraulic brake from the factory. We had vacuum assist hydraulic as standard on the Chevrolet trucks and, later, full air brakes.

We did a dealer install of the air over hydraulic brakes primarily when we were setting up a tractor so we'd be able to actuate the full air brakes on the trailer. I had one customer that bought a new tractor from us about every three years that hauled cattle from Greeley to Denver two or three times a week. They weren't very heavy trucks, but they worked OK. The air over hydraulic brake could apply more pressure the the hydraulic system and you could lock up the wheels.

Chevrolet trucks could get factory installed Air Over Hydraulic Brakes starting in 1959. They offered Full Air starting in 1957.

Mike B