Machinos

Well, I'm pretty sure they do exist since I seem to remember hearing about them on old military trucks, but I mean in a modern, usable application. I've got a 5.9 from a bus with an air compressor/PS pump instead of the vacuum/PS pump on our trucks. I could really use the air compressor for air suspension and air tools (especially inflating tires, this is a car hauling truck).

I have no idea if the PS pump on it would be able to handle a hydrobooster, and having that huge (and heavy) air compressor turning all the time would be kind of hard to justify for things I would only use occasionally. Anyone have any idea?

wannadiesel

I'm sure the PS pump will handle a hydroboost with no trouble, that is the route I would go.

The compressor should have an unloader (may have gone missing but you can get another) so it will just freewheel when the air tank is at full pressure. The unloader holds the intake valves open so the compressor does not pump.

If you have A/C you will need a small electric vacuum pump to run the mode doors.

BearKiller

Yes, they do make such an animal and it is very common on mid-size single-axle trucks, such as the ISUZUs and such.

Air-over-hydraulic.

The foot-pedal puts air-pressure to work against a usually frame-mounted (as in not on the fire-wall) hydraulic master-cylinder.

These systems also have the octagonal red PARK button, but I am uncertain as to how it works, seeing as on a real air-brake system the PARK button evacuates the air, thus applying the spring-brakes.


I have driven a few of these trucks and the brakes are very "touchy" as in get you killed on a wet road.

Cowboy_Customs

It is a BAD system. Instead of taking air away to apply the brakes, it APPLYS air to apply the brakes. No air, NO brakes.

wannadiesel

Amen to that!

BearKiller

So not to confuse anyone, all big truck air-brake systems apply air pressure to the brake chambers, thus applying the brakes under air pressure.

Where the "no air = brakes apply" comes in is through the seperate spring brake.

So long as there is sufficient air-pressure to be safe, the air pushes the spring brake OPEN.

When air-pressure drops below a pre-set level, the spring over-rides the air and automatically/mechanically applies the brakes.

Once the spring-brakes apply, without sufficient air-pressure to open them, the only way they are going to release is by loosening the shoes themselves, thus putting the axle in a free-wheeling brakeless condition.

Spring-brakes are not 100% fail-safe, as they do have an adjustment, plus many other factors have a bearing on their effectiveness, such as shoe adjustment, condition of the drum, S-cam, etc.

I have driven old dangerous dump-trucks that would roll off when loaded with the spring-brakes applied.


Back in old timey days, trucks did not have spring-brakes; so, when you ran out of air, you had no brakes.

Alec

I don't know if you saw my post hydroboost-gear-drive-air-compressor, but until priorities got re-shuffled in the past month I was working on doing the same thing to my truck. Probably not the clearest or most informative post, but it lays out what I was thinking about doing and using.

My "new" power steering pump is a TRW PS 251615L10002 where: PS(power steering) 25(25cc/rev)16(16 l/min)15(15 bar or ~ 2,175psi)L(ccw rotation) 1(11 tooth input) 0002 (last 4 digits have to do with port configuration). From not very good internet research, I believe that the stock steering gear and hydroboost should not be subjected to greater than 1500 psi. There is a combination flow control and pressure relief spool valve in the pump that is adjusted with a shimmed spring. I hope that I can remove some shims and get the pressure relief down to 1500, but I have not been able to work on it yet.

Do you have a similar pump? Would you be able to explain to me how the coolant lines for the air compressor are routed on the engine that you have? I am not sure which port I want to return to.

The hydroboost conversion is popular in its own right, the parts are readily available, and if your pump is anything like the one I have, there is more than enough flow to go around. I have driven a 5 ton army surplus truck with air over hydraulic brakes, and even if you needed to send an air signal line to a trailer, I would not recommend going there.

The biggest downside, as you pointed out, is the pumping losses from spinning the compressor (even if it is unloaded, it still drags a few hp), and the added complexity of an electric vacuum pump for the heater controls -- but you can buy one for a Ferd, or cobble something else together.


If you could let me know about those cooling lines, (and any other useful information about the conversion) I'd really appreciate it.

Thanks,

Alec

Machinos

Thanks for the info everyone! I'm not entirely sure about the details of the air and PS pumps on the engine I've got, but I think I'll take some pics this weekend.

Alec

Pics would be great!

Alec

Machinos

Got some pictures, with some bonus questions if anyone sees them (so I don't need to make a new thread):


The fitting where the coolant hose enters the block is circled.


Here's the bottom, what I assume is an oil line for the compressor is also pictured, it goes into the block higher up behind it.


Back of the block if you need to see it - why does it have a temperature sensor (I assume that's what it is) on the back and on the front by the thermostat? Does one run the fan clutch?


Bonus question 1: Are there part numbers for the two parts I have circled? The one on the left is hard to see but it's that short, curved line connected with a banjo bolt on the pump, the line is separated from the fitting somehow.



Not counting the boost tube and possible starter interference, is it possible to flip the exhaust manifold over on this?

BearKiller

What application is that engine from ??

That manifold/turbo configuration is exactly what I need to cure my A/C air-box interference issues.

As for your question; yes, you can flip the manifold, but I don't think that you can then use a turbo, as the port facing straight downwards would pivot the turbo into interference with the engine.

Look at the manifold/turbo on a standard 1st Gen. Dodge/Cummins and what I mean will be obvious.


What turbo is that ??

Thanks.

BearKiller

Forward-engine school-bus or rear-engine tour-bus ??

Thanks.

Machinos

It was a 1990 Bluebird front-engined, flat-nosed bus. I think they came with a Cummins up until maybe 2000 or so, but I'm not positive.

wannadiesel

My comments in red.

Hey Bearkiller - you will find that manifold on any 12 valve Cummins that's not in a Dodge. That's the standard truck/industrial manifold.

BearKiller

Thank you, sir.

Now to just find one.