official brake pressure or brake power

[Robo McDuff]

OK countdown is running. Next Saturday, if nothing goes wrong (touch wood, burn a candle, vingers crossed, etc, don't be too optimistic), I will take possesion of my first truck, a M51A2 (with pictures). ONe week later, I have an appointment with the "State Road Service" to get the thing on Dutch papers with a valid inspection certificate.

Most things will not be a problem, but the main issue will be the brakes.

1) Does the M51A2 still has the "air assisted hydraulic brake system" or is it completely airbrakes already.

2) If air assisted hydraulics, do I understand correctly that there are only short air hoses between the air tank and the master cilinder?

3) One of the criteria is that the brake power delivered to the wheels is 4,0 m/s2 (meter per second square) by a pedal pressure of less than 700 N (demand for trucks built between 1967 and 1998 . Any data on that for a 1973 M51A2?

4) The hand brake should apply power to at least two wheels. With a axle-brake on the rear power output shaft, I would think that should be ok.

5) The hand brake should deliver a braking power of 1,2 m/s2, sufficient to keep a standing truck in its place on a 16 degrees hill, should work equally when going forward or backward. Any data or comments?

6) Connections to the trailer (I am talking big onese here for transporting other vehicles or larger loads, not the small things). The trailer is supposed to get its braking power from the motorzied vehicle. How did that originally work on this type of trucks?

7) Most modern trailers are full air-brake system. Can you connect them to thses trucks or which adaptations do you need?

8 The air brake pressure in the command line to the trailer, by a maximum supply pressure, should be between 6,5 to 8,5 bar. Doable?

Thanks for the info already

 

[Robo McDuff]

OK countdown is running.

Thought I bumped this up the line a bit. Really nobody knows about this or am I posting it in the wrong topic line . . . ?





Thing is, If I have to make adjustments, maybe its easier and, if so, definitely cheaper to get the necessary stuff here in the Czech Republic than in the Netherlands.

Besides, in the Netherlands I have only two weeks before I have to go back, preferably with a driving and registered truck

 

[clinto]

1. Without seeing pictures of the brake backing plates, it's impossible for us to know, but the odds are overwhelming it is still the stock air assisted hydraulic setup.

2. I believe the only "hoses" (rubber) are downstream, where the steel brake lines running along the frame meet the steel lines on the axles. There are 2 rubber front hoses where the wheel cylinders meet the steel axle line.

3. No clue......... I wonder if that's even in the TM.

4. I suppose that's up to the interpretation of the Czech official.

5. The parking brake will have to be in good condition and properly adjusted but should be up to the task.

6. These trucks were never equipped to pull trailers with electric brakes, so the only electrical connections to the trailers are for lighting. The 2.5 ton and larger trucks were expected to always pull larger trailers equipped with air brakes or air over hydraulic (like the M105). So you will have a pair of "gladhands" at the rear, one service and one emergency, for air operated trailer brakes.

7. No adapters needed, assuming the modern trailer has gladhand type connectors.

8. 1 bar is approximately 14.5 psi, so that would be 94-120 psi. I think that's within the system parameters, but that's a guess, I've never read the TM spec for gladhand output volume or pressure.

 

[Robo McDuff]

Clinto, thanks for the reply.

1. Without seeing pictures of the brake backing plates, it's impossible for us to know, but the odds are overwhelming it is still the stock air assisted hydraulic setup.

I think youe right, maybe I should have asked, does anybody know if these later trucks (that is, M39 M5x early 1970s) were ever fitted with something else than air-assisted hydraulics? All I found says no.

2. I believe the only "hoses" (rubber) are downstream, where the steel brake lines running along the frame meet the steel lines on the axles. There are 2 rubber front hoses where the wheel cylinders meet the steel axle line.

Again, wrong formulated question. What I was trying to figure out was if the air part for the truck brakes was only between tank and master cylinder (it is) as opposed to running to the brakes themselves and assisting much more locally (no). In the back was also the question 7 and 8, if the system is geared to provide air for a coupled trailer. As you explained, it does. The double system is good because that's a must here.

3. No clue......... I wonder if that's even in the TM.

6. These trucks were never equipped to pull trailers with electric brakes, so the only electrical connections to the trailers are for lighting. The 2.5 ton and larger trucks were expected to always pull larger trailers equipped with air brakes or air over hydraulic (like the M105). So you will have a pair of "gladhands" at the rear, one service and one emergency, for air operated trailer brakes.

That's what I was hoping for. Looking at enlargement of the pictures, seems something is there, but in rusted condition, hope they work.

7. No adapters needed, assuming the modern trailer has gladhand type connectors

They do.

8.1 bar is approximately 14.5 psi, so that would be 94-120 psi. I think that's within the system parameters, but that's a guess, I've never read the TM spec for gladhand output volume or pressure.

That's close enough for me, wonder if they will actually check it if it looks clean and nice (which it will do next week).