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This past week we were in Mountain Home, AR with trucking experts doing an inspection on an 18 Wheeler. The 18 Wheeler was at the center of attention that day because it crossed the center line and hit two vehicles causing one death and three serious injuries. One of the issues during the inspection was whether or not the pitman arm had broken off of the power steering box (gears) before or after the 18 wheeler rolled over on its side.

Jeff Neiderer from R.H. Sheppard Company, Inc. in Hanover, Pennsylvania flew down here for the inspections. Mr. Neiderer completely disassembled the power steering gear box and was able to determine the pitman arm broke after the 18 wheeler made impact and rolled on its side. Therefore, it was not a causing factor in the wreck.

While I was watching Mr. Neiderer I was quite amazed at the technology involved with the M100 Power Steering Gear Box. The M100 is designed for heavy duty line haul trucks and heavy bus applications with a front axle rating between 10,000 and 14,000 lbs.

The Specifications for the M100 are as follows: (the left column is in US Standard Units and the right column is metric units)

Front axle range*

10,000 – 14,000 lbs

4,545 – 6.363 kg

Output torque
@rated pressure
90% efficiency

45,350 in/lbs

5,124 Nm

Rated pressure

2,350 psi

162 bar

Minimum pump flow
@1.5 H.W.T.

3.0 gpm

11.3 lpm

Pump flow range
single systems

3.0 – 4.5 gpm

11.3 – 17.0 lpm



Gear travel

95 degrees

Maximum operating temperature

250 degrees F

121.1 degrees C

Output shaft diameter

2.00 in

50.8 mm

Approximate dry weight

75 lbs

34 kg

Pump flow range
dual w/M80 slave

5.1 – 6.0 gpm

19.3 – 22.7 lpm

Pump flow range
dual w/M90 slave

5.5 – 6.5 gpm

20.8 – 24.6 lpm

Output torque
@2350 psi 90% efficiency
dual w/M80 slave

73,440 in/lbs

8,297 Nm

Output torque
@2350 psi 90% efficiency
dual w/M90 slave

83,275 in/lbs

9,407 Nm

I am going to simplify this quite a bit and for a more detailed explanation, you should contact R. H. Sheppard, however inside the M100 there was a shaft. If the shaft has little indentations on it, then that meant the pitman arm broke after impact, however if the shaft was indentation free, then the pitman arm broke before impact. Well, he counted 16 dents. This was good news for our clients’ cases in litigation.

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