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M939 (M923A2) power steering assist cylinder travel adjustment

Alexsha

Alexsha

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My power steering assist cylinder (PSAC) was leaking so I'm tearing it down and replacing the seals. I'm waiting on new felt pads and dust shields, so I've been reading up on reinstallation. The only part I'm a little confused about is the travel adjustment. The TM states that when properly adjusted, the distance between the centers of the 2 ball studs (one on the spring shackle and the other on the knuckle arm) is 25.5" when the wheels are straight ahead.

The way I'm reading this is that I should reconnect the hydraulic lines to the cylinder, but not have the cylinder connected to the ball studs. Have a soldier b in the cab turn on the truck and turn the steering wheel until I measure 25.5" between the ball studs. Once there, mount the cylinder to the spring shackle stud and adjust the socket on the other side until it fits on the knuckle arm stud.

Thoughts? Suggestions?
 
B

Baradium

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Alexsha said:
The way I'm reading this is that I should reconnect the hydraulic lines to the cylinder, but not have the cylinder connected to the ball studs. Have a soldier b in the cab turn on the truck and turn the steering wheel until I measure 25.5" between the ball studs. Once there, mount the cylinder to the spring shackle stud and adjust the socket on the other side until it fits on the knuckle arm stud.

Thoughts? Suggestions?
Click to expand...
It says when the steering is dead ahead and turning the steering wheel would make it not be dead ahead, right? I'm not near my truck to look at the adjustment on the ram to give a better response right now.
 
Alexsha

Alexsha

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Well, my thought is how do you know what dead ahead is? I would think that 25.5" from stud to stud would be that. Plus there's no good was to measure that when the cylinder is on. I don't know too much about hydraulic systems, but I'm guessing as the cylinder fills back up, dead ahead would make it fill close to halfway out on the piston rod, then the adjustment is there to get it to that 25.5" so there's no pressure either way.
 
B

Baradium

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Alexsha said:
Well, my thought is how do you know what dead ahead is? I would think that 25.5" from stud to stud would be that. Plus there's no good was to measure that when the cylinder is on. I don't know too much about hydraulic systems, but I'm guessing as the cylinder fills back up, dead ahead would make it fill close to halfway out on the piston rod, then the adjustment is there to get it to that 25.5" so there's no pressure either way.
Click to expand...
Dead ahead is when the tires are pointing directly towards the front, as in going straight.
 
Alexsha

Alexsha

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Measuring stud to stud would be more exact. If the specs say 25.5" then I'll go with that. I guess the real question is how do I make sure the cylinder fills evenly? At dead ahead, the piston should be close to 50/50 in/out, with the adjustment end to get the final way there. Once hooked back up to the lines, can the cylinder fill unevenly?
 
A

alexnyc

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Alexsha,
My power assist cylinder is leaking also. Can you post where you got the rebuild kit? I would like to repair mine as well. (M923a2) Thank you.
 
Alexsha

Alexsha

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I have all the new seals installed. I'm finishing cleaning out the cylinder itself. I need to flush out rust-dust and metal shavings. Let me know if you need help.

You'll also probably need 2 new felt pads and 2 new dust shields.
 
Alexsha

Alexsha

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So I have everything back in place and adjusted close to where it was. Looking at it, the purpose of the travel adjustment should be solely to prevent the piston from contacting the gland or the cylinder back wall when the wheels are turned. Straightening the wheels and measuring 25.5" from stud to stud would not help in that.

If someone could take a close up picture of the threads on the piston rod that the adjustable socket goes on and post it here, I would be greatly appreciative. I'm guessing every one of these trucks would have the socket screwed to about the same position.
 
Alexsha

Alexsha

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The wording in the TM is very vague. What's supposed to happen with the travel adjustment is basically assuring that you've got even fluid on each side of the cylinder when the wheels are straight. That way you have full travel on the cylinder (so you don't lose any turning ability on one side or the other). Basically, if the measurement isn't 25.5", the cylinder is either pulling the axle forward on the springs or pushing it back. Eyeballing straight head on the wheels isn't much of an exact science though. I'm going to use the arm on the driver side wheel to hopefully get the wheels straight. #2 in exact science is the fact that you have to guess where the ball studs are since the cylinder sockets are covering them.
 
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