Turning the Pitman Arm / Steering Linkage

[300SDog]

Pitman arm attaches to the steering box on splines.

Standard procedure for truck diesels is to turn this arm several spines one way or another, after about 120k miles. The results directly effect steering tightness, taking up slack and slightly changing the turning ratio. Its something that requires expert skills as turning the Pitman arm too far, or not far enough, can ruin the steering characteristics.

Has anybody had this procedure done on their 123 deisels?

My '79 240D with 115k miles has sloppy steering and this is one thing I'm looking into.

[md21722]

The pitman arm on Mercedes is keyed and only goes on one way. Tighten the steering box to remove play. Steering box MUST have 10 mm of play or more. If its too tight it will wear out and need to be replaced.

No, you should turn the pitman arm on this box. In fact, I'm shocked that anyone would move the pitman arm on ANY box. I've been around truck shops, and this kind of Cowboy Engineering does not surprise me.

The only way you could get by with moving the pitman arm would be to make up for its new location by shortening one tie rod and lengthening the other.

The reason for this is that at the CENTER point of the steering box, the gears are at their tightest. As you turn away from center there is a touch more slack.

What you are dealing with is one of the few Achilles Heels of a 123 MB. These steering boxes are unusual and prone to loosening.

They do not tighten in the same way that an American box does. In fact MB recoancemmends that you DO NOT adjust these boxes. That said I have adjusted a number of them, sometimes with success and sometimes not. I have also gotten a salvage yard box and performed exploratory surgery. The sector shaft bearings will sometimes get loose. If this happens, no amount of adjustment will correct the problem. You have to shim the bearings carefully, they must be tight, but if you get them too tight the steering will be "sticky."

To adjust, loosen the nut, turn the allen headed shaft counterclockwise until just a little resistance is felt. Hold the allen headed shaft at this exact position while teghtening the locknut.

If this does not tighten the box, most likely the sector shaft bearings are loose.

Good luck,

[300SDog]

Cowboy engineering? Actually slack or cracked Pitman Arm is on Dept. of Transportation list of items for pre-trip inspection on over-the-road diesel trucks.

Adjusting tie rods does NOT replicate movement of the Pitman on its spline, as the arm moves in an arc directly linked to the gearbox... a question of arcs and angles where suspension components interface with gear box.

What the Pitman does is control steering radius. And its S.O.P for trucks to have the arm turned a few splines by certified Pitman specialist after the suspension and box has "settled" on new truck after the first 120k miles. Apparently this procedure is done only once.

With 3 new trucks in the depot approaching 100k+ miles, I've already asked the maintenance shop to tell the Pitman tech to look over my 240D when he shows up.

Otherwise yes, I've heard the 123 steering boxes are junk.... am wondering if steering box from 115 or 114 might solve this problem??

Thanks for the replies, am basically a scavenger when it comes to making improvements on the car.

Excellent bennies driving truck and owning 240D, the crew at work has already installed a water-separator..... am eager to install a fuel heater.... and have even looked into fabricating an exhaust brake to the manifold that can bring the car to a rumbling slow down when approaching traffic.

OF COURSE you would check the Pitman arm for slack or for cracking, but that has nothing to do with moving it on the shaft.

Have a great day,

[Diesel 924]

Are you saying that the 'Pitman tech' is re-indexing the pitman arm on the steering box shaft? 20 years working on class 8 trucks and buses and I've never heard of this. Are you sure you are saying this right?

[dabenz]

When I was a kid a toot on the horn meant I dropped the broom, ran to the door, and pulled the chain for the door opener. I guess I was a chain fall tech.

Too much slack (more than the WRITTEN spec) in the Pittman arm means something is wrong. It has two ends so the problem could be at either or both ends. Shaking the arm is DOTs quick and dirty way of finding "something" wrong and generating a fine on a roadside inspection. Been there.

Reindexing (a truck box) means getting the box to "center the steering wheel." The road camber puts wear on one side and the arm gets adjusted to make up for it. Once and only once.

If it was me, I'd start at the ground: wheel sidewalls too soft for the car model? Wheel bearings OK? Bushings OK? Everything tight and aligned? Steering box mounting bolts tight? Correct oil in the steering box? Then and only then would I consider the box adjusting bolt. Too tight and you increase the wear, too loose and you stop the car where you don't plan to. The car box is very different from a truck box, so I wouldn't let your Pittman tech do it.

Good to hear you put a water separator in. Should be a required item for American fuel, in my opinion.