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Variance in thrust bearing pre-load on PSC gearboxes


NAXJA Forum User
Vancouver Island
I have a PSC SG-621M variable ratio, big bore gear box that I recently rebuilt with seals, teflon slides, sector shaft bearing, and stub shaft bearing. My question is mostly concerning the thrust bearing pre-load.

According to this nicely documented saginaw rebuild guide: https://www.jeepforum.com/forum/f13/how-rebuild-your-saginaw-zj-steering-gear-1287958/ , I should tighten the adjuster plug (that large threaded cylinder with the two holes needing a "spanner wrench") all the way down until the thrust bearing is fully seated. Basically, until the adjuster plug cannot be turned anymore with normal pressure on the handle, meaning the assembly is fully bottomed out in the casting. According to another guide, that light-ish pressure is about 25 ft-lbs. As I don't think many have a torque wrench attached to a spanner, this 25 ft-lbs is by feel and experience. Basically, tighten it down just snug, but don't put your body weight into the spanner.

OK, so once the thrust bearing is bottomed out, this rebuild guide says to back off the adjuster plug by 0.5". Another guide says 0.2". That's a big difference, but anyway, when I back-off the adjuster plug by 0.5", I am a full 1/8th of a revolution TIGHTER than where the adjuster plug was before I took the box apart (I marked them with punch).

An 1/8th of a revolution seems like an awefull lot to me. I mean, the thrust washers can wear a bit, but I wouldn't expect them to wear that much. So what do I do - listen to the web guide, or put the adjuster plug back where it was previously? Cut the difference between the two?

Another issue I noticed is that just about no matter where I have adjusted the pitman adjuster screw to, the stub shaft, turned 45 deg. right/left, always requires about 7 in-lbs of torque, not nearly the 10 in-lbs noted in the web guide, or the 8-15 in-lbs noted elsewhere. I even tried it with having the thrust bearing not backed off at all, but I still get about 7 in-lbs. Obviously I can get it tighter, but at that point, there is a kink in the flow of the piston at about 90 deg. off centre while traveling in the bore, thus I've adjusted the screw so that I just don't feel that kink, but again, 7 in-lbs at the stub shaft.

My gut feeling is that these variances aren't a big deal, but this is only my second rebuild. What do I know. Any ideas? Thanks!
I think you are miss interpreting his instructions or I am. I would look at the FSM. He is using a beam torque wrench. I used a dial one. From memory ( someone can shout I'm wrong if they want to.) , You have to rotate or sweep the torque wrench side to side. I think 45 degrees each side. Then turn in the end cap to get the torque spec. I remember one for a new set of bearings and another for a used set. Then assemble in the sector shaft and do the same for it. Again, I'd look at the FMS for instructions. His is a good rebuild instructions and photos. I probably referenced his when I rebuild a few steering gear boxes.
Hello. Thank you for your reply. To confirm, I am using the exact same type of torque wrench as in that pictorial web guide, that is, you can view the live torque displayed on an analogue dial.

OK, so in the web instructions, the guy is in fact adjusting the adjuster plug to get to get to 5 in-lbs (thrust bearing pre-load) WITHOUT the piston or pitman shaft installed. He then installs the piston and pitman assembly and adjusts the stub shaft to get 5 in-lbs more than the thrust bearing pre-load, so 10 in-lbs.

However, in another guide (I am not mentioning it by name, as the last time I did, my post was deleted), the thurst bearing preload torque is not measured. The instructions are to tighten the adjuster plug until fully seated (25 ft-lbs ish), then back it off 0.20" (with the piston and pitman shaft already installed from what I can tell).

As I am getting around 7 in-lbs on the stub shaft with the box assembled, it is unlikely that my adjust plug is over tightened. My question is really concerning where to place that adjuster plug. Do I follow the guides to back it off 0.2", 0.5", or place it back where the factory had it (some instructions call for this). I didn't really measure out the 5 in-lbs with the piston and pitman shaft out because the unnamed manual/guide didn't call for this. I wasn't expecting the discrepancy to be a whole 1/8 of a turn! Perhaps dialing in that 4-10 in-lbs isn't such a concern?

The torque wrench is not in question. A beam mount one is good and will show the torque in a 'dynamic' load or sweep. Hope that makes sense.
An aspect is that you have a specialty gear box. I would assume that the torques and procedures would be the same.
Going from memory, I torqued the main shaft to say 5 inch lbs in a sweep of 45 degrees both right and left adjusting the end cap. Then I 'clamped' that in place with the 'sheet metal' nut. I forget the torque spec on that. I want to say 75 ft-lbs. I just smacked it with a punch and hammer. I need to make something to fit that flanged nut. I might try a fuel pump nut thing I bought. Then recheck the torque value. Since yours is used, I try 5 inch lbs or maybe 7.
Then install the sector shaft. I remember to add the torque value to the main shaft one. I think. So, say you have 5 ft-ls, then plus 5. So 10 Ft-lbs. Adjust the sector shaft in and out till you get that value while sweeping the torque wrench through the 90 degree arc. Tighten the nut for that. I don't remember the torque spec.
A back yard trick to this, is to tighten down the sector shaft. Just a soft synch. Then back of a 1/4 turn. I did try this and mark the rotating for comparison
to the torque method. The placement or index was the same.
I meant to check the FMS. I'll see if I can check it over the weekend. I've done 3-4 boxes. Two I have used on the road. One I plan to install on my present build. My first one, I used to thick of an oring on the front cover. oil all over the floor. That was in the late 80's, and Amsoil so not cheap. I bought a NOS box at that time.
The FSM does not measure the torque on the stub shaft alone. It tightens the adjuster plug down, then backs it off by around 5 mm, and calls it done. The issue with this is that in tightening that adjuster plug down, there is a lot of variance. Some people might tighten it down an 1/8 of a turn more or less than others.

No matter how much I tighten that adjuster plug, I don't get more than about 3 in-lbs on the torque meter.
I noticed that if I look in the return fluid port on the gear box, you can see this gear looking spindle thing on the thrust support assembly turning as the stub shaft is turned. If I tighten the adjuster plug to where the factory had it, sometimes I can see that gear/spindle thing turn, and sometimes not (slips). This implies to me that the bearing pre-load on the thrust bearing is not engaged sufficiently and that there is a gap between the spindle and the mating part. If I tighten the adjuster plug down another 1/16 of a turn, that gear/spindle thing ALWAYS is engaged and turns when I turn the stub shaft.

I presume the gear looking spindle thing should always turn when I turn the stub shaft, that is, it should always been fully engaged? If so, perhaps I'll just tighten the adjuster plug about 3/8" more than the factory position. This is still a far cry looser than the amount of tightness defined in the guides (turn the plug all the way down, then back-off 1/4"-1/2").

What do you guys think? I doubt these PSC saginaw gear boxes are any different than the factory ones. I rebuilt my Durango gear box a few months back and the parts look identical, the main difference being that PSC has their own end cap and top cap. Makes me wonder if the PSC gear boxes are just rebuilds, like the Lee boxes are. With the Durango box, I just put the adjuster plug back to where it was, but got to thinking that it would make sense that it should be tighter to some degree as bearings and metal wear with 22 years of use.

I was wondering, has anybody measured the correct over-centre turning torque on the stub shaft with the box in the car, steering link disconnected, and properly primed with fluid?
The FSM does not measure the torque on the stub shaft alone. It tightens the adjuster plug down, then backs it off by around 5 mm, and calls it done. The issue with this is that in tightening that adjuster plug down, there is a lot of variance. Some people might tighten it down an 1/8 of a turn more or less than others.

No matter how much I tighten that adjuster plug, I don't get more than about 3 in-lbs on the torque meter.

I looked at a 97 FSM. Yes, the instruction are to tighten up the Adjuster nut. Mark the position of one of the spanner wrench holes to the case. Then make another mark 1/2" from that mark. Rotate the hole to that mark. Use the spanner wrench to keep the adjuster nut from rotating. Tighten down the Coupling Shield nut to 80 ft-lbs.
Then install the pitman shaft. Keep it up as far as adjustment, so no load. Rotate the assembly 'lock to lock'. Then count the number of turns. Half of them to center. Arc in 45 degrees both sides. Adjust preload to 6-15 in-lbs. Hole the shaft in place and tighten the lock nut to 36 ft-lbs.

When you get the center shaft adjusted, can you take a torque reading? From my 5-10 -inch-lb, might have been from MB gear box instructions. Also, the pitman shaft to tighten and turn back 1/4 turn is on Kevin's Offroad website.
I'm setting this aside for the time being. Not seeing any increase in the stub shaft torque no matter how tight I made the adjuster plug makes following this procedure questionable. I've set the tightness on the adjuster plug/thrust bearing to be about 1/2" tighter than factory. I'm pretty sure it shouldn't be where the factory had it because I can see that component mentioned previously not engaged as I turn the stub shaft.

Now I can adjust the adjuster screw (allen head) to see 10-12 in-lbs on the stub shaft, but as I said, doing so causes a "kink" feeling at certain positions of piston in the chamber. I have adjusted the adjuster allen screw to be to the point where there just barely isn't that "kink/drag". Basically, the "kink" feels like there is a grain of sand in the chamber at a certain position, but there isn't anything in the way. The torque measured on the stub shaft as set now is only in the 6-8 in-lbs range though.

This leads to me to wonder - when the gear box is adjusted to spec, and you take a vice grip (pliers) to the pitman shaft and turn it back and forth, should there be any noticeable backlash at over-centre? Should it be tightened such that there just barely isn't any over-centre backlash? Thanks.