XM757 steering

[cranetruck]

Slowly but surely, moving those linkages is beginning to feel like work, gotta watch my back, don't want it to snap out.
When they get a bit easier to move, I'll use the power steering, if the steering wheel alone won't handle it.

Kenny, as far as you driving/riding in it, you bet! You know a lot more about truck tractors than I do.

 

[OPCOM]

hey maybe.. could be ready in time for MVPA convention... A huge drive though.. maybe a crazy idea. But I really like the truck and I hope everything frees up like that. There should be some big rubber industrial "O" rongs that could be used as seals.

 

[cranetruck]

According to the SAE paper, the purpose of the seals was to keep dirt away from the rod ends. They probably, like Jon suggests above, did more harm than good by trapping moisture.
I'll be leaving them out.

 

[alphadeltaromeo]

Exercised the drag link some more (image above) and it now drops in about 20 seconds. If they all loosen up like that, I should be in good shape.

Pun intended...you shall be in good shape!

 

[cranetruck]

Eggsactly, you got it, but I have to watch my back, dont want it to go out (again), it's like pushing a shock absorber in and out, a constant resistance. I also don't know how loose these joints should be by design.
A four-wheel front end alignment is next. The right front tire is worn pretty badly.
Love this thing, an engineer's dream truck!

 

[cranetruck]

Not making a heck of a lot of progress here, the tie rod ends have been soaking off and on for a week almost. They have the stud up and the ball cavity down for supposedly easy soaking, but PB blaster hasn't done much at all. Takes about 150 ft-lb of torque to turn the tie rods using a pipe wrench...
Wonder if CLP Break free is any better.

Edit: (added image) The ball is nice and shiny when it's showing, maybe the dry lubricant packing has swelled up some over the years.

 

[Towman2277]

Bjorn, looks like it's coming along nicely now!

 

[cranetruck]

Removed the second axle tie rod a little while ago.

Will put a couple of jam nuts on the studs for turning with impact if nothing else works, but they will get exercised. With plastic and fiber inside, heating is out.

The hub turns with finger pressure, which is nice.

 

[devilman96]

Bjorn I wouldn't sweat those joints to much, the studs look good and tight is far better than loose.... Just keep an eye on them for the first month or so of driving.

If you do find that replacement is needed 99.999% of the time you can cross the size thread sizes via Napa's truck line or through a truck shop...

 

[doghead]

Bjorn, do the steering axles have rubber boots similar to the deuce? (the zippered ones) If so, how are they? Is the power steering pump gear driven on the front side of the IP or is it belt driven? So the jam nuts and impact is working well for loosening the tie rod ends? If so, GREAT!

 

[cranetruck]

Boots? Yes, about the same size, perhaps a bit smaller and four of them, I know the deuce is only ten feet away, but I haven't measured them. They are all punctured and need to be replaced.

The power steering pump is gear driven in front of the IP.

Need to get smaller profile nuts for the studs to jam them, maybe tomorrow.
D-man, I really do need to get the joints loosened up some, they are way to tight.

 

[OPCOM]

Glad to see all this progress! Its very interesting to learn about the 757 by seeing the maintenance.

 

[cranetruck]

Removed the forward drag link today. The ball joints of it and the rear tie rod are now soaking in CLP "Break Free".
The jam-nut-impact-wrench idea didn't work very well, couldn't get the nuts tight enough and the turning action of the impact wasn't right for this.

 

[cranetruck]

This is how I work the ball joints. They only loosen up so much and then that's it, still pretty firm, but maybe that's the way it's designed to be.

Spec on how many ft-lb of torque should be required to turn the balls in their sockets would be nice....

 

[cranetruck]

Using my trusty torque wrench on the ball/stud shows that it takes about 70 ft-lb to start it turning in its socket.
There are 11 "sealed for life" ball/stud joints in the steering linkages. They are now swimming in CLP Break Free.

Ideally, the ball should move without friction and be tight.

 

[alphadeltaromeo]

Delrin is a very slippery plastic, with many similarities to Teflon (both are made by DuPont) except Delrin is harder and less subject to deformation under pressure. If those joints have Delrin inserts in them, then as long as they are not sloppy or rusted solid I would think they are okay.

They're obviously very different from a traditional ball rod end... personally I would not add grease since they were never designed to have grease in them - they were designed to run dry. It's possible, (and this is pure speculation on my part), that there was a technical bulletin issued at some point instructing that the rubber seals be cut off because they trapped moisture which could cause rust rather that allowing the joint to dry out. This possibility occured to me because I think it's very odd that ALL the seals are missing.

Regards,
Jon

Bjorn

I have a different perspective here. While I understand that the joints weren't designed to have grease in them, they were also designed to have the seals as well. The seals aren't there...with only 3k miles and I think that is indicative of a design issue, as they were removed...for whatever reason (opinion here of course). With that said, I'd question the design of the entire joint. Perhaps the actual joint design with the Delrin inserts was good. But if the joint was supposed to have a dry lubricant as well, either the water over 10 or so yrs, or the CLP, etc. is certainly compromising the original design anyway. The original intended joint won't be the same regardless moving forward.

So how best to move forward? I'd side with rdixiemiller on this one and suggest tapping a zerk in the joint and grease it. I believe that the zerk and grease will work well and that as with all maintenance, periodic greasing will keep the joint functioning well. Is it the intended design? No, but just because it's not, doesn't mean that it isn't a strategic approach that will yield excellent results. As commented before, the original design has been compromised, as it isn't working currently and moving forward, it can't possibly be the same unless you restore it to the original design.

Who says the original design was best anyway. Look at the door hinges on a deuce. There are many...I'd suggest, design flaws in these vehicles.

Just my 2 cents

Andy

 

[OPCOM]

Maybe contact DuPont and find out the reccommended grease-type lubricants, so there are no attackson the metal or the plastic. It is a very unique material.

http://heritage.dupont.com/floater/fl_delrin/floater.shtml
http://en.wikipedia.org/wiki/Delrin

 

[JDToumanian]

It certainly wouldn't hurt to call DuPont if grease is to be considered, but I've worked with Delrin quite a bit and can attest to it's chemical neutrality... I can't imagine any normal grease having a reaction with Delrin.

But like the Wikipedia article said, it's self lubricating. Very similar to Teflon in that regard, unlike some other plastics that can gall without lube when used in a friction point.

More semi-random thoughts: If CLP is not penetrating the joint and loosening it up, why would grease? Maybe these joints are supposed to be tight? What we think of as 'too tight' may be nothing to the power steering system's hydraulics.

Unless they were completely rusted solid, I don't think I would have been worried about these joints being too tight. It never would have occurred to me to disconnect them and exercise them as Bjorn is doing... I would have just given the tie rods a yank back and forth to check for looseness and moved on to other items on my check list, but maybe it's more of a problem than I perceive.

Hopefully the issue can be resolved one way or the other without having to replace those joints... that would be expen$ive I am sure.

Regards,
Jon

 

[cranetruck]

I have my doubts about grease doing anything at all.
Look at the images below, the part of the ball becoming exposed when it's exercised is free of rust. That's how good the seal is along the lower edge (top edge in that image). Rust above, no rust below after 37 years. A hermetic seal couldn't do much better!
Soaking with CLP from this end may take a very long time, but I'm tempted to drill a very small hole in the top cover to see if the penetrant can do any better from the "top" end of the joint. Grease would only remain on top if a zerk fitting was installed. The movements of these joints are not very extensive.

Tight ball joints will result in the wheels not returning back to staright forward after a turn. The caster effect of the wheels will not work well and the result will be a driver effort to keep the vehicle straight, with or without power steering. A very exhausting task for the driver and even dangerous in some situations.

"Spoke" with Frank in Tulsa and he has tight ball joints as well, but lives with it. He only drives his XM757 in parades and such.

These joints are certainly not supposed to be tight. What would the reason be for that? The wheel hubs sitting on their kingpin bearings turn with finger pressure.
Some spec I have found for other ball joints call for about 5 ft-lb of torque to turn, mine are a whopping 70 ft-lb!
They must have been sweet coming off the assembly line, probably as near perfect as can be.

One reason, according to David D, that this series of 5-tonners didn't become the new standard for the Army was that they were cost prohibitive. With some of the technology I have seen so far, I can understand that.

Stay tuned, this problem will be solved.

 

[DDoyle]

I'd be REAL reluctant to start drilling holes and reengineering the joints and vehicle without any more data. In fact, my inclinition would be to reassemble the vehicle and take it for a CAREFUL test ride.....a few passes over even mild off-road conditions (a plowed field, for example) will exercise the entire vehicle far more than can reasonably be done with pipe wrenches and back-breaking labor.

Also, there are sources for NOS parts out there - though they may be difficult to find. I suspect that they will be cheap due to their limited utility for commercial users - though some dealers may recognize the "scarcity" of the truck and price bits accordingly.

Regards,
David