M1078 LMTV planetary hub setup

[m-35tom]

as bearings wear and need adjusting the gear lash needs adjusting. plus if it was ever done by the army it is wrong.

 

[Keith Knight]

Correct, so that's why Steve's method would take into account for spider gears/bearings and the hub bearing wear. Setting it to the factory settings would only take in account the hub bearings not the spider gears/bearings.

 

[Ronmar]

Correct, so that's why Steve's method would take into account for spider gears/bearings and the hub bearing wear. Setting it to the factory settings would only take in account the hub bearings not the spider gears/bearings.

Well in order for gear wear to be a factor, you would have to have a LOT of metal shaved off of the teeth of those very hard gears, left lying in the hub to make a significant difference In lash.

Remember, the spider gears are sandwiched between the fixed inner bevel gear and the rotating outer bevel gear. The only bearings that can really effect lash are the thrust bearings outside each spider gear or the thrust bearing outside of the rotating bevel gear against the spacer washer and the inside of the cover. The thickness of those thrust bearings is easy enough to measure… if they were worn, the spiders could slide outward, increasing the gap to bevel gears and lash.

Thats why the shims are placed on the inside, to account for the variable position of the wheel nut when it is set to deliver the proper bearing pre-load. The outer spacing should never change, as long as that outer bevel gear thrust bearing is to spec And the cover is not damaged.

Usually the hard part of measuring lash is getting the dial indicator into the right place perfectly tangent to the gear rotation to accurately measure the linear movement of a tooth. All you really need to do to check the shimmed side is to hold the spider in the hub. That should set the spider thrust washers in proper position(against inner edge of the hub), then a dial indicator should be able to show how far the spider teeth can rock back and forth(lash).

You should be able to do the same thing on the bench with the spider set in the cover on top of the bevel gear, outer thrust and spacer washer. In fact if the bevel gears are the same thickness, the measurement from the top of the thrust bearing and spacer to a straight edge across the cover opening, should be about the same as the measurement from on top of the spacer shims placed on the wheel nut to the hub opening. 2.168-2.173”

regardless of the measurement from wheel nut shim stack to hub opening, you should get the same basic spider tooth lash with the spider clamped in the hub as you do with the spider clamped into the cover, which is what the proper shim stack should achieve as the outer cover spacing is fixed…

 

[GeneralDisorder]

The fact that these are rather beastly units and don't often fail even in military use speaks to the lack of need to be ultra-precise. You should of course be as precise as possible but I assure you there are a LOT of these running around with just the original stock shims and a HUGE variance for spindle nut torque. My truck had over 11k miles on it when I recently did the hub service and three of my four spindle nuts weren't even finger tight and whatever grunt did the service rolled the lip on one of the CTIS seals.... I put 9k miles on it like that and also my rear diff seemed like it was a little low on gear oil, and both my front hubs had evidence of water intrusion - some pitting on the reductions gears - didn't really do any significant damage to anything. All the bearings looked in great condition .

I would imagine there's a TON of these rolling around being abused at WOT at every opportunity by PVT Snuffy and they really aren't failing so keep that in mind. It's not a Swiss watch and wrenching on these is not rocket surgery either. They let 18 year old kids do it and for the most part they take this abuse with zero F*cks.

Shims kits are NOT part of the annual service kit and in the VAST majority of cases no attention whatsoever is paid to shimming. The grunts assume the shims that are in there are right and slap that junk back together. Heck the special socket required for the spindle nut isn't even standard issue at the unit level. It takes a discerning Motor Sargent to know about it and order the socket.

 

[Awesomeness]

There has to be a different result. New gears with precise new parts vs old gears and parts with wear and break in. If it doesn’t matter then if everything is currently running good and no issues at all, why would anyone bother even though they say it should be done annually, unless there is wear to count for. There for just setting them up the same as before would only be putting it back the same as factory. Unless only the wheel bearings wear and need adjustment and the spider gears don’t wear but we all know things wear and out of tolerance.

Realistically, there isn't much wear to account for. Our trucks aren't driven enough, or hard enough. So it's not similar to videos of people checking the slop on the ring and pinion of an axle with 100,000 miles on it. So "just setting them up the same as before" isn't a bad option, if you weren't having problems, because even 10,000 miles on them would barely be breaking them in (as far as change goes).

The bigger issues is probably that I don't trust the 18 year old motor pool mechanics, that did all the rest of the crazy stuff to my truck, to have set it up any better. But again, if they aren't running hot or experiencing other issues, I wouldn't consider it urgent.

 

[Ronmar]

Yea where refining the lash pays off is in it running quieter and cooler with the most efficient gear contact. As mentioned it is not rocket surgury. And I agree, because of that, that is probably why we don’t see many hub issues, in fact the only ones I recall from recent history it was discovered the outer thrust bearing and washer were left out of the assembly(probably made for some interesting lash) and on another one the front hubs were dry… so if you put it all together with in spec parts, and keep it properly lubricated,..

probably more important to get the bearing nut torque/preload correct…

Since the outer bevel spider spacing is fixed, that lash is also fixed, unless you tune it, it would make sense to me to shim the inner side to get the same bevel to spider lash on the inner side after the wheel nut is properly torqued. With in-spec parts though, I suspect you will get a matching lash with a shim height that drops that shim to hub opening length within that 2.168“-2.173“ dimensions Found in the manual.

 

[Keith Knight]

So I’ll explain why I’m asking. I just finished up a 3,500 mile road trip with my 2003 M1078A1 ex-Air Force truck with 13,500 miles on it. 10,000 miles I’ve driven over the last 8 years. I’ve converted it into an expedition vehicle and she weighs 28,000lbs fully loaded with full tanks. My wife and I are traveling the country in it. We are about to leave Florida and head up through the New England states all the way up to Maine and back to Florida over the next 6 months. The truck is running great with the high speed gears. The fastest I ever drive it is 60MPH. No noises or any other problems. Just occasional gear oil that comes out the rear dif vent cap. The tires are wearing nice and even, I keep them at 85psiwhile on paved roads and was considering doing a hub and seal overhaul before I leave “ OR “when I get back???
Thanks for the info earlier, I agree with your explanations and will plan to set it up the standard TM way.

 

[Awesomeness]

No noises or any other problems. Just occasional gear oil that comes out the rear dif vent cap. The tires are wearing nice and even, I keep them at 85psiwhile on paved roads and was considering doing a hub and seal overhaul before I leave “ OR “when I get back???

I recommend leaving them alone for now. I'm sure you have plenty of other things to check or rebuild, but I'd spend the time and money on something else (instead of the hubs), like putting good synthetic gear oil in the axles/hubs.

 

[Keith Knight]

Thanks for you info, Just jacked up each tire and checked bearings like I would check a trailers wheel hub bearing and they were perfect not even a hint of play. Also pulled the plug on each front hub and the magnet looked good on each and the gear oil was still pretty clear. I did drain and refill 7 years ago with synthetic. So everything looks good and no gear oil leaks any where so that job is going to wait till this winter.

 

[BigMontana]

Relevant Thread:
ECO Hubs Who needs 3:07 gears? | SteelSoldiers

 

[BigMontana]

I'm not sure what an LMTV weighs when up armored and pulling a trailer as designed, but if all anyone has on the back is a camping box, they may have nearly already "halved" the expected operating load on the vehicle axles. you know, not to include the camping boxes where people give them all the areydynamic properties of a brick wall...more folx who take some account of wind force while moving.

They look like LMTV axles, or very close relatives. I think what he was saying was they came off an LMTV, hub gearing was removed, and were destined for a truck that weighed 1/2 as much as an LMTV. If you weld the planets, you put all the torque directly on the axle shafts, and they were only meant to handle 1/2 that (2:1 ratio). So unless you're using them with smaller tires, on a smaller truck, etc. you're just going to break things and have other problems. Yes, they have some safety margin on the design.

What's your goal?

 

[BigMontana]

I tried to have my mechanic check the gear lashing before i left, they prioritized other projects and then blamed a driveline vibration on the slip joint...that may have been incorrect, and it might have been in my best interests to have trusted my original gut telling me to check the gear clearances...live and learn.

as bearings wear and need adjusting the gear lash needs adjusting. plus if it was ever done by the army it is wrong.

 

[GeneralDisorder]

I'm not sure what an LMTV weighs when up armored and pulling a trailer as designed......

M1089A1P2 LTAS Wrecker weighs 40,050 lbs and has a towed load rating of 55,000 lbs. For a combined weight of 95,050 lbs.

Engine is the 330/860 C7 and transmission is the Allison 3700SP.

My M1079A1R Van weighs about 21,000 lbs by it's fat self. An unloaded M1082 weights about 8,500 lbs......

 

[Keith Knight]

with what motor?

 

[GeneralDisorder]

with what motor?

I updated it with specs.