Frequent Towing: pull axle shafts, drop u-joints, or install 2nd trans oil cooler

[sideburnie]

I know people joke about towing a parts car, but I'm actually kind of seriously considering towing a second FMTV on a regular basis.

Background: I'm designing an FMTV RV / overlanding vehicle. My girlfriend wants to join. I'd like more space (given we will be doing this full time and trying to do contract design work remotely), and I am now considering using one vehicle as a living space, and one as a work space + tools storage. We would be fine both driving a second FMTV, but there may be times when I'm solo, and it would be nice to be able to ride together when it's not necessary to drive the secondary FMTV. And... I've also thought it'd be nice to have a capable recovery vehicle when I'm a few hundred miles out of cell coverage down a dirt road (or in kazakhstan or whatever).

I know some folks prefer to pull axle shafts, while others prefer to disconnect a CV joint. I've thought both of these options are relatively labor intensive for the frequency that we might want to switch from towing the second FMTV to driving the second FMTV.

I wanted to ask the experts: Have any folks who tow frequently (and don't use a flatbed for the towed vehicle) considered installing an aftermarket transmission oil cooling pump that could run on the towed vehicle when towed? I imagine there are many reasons this wouldn't work, but I don't yet have an FMTV to tinker with and I wanted to open it up for discussion.

In the case that adding a secondary transmission oil cooling pump is completely impractical or would not save some parts from destruction while towed: have any folks looked at any sort of remote axle disconnect options (presumably at the interface between the CV joints and the diffs or CV joints and the transfer case axles)?

Many thanks!

 

[wheelspinner]

Have you considered a trailer like the M1082? Just seems simpler by orders of magnitude.

 

[sideburnie]

Have you considered a trailer like the M1082? Just seems simpler by orders of magnitude.

Yeah, definitely. Something like the 1082 may end up being the route I'll go, but there are a few negatives:

- recovery: no recovery vehicle immediately accessible (and 30 feet and 30k lbs requires a somewhat unique recovery, I think)
- parts: no parts vehicle immediately accessible to hold over until I can get parts shipped (or whatever)
- capability: there are some fire roads / jeep trails in canada that come to mind that would be harder to traverse with a trailer
- reversing: if i'm 50 miles down a one-lane road with a cliff-side, and I need to back out, I now have to back out with a trailer on.

 

[Gunzy]

I would consider this for both drive shafts.
https://www.youtube.com/watch?v=eCQh5jTgLHA

 

[sideburnie]

I would consider this for both drive shafts.
https://www.youtube.com/watch?v=eCQh5jTgLHA

I had been meaning to call these folks, and I'm glad you brought this up! I finally did, and the sales person I spoke with said they "get a lot of people calling about using these on their vehicle" and that "they won't sell them for anything other than their own coil coating machines." I asked about torque specs and she said she didn't know but that they couldn't go above 300RPM or 100 degrees F. By my simple calcs I need ~3400RPM. Very possible they'd be just fine, but they just don't want to deal with automotive servicing. Looking inside the unit, the diameter of the engagement pins is a little bit worrying, but still too bad they don't publish torque specs.

 

[Adventure Driven]

Pulling rear axel shafts is not very hard at all, I carry socket and breaker bar, just messy, so I also carry a huge trash bag to stow it in

Seth

 

[Awesomeness]

Those driveshaft QDs are cool. They seem like a very simple design... I'm a mechanical engineer and once designed something similar to make QD mixing paddles for a candy mixing machine. Only having two small drive pins inside seems weak, but it looks like you could easily add many more, and/or larger, pins. I don't know why that RPM should be a problem, since if you machined them they would probably be the most precisely balanced part of the whole driveshaft. You'd have to shorten your drive shafts quite a bit, and would probably want to install guards to protect the QDs. It will be an expensive project, but super interesting.

 

[sideburnie]

Called these guys: http://www.remcodsc.com/driveShaft.php and they make a coupling for up to a 1480 series u-joint yoke. From googling it looks like that might be the size on the M939, but I haven't yet found the LMTV / FMTV yoke szies. Anybody have it on the top of their head?

At remco I talked with Bill and he quoted me $890 in parts.

 

[Suprman]

If you are only going a short distance at low speed you can flat tow without pulling the driveshafts. The transmission oil pump is direct coupled to the transfer case outputs and if the axles spin fluid is circulated. This is direct from Allison.

 

[sideburnie]

Given people recommend this u-joint puller: https://www.amazon.com/OTC-Tools-5190A-U-Joint-Puller/dp/B00UF4L9BU and that it can be used for a maximum bearing cap size of 1".

And that the 1480 series u-joint has 1.375" bearing caps http://www.dennysdriveshaft.com/p13...niversal_joint_1480_series_greaseable_u_.html

it seems it must use smaller than 1480 series u-joints?

(EDIT, I think the 1" on the u-joint puller is referring to impact wrench size. found another post describing: "Fits all spicer drivelines 1610, 1710, 1760, 1810, 1880 Spicer SPL 140, 170, and 250...")

 

[sideburnie]

If you are only going a short distance at low speed you can flat tow without pulling the driveshafts. The transmission oil pump is direct coupled to the transfer case outputs and if the axles spin fluid is circulated. This is direct from Allison.

ah interesting! is the failure mode in a long-distance pull an overheat because the transmission oil cooler fans aren't running or something else unrelated, you think?

 

[srodocker]

Would love to see build pictures of it!

 

[Awesomeness]

If you are only going a short distance at low speed you can flat tow without pulling the driveshafts. The transmission oil pump is direct coupled to the transfer case outputs and if the axles spin fluid is circulated. This is direct from Allison.

By "short distance" are we talking a couple miles to the nearest shop, or is this meaning something like needing to tow it off the road into a parking lot 100' away?

 

[sideburnie]

By "short distance" are we talking a couple miles to the nearest shop, or is this meaning something like needing to tow it off the road into a parking lot 100' away?

I think some use these rules:

https://www.steelsoldiers.com/showt...owing-a-LMTV&p=1771441&viewfull=1#post1771441

(and I would like to be able to flat tow, say, 300 miles in a day if I need to--and would rather not have to pull the axles every time I want to do that.)

 

[firefox]

Crazy idea: If you used a trailer, back the truck on to the trailer. If you get in a tight spot,
drive off the trailer and hitch the back end of the trailer to the rear of that truck and then detach the front from the primary vehicle. May need to set up some stuff so you can pull the trailer from the back end.

If you want to get fancy, you could get a trailer that could both be pulled from either end and be loaded from either end.
This way you could use the second truck to recover the first.

Add in a winch for even more versatility.

Just some crazy ideas. I have no idea if these are practical or not.

 

[DiverDarrell]

You have to disconnect the axles in some manner. You can pull the rear axles out, and disconnect the front u joint. That would be the easiest option. But often towing a whole truck 300+ miles. I'd expect 3-4mpg or less. Flat tow's and tight corners are no fun. Accelerated tire and hub wear. CDL territory

 

[sideburnie]

Crazy idea: If you used a trailer, back the truck on to the trailer. If you get in a tight spot,
drive off the trailer and hitch the back end of the trailer to the rear of that truck and then detach the front from the primary vehicle. May need to set up some stuff so you can pull the trailer from the back end.

I like it! That's really clever! I think my only concern would be some combination of either ground clearance for the trailer or high center of gravity / high roof height for the tow vehicle (max is typically around 4-4.2m or 13' 6", I think--I'll be building to 13', I think).

 

[sideburnie]

You have to disconnect the axles in some manner. You can pull the rear axles out, and disconnect the front u joint. That would be the easiest option. But often towing a whole truck 300+ miles. I'd expect 3-4mpg or less. Flat tow's and tight corners are no fun. Accelerated tire and hub wear. CDL territory

That's the thing--I'm wondering 1) maybe you can get away with not disconnecting the axles in some manner (through auxiliary cooling?) or 2) disconnecting the transfer-case axles using some form of quick-disconnect.

yeah low MPG is expected--we'll be taking our time. that said, i don't expect the net to be significantly lower than if we were driving both of them.

I'll likely be getting a CDL anyway (just got my company setup with the state to issue CDL education certs ) 1) so that international cops / customs can't ask for a bribe because I "have an RV license" and 2) because I need to be able to drive them before they're converted.

 

[ramdough]

I think you are asking for trouble you don't want.

If you are towing such a huge vehicle like that off-road, I think you will get stuck a lot. Your combined weight would be huge, you will be very limited on maneuverability, your mpg will drop a lot, you will wear your towing vehicle a lot more.... the list of issues that creates imho is greater than the benefit.

I would opt for stowing a parts truck at a friends house and have him ship parts as needed. Or, have a list of parts people like Superman in your phone and overnight parts as needed. Cary a decent set of spares with you. Invest in a front and more importantly a rear winch. Get good recovery gear. And, then have a quad or dirt bike handy for emergencies. You could also tow a trailer for more gear if you want. All that seams like it would be easier and probably cheaper.

Just my 2 cents.


Sent from my iPhone using Tapatalk

 

[sideburnie]

I think you are asking for trouble you don't want.

Yeah, I understand that's very possible. Just wanted to explore the options and understand the failure modes of flat-towing.

If you are towing such a huge vehicle like that off-road, I think you will get stuck a lot.

Very true. I think the idea would be to drive them independently in a serious off-road scenario--so I think it's better than towing a trailer in that regard.

Your combined weight would be huge, you will be very limited on maneuverability, your mpg will drop a lot, you will wear your towing vehicle a lot more....

True, though the m1088 is rated (_by the US military_) to tow 60,000 lbs.

Don't get me wrong--I'm also worried it may not end up being the optimal solution. I just want to fully explore the options & failure modes.

Anyone have any links to stories of failures during flat-towing, what failed, and why?