fishing for thoughts on a 5 ton 8x8 (fake hemtt)

[illtemper]

first off this is just an idea as I really like the hemtt's but know i can never afford one.
I don't even have my first mv home yet, m52a2, but I do have a set of 5 ton axles sittin here,complete with transfer case and drivelines. far far away in the future , I was thinking about putting 2 steer axles on a rear bogie spring setup, just like a regular rear but with steers. I know the steering wouldn't be quite right but should be close enough to work,then just bolt the thing to the frame. for the cab I figured I'd use 2" tube to frame a basic hemtt shape then just skin it.
well any thoughts? again its just a thought, if its been said before just point me in that direction please.I've read a little on the baby hemtt (cool rig),but I like the 8x8 thing.
thanx...jon

 

[M1075]

It sounds like a lot of work, but the one good thing you have going for you is the ability to power a second front axle with only a driveshaft. Plenty of HEMTT surplus cabs are available so I would look for one of those.

 

[Recovry4x4]

IIRC there is a M.A.N. wrecker on ebay starting cheap

 

[mhodges]

I've climbed all over the MAN wrecker- it is in ROUGH shape- it's at a junkyard a buddy of mine frequents for cheverolet parts- its in VA beach outside of oceana...had a bunch of pics saved on my phone and planned on posting them back around december, but the phone met an early demise!

 

[wreckerman893]

Jon,

Evidently great minds do indeed think alike.
I have mentioned the same idea to several people who already think I am crazy.

My idea is to cut the frame with the rear suspension and put it in front of the engine.
Replace the rear axles with steering axles and fab a power steering system
The engine would then be about where it is in a regular HEMMET.
Unless you used the engine/tranny out of a 900 series you would have problems with shifters and linkage.
You could then mount a HEMMET cab over the steering axles just like the real thing.
So many ideas......so little money.

 

[tcody]

Macon - sent you a pm.
Thane

 

[BobS]

TRW and Ross both make light and heavy duty steering gear setups for twin steer's that are available off the shelf. IH (Navistar), Freightliner, Western Star, PACCAR, and others all make twin steers, so make friends with your local dealer. You must have a relay link to tie the 2 steer axles together on the right hand side (assuming you are driving on the left), and the 3 slave gears (if you use a conventional system), or 2 gears (if you attempt to only "steer from one side") require a great deal of hydraulic fluid (quantity or volume, not pressure), so you would need to change to a hi-volume p/s pump.

To prevent extreme understeer, you MUST use an interaxle differential on pavement, or a disconnect to prevent the 2 axles from being forced to rotate at the same speed (do an off-track diagram and you will see why-each wheel tracks on a different raduius and will horrendously scrub.). If you don't plan on plowing through many gardrails and fences as the truck slides the tires, instead of turning (same effect as a conventional 4x4 wit ha Detroit locker in the front axle on pavement).

This ain't a place to cut corners, you WILL die if you screw it up and possibly kill others. An 8x8 is a blast to drive though...

....BTW-shifters for a manual trans and various throttle cables, etc. are no problem-use shifter and clutch parts from a COE Freightliner Argosy. Just get longer cables from Morse.

 

[m.walker]

One problem James , if you do get a cab GL might want it back ! Like mine , I'm pissed !!!

 

[maddawg308]

Buy a HEMTT cab from a private company. Once it's sold from their lot, GL/FedGov can't ask for it back. I think these guys have a few:

http://www.murphyjunk.bizland.com

 

[BobS]

Addendum to previous message on steering:

I do not want to seem anti-conversion. I am not. A twin steer is a great idea. You can make it ride better, be more controllable, have a higher VCI mobility rating (means tear around offroad more and in worse places), and it also has a whole host of other advantages.

You can increase the accessibility to the drivetrain for servicing when "stuff" happens, have parts that live longer and do not "work as hard".....

All in all, it would be an exciting project.

ADDENDUM 2:

If you have the steer axles now and the suspension, the steering setup from an IH Paystar twin steer would cost you about $2500.00 from a junkyard. Look especially in the oil producing regions of the US and Canada for the parts-one of the biggest users of twin steers is for offroad mobile oil rigs.

As a sidebar, when I was with IH in the 1970's, we built 6 for use in the 3rd world. Great program as I got to go to South Africa and Rhodesia to help out installing the bodies and perform testing.

 

[frodobaggins]

Reviving an old thread, I'd like to do this someday too. Anyone got any constructive help on making this happen ?

 

[Elwenil]

I've pondered all of this many times for a future APC project. The hardest part is to get eh steering right. Unless you use parts from another 8x8 vehicle, you are going to have to fab up quite a bit of stuff. I plan on copying something like Bjorn's 8x8 with a drag link that goes to the second axle. Keep in mind that the second axle cannot steer as hard as the forward axle so you have to play with the arms on the steering to get the right ratio. I wouldn't bother with a rear steering axle unless you plan on a 10x10 or a long wheelbase. At a certain point the rear steer becomes less necessary and ,more of a pain to setup. I'm not using one so I am unsure about how much one of them steers but you can look at a HEMTT PLS for ideas.

Braking could be an issue depending on what system you use. More axles equals more brakes and that may require more volume to stop effectively or you could just not run the brakes on the extra axle depending on your uses. Linkages are a pain for certain setups but Morse cables are easy to setup for shifters and other uses just like with a front wheel drive car. As far as suspension, I would not use the rear suspension as found under a Deuce or 5 ton cargo as I'm pretty sure that would be rather unstable at speed when hitting bumps as the suspension loads and unloads. Probably much worse than the old Jeeps with the shackles at the front. A better idea would be to use normal front leafs but put one set inboard of the other so they do not interfere with each other. I will most likely use a scaled up version of a off road 3 or 4 link setup with airbags but that's not set in stone as weight is definitely a concern.

As was said before, a simple drive shaft will connect the axles, but you will need something a little more than the short shaft between the rear axles as it's not designed to handle two axles moving in different directions like could happen with two independently suspended axles. Just my .02

 

[hklvette]

Is there any reason that a panhard bar can't be attached to the top of a rockwell diff? If it can, I think that would resolve the wandering axle problem pretty easily.

my

 

[Flat Black]

^^ search on pirate, its been done a few times... pretty tough fitting it because of the tall center section.

 

[Coldfusion21]

I'd like to bump this up again. Thinking about doing essentially what WM said with a M920 as the base vehicle. Then use the rear suspension from another m920 fitted with two steering axles. Tie rod connecting the two axles would have to be fabbed as would the arms to achieve the right steering ratio. Wondering if current cab can be made to work or if using a surplus hemtt cab would be just as easy.

Where is the front of the engine relative to the end of the frame on a hemtt vs M920?

Obviously this is just pondering/planning right now, but if I can sort the project out I'd like to get a truck this coming spring and get on it.

 

[M920]

I'd like to bump this up again. Thinking about doing essentially what WM said with a M920 as the base vehicle. Then use the rear suspension from another m920 fitted with two steering axles. Tie rod connecting the two axles would have to be fabbed as would the arms to achieve the right steering ratio. Wondering if current cab can be made to work or if using a surplus hemtt cab would be just as easy.

Where is the front of the engine relative to the end of the frame on a hemtt vs M920?

Obviously this is just pondering/planning right now, but if I can sort the project out I'd like to get a truck this coming spring and get on it.

You are on the right path I think. It is along the same lines of what I have been working on. I started with the 5-ton idea but quickly decided to go with a M916 for the base vehicle. I want to have good off-road capabillity and choose the M916 over the M920 for it's shorter wheelbase. I have not made the final decision on whether to leave it a 6x6 or add a second front steer axle to go with the 8x8 configuration. It looks like the HEMTT cab I got will work great on the front of the M916 chassis and the engine ends up in the correct location versus the cab and radiator.

I got the M916 with Allison tranny and the HEMTT cab but I'm still rounding up more parts. I will do a thread on the build here on SS when I get started.

Stay in touch

Soni

 

[Coldfusion21]

Good to know I'm not too far off in left field. Any thoughts as for the front axle and getting power to Axle number one? Obviously the rear axles have the right setup but don't steer. Can I somehow swap the center chunks from a rear axle onto the tubes from a front? Finding a steer axle setup to provide power to second steer axle I fear will be tough. Once I get the big bits figured out I will be a lot more comfortable jumping in.

Thanks again guys.

Jared

 

[American Patriot 1960]

Anybody ever do anything with this idea?

 

[Coldfusion21]

Not yet, and honestly it's a pretty ambitious project for me, more of a someday sorta thing. However I'm constantly thinking about it and the details involved. If you plan on doing serious hauling at some point you might also investigate your applicable laws regarding legal weights. I've been reading about my laws in Oregon and it seems like having three rear axles vs two rear opens up a lot more weight in a good place, under the kingpin.

Question: does the LVS use regular axle steering in addition to the articulation? I'm pretty sure the answer is yes...

I'd love to see some home built twin steer axle trucks or trucks using a hemtt cab.