The 5-Ton HMTT Saga

[paradeduty]

Well, finally got a chance to do a little bit of wrenching on the HMTT this afternoon.

Got the original flat aluminum grille off and out of the way. It was pretty mangled from lots of heavy handling and no brush gard so it had to be replaced anyway. Being as there is no radiator in the front of the engine (has custom experimental radiator and hyd drive fan behind engine over trans) this makes getting to the cables and belts and pumps one whole lot easier (maybe the new one should be on hinges!).

Got the front bumper removed so that a new one can be fabricated. Had a little good luck - while up in the bed checking things out and scratching my head, what should I stumble upon but the other third of the bumper that for one reason or another (probably tugged too hard) was cut off quite a while ago. Very cool - now we don't have to make one or two new matching lifting eyes for the ends (one would have been missing - didn't know it was in there under 2 foot of snow!).

Had a chance to crawl under and check out the shifting setup for the transfer case (never could get the shifter to budge). And the problem is.........Ta Da........yup - frozen shifter cable. They totally disconnected it and left it in low range. Due to the tilt cab, this cable has to be all of 20' long! Have to put that on the list.

Checked out the mildly cobbled rear end. Mudflaps are basically garbage. Added on low slung pintle hitch has to go. The rear frame cross member has seen some signifigant tugging from the looks of it (probably draw bar testing at the proving grounds may have helped cause this). Plus between the over stock height tires and suspension spacers from the original M656 donor vehicle, the stock pintle height is now about 9" over standard. I took some pictures of the rear of my M54 5-Ton 6x6 frame. Its some work, but I think it might be better off in the long haul to just replace the entire rear cross member with a decent one off of a 5-Toner (drop pintle, bumperettes, and all). The frames are the same width and rail height so except for a few thousand bolts - no big deal. Plus they did remove and discard one of the original bumperettes (not a match for the 6x6) and I will gain proper pintle height and rear chain clevis attachment points. Hopefully I can find a 5-Ton with some good mud flaps, too - the ones on my M54 would work well.

I was kind of hoping that I could just exchange the drop sides and tailgate off of the bed (supposed to be an M813 bed). But as I was again scratching my head (something just didn't seem quite right) - it dawned on me.......oh yah! They changed the HIAB Crane from the original one that they were trying out. This replacement had manually extendable outrigger supports which the first one did not have. This (as the domino effect begins....) is a physically larger unit which required the widening of the space allocated to it in the front of the bed (the space normally reserved for the spare tire I believe). To do so they shortened the Drop Side Panels by about 6 or 7 inches - so that rules out that easy swap, hey! Oh well - I'm mulling over some options to keep this realistic (one of which is just leaving well enough alone!).

The other thing I still have to track down is a front crank pulley accessory attachment to go between the Detroit V6 and the Auxiliary Hydraulic Pump (for the Crane and Winch and Rear Aux Hyd.). Just because the original pump was designed to attach to a custom shaft (with remote engage/disengage feature), I will probably end up having to get a new/different pump as well.

Anyways - nothing earth shattering - but it might be interesting to check out.
Pictures and captions to follow (if I don't mess them up!). Happy wrenching!

 

[paradeduty]

The Saga Continues

More Pictures

 

[srodocker]

awesome!

 

[cranetruck]

Thanks for posting! I'll be following this with interest.
Here are a couple of rear views for reference; M656 and XM757...

 

[paradeduty]

Thanks for putting up the pictures, Cranetruck. Looks like the mudflaps, bumperettes, Trailer accesssory "plate" below the frame and tail light assembly brackets on the sides were original after all. Excellent reference. I thought for sure that with the mudflaps hanging from simple angle iron bolted to the bottom rear of the bed that they were "shop custom" - looks like they were the ones that came off of the 656 to begin with and just installed on the 813 bed. Must have decided on the 813 bed due to the limited nature of the 656 bed and the strength of the steel bed over the aluminum for the crane. I can't remember how long the 656 bed is - but it could have been a matter of space as well, with all of the changes they had in mind up front. Very cool - Thanks again. Dave

 

[paradeduty]

Hey Cranetruck - Question:

Does either of your rigs have large suspension travel limiting chains on the #2 and #3 axles? This truck does and I was just wondering if they were added maybe because of the suspension lift or the low tire pressure (control bounce?). Just curious. This one definitely did not start out as a 757 as it does not have the rear shocks as yours shows. Take Care, Dave.

 

[cranetruck]

Dave,
Only the truck/tractor (xm757) has the rear shocks. They all have front shocks.
I can imagine that there has to be some suspension travel limiting means with those oversize tires. The original tires are 16/70-20 and with the higher aspect ratio are not as tall.
I'm still working on the mud flaps, second image shows current status.
The 3rd image shows some articulation where larger tires may be a problem (my son driving).
Edit: Added images.

 

[paradeduty]

Hi Bjorn,

Boy the pictures sure help bring back the memories/piece history together.
Looks like they used the same stock front bumper (with the 45 degree bevel on the bottom of the front face) and fabbed a back to it. Welding it up and effectively boxing it all in (for strength? for the winch cable rollers? for the lifting eyes that were added to the ends of the newly boxed bumper?). My truck doesn't seem to have the lifting eyes in the center of the exterior (sealed?) brake drums as your's do. I don't know if they changed the drums for braking capacity (kind of doubtful) or if they just didn't think that they would extend far enough with the oversized tires. From the diagram, looks like mine has the same shock locations (front) but they must have stepped up their size (at least in length) for the lifted suspension (same mounting locations on frame). Do you have a line on dimensions for the original mud flaps - I can measure these if you don't - should be easy to make - just apear to be flat steel w/ about 12" flap on bottom (looks like you are keeping it as original as possible, good for you!). The suspension limit chains seem to be additions for the inner axles only (if neither of yours have any). Maybe they were afraid of them dropping too far with the lift and different shocks and possibly dropping the driveshaft(s) from the transfer case apart at the slip joint (chains only on the middle axles). Talk to ya soon, Dave.

 

[cranetruck]

The center-of-the-wheel-anchors were supposed to be for tying the vehicle to a rail car bed or something, not for lifting according to the TM. However, they were also used when rigging for an air drop. There are other "lifting points" specifically meant for lifting.
The radials on your HMTT are not any wider than the original tires, just taller and probably made for a narrower wheel, 10 inches or so. The wheels on our trucks are 12 inches wide.

The mudflaps on the cargo version were hung from the bed and installed on a frame on the xm757 as shown below.

In general, I get the impression that your HMTT is a redesign where all the "extras" were replaced with more commonly available parts, including tires and engine and certain capabilities were deemed "not needed", features like swimming and multifuel operation. The light weight features were eliminated also, like the aluminum bed and cab structures...could be a big cost saving also.
The original tires were designed for continuous operation off road at 10 psi and the 70% aspect ratio lowered the CG for stability (= 40% side slope capability).

Are the axle housing (wet) and brake drum (dry) pressurization systems hooked up on yours?

 

[tcody]

Love the pics - keep em coming!

 

[paradeduty]

The HMTT has New Shoes!

Well, the Heavy Tire Shop in Jackson, MI, finally got the tires all changed out on the 5-Ton HMTT Prototype. Not complaining or anything, but I bet it took longer than they thought it would. They told me they had to use one of their boom trucks to break the old tires' beads down! They were squeezing it in between their other work - and that is fine with me since it helps keep the cost down a bit. But I would rather the pros did these since they were still the split ring rims, and old ones at that. They still have to get to the spare, but they wanted to get it back to the mechanics so they could finish their things. Was just making me a tad nervous with the days flipping by for the July Veterans Weekend/TACOM Show! Dave.

 

[73m819]

That truck sure would look good parked next to it's big brother