Swapping transmission on the Hemtt... - Steel Soldiers::Military Vehicles Supersite

dma251 · 10-25-2007, 03:03

Well, after putting about 200 miles on the hemtt with the old slipping HT740D Allison tranny, I decided it was finally time to get my ass in gear and get the new transmission I got from Bruce Kubu put in.

It took a while to find someone I trusted completely to do the work, but the guy I found is also the fabricator that made me the new front fenders that are yet to be installed, and his work with metal is so perfect I had to give him a shot at the transmission. He does that type of work often, and since he is also installing the cargo box for me it made sense to have him do it all at the same location.

The transmission I bought from Bruce was a more modern updated 5-speed version of the HT740D 4-speed transmission that I was replacing. It is a direct swap, except the driveshaft has to be shortened by 3.6", but we are doing the shortening there, and I only have to take it out to be balanced. I will be left with a mighty short driveshaft, as they are only a couple feet long to begin with.

One other detail we are doing is kinda interesting. While researching the technical details of this swap with a mechanic for our county (they deal with Allison's a good amount) we were informed about a design concern involving how the Allison HT's mount up causing increased case cracking and breakage at the bellhousing area. Turns out the engine in the hemtt is supported at the front by a motor mount, and is then also supported by mounts that bolt to the sides of the transmission on either side of the bellhousing. The entire engine/transmission sits on a tripod mount arrangement, and then the remaining length of the transmission cantilevers out from the mounts. This causes all that weight to hang from the bellhousing area. The county shop began installing adjustable flex-mounts (similar to marine engine mounts) on a new crossmember directly under the tailshaft to support the transmission and they stopped having broken bellhousings... I'll add some pics of the new mount tomorrow when I get out there.

Since I have had zero luck locating a stock hemtt 18' cargo box anywhere near me, and the costs of shipping one to me seem very high I am going ahead with my plan to lengthen and install a 15' ISO drop-side 5-ton box that I picked up brand new for $500 complete with the new extruded aluminum extension rails/troopseats. We are going to add 2 more drop-sides to make it a 3-door per side arrangement. What the ****, you do what you have to. As soon as it's installed I will probably locate a brand new hemtt box right in my town for free....

dma251 · 10-25-2007, 03:12

Also figured I'd show you all a couple pics of the garage/shelter I put up to restore this hemtt in. Before I could do anything to the truck I had to have 100 yards of dirt removed from my backyard and a elaborate basalt retainingwall/rockery installed. Then they had to landscape around it and deliver 20 yards of 2-4" rock to gravel the driveway with. Only after all that was i able to set up the 40' long, 16' high, 16' wide steel/canvas shelter.

It has worked out really well so far. The cover is a 20 year lifetime 14.5 oz. cover, so it should last as long as I'll need it for. the frame ribs are on 4' spans, so it should hold a fair amount of snow before I have to start worrying. We hardly get any snow here anymore anyhow.

I installed 8 8' light fixtures along the sides, and it lights it up like a paintbooth in there. The ends roll up with a pull of a rope. It works pretty well.

I would have loved to build something more permanent, but because I am on a .25 acre lot with a septic system, there is no way I could get the permits to build anything permanent.

Boatcarpenter · 10-25-2007, 08:33

dma251, nice temp building. Would it happen to be a FarmTek? If so, how is the quality, etc.?
Thanks,
BC

dma251 · 10-25-2007, 08:41

No, it's made by Shelterlogic. I think it's pretty solid. We had some 60-70 mph winds last week, and it didn't flap or act any different then a steel pole type building. It's definitely a compromise, but I think it will work very well for what I need. There is plenty of room around the truck for working on it. I have about 4' on each side of the truck, and 6-7' on the end. It's do.

spicergear · 10-25-2007, 08:41

I was just looking at an Allison 750 CLBT transmission. They appear to have four mounts on them, not the at the bell. A LOT of trucks are mounted in that three mount set up-

JDToumanian · 10-25-2007, 15:08

Wow, that garage unit is just what I need. Standard ShelterLogic garages use the 9 oz fabric covers... how much extra did it cost you to get that heavy duty fabric? What model is that? I've looked at carport / shelter units and figured they wouldn't last... between the desert heat, sun and wind it would be shreds in just a few years... but with heavy duty fabric and a good warranty? Hmmm....

Jon

OSO · 10-31-2007, 01:51

dma251 that shop is that's Sid's on the Whittman rd out in OSO? Just wondering Nice pics.

dma251 · 10-31-2007, 05:02

Yup. Syd does great work and he's a consummate perfectionist. He reproduced my front fenders from the rumpled up old ones and they are BEAUTIFUL.

I just got the driveshaft back from the largest and most well-respected driveshaft shop in the area, Driveshafts Northwest after having them balance it. Syd had done the shortening of it at his shop himself. When I picked it up at the driveshaft shop they asked me what shop did the shortening, it was some of the best work they'd seen outside their own shop.

That says something to me.

Next Monday I am picking up a 5 foot long section of ISO 5-ton cargo bed that we will graft onto the new ISO box I already have to make a complete 18' HEMTT bed.

Work continues..... I'll post more pics when I have something worth looking at.

M1075 · 10-31-2007, 11:06

Keep up the good work. Your finished product is going to be awesome. Not many members in the HEMTT club afterall.

Jones · 10-31-2007, 11:11

Great progress!! My hat's off to you.