Patracy's "SEMTT"

[patracy]

I've been watching yours and Soni's builds and am amazed at the ingenuity and fab skills both you guys have. I do have an issue/concern, this is also a concern I had when I drove HEMMT's in the Army. They had no mechanical linkage from the steering wheel to the steer axles, just hydraulics. Do you have any failsafe mechanism in case there is a shaft or joint failure? I remember years ago one of the commercial rigs I drove (no power steering) had a spring system that would keep the truck from pulling hard to the right or left if you had a blowout on the steering axle. Not criticizing, just wondering.

Our setups are both mechanically linked to the steering box. A joint failure would result in serious problems. My setup has one less joint than Soni's setup. However I do plan on making safety loops to keep all the shafts in place in the event of a failure. When it's all setup, there should only be enough movement that say a joint completely broke, the yokes would still hit each other and allow for "sloppy" steering. You have to consider however all these joints and gear boxes are only subject to human power. For years automotive manufactures used "rag joints" on steering. That setup worries me more. (CUCV's have them)

 

[Stalwart]

. . . a concern I had when I drove HEMMT's in the Army. They had no mechanical linkage from the steering wheel to the steer axles, just hydraulics.

What you talking about Willis? HEMTT's do indeed have a mechanical linkage, I just walked out to the garage and turned the steering wheel on my truck and the tires turned a bit. Is it stiff, YUP, but you do have some control without hydraulics.

 

[PETE BALLARD]

i've been watching yours and soni's builds and am amazed at the ingenuity and fab skills both you guys have. I do have an issue/concern, this is also a concern i had when i drove hemmt's in the army. They had no mechanical linkage from the steering wheel to the steer axles, just hydraulics. Do you have any failsafe mechanism in case there is a shaft or joint failure? I remember years ago one of the commercial rigs i drove (no power steering) had a spring system that would keep the truck from pulling hard to the right or left if you had a blowout on the steering axle. Not criticizing, just wondering.

i think to have a vehicle dot certified it must have a hard wired steering system, steering systems that are all hydraulic are not for on highway applications.

 

[patracy]

i think to have a vehicle dot certified it must have a hard wired steering system, steering systems that are all hydraulic are not for on highway applications.

I can't speak to the HEMTT as I don't own one, so I can't say. However Soni and my trucks are mechanically linked from the steering wheel to the road wheel.

I'm about beat today. My Sister and Brother-in-law have came down to stay so yesterday and today were the first days I've seen my new nephew. (first one I've had not counting the ones I gained instantly being married.) Anyhow, I did manage to get the radiator holes plugged. I also tore down the parallel box and pressed the 931 steering column shaft into it and welded it on. I've reassembled the parallel box as well. Everything is just laying in place for now. I still need the 1/4" keyway and a few bolts before I start any further. I'll pick that up tomorrow. My other parts are due in as well. So maybe I'll get the throttle knocked out as well.

I've been staring at the brake system. I think I've figured out five of the MK48 air ports already. Hopefully that'll be a little easier than I'm worrying over. (I've just got to admit, the 931 is the first air braked truck I've ever dealt with.) There's a truck repair shop nearby, I plan on stopping by there this week to see if I can purchase some air hose.

Well, I guess I'm off to shop for more parts. Need to find a cable to actuate the t-case.

 

[patracy]

I believe I've found the cable needed for the t-case. Awaiting an email back and hopefully it'll be on the way!

 

[Nonotagain]

Try these guys. http://www.easternmarine.com/Air-Brake-Tubing-Bulk-Lengths/

I purchase a fair amount of stuff from them.

 

[wreckerman893]

What you talking about Willis? HEMTT's do indeed have a mechanical linkage, I just walked out to the garage and turned the steering wheel on my truck and the tires turned a bit. Is it stiff, YUP, but you do have some control without hydraulics.

It is possible to turn a HEMMT without the engine running but I think it's due to the fluid pressure in the system. We routinely dragged them around the Motor Pool in Korea when we had some that were deadlined that had to be relocated. It's entirely possible I'm wrong but I think if you follow all the lines you will see that the draglinks are moved by hydraulic pressure and not by mechanical linkages.....again I could be wrong but I put a lot of miles on HEMMT's in Korea.

 

[Stalwart]

There isn't any remaining fluid pressure in the system, the truck hasn't run for 5 months. I have on occasion followed all the linkages and I ALMOST responded without going out to the truck. Since it was you, I went out to the garage and did it anyway. There IS a mechanical connection in MY HEMTT.

 

[patracy]

Well I started fabbing the throttle cable. I've got to pick up some threaded rod to make it work. I also got started on the driveshaft for the steering. But I should have filed it slowly as I took off too much metal for me to feel good about it with the keyway. I'm just going to drop it off at a driveshaft shop tomorrow on the way into work and have them change the yoke to the correct end. I also started tracing out the air lines. I'm just going to replumb a lot of stuff in the MK48 cab due to it's design. Stinks I only got this far, I'm not going to be able to work on it for the next two days. MAYBE I'll get the throttle built tomorrow. I also cut a few pieces of steel for the parallel box too for prelim work.

 

[camoyj7]

Are you planning on adding any more supports to the frame extensions. I was just worried with not having cross members on the extensions they will flex a lot. I know you can't block off flow to the radiator maybe some x braces on the bottom and plates on the sides. Wouldn't want the front mount to fail and run yourself over.

 

[patracy]

Are you planning on adding any more supports to the frame extensions. I was just worried with not having cross members on the extensions they will flex a lot. I know you can't block off flow to the radiator maybe some x braces on the bottom and plates on the sides. Wouldn't want the front mount to fail and run yourself over.

I haven't build the front bumper yet. That will tie in the front frame rails on the bottom. But X braces on the bottom aren't a bad idea. The rear section of the cab has mounts tied into the original frame. Also the cabs are actually not just sheetmetal, there's a light tube "skeleton" that all the sheetmetal is riveted to on the MK48 cab. Back behind the vertical bar you drew is a 2" wide 3/8" thick bar stock that along with the angled front bars help reduce the flex at the point you're worried about.

Let's say for arguments sake, my brackets totally fail. Or let's even say they disappear. The cab would drop only a few inches up front before the cab would straddle the frame rails. The only way what you say could happen is if the front bracket catastrophically failed, along with the frame extensions sheering from the frame, along with the rear mounts sheering off the frame as well.

The frame extensions are meant to also bear the weight of the entire vehicle while being flat towed. And given the fact there's like 30+ grade 8 bolts holding it on, something very very very bad would have to happen to cause any issue.

 

[patracy]

Oh and what I'm thinking on the front bumper is 2x6" 1/4" wall rec tubing to form a "bumper". I'll recess some tubing into the holes I'll make for the shackle mounts. I'm also planning on making a cut in the center of it to help with airflow. Like about 3" of it at least. Kind of a \____/ shape into it where the "radiator" would be. The tubing will extend out at the sides of the cab. Then four at least 1/2" plate bar stock to extend upwards. Along with 2x2" 1/4" wall tubing horizontally to tie in the vertical runners horizontally. I know Soni used some thick steel for his bumper. But since I have more weight limit to contend with, I'm going to make a tough skeleton bumper and just use sheetmetal to cover it. Hopefully it'll help save some weight, but still be plenty strong. Think kind of one of those Australian semi truck cattle bumpers, only with a flat skin on the outside to make it look more like the MK48/HEMTT style bumper.

 

[patracy]

Quick update, no threaded rod out there or joining nuts that match the fine thread 5/16-28. So I picked up a few crown nuts and bolts. I'll just make something that will work instead. Also dropped the driveshaft for the steering off at the shop on the way into work this AM. They had a yoke in hand. So hopefully that'll get knocked out today. Also picked up more hardware I needed for the throttle. There's not a throttle stop on the linkage of the PT pump, so I'm going to have to build one of those as well. (Thinking KISS, a bolt with two nuts welded to a bracket to work as a stop.)

I'm worried that I won't have the SEMTT ready for Zout's due to all these road blocks I've hit. Hopefully the air system replumb will go better.

 

[wreckerman893]

I haven't build the front bumper yet.

My CRS and AHAD is working overtime......did I ask you if you were interested in one of the HETT bumpers I have? I can bring one to Zout's if you are.

 

[patracy]

Not a lot to report today. But the stub shaft has had the correct yoke installed and welded. Also picked up some hardware I needed for the throttle. I've got all the parts bolted together and have things dangling. Just ran out of daylight (and I've gotta get up early in the AM). I've changed my mind about the steering column shaft bearing/rubber. It will allow too much flex I think. So tomorrow if time allows I'll get everything finalized on alignment and weld in the tabs. Also I'm going to build a small mount for the front of the shaft for the pillow bearing I have.

 

[Stalwart]

Looks to be coming along nicely, and I thought a HEMTT had a lot of shafts, bearings and u-joints in the steering. Looks pretty tidy and as simple as possible. Not that forward control is simple at all, especially from scratch. Saying that I need to go back and look at Jones Baby-HEMTT build and compare.

 

[patracy]

Well I've got the steering mounted to the frame. I need to make a few brackets to reinforce things, but it steers correctly! Also trying to decide on what type of lube I'm going to run in the parallel box. Unfortunately I found out while I had the box disassembled, that the gears are just square cut. I'm thinking 00 grease from the local lawn mower shop. It's basically grease that will flow. My thoughts are that it will help "take up" and slack.

Weather is supposed to be bad here tomorrow so I doubt I'll get anything done. Friday is supposed to be nice though. Maybe I'll be able to make the brackets I need tomorrow inside my shop. I need to get this steering wrapped up!

Also have the cable for the t-case on the way as well.

 

[wreckerman893]

Here is the bumper info....appearantly you can't post pics on PM's.

 

[patracy]

The weather is about to get bad here. But the steering is done and braced. I've got the brake and throttle pedals out. I'm ripping out all that MK48 plumbing. It's a total mess that wouldn't work with the 931 system. Ugh this is going to be "fun".

 

[patracy]

Got the dash all apart. (well for the most part) I still need to remove the heater box. Got the treadle valve plumbed in. Bought $200+ worth of hose and fittings and ended up missing a few fittings I'll need. I'm a little puzzled by the 931's plumbing verses the MK48 cab. Most everything in the 931's vent drains back into the air system. Where as everything in the MK48 vents to atmosphere. To KISS it, I'm going to try to go with MK48 route and vent everything to atmosphere instead.