Spicer auxiliary box in my M820

[hethead]

I have an M820 chassis cab (so the extra long wheelbase) that I am modifying into a tractor using a '53 International Metro van body as the cab. I'm sliding the tandem all the way to the back of the rails, moving the Rockwell transfercase back and (I'm thinking atm) I'll add a Spicer 7041 4-speed auxiliary behind the 5 speed driving the transfer case. I'll end up with a 2 piece drive shaft for the front axle and add a support bearing/crossmember where the transferase currently is.

This setup will give me an overdrive 3rd and double under drive plus under drive 4th to fill in all the gaps. I see that 5 speed Spicer mains and 4 speed Spicer auxiliaries behind 855 Cummins wee a thing and the 7041s seem to go for a pretty reasonable price. $800-1200. I like twin stick shifting and have 3 gearboxes in my diesel Land Rover already (if you count the transfer) so I see this as a plus. A good ratio for every speed and not much cost.

Any experienced people with strong aversions to this gearbox would be appreciated, but I'm not seeing a problem. This is already gonna be a very modified rig.

 

[msgjd]

I used to enjoy the non-boredom of twin-sticks and triples when younger , but if I were relocating everything as you are, I would just drop in an 18sp roadranger and call it a day .. To each his own and good luck . As far as the 7041 goes, I have not known of any problems with those other than they get stuck in gear or caught in 2 gear ranges if shifted too quickly, The problem is multiplied as the shifter contact points wear out. I have two farm tractors with this same problem. The other thing you may have already explored is the HP/Torque rating of that gearbox. In my experience, I have only seen the 7041 in trucks less than 250hp

 

[hethead]

I used to enjoy the non-boredom of twin-sticks and triples when younger , but if I were relocating everything as you are, I would just drop in an 18sp roadranger and call it a day .. To each his own and good luck . As far as the 7041 goes, I have not known of any problems with those other than they get stuck in gear or caught in 2 gear ranges if shifted too quickly, The problem is multiplied as the shifter contact points wear out. I have two farm tractors with this same problem. The other thing you may have already explored is the HP/Torque rating of that gearbox. In my experience, I have only seen the 7041 in trucks less than 250hp

Thanks! You're probably right about the 18 speed. I may end up wishing I went that route in the end. Thanks for the input on the 7041. I haven't found any torque/hp specs on them (probably because it's an auxiliary so who knows what gearing someone puts between it and the engine) I'm going to run the 250 at about 300 hp and try not to be too hard on it. It will usually be running loaded, but not excessively. Shooting for around 60k gross.

 

[msgjd]

you are very welcome ... i need to clarify that the "stuck" issue with them is when the shifter parts are worn and that it becomes more frequent / troublesome with additional wear. It is apparently a good box otherwise, because they were bragged about when it came down to who's truck could pass others loaded on hills etc... There must be someone out there who can tell you a lot about the 7041. As mentioned, I had only seen them (decades ago) in smaller single-axle trucks such as chev C60 , IH Loadstar, Autocar 4T, ford F8, etc , all with gas engines .. This is not to say they weren't behind diesels or not in larger trucks. I just had not come across any around here.

 

[hethead]

you are very welcome ... i need to clarify that the "stuck" issue with them is when the shifter parts are worn and that it becomes more frequent / troublesome with additional wear. It is apparently a good box otherwise, because they were bragged about when it came down to who's truck could pass others loaded on hills etc... There must be someone out there who can tell you a lot about the 7041. As mentioned, I had only seen them (decades ago) in smaller single-axle trucks such as chev C60 , IH Loadstar, Autocar 4T, ford F8, etc , all with gas engines .. This is not to say they weren't behind diesels or not in larger trucks. I just had not come across any around here.

Thanks again for your input. I have zero experience with that box. I was mostly going off of a YouTube video I found with a Spicer 5 speed and 7041 behind a Nifty 250 on a cab over. I did read about the linkage interference when the joints get worn so I’ll try to design around that best I can when I install the auxiliary. The low cost of the 7041 is also a big draw for me. Plus, like I said I already know I like twin stick shifting!

 

[msgjd]

I was mostly going off of a YouTube video I found with a Spicer 5 speed and 7041 behind a Nifty 250 on a cab over.

was that cab-over original with that box? I have to wonder if it's being used to haul any considerable weight or if it's just a play toy. Did you try to contact the poster of the video for info? sometimes they will respond to your questions in the comments section on the video

 

[topo]

I have Put some miles on Ford single axle gas engine with a 5x4 transmissions it had a power tower on the 7041 to run the winch and a Mack with a 290 Cummins and 5x4 also had a power tower for the winch . The power tower mounted on the top held up so much better then the 8 bolt PTO both where rated for the same torque .

 

[hethead]

was that cab-over original with that box? I have to wonder if it's being used to haul any considerable weight or if it's just a play toy. Did you try to contact the poster of the video for info? sometimes they will respond to your questions in the comments section on the video

I don't know if it was pulling any real weight. It was an old video too, but it did get me looking around more and seeing that yeah, I usually see them in single axle trucks, sometimes gas or small diesel, but not a lot of the bigger class 8 trucks. hmmm. It's looks like I'm running across more Spicer 8341's in the Peterbilts etc. Maybe I should start looking for one of those near me. The ones I've found are far away and heavy.

 

[hethead]

I have Put some miles on Ford single axle gas engine with a 5x4 transmissions it had a power tower on the 7041 to run the winch and a Mack with a 290 Cummins and 5x4 also had a power tower for the winch . The power tower mounted on the top held up so much better then the 8 bolt PTO both where rated for the same torque .

Thanks Topo! Did the Mack with the 290 also have a 7041? If so, I'd be curious what your GVWR or GCWR was. My Cummins will be tuned close to that and be running around 60k I'm expecting.

 

[topo]

The Mack Truck with the 290 Cummins did have the 7041 ( 2 shafts ) at the time other trucks had the Spicer 4 speed with the 3 shafts . mostly pulled a 3 axle lowboy hauling oil field equipment 80.000 plus + I don't remember any problems with the running gear or truck .

 

[hethead]

The Mack Truck with the 290 Cummins did have the 7041 ( 2 shafts ) at the time other trucks had the Spicer 4 speed with the 3 shafts . mostly pulled a 3 axle lowboy hauling oil field equipment 80.000 plus + I don't remember any problems with the running gear or truck .

Thanks Topo! I appreciate you responding and I appreciate hearing from someone with experience with one. That was exactly what I was hoping to hear. I'm gonna pull the trigger on a 7041. They seem a little easier to find, a little cheaper and if it held up to what you used it for it'll be more than capable for the playing around I plan on doing. Plus it's a little smaller than the 3 shaft, so it should be easier to fit.

 

[Jbulach]

I think a good place to start is to see what series yokes that you can get, or they have on them.

 

[hethead]

I think a good place to start is to see what series yokes that you can get, or they have on them.

Just looking at pictures, it looks like the 8341 has yokes close in size (or the same as) what's on the truck now. It also looks like the 7041 has a different size yolk on the input vs the output. Smaller on the input I believe. I expect I'll have to do some machining to get things to match up... Be nice to get my hands on one of these and be able to do some measuring. I haven't had to change any u-joints on the 5 ton yet so I don't even know what size they are. Just big!

 

[hethead]

I finally pulled the trigger on a 7041. I might be misinformed, but the trans has to have an input torque rating of some kind. What I've found is that in the case of the Spicer auxiliaries, the first two numbers (x 100) is the rated input torque. So the 7041 would be rated for 7000 lb ft. My main gear box multiplies torque around 6 times in 1st gear, so I if tune the 250 to about 300 hp/1000 lb ft..... x 6... I'd be at 6000 lb ft coming out of the main and into the auxiliary.

So a 7000 series auxiliary is right in the ballpark. Especially for a truck that I'll be running 60,000 gross at the heaviest.

 

[neomadic]

I considered a brownie in my deuce bus, but ended up with a Fuller six speed.

I'd love to see a build thread on yours. Coming up with a zero torsion subframe to mount the bus body on mine was quite a challenge.

 

[hethead]

I considered a brownie in my deuce bus, but ended up with a Fuller six speed.

I'd love to see a build thread on yours. Coming up with a zero torsion subframe to mount the bus body on mine was quite a challenge.

I’ll post everything as I do it. Maybe in lots of threads though, because it’s gonna drag out for a lot of years. I just finished building a 57 ft. trailer to pull behind the 30 ft. 5 ton, so I’ve been busy with that. It’s important to always be doing something stupid.

 

[gimpyrobb]

Sorry I'm late to the discussion, for a simple O.D. you could used a Tcase from a 939 series 5ton. Same basic mounts but the Tcase is O.D. in high range. Less custom to engineer imho.

 

[hethead]

Sorry I'm late to the discussion, for a simple O.D. you could used a Tcase from a 939 series 5ton. Same basic mounts but the Tcase is O.D. in high range. Less custom to engineer imho.

I'm actually pretty happy with the final gearing. The 5 speed, being an overdrive, with the 395's I sit at around 60 mph at 2200. I mainly want the auxiliary box so I can have two more gears (3 over, 4 under) between 3rd and 4th. I also like shifting twin sticks. And I also like the double under for crawling' round real slow like.

 

[topo]

When using a 5x4 and starting out on a hill or starting out to get up a hill on to the roadway when using 1 gear in the main box and with 2100 RPM and you try to shift the brownie is almost imposable the truck will be at a stop when you push the clutch then you will be trying to take off in a to high of a gear gears in the brownie are very close together .

I found it was much better to put the brownie in 1 ( deep under ) and use 1 or 2 in the main box to get started and then shift up in the main box till 4 or 5 the truck is moving slowly but it won't be so slow that it will stop then you push the clutch to get the brownie out of 1 and continue moving in a better gear ,

The gears in the 5 speed main box being spaced farther apart will give you more time to shift and smoother gain of speed .

The 5x4 is a great set up

 

[hethead]

When using a 5x4 and starting out on a hill or starting out to get up a hill on to the roadway when using 1 gear in the main box and with 2100 RPM and you try to shift the brownie is almost imposable the truck will be at a stop when you push the clutch then you will be trying to take off in a to high of a gear gears in the brownie are very close together .

I found it was much better to put the brownie in 1 ( deep under ) and use 1 or 2 in the main box to get started and then shift up in the main box till 4 or 5 the truck is moving slowly but it won't be so slow that it will stop then you push the clutch to get the brownie out of 1 and continue moving in a better gear ,

The gears in the 5 speed main box being spaced farther apart will give you more time to shift and smoother gain of speed .

The 5x4 is a great set up

Thanks! I’ll definitely be learning a lot with this set up. All I know so far is to avoid a low gear in the main while running high in the auxiliary. Better to multiply torque with the auxiliary.