I know there are many very knowledgeable people on this site and would like to pick your brains on adding an auxiliary transmission behind the main transmission. I have found a few people that have done this, but I am having trouble finding some information. My trick has 4.10's with the, I believe, NV5600??? 6 spd. The highways in Texas are increasing the speed limit to 75 mph. I would like to keep up with traffic without running 2400 rpm, but I would also like to have the option to keep the ratios the same for pulling. So my plan is to add an auxiliary tranny with an overdrive. I have found others using is a Spicer 5831 B. The Spicer 5831 B is a three speed with under 2.35:1, direct 1:1, over .85:1. There is also a Spicer 5831 with .73 overdrive. Having this would let me step up the mph versus rpm ratio, keep my towing ability with the direct drive, and give me deeper gears for the farm. I have looked at the over/under drive units from Gear Vendors and determined I liked the auxiliary tranny better.

The Plan: Find a Spicer 5831 B. Fabricate a bracket to mount it behind the main. Fabricate drive shafts for main to auxiliary and auxiliary to dif. Bolt it all together.

Good/Bad idea? Are there any drawbacks? What do you know about this Spicer model? Where would be the best place to look for a 5831 B? How do I determine what the rpm vs mph?

Any and all contributions are appreciated. I would like to know what everyone thinks and need some help with the questions above. Thanks for the help.

 

With a 2wd, there are few drawbacks. Cost, time, and weight mostly. Otherwise it sounds like a very cool project. Those spicer boxes are very stout, and I would start looking for one in a heavy truck junk yard.

There are lots of online calculators for rpm vs gearing vs tire size vs mph you can fuss with.

Between the two, I would go with the .85 ratio OD. It is not as violent a step, and would get you the MPH you wanted.

 

Thanks jstone44720. I appreciate the info and am glad someone thought it was a legitimate idea.

 

That is exactly what I tried to do but I was not able to find one, so I went with the gear vendors. In Canada In the early 50s the GMC two tons had that trans as an option. It must have been an expensive one because I only found two and they were not for sale. I was told that there was also a small spicer two speed that was direct and could be either a underdrive or an over drive by changing the gears around or by turning the trans around. I was not able to find one of them either.
Jim O

 

I've heard of this being done on hay hauling trucks. It was said that a 4X4 transfer case was added but it was used to slow the truck to a crawl so it could be left idling, and someone can walk along side it and toss bales of hay on a trailer. I would be concerned that the cost to pull this off would be prohibitive or just not worth it in the long run, but I do see the logic in the idea.

 

Thanks for the info Jim O. I'm hoping to find one around this area. How did the GV over/under work out? Any problems?

1-2-3 It's a small world with you being from Carlos. I grew up in Navasota. The transfer case is an option I will probably go to if I cannot find a spicer for a reasonable price. I would also like the deeper gears for hay hauling and general use. Thanks guys.

 

My Gearvendors works well. There has been some bad info on this and other sites by people who never had one. like you can't use it with an exhaust brake etc. I have and ex brake and I wired it so that when in overdrive the exbrake will not engage when the gv is not in overdrive the brake works fine. They cost a lot of money and the payback is away to far down the road but it is sure nice to only have to go down half a gear on a hill instead of a whole one.The one thing I don't like is the small sump and the short oil change period. I fabricated a larger sump and now I can go a full 10,000 miles on a oil change. I have had it on the truck for a 169,000 kms or 105,000 miles. At 70 MPH in double overdrive I am turning about 1600 RPM
Jim O

 

Hey Jim O,

Curious - what is your MPG on the highways? Thanks!

 

009-I tried the spicer box with a FordF350 5 sp 7.3 AND it worked BUT the Spicer got hot/I mean Hot.
I wouldn`t recommend it.
One of those things that looked good on paper(gear wise)but failed the reality.
just my .02 from personal experience.

 

I have to say I am not sure what the milage is not towing as I have a 40 US gallon tank that runs by gravity into my factory tank and it is very rare that I haven't towed something before filling up again. I have logged every mile that I have towed my fifth wheel and it works out to 96000miles and the total milage of the truck is 174,000. If you are looking to by a gearvendors for fuel milage alone don't do it. The payout is to far down the road. however if you are looking for a nice quiet cab at 70mph it is the answer and as I said in the previous post It is nice to be able to go up and down a half a gear just by pushing a button and dipping the clutch. I did have one trip to BC. pulling my open car hauler with Miata on it one way and the empty car hauler on the way back and I got just short 22mpg and thats US gallons. Also that is across the Rocky Mtns. both ways. My truck is an 03 so it does not have a cat or egr or any of that other stuff that make us use more fuel and pollute less.
Jim O

 

sojoe, Other then running to hot for the 5831, did you like it? I have one in real nice condition and am thinking of adding it my 96 3500. I have the nv 4500 trans currently without 5th gear. Gear ratios are to far apart on this one(nv4500) anyway, adding the aux gives me plenty of gears, and no reason to fix 5th gear.

perhaps synthetic oil, or maybe even a cooler would fix the heat issues?

 

Ronnie--I think it will work for you, especially with a 5th direct. I also think the temp could be controlled with an aux cooler, especially if you could get a way to pump it through.
I have ALSO tried the Brownie thing with a 4 spd Suburban turbo 6.2 diesel--definitely not enough power to run it though.
I think you will really enjoy all the gears -great for maneuvering.
It will be an adventure for certain
Best wishes

 

Thanks, looking forward to more gears, miss my old International dump truck sometimes, 4 and 2 speed rear.

 

I knew a guy that pulled RVs from Indiana to Alberta with a 99 F--d 7.3 with a six speed manual and a spicer box behind it. He told me that when he was empty on the hiway he was in double overdrive and when he was towing he would leave the six speed in fifth and use the spicer overdrive. He felt that the OD ratio was better for pulling than the six speed . he did not mention overheating at all. When I saw him last his truck had over a million kilometers = 620,000miles.
Jim O

 

Right now I have fifth gear removed as it broke. But when it was in, it was a bit to steep for the hills where I run. The Brownie has a .85 overdrive so that should be right in line with what I need for the loads and hills I typically run.