The Stovebolt Site Forums The Shop Area Engine Shop Think this will work?

5.13:1 ratio rear end and a SM420 = 45-50 mph top speed. :mad: I don't want to set any land speed records (especially not carrying a load) but would love to be able to travel interstate (empty) at 65-70.

I found a Spicer auxiliary transmission (7041... its a biggee ). Made for 250 hp gasser 5 ton road tractor. Lo-Lo, Lo, Direct, OD (2.3, 1.2, 1, .8). What would keep a fella from putting one of these in backwards?

In reverse... lets see now... Lo = 1.2 that's the same. Direct is the same. OD = 0.8 that's the same. O-OD = 0.45... hmmmmm. Maybe that one should be called warp drive. Cruising interstate at 1500-2000 rpm sounds intriguing. That would give me a (theoretical) top speed of 170 mph . Fastest bolt on the planet?

So other than the fact that this thing weighs 300+ lbs, and I'll have to figure out how to shoehorn it under the truck, and I'll have to get a new axle made... Will this work? Do you think a stock 235 engine can push a 58 1 ton at 70 mph at 1500ish rpm?

P.S. I have no intention of traveling 170 mph even down hill with a wind to my back.

Capable of pushing it 70 mph.Yep. Capable of stopping with stock brakes. A little more skeptical.

Stock rear brakes = 14" drum, front are 12" (I think) with hydrovac assist. It was made to stop up to 9600 lbs... in an acceptable distance. Course what's acceptable today and acceptable 50 years ago are different things.

I did this on a 46 1.5 ton chevy with about the same ratios as you said. Works great with a top speed some what over what the brakes will handle some where around 80. The aux that i used came with the brackets from the big truck almost a bolt in job, did have to build two new drive safts and twin stick shifters. I didn't haveto change the rear end.

I dunno, sounds like a lot of work to me. You might be happier changing the rear gear or maybe looking into a Ranger or Gear Venders overdrive. Running that aux. trans backward may not give the performance that you want. Plus you will have all the extra weight added. Not saying that it can't be done, the theory is sound. You will be making the trans runnung in a direction it wasn't designed for, you could end up damaging it or the truck.

running it backwards would sure confuse the hell out of your speedometer.

I found a small overdrive after looking for more than a year to put on my 59 1 ton and its a .75 over. Looks to bolt right up to my sm420. The model number looks to be a 2091 and its just a direct and over. All I have is the box and I'll have to make my own shift lever. It has no govener or solinoid. Very basic for an overdrive.

As for brakes - www.praisedynobrake.com has kevlar brake shoes for your truck (I have them on mine) and that with new drums up front will make your truck stop very well. I didn't want to loose my 1 ton rating or make a lot of mods up front. This was the easiest and cheapest solution even if the brake shoes were a bit pricey. My front drums were also out of service limits, and I still had them work very well.

I say go for it!

You can also get a 4.10 gear set that plugs into your rear pumpkin very easily to get speed up and you can also put on big big tires which also help. I did both of those things first. The OD will go on when I get did with my 72 project.

I think a 70 series spicer is to big for a 1 ton.
I would look for a 5831 or a 60 series is not much bigger.
I am not sure about using one backwards, I'll have to think about that. As I remember they have straight cut gears, so what's to hurt it?
They run backwards part of the time even when put in normaly..

GMC, Dodge, and International have all used the Dana/Spicer 70 in 1 ton applications. Some of the Dodges and Internationals even used them on the front for 4x4s. You may be thinking of the Dana 80, which is a 1 1/2 ton axle, though it does see some use in Chevy/GMC 3500HD models.
The 70 has the same 10 1/2" ring gear as the 14 bolt GM full float diff. The 60 is a 9 3/4".

That's a one ton, if I'm remembering my Gear Ratios right.

One tons and three quater tons used the same ring and pinion setups from 1946-1972, if you wanted to do something a touch easier...

Any stock 3/4 ton will have 4.55, 4.11, or 3.90 gears, depending on the year and the options. The latter two became available in the late fifites or early sixties. There used to be a kit that you could get to change out your gearing to 3.90 gears that used the 68-72 style diff, but they've stopped making them.

You really only need the carrier end of the diff, but if you wanna pull the entire pumpkin, that'd work, too.

I put a Saginaw overdrive unit in a '54 'bolt, moved the 2000 RPM cruise from 55 to 75. The problem is the brakes just don't have a lot of stopping power, so be careful if you do that. The transmission with o.d was exactly the same length as the 3 speed so drive shaft fit perfect, shift linkage and all. I happened to have a few o.d's around so it was a no cost item for me, but I think a 3 sp. w/o.d. is available in older wrecking yards for $50 to $100. I really think this is the most practical solution to raising the freeway cruise speed, and lowers the noise from the drive train too.

Thanks All.

ttodd - The brackets do look like a bolt in job. At most it may need about 1/8" shaved off each side to fit. It'll come with the shifter / linkage and the drive shafts. Some shortening of shafts will be necessary.

LongBox - Yahh.. about the running backwards. I don't see why it won't work. I probably will run it forwards, and just get the 0.8 over (and 1.2 and 2.3 under). Those on the market overdrives are expensive.

Arnswine - I want some over and under gears. I'm still looking for a 4.1 rear gear (or 3.9) but the only ones I find people want too much for ($300!). I'll keep looking. I have time. I already have 8 R 19.5 wheels on it. Don't think I can find anything taller. Thanks for the link to the brake shop. I'll probably use that. My drums are clean inside (no grooves!) and look to not be turned at all. Those kevlar brakes with the hydrovac should supply good stoppin power.

All - My goal is to start pulling the Spicer 7041 this weekend. Yah it's too big, but my truck can handle the weight. I'll install it in normal direction. I'll be looking for a 4.1 rear end (carrier). Even with the lower gearing rear and the tall tires, in Lo Lo and 1'st gear, I'll be traveling 5 mph @ 3000 rpm. On the other hand, in OD and 4'th, I'll be traveling 74 mph at 3000 rpm.

I DO NOT intend to ever drive 74 mph in this truck. (that's illegal in this state and foolish to boot). I DO NOT intend to drive 70 mph with a full load or trailer on the back. I would like to be able to drive the highway at 65 mph (with an empty bed) and not have the engine screaming at 3500 rpm. I can take it easy while carrying a load, and probably not exceed 50.

I can remember my dad talking about his hotrod buddies putting an extra tranny in their cars. They would mount it backward, hooked to the stock tranny. It gave them lots of gears and a tall highway gear. I was too young to care about how it was done, just remember him talking about it.