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Yea, pretty costly considering my 3-speed aux. box cost me around $300, and is in mint shape. Bit its also heavier and takes up a bit more room. I don't consider anything over $2000 in the "cheap" bracket. If it was $500, maybe even under $1000, then it would be something to consider. I like people who look for ways to do it themselves and save some money, and come up with something new.

Jim
 

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like said befor guys are running two trannys in line, but mostly for gear reductin on the trail (have a friend who is running one now). Everything would have to be perfect to keep vibrations down when using it as an overdrive. HMMMMMMM... turning arround a devorced 205 to make an overdrive, and you could even switch it back to 1:1 by puting it in high gear :rasta: :rasta: bounce
I have not messed with divorced transfer cases. Would this work to turn it around? Since they are devorced they do not need the bearing support from the transmission. Would the gears "care" if they were spun from the other end? If they are helical gears they would be turning reverse of the intended bevel. Does that matter? Could this be shifted on the fly? It would be worthless to me if I had to put it in OD before moving.
My conversion is a 1/2 ton with 2wd. I am using a P30 setup with the 400 turbo auto trans. The conversion isn't done yet (Im slow). I currently have 2.73 rear axle gears. This was an attempt to get a good cruising speed at reasonable engine rpm. I am concerned that the motor won't be able to pull the big gears and will really be a dog when it upshifts. With a overdrive added after the transmission I could lower the rear gear and still be able to shift to OD for the highway. I have been considering pulling a 14' enclosed trailer behind the truck when finished. Think it will pull it with this gearing? I doubt it. If it doesn't I will just have to tow with my gas burner truck.

Thanks everyone!
 

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Some t-cases wouldn't care, especially gear driven ones, but the gearing would be way too much. Even using extreme gearing it wouldn't work well. About the highest geared t-case I know of is around 2:1. Using 5.38 gears as an example, with a 4-speed trans (1:1 direct drive in high), and 31" tall tires, RPMs at 60 mph without the t-case would be 3499. By engaging a 1:2 OD, your RPMs at 60 would be 1750. So if you had 5.38 gears it doesn't come out too bad. Except for one thing most people don't think about- running 5.38 gears at 60 mph would overheat the gears in a hurry. Your axle would get quite hot.

Using a more realistic gear, lets try 4.11 at 70 mph. You would be turning 3118 RPMs in direct drive, or 1559 RPMs in OD. Thats too low of RPM to tow with, even on flat ground. If it was a lightweight commuter vehicle it might work. But you would never get it to shift while moving, so you would need to plan in advance.

I think good gears for what you are going to be doing would be 3.54. That would put you at 2500 RPMs at 65mph. A little high, but workable for towing. It sure wouldn't work for economy though. I would seriously consider a manual trans, or at least an auto with OD and a lockup torque converter. Then you could use 3.73 gears and turn around 1900 RPMs at 65mph, and have a steeper gear for getting moving.

Jim
 

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Just for info, I saw a really great bus conversion almost 40 years ago. It was turned into an RV and he had some kind of diesel driving through a pair of s speed Torqueflite trannys, 9 speeds forward, manual shift or auto shift. Worked great.
 

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Heres a few pics of the U.S. Gear divorced overdrive I will be installing in my 72 K-30 when I do the 4bt swap. This will be going behind a TH475 and should really help out with my 4.10 gears. These pics are of when it was behind a 4 speed in another 72 K-20



 

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Torque questions with two trans

I'm looking at powering a 62 foot home-built boat using a tractor engine. (There's a lot of diesel tractor engines around here, in the heart of the Prairies.) Engines in boats work hard most of the time. To avoid having to go with a very big, very heavy engine, could I multiply the torque at the prop by stepping down the engine RPM's through two transmissions? Prop should turn around 600 RMP. Revs would be steady, seldom varying, for several days on end, perhaps 30 days of the year.
 

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you would be best off with a marine transmission, and it will probably be either direct or about 2 or 3 to one reduction, all depends on the engine and the boat and the prop.

lots to figure out to make it work well, best talk to some boat people on that one.
 

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I've talked to a few. Some support, some don't. Anybody who is in the business of selling marine equipment says, "Horrible, you'll all burn up!" People who have already done it say, "No problem. Just make sure the engine powerband and prop speed are compatible." And, yes, I know about the thrust bearings, and there will be no problem in that area.
So, back to the question.
Would running two transmissions in series allow me to keep the engine at its optimum torque, while swinging the prop at around 600 RPM? What problems... associated with the concept, not the marine aspects... might arise?
 

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Very nice install and mighty fine craftsmanship, Chevyholic!

On that diesel boat engine you might want to consider an under-drive matched to a strong transmission to get your ratio. Been there on the marine $$$ thing but you can get some good solid info from a good prop shop. That's their business and many factors involved, such as wetted surface, hull shape, hull cruising speed related to prop diameter & pitch. Thing with a good prop shop is they WANT to help you make it work! not only that, but they know how!
 

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JimmieD - Yeah, the prop guys aren't concerned too much with how the power gets to the prop, and they're always a great source of information and assistance.
The 'underdrive' that you mention, would that be like another transmission? Also, would that be another 'marine' item? I mean, if there's a premium to be paid because it's got special name, then would it be worth paying it?
Transmissions are realtively cheap, and they can be repaired almost anywhere.
 

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No, the item is a standard auxiliary transmission used in some applications. It's near identical to an overdrive turned around backwards. In many cases you can do just that. However an under drive may have a much wider ratio change and be more desireable, and gear design and thrust washers etc are meant to go in the direction you're going. That last part doesn't matter much in some cases.

Some Brownwell auxiliaries, called Brownies, common of heavy duty trucks, can be installed in either direction. Some Brownies have 3 speeds available, maybe getting closer to your desired ratio change.

Check around agricultural equipment or heavy duty truck service companies, either online or locally, for some applications that use under drives. Bob S and several others here may have more info, maybe post a new thread for under drive info?

I know from my boat years that with a 62 footer you're talking some serious bluewater. Torque loads on the prop in heavy seas are tremendous, so I agree: NO FOOLING AROUND HERE! The heavy-duty semi truck parts offer the beef you need, and probably cheap-er, but not cheap, than 'Marine' items.
 

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Thanks, JimmieD. I'll start checking around here, see what I can come up with. With regard to the boating, I don't anticipate (hope like heck to avoid) too much heavy weather. And, I agree. On the water in a blow is no place to find out that you've cut one too many corners. I will be taking things slow and easy, and double checking every assumption and installation. Thanks for the help.
 

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Chevyholic -------Pictures in post # 26 show nice fabrication but the joints in the jackshaft are supposed to be in the same plane .Yours is 90 degrees off and is likely to cause a vibration .
I've been running a 5831 Spicer auxilliary behind a 3152 Spicer main [with short 4th] in my '70 GMC pickup for 25 years now .
 

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Tire traction is ALWAYS the limiting factor. If he's going to run super-sticky 44" tires, I would say you are right. Otherwise, all that torque is going to get wasted in tire slippage long before it does any damage.

Got to disagree with that notion. The input of a transmission is only made to handle flywheel torque, but if you were to take that and jack it up 6 and a half times, (T18 in low range as an example), then you are talking about in excess of 1800 lbs ft driving into the input of the second tranny. it is possible that the tires might spin, but if you are on decent tires on asphalt, and you hit it hard, it is going to pop the input of the second tranny with no trouble whatsoever. It's been tried, and there are a few threads on the subject, and in every case that I am aware of, it has been broken. A light duty transmission just isn't made to handle the type of torque that is possible.
 

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Your driveshaft is 90 degrees out of phase-any vibration?
I agree it's probably out of phase 90 degrees.
But, there are some times when that is the correct orientation, as explained in the Spicer Driveshaft installation guide on page 14 and 13.
Check the actual universal joint operating angle at the rear of the first coupling shaft. If it is less than 1º and the transmission
universal joint operating angle is greater than 1.5º, rotate the end yoke at the center bearing position so that the ears of the yoke
are 90º to the ears of the tube yoke on the transmission end of the coupling shaft. (See Fig. 10) As an alternative, rotate the slip
yoke on the driveshaft 90º if the slip spline has 16 teeth.
I recommend you read the whole manual and go back and double check and adjust your drivelines as necessary to be "by the book"

Many of you will also find this manual helpful in designing driveshafts.

Grigg
 
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I ran two 3 speed transmissions in a 73 Chevy with a 454. The second transmission was in backwards and I left it in 3rd gear which would be direct drive. At 55 MPH I shifted the 2nd tranny to 2nd gear and the speedometer dropped to 32MPH and when I shifted the 2nd tranny to first gear the speedometer dropped to 19MPH. It did not work very well because both 1st and 2nd gear were too much overdrive and you couldn't get any acceleration at 55 MPH and the low RPM plus the engine would get hot. It may have worked a little better if you were running 200 to 300 MPH where you had some RPM and torque. I expect the tires would fly apart at that speed. I figured if you could overcome the wind resistance it would go 375 MPH.
 

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we call these machines "jitneys" we use them in the woods i've had 4 speed mounted to 4 speeds , 4 speeds mounted to 3 speed autos thats best and easiest way cause you can only run one clutch a toyota 22r with a toyota 5 speed and a chev 3 speed will haul over a cord of wood easily..mounted on a 2 ton chasis at that, so a 4 bt yall could have fun with
I think it's a regional thing, where I grew up they're called 'doodlebugs'. The best one I remember seeing was a Model A frame and fenderless front clip with a Ford 300 six cyl. through two 4-speed truck trannys and rear end driving 24 inch truck wheels and tires. With tire chains on there wasn't much that could bog it down.
 
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