Anyone ever run a three speed backwards behind their regular transmission for an OD?

I know there are such things as auxilliaries, but anything that had an auxilliary in my area was ground up and turned into a Toyota 20 years ago.

I know there are new auxilliary units, but I don't have $1500+ to **** away.

I can probably pick up a good 3.03 for $50, and then have to do some fabricating. What I'm worried about is running the trans backwards is strength and possible lubrication problems...

 

What? You want to use a standard 3 speed transmission to make an overdrive unit???? I can't even picture how this would work...

 

You splice behind the main trans, backwards. Instead of 1.6:1 you get .625. Hang it from a crossmember, and make up some driveshaft parts, and a shift linkage. Cable would work probably. I'm just wondering if anyone has done this?

 

2Speed,

I think it may have possibilities, but durability may be an issue.

First gear, of course, would have the greatest OD capability. Most transmissions range between 2.0 and 3.0 to 1. Therefore, reversing them would result in about about a 2/3 rds reduction. In most cases, that is way too much.

Ordinarilly, OD's result with about 1/3 reduction in final drive RPM reduction. If a reversed application of a transmission is used, one of the higher gears (2nd in a 3-speed) or (3rd in a 4-speed) could only be used in a practical manner. If the vehicle is limited to the Bonneville Salt Flats, you may be able to take advantage of the greater overdrive ratios.

The other consideration is to determine if the gears in the geartrain are rotating in the same relationship. I haven't thought this through yet to determine if they are going in opposite directions.

If going in opposite directions the thrust on the helical gears will be in the opposite directions and will put thrust in oppoite surfaces not designed to do so.

If the thrust surfaces are no problems, then it is several set of gears to produce more noise. That's why most OD's are planetary gears to keep the part count down.

The other reason for planetary gears is that several gear teeth are engaged at any particular time. Thus giving more durability in shelling off teeth.

With the reversed transmission (homemade OD), the torque multiplication has already been done in the primary transmission when in a lower gear and the teeth in the homemade OD transmission will be very vulnerable to the high torque.

Just a few thoughts.

Ken McWilliams
Dayton, OH

 

With all the OD 3, 4 and 5 spd truck trannies in the bone yards why ask for trouble?
At least up to F350 size anyway. A friend gave me a 3 and 5 spds out of 80's effies when he junked them.

Adaptors are available I believe even for Y blocks at Wilcap or Flatomatic

 

The biggest problem I see with this idea is your making the input shaft an output. With nothing to support it would surely fail quickly. Remember the input shaft is supported in the pilot bearing.

 

I have a 1952 F-2, with the 4 speed heavy duty transmission. It has the emergency brake on the back of the transmission, effectively using the driveshaft to hold the truck. With all the 3OD, 4 and 5 speeds that are so common, NONE have that arrangement in a small truck. So if I replace my transmission, I wouldn't have an emergency brake any more. Adaptors are pretty expensive also. Earlier F-2's had a handle under the dash and I assume cables back to the drums, which finding that arrangement from a donor truck would be nearly impossible. 5spd OD's from larger trucks are also quite rare.

Helical gear teeth could be an issue, but what happens when you go down hill and the engine holds you back? Isn't the pressure reversed then? Of course that's not a continuous operating situation....

I know a lot of fabrication is involved in making the supports necessary and change an input to an output. But slip joints from larger trucks can be adapted and in my F2 it has a split driveshaft with a center support bearing.

 

ECI has a disc emergency brake kit that mounts on the rear end. There's supposed to be a Ford 4 speed with O/D that was used from 1978 on trucks and vans.

 

2spd, what you say about the setup in your F2 holds also for my 54 F350 except that Ive the partial syncro 4spd and not the standard earlier crash box. Those old rears have no provision for cable operated emergency brakes.

What Angus says is correct, there are a few companies building friction style driveshaft brakes for rodders that have gone disc rears, I remember a write up a year or so ago in one of the rags.

Now, if you were to change the rear to a 9" or Dana 60 and use the complete E brake assembly from a similar wheelbase truck I would think the swap would be fairly straightforeward.

Ive looked at similar ideas since my rear is 5.14 gearing and going to a 80's era 4.10 Dana 60 is about the only option I have and still be able to overload the bed. I know they made taller gears but havent found any.
Ive also a 2 piston dump under the bed that runs off the tranny PTO and that is just another damn problem to get around. I dont want to add messy pumps and hoses under the hood pissin' fluid all over my purty new 292.

Heck, you just reminded me of something else I have to do. The friction shoe on mine is almost down to a bare metal band, got to pull a good one off one of the 4spd trannys I tossed out in the woods. Damn things keep following me home when I go engine hunting; cant even give them away.

 

Ok, so you start out for $50. Then, with all the fabricating, B.S'ing around, Mickey-Mousing this and that, THEN hoping the thing works and doesn't fry itself and/or your motor or rear end? Where's the savings there??? You'd be at or above $1500 and pissing it away on rebuilding everything your home-grown OD messed up!
Save your nickles 'til you can afford to do it right. Why risk the rest of your driveline on "chance"?
Good luck.

 

2speed,
Thinking 'outside the box' has brought a couple of possibilities.
If you are willing to bolt an entire extra tranny under your truck, what is out there? Rather than running a 3spd backwards, how about finding a manual trans that has an OD?
Say you found a 78-up Ford 4spd OD with side shift arms. This is the top loader where they turned 3rd gear into an OD. For your use all you need is 3rd and 4th gears. In other words look for a broke tranny with good 3rd and 4th for cheap. Straight through is pretty strong on this tranny, not so sure of how much torque OD could take. But it would be operating within it's designed parameters. The rest of the tranny could be gutted as long as whatever pieces are needed to plug holes and sling oil for lubrication are left. You would only be using the 3-4 shift arm.
I can't think of a cheap easy way to support the input shaft. Scenarios like whacking off a tailhousing to support the bushing, and you'd still have to come up with a yoke cut to fit the input shaft 1-1/16" by 10 spline, or a spud shaft adapter. If you were a good welder you could weld a clutch disk center hub to a yoke, then have it turned down for a home-brew spud adapter.
This sounds like it would all be do-able. Just require some good welding skills and some machining. If you'd have to farm that out, could get expensive.
Whadya think?
Brett

 

I already said why I can't/don't want to use a "modern" transmission because of my emergency brake issues. Sticking another trans is not really that hard because I already have a split drive shaft. Supporting the input shaft can easily be done for about $30 by using a support bearing setup from larger trucks with multiple driveshafts.

$1500 is the absolute CHEAPEST, USED overdrive set up I've seen, most are much more. So for like $200 and time, which is pretty much the cheapest thing there is, I can get my OD. If I didn't want to spend the time, I wouldn't be driving the truck at all. What of my original drive train would I be screwing up? How am I going to smoke my rear?

 

GO FOR IT !!!!!!
it will be fun, I built a pulling tractor out of an old oliver 88 and hooked up a big block ..... with a 4-speed that ran into th tractor tranny wich has hi and lo with like 5 speeds. there are alot of gear possibilities to play with. dont know how well it would hold up but if you used an overdrive then you would have a super granny gear also, if you mounted it backwards.

 

Here's another cheap idea for you. You could use a divorced transfercase from a 4 wheel drive truck, running backwards. Yes backwards. There is a guy around me who is running a transfercase backwards for an overdrive effect. You can check out his rig here
http://www.bc4x4.com/fv/2002/hulk/

The way I see it, it's not a bad idea.

 

I got to thinking about this idea today, which sounds simple enough and should work. I'm sure it would be great in an off-road vehicle like you showed. The problem I see is that you can't shift a transfer case from 4-low to 4-high without stopping or grinding gears. At least I haven't ever driven one you could. So that wouldn't work unless you wanted to take off in a high gear. Ok, to change the subject a little, I saw a truck in a magazine a guy built that used a transfer case to make it a twin-screw rearend like a big truck. I think it was like a old 1-ton cheby. It was a neat set-up though.