Transmission strength

Sun Dec 14, 2008 11:27 pm

I am currently in the middle of a conversion, I am going to mount a v-6 on to a 1948 farmall cub that we are currently restoring. My question is how stong is the tranny? The main reason we are building this tractor is for sled pulls, so it will see a beating. I just dont want to finish the tractor and have to tear it down because i blew the tranny up on the first pull.

Re: Transmission strength

Mon Dec 15, 2008 2:19 am

From all that I have read here, and all the advice i have gotten, It is not the tranny you need to worry about near as much as it the final drives and their housings.

Re: Transmission strength

Mon Dec 15, 2008 4:09 am

Dale has an excellent point. The castings and driveline on a Cub are designed specifically for 13 horsepower and 40 ft/lbs torque delivered at 1800 rpms from the flywheel. You'll discover most components are not robust enough to handle 120 horsepower or 130 ft/lbs torque or 4500 rpms.

Re: Transmission strength

Mon Dec 15, 2008 4:44 am

You might get a better answer here: http://gardentractorpullingtips.com/index.htm or here: http://www.midwestsupercub.net/trans_parts.htm

They run 50HP through the garden tractors and have lots of speed parts for the gearbox and rear end. Same gearbox. Trick gears, shifter forks, automotive rear end, ....You will be on your own with the final drives, but at least you will be talking the same language.

have fun.

Re: Transmission strength

Mon Dec 15, 2008 7:39 am

When I stuck the Chrysler V-6 in "Harley"(143hp), the first thing I did was buy some extra gears "just in case". I did take Harley to Bigdog's CubTug and pulled the sled, but never ran the engine hard. Just enough :D :D There's no doubt in my mind----If you "pour the coals" to the cub's components, you'll scatter something :( That long input shaft bends easy, the trans gears are small, and things aren't balanced enough for high rpms.

Let's see some pictures. What engine are you using?

Have fun with the project. You'll get alot of replies from people at shows, some good :D , some not so good :( .

Rick

Re: Transmission strength

Mon Dec 15, 2008 7:43 am

Metal fatigues when stressed. Even if 100 HP does not break the transmission immediately, that stress will rapidly age the components and failure will occur much sooner than it would at lower stress/torque levels. Expect it to be a high-maintenance machine.

Re: Transmission strength

Mon Dec 15, 2008 8:19 am

Will the Cub drive train handle a 20 HP diesel?

Larry Dotson

Re: Transmission strength

Mon Dec 15, 2008 8:36 am

Everybody knows you can't fit a diesel into a cub :( . It'd look stupid and out of place :D :D

Rick

Re: Transmission strength

Mon Dec 15, 2008 10:13 am

The cub and all the farmalls were way overbuilt. The drivetrains were especially strong. The cub drivetrain is very strong. The reason that the finals failed is mostly because of coming loose or hitching to the wrong place on the tractor to pull. as long as you hitch to the drawbar I doubt the finals will give out. All the finals I have had brake were due to coming loose or the owner was hitching to the improper place on the tractor allowing the finals to rip themselves from the tractor. I would say that the weakes point would be the clutch. I would assume that with converting a V6 to a cub you would also install or beaf up the clutch.The second weakest point would probab;ey be the driveshaft.

Re: Transmission strength

Mon Dec 15, 2008 11:25 am

Rik Prentice Wrote
Everybody knows you can't fit a diesel into a cub


I agree with you Rick a diesel engine in a cub would look funny. :lol:

Re: Transmission strength

Mon Dec 15, 2008 12:06 pm

Thanks guys for all the response, as far as the drive shaft I was going to have a new one machined to fit up with the new clutch. I was thinking a ford 4.0 but that might be a little big. And Im already up setting my brother... hes a purest in a way. For his senior project in high school he restored a farmall b. Ill try to post up some pics tonight.

Re: Transmission strength

Mon Dec 15, 2008 12:07 pm

Rick Prentice wrote:Everybody knows you can't fit a diesel into a cub :( . It'd look stupid and out of place :D :D

Rick


I think that you could fit a 4bt cummins in it....

Re: Transmission strength

Mon Dec 15, 2008 1:20 pm

Larry Barb Dotson wrote:Will the Cub drive train handle a 20 HP diesel?

Larry Dotson

:bellylaugh:
Who would ever want to do that to their Cub? I agree with Rick.

Re: Transmission strength

Mon Dec 15, 2008 2:21 pm

farmboy99 wrote:Thanks guys for all the response, as far as the drive shaft I was going to have a new one machined to fit up with the new clutch. I was thinking a ford 4.0 but that might be a little big. And Im already up setting my brother... hes a purest in a way. For his senior project in high school he restored a farmall b. Ill try to post up some pics tonight.


1. There would be no advantage to machining a new drive shaft... the current one is a match to the rest of the drive line and plenty strong. Keeping it as original would at least make replacement possible without breaking the bank. Machining accurate splines on a replacement (both ends) would be VERY expensive, and nothing would be gained!

2. As long as the load is applied to the standard drawbar it's not really all that far from the center line of the axle. The final drive housings aren't under a lot of eccentric load.

3. The amount of loading for the drive line is limited by traction. Don't try to pull a Cub in the heavy classes by adding excessive weight. :( Wheel spin is good. :lol:

4. Furthermore... As everyone already knows it's not even possible to convert a Cub to diesel neatly. :mrgreen:

Re: Transmission strength

Mon Dec 15, 2008 3:48 pm

Farmboy99,

Sounds like you have an interesting project in the works.

I noticed that you have only made 3 posts, so you may be wondering about the comments about a diesel in a Cub. My suspicion, based on earlier posts, is that a 'Stealth Diesel Cub' has been completed, or nearly so. Whatever it is has been seen by some but the masses are still waiting.

So enjoy your Cub conversion. There is a lot of knowledge out here. Feel free to tap into it.

Bill