Technical how much power can a 39 trans take?

i have a 39 trans and a 390 engine i expect to make 400 ish lb ft of torque. i plan on running a quick change and skinny tires. its going to be a street car. have any of you run a setup like this how did th trans take it?

thanks

 

well they use to brake second gear with a flathead ford, maybe on a good day 90 h.p.

 

Dont even think about it. The stock flathead eats transmissions

 

What manufacturers 39 transmission? I see some assumptions being made.

 

Use a top loader 3 or4 speed,and change the shifter to the top.Long ago Street Rod,or Rod and Custom mag did a article on putting the early ford top shifter on a top loader so it looked Genie.I think guys are using a Jeep trans top plate/shifter to do it now a days.You can do open drive on a quick change........ Im back a couple minutes later....A guy on here ,51504bat did the conversion...jeep T176 top shift on a 66 ford 4speed. Looks genie,and stronger.

 

The '39 will be fine as long as you have a pile of replacements…. LOL

 

Run 2 inch wide rear tires

 

A four banger would be a better choice!

 

has nobody come up with aftermarket parts to strengthen those 39s?

 

Back in the day - My Dad had a J-2 Olds 371 cube - in his 1940 Ford , the 1939 Ford stock trans did not last long. He went through 2 or 3 per year. Kept and coffee can and screen wire to filter out the broken gear teeth to get back home.

 

Everything hinges on your driving style.
If you "nurse it," it will be OK.
If you "get on it," It will break. If you just putt to the ice cream shop, it might live, they are fragile.

 

Simply adjust clutch to slip ! Easy Peasy !

 

Inflated to 100 PSI........

 

39's and 40's transmissions were basically the same. I ran a 327 SBC that was either a 250 or 300 HP with a 40 column shift. I still have the transmission and though it is rusted it was not broken. They weren't the strongest but they did pretty damn well if you learned how to drive them with care. I had more problems with axle keys than transmissions and that was probably due to negligence on my part for not tightening the nut enough. 400 pounds of torque is twice what the transmission was designed for.

 

They were built to take 85HP but would stand twice that on a steady pull - back in the forties and fifties when they were new. Now you have 80 years of wear, age and metal fatigue to worry about. If you really have 400HP the trans will likely break the first time you get on it hard.

 

In the late 50's early 60's we broke them on a regular basis-axle keys too. Same with 49-51 fords. Transmissions were cheap at 3 Boy Wrecking yard ($10) and we got real good at changing them-this was with flatheads. Some years ago I had a nice 40 sedan with a stock 283 and 40 trans etc. Drove it alot but used common sense-never an issue.

 

Torque will break it 1st -2nd , all so modern lubes well eat the original internals ( Bronze) , to source correct / compatible lubricants is pricey , I Believe I paid around $160 for 5gal , Not off the shelf auto parts store , industrial line lubricants .

 

I think by now with all the answers you have received you can see that by being real easy on your car the trans MIGHT hold up. The first kid that challenges you with their hoped up VW or Honda, you stand a good chance of having to replace the gears in your trans. If you would rather work on your car then drive it, install the trans and replace it with one that will hold up at a later date. Just remember how hard it is to replace that trans every so often!

 

In the esteemed words of "Hnstray" : “In any conflict between Physics and Style, Physics always wins”

 

I did a 350 Chevy hooked to a 40 trans. I would never bang shift it or dump the clutch, I would always roll in and out of the throttle, never broke anything. It's those sudden applications of power that will break them in a hurry. I did break loose the bias ply rear tires a few times, so I wasn't driving like a grandpa, just gentle on the shifting.

 

Those trannys with the bronze parts need GL4 gear lube. GL5 will eat the yellow metal. Sta-Lube makes it relatively cheap and you can get it at Napa (special order)

Broke the right rear tire loose briefly on a right hand turn. Only getting on it a little. Lots of sand right there. When I let off the gas and the tire caught, the transmission exploded. Flathead, mostly stock. Learned to baby the next one.

Andy

 

I had a healthy 276" Merc with all the "goodies" ahead of a '39 box I had rebuilt with later gears and new synchronizers, bearings, etc. The transmission never gave up on me because the axles would break first. Did I mention I HATE changing axles in a banjo? Even if you could "bullet-proof" a '39 box, what would be the point? You'd just start having problems with the rear end. I had a life-long dream of owning a '36 3-window with a "Full Race" Merc, a '39 transmission, and hydraulic brakes that I finally realized when I was 53. I sold it five years later because it was very cramped inside and the driveline problems. I don't miss it at all. It was kinda like being married to a real bitchy beautiful woman. Five years is more than enough.

 

If you do put in a stronger trans better think about replacing the rear axle too, it will be the next thing to fail. 39 Ford V8 was rated 90HP 155 ft lbs torque. It was understood that they would stand up to double that, if you baby it and don't dump the clutch off the line. That was back when they were new.

 

Guy's are even installing later model 5 speeds and C4 auto's behind flat heads now. That's should tell you what they think of the old trans.

 

Why add horse power if you can't use it? It's no fun driving a car and wonder if it will get you back hone.

 

Back in the 70’s, I tore up 5 early Ford trans in a matter of 5 weeks with my stroker flathead. Always seemed to break the same parts—-destroyed second and cluster gears repeatedly. I started using gm trans(4 spd muncies and 5 spd t5) and can pop the clutch and spin the big tires over and over with NO drivetrain problems whatsoever!

 

I seem to remember they were used a lot behind 283 Chevys in the sixties but the 327's were too much.

Charlie Stephens

 

In 1958 I put a Olds in 40 coupe. My buddy gave me a 39 box that had been setting out in a field for who knows how long,the thing was full of water and gears were pitted from the rust. The 40 box looked good inside and I thought about putting the 40 gears in the 39 case. Then I got to thinking its only going last about two weeks anyway so I might just as well run the rusty 39 and when it blows I will put the good 40 gears in. To make a long story short I built the car for street racing,car was completely gutted not even the glove box door, locked 4.11 rear end 6.70 tires. I did run it at the drags one time with some 7 inch hard rock slicks. I drove the car for two years and it still had the 39 gears when I sold it.

 

I had a 39 3 speed in front of a healthy 265 Chevy, triple carb, Isky cam, solid lifter motor that was in my model A truck. The gearbox came to me from a drag racer who'd had it in a high 12 second quarter mile T. Long story short that box held up no problem and never caused me any problems


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