Technical How much can a flatty drivetrain take?

So I'm getting ready to build a 283 Chevy I'm hooking up to the rest of a stock 1948 Merc flatty drivetrain via an Offenhauser adaptor.

How much abuse can I expect this stuff to take?

I've heard tales of woe, blown trannies and sheared axle keys.

I'm okay with driving it a bit more conservatively than my other ****, especially since I'd like to keep the stock column shift, I just want to know how far I can go and keep this stuff together.

The 283 is 40 over, and my head choices are ported Powerpacks or 1.94/1.50 462 Camelhumps. Thought about a rumpity camshaft while I've got it apart, but don't want to set myself up for failure.

So what kills this flatty stuff?

 

Make sure the clutch is fully home and the car develops some momentum before you give it the works and it should last indefinitely.

Popping the clutch, slam shifting and drag racing starts will blow the trans or shear an axle before the engine is broken in.

Your car was built for 85HP and that was when it was new. There is such a thing as metal fatigue. Back in the day a 125 or 150HP hop up would blow the trans in the hands of a drag racer. On the other hand, at Bonneville under a steady pull the same trans would stand up to several hundred HP.

A 283 should work great for the street. Build it on the mild side and baby the clutch and gearshift and you should have no problems, provided the trans is in good shape to begin with.

 

Depends on how much you want to enjoy performance driving.
Using a '39 transmission, closed driveline & '41 rear with std.radius rods, Offenhauser adapter to a 260 cid Cobra engine, it only took me 1 year to realize all that early parts would not hold up after twisting both axles, YES, I did the old school thing using tin foil in the keyways too!
Also shearing the "Cobb"(main cluster in trans.) was a disappointment.
All this occurred driving to local SoCal car events 1968-70.
Wanting to experience cross country street rod enjoyment, I jacked up the roadster & removed ALL early components, including engine/trans. adapter.
Purchased 4 spd. aluminum housing to engine, open drive line, 9 inch rear end, fabricated my own rear radius rods, & started driving cross country without any fear of early parts failures.
I'm still using the same basic LATE parts today at 300,000 happy miles with 5 trips cross country trouble free!

 

This was my thoughts, I just wanted to guestimate how much power I can reasonable make before stock **** starts failing. I figured "jack rabbit" starts would be where my problems would be. Something that's built with a strong mid to high range would be okay? Does high RPM not hurt this stuff, ***uming it's already moving?

I've even considered picking a less than ideal cam or retard it to kill off some of the low end just to put a little less stress on the stock stuff.

My whole thought process was to keep as much early stuff in it as possible partially because I like that stuff and I've never experienced it, plus to get it on the road ASAP as the more I changed the longer the project would take.

I have other 'fast' cars to wail on, a peppy cruiser would be fine for now.

Thanks for the input guys!

 

There's no guarantee on 70 year old used parts. But, if you take it easy, it will last longer than if you beat on it.

In other words, drive it like you stole it and there is a cop car on the corner.

 

I'm just starting to experience my '32 pickup with a stock 265 4bbl and power pack heads attached to a '35 top loader, torque tube and stock '32 4cyl rear. So far, so good. I have no plans to try to spin tires nor do much highway speed long distant driving.
Same reason as you.....I had this stuff and it went together real easy.
I can tell you I really enjoy driving the truck with buggy spring and all of it's creeks and rattles.
Good luck!

 

The highest load that car feels will be in high gear. While you may indeed reduce shock loads with tenderfoot launches, once in top gear and pouring it on there's no more mechanical advantage. As to considering back in the day we should also consider the availability of the weaker parts. I'd bet a good cup of coffee that many were like my dear ol Dad and had spares littering various garages and yards. Those guys would get really good at swapping out everything and didn't have the decades of rust and seized fasteners we have to deal with. Still, what you're building sounds fun and might last a while based on how you use it.

 

Floor it until something breaks and then back off 1/4 throttle.

You break anything, just depends on how you drive and if your tires can hook.

 

When you are in high you have a direct drive, the main shaft is the only thing under load. No gears involved.

In low or second, under a steady pull, you will be ok until a gear tooth breaks, lubrication is overloaded and fails, or the shafts bend away from each other. This takes a lot more pressure than a sharp blow.

If you only give it full throttle in high gear there is very little danger of trans or drive train failure. Especially if you have a stock clutch and stock size bias ply tires. Either of those should give before you break anything.

 

Scotto,
The killer is traction. If the tires don't break something else will.

You can get away with it if you keep everything up to par. If you don't want to shear axle keys make sure that you union is good and tight, IE the taper is good and snug when you pull it down and the key is not sloppy in the keyways. You can check the taper with ****m ( machinists blue) or gear marking compound. Smear the taper on the axle shove the hub on without a key and turn is one full turn then pull it straight off. if you got high or low spots get yourself some course valve lapping compound and lap it unless it is really bad in which case it will need to be turned. If the key is loose go to the next larger key and fit it by hand or have new keyways cut. You can also add a key, something that we used to do before we ever sheared a key if we were building a hotrod and had the time and the funds to do it.

The transmission can hold together but you have to learn to finesse it. No power shifts and no missed shifts. make sure that your linkage is not sloppy this will help. More transmissions are broken by user error than by power.

I personally would stay with the power pack heads if it were me and there are a number of old camshafts that will give you a lope with a small bore small block. Or you could do like Smokey Yunic suggested, stick camshaft and pull the choke when you cruise into the hot dog stand.

Anyway the key is not think you are Ronnie Sox in a Super Stock Cuda and that the drive train is not loose as a goose.

 

I did a burn out in my '40 once with a 8BA flathead stock trans., solid drive shaft and stock rear end, it eat up the rear main barring on the 3 speed trans in a spit second! 3 days to tear it down clean up all the metal frags, no damage to the trans and installed a new rear barring. The rear barring was old, mind you.

 

LOL when I was a kid those were 15 dollar ( some went as high as 30) transmissions. Anyone who hot rodded an old heap bought a spare as soon as they had the extra cash and carried it in the trunk. I did the same with Saginaws in my later model cars ('50s and '60s) they were cheap too back then and you would be surprised how quick we all got and changing a transmission out.

if you don't try and shift one like you are trying to win the Winter Nationals they will hold up just fine.

 

There was a time that the '39 was the mainstay of our hobby. I have driven a few and they just feel right, at least to me.

I think ( although don't quote me on it) that kevin lee had a '39 ****** in his roadster and he drove that little car like he stole it from the first time out the door. He p***ed me like I was standing still in the Pusher on the way to MOKAN one year and I never babied that old truck.

 

In 1963 I had a 46 Ford with a built Y-Block (3-2's) and a 39 ******, I popped the clutch just one time, sure made a huge noise when the ****** went.

 

I built a '36 3-window with a healthy 276" flatty, a '39 box with later gears, and a 4.11 rear gear. After one bad experience shearing an axle key, I had a bunch of 1 1/2" long mild steel keys made that I ran. I blew a bunch of them, but never anything else. I had the proper hub puller and wrenches in the car and could swap a key and be back on the road in 5 minutes. It's like back in the WWII, F8F Bearcats had explosive bolts holding on the wingtips. In the case of a steep dive, pulling out too fast could rip the wings off the aircraft. In such a case, the pilot would blow the wingtips off to prevent total wing failure, and possibly survive to fight another day.

 

The weak links are the axle keys and transmission. Remember the advertised HP for your motor was about 100. I think your worked 283 could be three times that! I suppose you can drive the car and have a great time with it, but the first kid that pulls up to you in his ground s****ing Honda or VW and revs his engine, what do you do. Too tempting to blow his doors off, but do you want to go thru all that work of replacing the trans and axles.

 

About (exactly!) 6 '39 boxes, within a year...a peeled axle shaft, and a broken set of spiders in my '36 five window (276 Merc) kept me '$$-humble' when 17.
About wore out the rear 'U' bolts and bolts around the front driveline coupling with all the replacement going on...Got pretty fast at it, but then: Called Dean Moon, and had him send me 3 pair of Moon Soft Axle Keys!
I must have lightened up on my right foot, too...Finally stopped the Cluster Crash Capers...
Did have a similar problem in my '32 five window, Ohhh...those 25 tooth Zephyrs...
Replaced them with rotten old 28 tooth 'genuine Ford parts'...
Heck, I even murdered some LaSalles. Nothing is 'bulletproof'....

 

My opinion, if the flathead is going, then so should all the rest of the drivetrain. If you want the 283, then swap in what will work with it and save yourself lots of grief.

 

Not likely 300 ponies from the 283. 230-250 is a more frugal number.

That said there ware other transmissions and rear ends when the swap was more common place and these were still in use. The trick is to learn to drive it and not continue to thrash it.

 

A 48 Merc had 180 ft. lbs. of torque a 57 power pack 283 had 300 or 66% more I don't think Ford built that much of a safty factor in.

 

Thrash on it , and it will self- diagnose.

 

I still remember my older cousin giving me (a very impressed 14 year-old) a ride in his early-olds powered fenderless/channeled A coupe and shooting the '39 shift lever (and probably a few other bits) through the roof insert on a missed 1-2 shift....

My mother *****ed about the gear oil smell (we both got sprayed) all the way home....

 

its the fun of R&D Replace and destroy , we replace the broken part with a heavier duty one and try to destroy it . basically thats how we found the weak links in the race car . as for looks , yea some of the old stuff looks neat ( like banjo rears ) , but the way it was produced and what it was built for are often the deciding factor on if your gonna keep it or upgrade it . most of the stuff wasn't built for high speed longhauls we do today or will hold up to the racing thats done with the tires we have now .

 

I twisted off the drive shaft in 1967 and still have it for use as a pry bar. Lots of transmissions broke no matter how many new parts I put in and no matter how carefully I drove it.
I wont use those axles or transmissions any more. Its no fun being hundreds of miles from home with an inoperable car