Technical How rough can I be with an open banjo diff from a 1940 Ford passenger car?

My new coupe has a non-posi/non-spool 1940 Ford passenger car with an open driveshaft conversion. Assuming all the guts are stock, how rough can I be with this differential? Anybody have a feel or general guideline for approximately how much engine torque I can throw at this diff?

The diff is very traditional looking and kinda cute. But I don't want to break it or replace it til I get some other matters handled first. As untraditional as it may be, my plan is to eventually go to a 9" because this car will go to the dragstrip some.

Lets neglect the dinky driveshaft and focus on just the differential and axles.

 

Double post (new to forum-sorry). Please delete.

 

you can delete it yourself.

 

It looks like you are running an SBC in your coupe. Even with a stock flathead you should be careful with a banjo diff so with the SBC you should be even more careful or you will be fitting that 9" sooner than planned. The drum to axle connection is by way of a square key and a very common problem in the early days was chewing the key or the axle out.

 

If you like the look of the traditional banjo , wait till other things are sorted and save up for something like these folk do, best of both worlds , though no spool or locker , do you really need it ?
http://www.hotrodworks.com/product/banjo-rear-axle-conversion/

 

Until it goes bang!

 

If that's your new coupe, what's to worry about? You have to act pretty silly to harm a '40 rear in a car that light. The 9" is a huge jump, likely much heavier than needed. Just one of those buzzwords, but you may want that buzz when racing that bench. I put a 9" in my Olds powered forty and the whole evolution over the years left me with a gutted frame monster that had to be sold to start over with a more conservative starting point. Most only recognize it when they get there. Good Luck: Fred A

 

Would you like to combine your identical threads to make easier reading.?

 

Keep the tire pressure high -- smoke the tires rather than the rear end.

 

As Swifty implied, the weak link in the banjo is the axles. If they don't shear the keys, the next weakest link is the spider gears (which are one piece with the axles.
A push in axle conversion would eliminate those problems.
If I were you, I'd save up for a Champ size Quickchange, and then you can have strength and beauty. Plus you can change the ratio at will. There are several styles of limited slip differentials.

9" rears are HEAVY!

 

As mentioned, when put under stress, the weakest links will fail first. The axles have a tendency to snap and you lose a wheel. I suggest the retainers Speedway sells. Also, the keys can break, if the force is on the key and not the taper. I've never heard of someone breaking a ring gear or pinion due to HP, but COOP did roast his pinion in his 46 on the way back to LA from the roundup.

If you want to beat on your car, put a 9" in it.

 

Yes, I would. Sorry to be so much trouble.

 

Thanks for all the input, fellas. My plan is to limp along with the drivetrain/powertrain that came with the car until I sort out all the issues necessary to have a good driver. Car is getting floors, pedals, electrical, then plumbing fuel and brakes currently (I bought an un-finished car). Then to get it running and driving, aligned, tagged and registered. I'm putting a year on this phase. Then to cruise it around nice and easy for a year before trying to make it fast/quick. I'm hoping to make it a 7.0 1/8-mile car with the dependability to do Drag Week and some Powertour-ing. I will camouflage the go-fast part of the car as much as I can. But I can't, in good conscience, intentionally build a slow car. I will try hard not to let the HAMB down in the process.

 

Umm, what is untraditional about a 9"? Ford came out with the 9" in 1957. The SBC came out in 1955. I see nothing untraditional about a buggy sprung 9" with ladder bars. If you abuse that banjo it will shear a key or brake an axle.
Brian Bass's '29 hemi powered Model A coupe is an excellent example of a traditional hot rod that is running a 9".

 

Correct Bass is running a 9" out of a bronco. The bronco "9s had a 5 on 5.5 bolt pattern and are .75" wider then the 1957-1959 9" rears. Still nothing wrong or untraditional about this set up.

 

Fuck it, sorry I got involved. Continue on with the HAMB history revisionist bullshit.

 

You can blow one with a 150HP hopped up flatty IF you use it for drag racing, revving up and dumping the clutch from a dead stop. If you drive like a sane human being, take off easy and develop a little momentum before you give it the gun it will last forever.

 

Awesome!!!! I'm psyched. That's why I've subscribed to HAMB-to learn.

 

Ask an old timer why they had a piece of pipe with a small cable looped through it as a regular service tool for these rear ends.

 

I,ve run my '47 pick-up for 6 years now with a mild 302" Ford engine. Cruise with the club any time and no problems in over 3,000 miles. ?? Go figure.

 

If you break an axle on a modern car the wheel usually strays with the car. On an early Ford rear end you will loose the wheel unless you run safety hubs or safety clips. Don't leave home without them.

Charlie Stephens

 

rear end choice and traditional is probably era driven. The bronco rear is an actual factory 9" which is evident by the bulge in the back cover. The '57 rears were actually an 8.75 and had a smooth back. You can stuff a 9" chuck in one but it didn't come that way.

In the '60s as far as I know the Pontiac/Olds rears were the more popular late model rears. Doesn't mean that no one used a Ford late Ford rear just that the GM rears were more popular.

 

My best friend in high school (early 60s) had a 40 Ford pickup with a 289 Ford engine, really wide real Indy rear tires, a stock early Ford 3-speed, and an open banjo. The rear end gears and bearings did fine with the abuse but he was changing out twisted rear axles it seems a couple times a month. He lunched the tranny a couple times too but was expert at rebuilding the components. If you plan on hot footing it occasionally but want to keep the banjo, consider converting to Ford 9" rear axles and outer bearings. I did that conversion for the Mysterion clone in my avatar. Wasn't too difficult and have a lot more peace of mind!