Hot Rods 9 inch rear ends

Can anyone tell me what length axle to axle I need for a 40 ford? Also what gear ratio is all around best for a 350 engine with a 350 auto tranny?

 

Any idea what size wheels youre going to run?

It works really nice when you set up the wheels in the fenders and measure for the exact rear width you want. Ordering a custom rear then having to order custom wheel offsets or use spacers kinda sucks.

Im sure theres some proven combos, based on factory wheel offsets, others will chime in.

How about some pics.

 

I have a pickup but the I believe the frames are the same. The 9" is from a 78 Grenada and is 58" wide. The wheels are 15x8 with a 3.75" backspace and a 255/70x15 tire and everything fits fine even with the rear lowered another 1" from where the Chassis Engineering spring kit would have it. For gear ratio I believe 3.50 is usually considered the dividing line between performance and economy.

 

On all the 35/40 chassis coming out of my shop I used a 58 outside to outside rear end. On most chassis I used a Chassis Engineering rear spring setup and that width rear allowed the use of their rear anti roll bar setup. plus an 8 inch rim with the right offset.

 

The best gear ratio could be anywhere from 2.47 to 5.38, depending on what you want to do with the car. Most guys pick something in the 3.0 to 4.11 range....3.0 if you will spend a lot of time on the highway, and you're not concerned about getting the quickest acceleration you can. 4.11 if you want quick acceleration for driving around town. 3.50 is a common compromise.

 

Do yourself a favor, put in a overdrive tranny. Then you can drive it anywhere.

 

This may help you with your figuring things out.
http://www.quickperformance.com/Suspension-Measurements_ep_44.html

 

I personally am running a 57" 71-77 era Maverick V8-8" rear end and 4" backspace wheels on my 40 with no issues.

 

Put a Granada rear in a 39. Fit perfect. Highway driving can use a 2.75 to 3.00 no problem .

 

The 66-77 Ford Bronco rear axles are 9" and 58" wide, they also have the 5 1/2" bolt pattern,the same as stock 40 Ford wheels. HRP

 

How do I tell what size ratio I have are there numbers stamped on the rear?

 

If you want to be accurate, then count the teeth. If you have the rearend opened up where you can see the gears, count the teeth on the ring and pinion. Divide the ring teeth number by the pinion teeth number. Example: 41 teeth on the ring and 10 teeth on the pinion = 4.10 ratio. HRP

 

Im going to see a rear end not opened. I was told that there is a stamp or casting no that can tell me the ratio.

 

Can anyone answer this?
Im going to see a rear end not opened. I was told that there is a stamp or casting no that can tell me the ratio.

 

When it was new, there was a thin metal tag hanging off one of the bolts on the center section. If it is still there, it will say something like 3.00, 3.25. That number is the ratio.

The beginners way to remember ratios is closer to 4 is for 1/8 mile drag racing, closer to 2.75 is for top speed. Post pics and we can help you out.

Good luck, -Abone

 

count the number of times the pinion U joint yoke turns, for every time that both axles make one complete revolution each. (or one axle makes zero revolutions, and the other makes two revolutions)

if it turns 3 turns, then it's 3.00 ratio. for example

 

Ok.....
The front axle of a F1 is the same width or close to it as a 41-48 Ford Car......a member here has converted a F1 axle to a buggy spring and used it on a hot rod. 52-53 inches inside plate to plate......The rear of F1 (Dana 40) has a similar track as the front axle.......52-55ish plate to plate.......
The 40 Ford my be a little narrow compared to. 41- 48......Don't Know....?

The 57-72 F100 9" rear axle will fit well under a F1 It's a bolt on. I do believe the Bronco rear mentioned above is the same as the F100 as early Twin I Beam trucks had a wide track front and a narrow track(F1) rear.....This was corrected in the 1973 model year. Very very rough measurement of a 65 100......55inches inside plate to plate......

So in theory.....a F1/F100 rear axle 1948-1972 should fit OK. And it shares the same bolt pattern.

The 8 inch from a 1964(little Fairlane) 51 inches ish......rough measurement......inside plate to plate.... Mustang Grenada may be similar.....
Keep in mind you will have some lee way under the fenders.....
Most of the time automatic cars have higher gear. 3.00 was standard on the automatic Fairlane. Manual trucks tend to have lower gears......3.89 to 3.70 in F100 six cylinder trucks....
As always measure to confirm......

 

A 9 inch in a 40 is heavy, bulky and not needed.
Don't be tempted to use a Lincoln versaille. No parts available.
Go with a n 8 inch.
Lighter and looks better.
59 in. is the WMS to WMS fo the stock 40 rear, if that is of any help.