7-1/4 info and help

-
Fstforward

Fstforward

Barracuda Freak
Joined
Jun 23, 2009
Messages
916
Reaction score
14
Location
Pittsburgh, Pa
Okay, having had my 1964 Barracuda for about a month or so now, I finally rolled under the back of the car to look @ the rear end and undercarriage to see just how good or bad it is.

I've ascertained, much to my dismay, that the rear end is a 7 1/4 rear, and am not sure what the gear ratio is, so I did what I was taught long ago while training to be a mechanic.

With the car up in the air, I put a mark on the drive shaft, and turned the rear tire one full revolution and counted the turns of the drive shaft. Well, the result I got was way strange, so I rolled under the car, marked the tire, and turned the drive shaft until the tire turned one complete revolution. Same result, numerous times with both ways testing.

The result, right about 2.00. Now,I got this car from a guy in New Mexico, and am wondering if he was planning to take it to BOnneville and run speed or what, but something just doesn't seem right about those gears, but I did it al least 5 or 6 times each way, blocking one wheel so the other would spin(not posi or limited slip).

Any ideas???? Did the 7 1/4's come with those shallow of gears?????

Inquiring mindless

FF
 
Ha, I`m interested in responces to this thread too, I have a old project someone started with a cheb 10 bolt. Did the same procedure as you and come up with 1.25-1, showed a buddy and he seemed speechless too.
 
It sees like I had a 2.71 gear's in a 73 318 Challenger.
 
If you block one wheel and turn the other, you need to turn the wheel two turns and count driveshaft revolutions.

If you have a SG and have to have both wheels off the ground, then both wheels will turn one revolution, and count the drive shaft turns.

PS: over the years 7 1/4 rears came with ratios from 2:4x to 3.91 from the factory. The old "Direct Connection" program had gears available in 4:10, 4:56, 4:88, and 5:13. Sure grip was also available in both clutch type and cone type, in different years. I run a 3:91 SG 7 1/4 in my 13 sec 66 Valiant, and also have the 4:56 and 5:13 rears
 
IMO, your rear gear is a 2.94:1 if the car is an automatic with the original rear axle assembly.

Factory ratios offered down through the years include but are not limited to:

  • 2.26:1 - This ridiculously high ratio was found in later M-bodies.
  • 2.45:1
  • 2.76:1
  • 2.94:1 - This was common factory install in mid-60s.
  • 3.23:1
  • 3.55:1
  • 3.91:1
The 2.26 & 2.45 ratios used a different case that will not accept other gear ratios. (The pinion gear on a 2.45 is about the same diameter as a softball.)

Aftermarket gear ratios available include but are not limited to:


  • 2.25:1
  • 2.45:1
  • 2.76:1
  • 2.94:1
  • 3.07:1
  • 3.08:1
  • 3.21:1
  • 3.55:1
  • 3.73:1
  • 3.90:1
  • 3.91:1
  • 4.10:1
  • 4.11:1
  • 4.56:1
Hope this is helpful
 
My 7 1/4 is 2.76. Which was fairly common with the automatic (904) transmission. You can always take the back off and count the ring and divide it by the pinion. That will tell you exactly what your ratio is.
 
if never touched it should have an Axel tag mid bodom pumpkin bolt it will tell u the gear ratio
 
You must log in or register to reply here.
-

Back
Top