ring/pinion swap in 7 1/4 for lower gears?

[MarcD]

Here's the situation:

1963 Dart GT 225 /6 with a 1972 A-833 close-ratio box installed in the distant past (no history)

Rear axle replaced with a big bolt pattern 7 1/4 from an auto '75 Dart; 2.76 gears


Result: feels like launching in second gear! Have to slip the clutch, barely get out of first in the city and bogs badly.

I do have a small bolt pattern 7 1/4 axle with 3.23 (approx) gears sitting on the garage floor.


The question: Can I swap the SBP 3.23 gears into the BBP 2.76 housing? If they fit, how much work is setting up a ring and pinion? I wish I could just swap axle shafts/hubs but I understand that the BBP and SBP hubs are not interchangeable.

I guess the ultimate solution is a BBP 8 1/4 with 3.23 gears; I'd settle for a BBP 7 1/4 3.23 as well, but just not finding anything available in the San Francisco Bay Area...

Thanks in advance!

Marc

 

[MarcD]

Any suggestions? I've been busy painting the body/restoring the interior but have to face the music on the drivetrain issue...

 

[DartVadar]

I'm not much help but I know your pain, I have the stock 2.76 gears in my dart, even with 400hp it still is slower off the line than I would like, couldn't imagine it with a slant.

In my opinion an 8 1/4 or an 8 3/4 would be a better choice, I think alot of 8 1/4 can be found with 3.55s. Or if you can find it an 8 3/4, but pricey.

 

[AJ/FormS]

That close ratio box has a 2.47 low ratio. This gives you a 2.47 x 2.76 = 6.82 starting ratio. Yup thats like 2nd gear. You need a lot of torque to pull that off. You might want to search for a box from the 64 up Valiants which had a 3.09 low. Thats 25% more gear, which would be the same as a 3.45 R&P; 3.09 x 2.76 = 3.45. Your slant will behave as if it were 25% bigger than it does now. IMHO A stickshift slant needs help.3.23s would help a lot. That 2.47 low box is a close ratio box and doesnt do well on the street unless you have plenty of torque (read stout V-eight). If you run across an OD box, theyre Ok on small blocks, but could work for you ,especially if you went to a 3.55 or better R&P. The ratios are pretty wide tho. I think for you the preferred option is probably 3.55s or better. 3.55 x 2.47 = 8.77. Even that might be a little sluggish. An M/T slant likes at least 10 to 1 start ratio; eg.3.09 x 3.23R&P = 9.98 or in your case;2.47 x 4.1R&P = 10.12. 4.1s suck on the highway. One last idea is to trade your close ratio box for a regular 2.66 low box.Then 2.66 x 3.73R&P = 9.92. That would work too. It might be cheaper to swap a V-8 in. You could keep both the 2.47box and the 2.76s. At least til the rear blows up. Should be fine with 245 tires. All the best.