What gears can I use?

[Mark1972]

Hello all. The project 1970 Plymouth Satellite is in its warm winter home until May 1st. It felt so good to drive it the 10 miles to storage last October. While I'm focused on getting the car painted and safetied, one upgrade I would like to look at is my rear gears. I will attach photos but it's the original 1970 rear 8 1/4" rear end with 2.71 open diff. Apparently there was 2 sizes of carrier that could handle different sizes of gears. Can anyone tell me what gears I could fit in mine? I would love 3.55 or something close. Thank you as always.

 

[PurpleBeeper]

I don't know your answer....but have you considered an 8-3/4" rear end? It would be quite a bit stronger than your 8-1/4", they were available stock (68-70 any b-body) and the BIG advantage is that you can change your gear ratio yourself in a weekend. The gears are pre-set-up in the "pumpkin" or "chunk" (center section). Just a thought....and 3.55's are available.

I did a little research on your question:
Two differential carriers were used in these axles with the exception of the 2.24:1 ratio. Any other ratios between 2.45:1 and 2.71:1 used one carrier, while anything above 2.71:1 used a larger carrier.
https://www.hemmings.com/magazine/hmn/2007/06/Chrysler-8-1-4-Rearends/1470391.html
It looks like you would need a different rear end to go with the higher number gears in a 8-1/4"

 

[Ron H]

What motor is in the car? Mine is a '63 and rebuilt the 318 motor to around 325 HP; some years earlier had installed a '65 rear sure-grip 3:23's and then after rebuild put in 3:55's. I would have preferred staying with what I had as for cruising speed the RPM's are up there to an irritating level for me.

 

[65-440]

Or just put a truetrac in it and pick your ratio ... 8.25 is easy to build, with the right tools of course ! I would have no issues running an 8.25 on a mild driver ....

 

[dvw]

Once you get to a 3.91 you have to run a notched cross shaft. The thickness of the ring gear won't allow the stock shaft to slide straight thru the carrier. The ring gear gets thicker due to less pinion teeth. As I remember the only carrier that won't work is the 2.45 gear.
Doug

 

[Mark1972]

It's a stock 318 motor. The reason I mention gears is because the car will spend most of its life driving in the city, not on the highway. I also read the Hemmings Motor news article, but was confused by the wording. Over 2.71, or under 2.71. But it didnt say which side of the fence exact 2.71 was for size. I've also read the 8.25 will handle 300 flywheel horsepower easily if you dont abuse the vehicle. So I'm sticking with the 8.25 for now. Even a 3.23 year would probably "feel" more responsive than the 2.71.

 

[69 GTX]

3.23 or 3.54 would work great with a SB.