70 challenger r/t which diff2

[greenmean]

Hi
car is a R/T383 auto How do you know which diff came with the car its not a special order on the fender tag.
mine has a diff with a 2.76 and 741 case ,looks like it was on there a long time but could obviously have been changed.
also how do you measure the drum brakes for size .
Thanks

 

[EV2RTSE]

The build sheet for the car, if any, would be the best way to determine what it came with originally. But it looks like the 2.76 was available as an option with a 383. Probably not very many built.

https://www.hamtramck-historical.co...DealershipDataBook/1970/70_Challenger0030.jpg

Most typically a 70 R/T would have a 489 case but perhaps with a 2.76 gear they just put in the 741? Most often these gears would be found in the low performance slant sixes and 318s. Any date codes found might offer more clues.

Pulling the speedometer gear out of the transmission and checking the number might offer a clue as well, post it if you decide to pull it out for a look.

On an R/T-
If the car has factory power discs up front then the rear drums would be 10". (AARs & T/As had 11").
If the car has drum brakes all around then they would be 11", easiest way to tell the difference between 10s and 11s originally is the 10s are smooth and the 11s have fins.

 

[greenmean]

The build sheet for the car, if any, would be the best way to determine what it came with originally. But it looks like the 2.76 was available as an option with a 383. Probably not very many built.

https://www.hamtramck-historical.co...DealershipDataBook/1970/70_Challenger0030.jpg

Most typically a 70 R/T would have a 489 case but perhaps with a 2.76 gear they just put in the 741? Most often these gears would be found in the low performance slant sixes and 318s. Any date codes found might offer more clues.

Pulling the speedometer gear out of the transmission and checking the number might offer a clue as well, post it if you decide to pull it out for a look.

On an R/T-
If the car has factory power discs up front then the rear drums would be 10". (AARs & T/As had 11").
If the car has drum brakes all around then they would be 11", easiest way to tell the difference between 10s and 11s originally is the 10s are smooth and the 11s have fins.

Thanks great reply,
Ill check out the speedo gear soon ,i saw that the ratio was an option ,but 3.23 was more usual .I also didnt know about the 489 cases so thanks ,yeah no broadcast sheets.

 

[Xcudame]

My 70 Challenger WSS came from the factory with a 741 case and 2.76 gears (Original 383 2bbl but upgraded to a Thermoquad and 3.23 suregrip now). The build sheet would definitely be the best confirmation. One would think an R/T would come with a 489 case and 3.23 standard, but with Mopar you never know. The dealers had a lot more pull "building" custom cars in those days and done unique and cool cars came out of it.

People kinda dislike the 741 case, and for maximum performance, I understand. But compared to a stock Ford 9" (seems everyone loves the Phord 9") it's very comparable. It's the after market add one that makes the Phord 9" better. Still not at good as a Chrysler 9 1/4" or the Dana 60 in my book.