[batarchangel]

Was wondering, since the rear end in my car is original, any idea what the rear end gear ratio would be? 3.70? I a 9 inch I know for sure

 

[CougarCJ]

Most common is 2.75 and 3.00.

 

[68PUMA]

Batarchangel, if you look at the data sticker (if it's still there) on the drivers door and as long as the data sticker is correct to the car (ie: VIN matches to the car or door wasn't switched) see what the AXLE code is and post the info and some will tell you what axle ratio the car came with. John

 

[cj750]

You can also look for the metal tag on one of the studs that secure the differential "pumpkin" to the housing. Usually the first digit is hard to read, but can usually be determined from the second and third. An "L" between the second and third digits, rather than a "." is a good thing, as it indicates that the car originally had a locking (limited slip) differential.
3.70 was never a factory Cougar option, to the best of my knowledge, but its a good street performance ratio.
My money is on either 2.75 or 3.00.

 

[1969XR7Vert]

...3.70 was never a factory Cougar option, to the best of my knowledge, but its a good street performance ratio...

Performance? Yes. Street? Not so much unless you have overdrive or don't care that your engine RPM's will be about 3800 at 80 mph with 26" tires. Not fun if you cruise much. I don't even enjoy my 3.25's much on the highway as I turn around 3400 at 80. Gets old fast. Need OD.

 

[Cougrrcj]

My two '73 'Q' code Cats came from the factory with 3L25s. Now AlphaCat has 3.91s and BetaCat has 3.70s. Both will likely get AODs or WR-AODs when the time comes for them to get back on the road. Just a FYI, even the 3.91s will have an effective rear gear ratio of only 2.62 or 2.74 with an AOD or WR-AOD respecively... the 3.70 rear gears would have an effective ratio of 2.48 or 2.59. (AOD o/d ratio is .67, WR-AOD or 4R70W o/d ratio is .70.) Can anyone give me a valid reason not to upgrade to the modern era with an overdrive trans????

 

[1969XR7Vert]

...Can anyone give me a valid reason not to upgrade to the modern era with an overdrive trans????

Sure. Cost.

http://www.amazon.com/Tremec-TCET4615-5-Speed-TKO-500-Transmission/dp/B002RPMNME/ref=sr_1_1?ie=UTF8&qid=1335223250&sr=8-1 Best price I could find and then there is the bellhousing adapter, the crossmember (if I didn't make my own), speedo adapter or cable, shift handle. It is something I'd like to do but with a good working toploader I rebuilt when I was a wee lad, nostalgia, the "talisman" aspect of my build, I kind of felt I should use it, at least to start.

My buddy says I should have sold the TL and used the proceeds to offset some/most of the cost of the new, he probably had the better plan than I did. But then there was the total nut I had spent (but knew better than to even attempt to add it all up) and the TL made more sense to me.

The Tremec 3550 seems like a cheaper possibility but I'm thinking in the end I would regret buying something used, ending up having to rebuild it, the time and cost associated with that, lower torque capacity, etc.

Someday - TCET4615...

P.S. Granted there are cheaper options for an AT, but I like to row the gears, always have, always will.

Regards,

Bob

 

[Bad69cat]

I was thinkng about this post last week as I was cruising down the interstate at 80 (at 1700 RPM) and then I realized ---- I could hear myself think! ;>) I might have lost some 60ft time - but dang that AOD was money well spent! Now I'm craving the Tremec....it was a 4 spd car originally! The pedal is still there waiting to be utilized! It would put a hurtin on the wallet for sure.

 

[Steve's 73]

it's been my experience that for 71-73, 3.25 was for CJs (4V engines) and 2V were always 2.75.

 

[Cedar Rapids Ia]

Easy way to do this...raise the rearend, place on stands, place in neutral, rotate the drive shaft to any starting point, like using one of the u-joint cups and mark it with soapstone (just one mark) and then rotate the tire one complete revolution, count how many times the drive shaft rotated... so if the tire rotates ...say 3 times and the drive shaft makes it about 3/4 revolution...then you'd have 3:70..know what I mean Vern?

 

[rvercoe218]

Or instead of jacking up and such... http://www.cougarclub.org/registry/decoderbook.aspx for the answer!


1971 2 2.75 Non-Locking
1971 3 2.79 Non-Locking
1971 4 2.80 Non-Locking
1971 6 3.00 Non-Locking
1971 9 3.25 Non-Locking
1971 A 3.50 Non-Locking
1971 K 2.75 Locking
1971 M 2.80 Locking
1971 O 3.00 Locking
1971 R 3.25 Locking
1971 S 3.50 Locking
1971 V 3.91 Locking</pre>

 

[Cougrrcj]

Easy way to do this...raise the rearend, place on stands, place in neutral, rotate the drive shaft to any starting point, like using one of the u-joint cups and mark it with soapstone (just one mark) and then rotate the tire one complete revolution, count how many times the drive shaft rotated... so if the tire rotates ...say 3 times and the drive shaft makes it about 3/4 revolution...then you'd have 3:70..know what I mean Vern?

You've got it backwards -- the driveshaft will turn more than the tire. So if one revolution of the tire makes the driveshaft turn 3-1/2 times, that's a 3.50.

 

[Cedar Rapids Ia]

You've got it backwards -- the driveshaft will turn more than the tire. So if one revolution of the tire makes the driveshaft turn 3-1/2 times, that's a 3.50.

Yep you got me on that...it's been a long day. Mea Culpa.

 

[batarchangel]

So according to this information mine is a 3.00 non locking. Axel code 6

 

[batarchangel]

So does this mean its a 8" instead of 9"? Or could it still be a 9?

 

[Cougrrcj]

All 71-73s came with 9" rears since 351C-2V was base engine.

 

[batarchangel]

That is awesome!

 

[Meddle]

So does this mean its a 8" instead of 9"? Or could it still be a 9?

Still a 9"