Differential for 1973 CS Automatic swap to Getrag 5 speed box,

[kentvonseverin]

Hello Forum,

I have assembled all the parts needed for the Getrag 265 swap. The last detail that I am concerned with is the differential. Any advice or insight into the diff's would be greatly appreciated.


-kent

 

[Mike Goble]

If you go to https://www.realoem.com you'll find that the automatic and manual differentials are the same 3.45 ratio.

 

[sfdon]

from HB Chris….


Differentials

The differential ratio is expressed as a fraction and is stamped on the right lower side of the differential on a flat boss. The presence of a stamped or painted S indicates locked or LSD.

3.25 = 39/12
3.45 = 38/11
3.64 = 40/11

These differentials were typically found on these models:

3.25 Open - CSi
3.25 LSD 25% locking - CSi and CSil
3.45 Open - Euro 3.0CS/CSA
3.45 LSD 25% locking - CSL, Euro 2800CS/CSA and 3.0CS/CSA and US 2800CS/CSA
3.45 LSD 40% locking - Euro 2800CS/CSA and US 2800CS/CSA
3.64 Open - Euro 2.5CS/CSA and US 3.0CS/CSA
3.64 LSD 25% locking - 2.5 CS/CSA

The LSD could be ordered as an option as well

 

[HB Chris]

If you go to https://www.realoem.com you'll find that the automatic and manual differentials are the same 3.45 ratio.

2800CS had 3.45 and 3.0CS had 3.64 in the US. The 3.45 is a great choice for the 265/6.

 

[Ohmess]

Agree with Chris. I had a 3:64 in my car when I first did my five speed conversion, then changed to the 3:45. I much prefer the 3:45.

 

[Stevehose]

Agree with Chris. I had a 3:64 in my car when I first did my five speed conversion, then changed to the 3:45. I much prefer the 3:45.

Curious as to what you like better about the 3:45?

 

[HB Chris]

Just five percent taller gearing is all, 3000rpm gives 78mph.

 

[sfdon]

Just threw away five 3.64 diffs. Nobody wants a car that you have to shift 1/2 through the intersection when the light turns green.

 

[kentvonseverin]

If you go to https://www.realoem.com you'll find that the automatic and manual differentials are the same 3.45 ratio.

Thank you Mike

 

[Arde]

Just threw away five 3.64 diffs. Nobody wants a car that you have to shift 1/2 through the intersection when the light turns green.

Bummer, they could be perfect for a one-gear EV drivetrain...

 

[OCCoupe]

Focus on the 5-speed swap then drive the car to see if you are happy. The 5-speed is essentially the same gearing as a 4-speed with the advantage of overdrive. The factory sold these with the 4-speed and the 3:64 diff. You can always change the diff at a later time.

 

[OCCoupe]

Just threw away five 3.64 diffs. Nobody wants a car that you have to shift 1/2 through the intersection when the light turns green.

@HB Chris’ mentor Murrey Fowler installed a 3:64 in his 5-speed e9 and loved it.

 

[sfdon]

We will talk in August

 

[mare9e12]

3.64 makes first gear too low with a manual. if you owned an auto and spent your time under 75 mph the 3.64 would be ok given the limitations of the drivetrain.

 

[Markos]

Just threw away five 3.64 diffs. Nobody wants a car that you have to shift 1/2 through the intersection when the light turns green.

Pretty sure @shanon has a 3.64 behind his dogleg 265/5. 3rd gear on the other side of the intersection sounds like fun to me!

 

[sfdon]

Proving there is an exception to every rule.
Wish he had picked up a couple of spares when Zack was at the shop last week.

 

[shanon]

Actually, for the record, it's a 3:45 w/ the C/R box.

 

[Markos]

Actually, for the record, it's a 3:45 w/ the C/R box.

Oh well that is far less entertaining!

 

[Stevehose]

All this trash talk about 3.64's is giving me 3:45 envy, what is the going rate for an open 3:45 in ready to go condish? My engine rebuild is preventing me from even considering an LSD.

 

[Arde]

All this trash talk about 3.64's is giving me 3:45 envy, what is the going rate for an open 3:45 in ready to go condish? My engine rebuild is preventing me from even considering an LSD.

Ignore them Steve. Real mean not only shift during an intersection, they also double clutch when that second gear synchro gets tired. The 3.64 increases torque. Humans do not feel power or speed, they feel torque.