Rear-End Gear ratio question

[bob32268]

Is it possible to tell the rear-end gear ratio from some external stamping or code on a late 60's rear end, such as 3:23 or 3:55 or others ?
My rear end is a 489 case on a 69 Charger 3:55, looking to swap to a 3:23.
Tks,
Bob32268

 

[33 IMP]

There MIGHT be a tag if it's a sure grip, but there might not.
If you are just trying to find out what ratio you have now, there are ways. The technique is slightly different if you have a suregrip on not.
I'm not sure what you are asking. Are you trying to find out if somebody can look at your rearend and see what ratio is in it? The answer is no.

 

[bob32268]

I have an 8 3/4 sure grip 3:55 rear end, looking to install a sure-grip 3:23, I have access to 3 parts cars (Coronets) but don't know what their gear ratios are and would like to know
what they are without disassembling the rear end.
Tks,
Bob32268

 

[RJRENTON]

I have an 8 3/4 sure grip 3:55 rear end, looking to install a sure-grip 3:23, I have access to 3 parts cars (Coronets) but don't know what their gear ratios are and would like to know
what they are without disassembling the rear end.
Tks,
Bob32268

IMO.....going from a 8-3/4" 3.55 ratio sure grip to a 8-3/4" 3.23 sure grip ratio is hardly worth the effort and cost.....assuming a # 489 case. 741 & 742 cases will likely be different or use different axle shafts (length and spline count).
BOB RENTON

 

[bob32268]

The 8 3/4 Sure-Grip 3:55 went South and needs replaced..... since it needs replaced I want to replace it with a 8 3/4 Sure-grip 3:23.
Tks,
Bob32268

 

[davek]

this might help you

 

[Sixpactogo]

I have an 8 3/4 sure grip 3:55 rear end, looking to install a sure-grip 3:23, I have access to 3 parts cars (Coronets) but don't know what their gear ratios are and would like to know
what they are without disassembling the rear end.
Tks,
Bob32268

If the three parts car you have have not been molested, there should be a tag under one of the mounting nuts telling you the ratio. if any of them are sure grip, they should have a sure grip tag around the filler plug. (as I said, "if they are un-molested")

 

[Bighouse]

Jack it up, rotate the wheels 1 full revolution and count how many times the drive shaft turns.

3.23 will turn roughly 3 and a quarter times

3.55 roughly 3 and one half times

3.90 allllllllmost 4 times but not quite

And so on.

 

[kiwigtx]

Jack it up, rotate the wheels 1 full revolution and count how many times the drive shaft turns.

3.23 will turn roughly 3 and a quarter times

3.55 roughly 3 and one half times

3.90 allllllllmost 4 times but not quite

And so on.

^^^^ This is the best method, as any tag found on a diff head cannot be trusted, unless you have personally owned the vehicle sine new, and no work has been done on the rear end in it's lifetime.

 

[33 IMP]

Jack it up, rotate the wheels 1 full revolution and count how many times the drive shaft turns.

3.23 will turn roughly 3 and a quarter times

3.55 roughly 3 and one half times

3.90 allllllllmost 4 times but not quite

And so on.

Assuming it's a suregrip. If it's open, that might not work properly. If it's open leave one tire on the ground, rotate the other tire, count the driveshaft revolutions, and double it. For a more accurate number, rotate the tire five or ten times.
I hope you know how to tell a suregrip (ok, posi) from an open.