rear axle codes

[TSL]

Please help,
I have a 72 SLC with a 116.982 engine. Trying to find out about this actual rear gear ratio. Grey market car came over in Jul 73.
4-speed automatic, tacking 4000 RPMs at 80 MPH. I am guessing that the ratio is the 3:92 set, but I do not want to assume anything. The only numbers that I have been able to find on the rear axle are these:
R1163510308 (pass. side)
011884346 (drivers side)
I read that whereas the actual ratio is to be stamped on the lower driver side on case. Is there a place that we can go to and find out what was offered on these cars in 1972?

Thank you,
Tim

[rmadison]

Can't help but I can share the frustration.
I'm also trying to pin down the rear end ratio on a 1971 280 SL with manual transmission. The books say it should be 3.69 but some had 3.92. Was told that to do the math using the RPM's and speed, I need to know the rear tire circumference. The tires are 205 75R 14 and measure 81 inches around. When I do the calculation, I get a number between the two ratios. I'm going to check out the accuracy of the speedo , eyeball the RPM's exactly, and do it again.

The ratio is supposed to be stamped on the passenger side of the unit on 280SL's but I can't see it.

Richard M

[TSL]

Here is some info from the old Pontiac days.

These are close:

Miles per hour, per 1000 RPM in final drive

3:08=25.6 MPH
3:36=23.1
3:55=22.2
3:70=21.3
4:11=19.2
4:56=17.0

example: 3:55=22.2 x1000 rpm=(3000rpm)=66.6MPH

This was from the early 70s.

Good luck
Tim

[Tom Drew]

Can't you just figure out the rear end ratio by making index marks on both the rear tire and driveshaft, then take the tire through one complete revolution and count the corresponding revolutions of the driveshaft?

One revolution of tire & 3 1/2 revolutions of driveshaft = 3:50 ratio