I have asked two reliable resources to answer this question which I believe they are correct. I'm just looking for reassurance for the owners sake.

What is the correct differential code or gear ratio for a 1970, 442 4 speed convertible with A/C? Is it SF 3:23 or SH 3:42?

 

I do not think they would let you have A/C and 3:42 gears in 70. 3.23 is correct.

Don W

 

When you ask me the other day I did not realize it had A/C. I thought it was just 4 speed. With A/C it would be 3.23

 

Ok, thanks

 

After seeing this post, went back and read some older post about the possibility of the TM code 3:42 in W30 with A/C. Never saw a consensus that could prove either way.

 

I have always heard that if the car had AC, then the rear gears could not be numerically higher than 3.23 as to keep the compressor from spinning to fast (over many miles) & burning it up.

 

The only Oldsmobile documentation is that 3.23 is the only rear end with A/C. Many believe that 3.42 could have been had and that maybe true but there are no documents to have surfaced to prove it yet.

 

The dealer wasn't supposed to order 3.42 gears with A/C, and the factory wasn't supposed to install 3.42 gears with A/C. What we don't know is what happened when the dealer broke the rules; did the factory then break them, too? My guess is that occasionally it happened, whether by mistake or on purpose.

 

66/67 cars with A/C were available with 3.55 rear axles. Not sure why they changed it.

 

I was referring to the 1970 through 1972 cars. I don't know much about the '66-'67s yet.

 

The letter code also depends upon open diff/limited slip and disc brakes/drum brakes, so a 3.23 rear could be one of many different letter codes.

SE = open diff, front drum
S6 = open diff, front disc
SF = anti spin, front drum
S7 = anti spin, front disc

and then there's SH for the Hurst Olds.

 

Apparently the consensus is correct. Sales literature says that the 1970 standard 442 (not W30) with the M21 & C60 options had only one possibility: 3.23 (option number G91).

 

In 1965 the dealer, unknowingly, broke the rules, at my request, on an order. The rule was not written down on any literature he or I had available. Someone in Lansing caught it and "bounced" the order. I've always wondered what would have happened if it hadn't been "caught".

 

Disc brakes have nothing to do with rear end code. For example, An A/C 70 W-30 had an SF code rear end and all W-30 cars were disc brakes.

 

I will ad that my 70 442 project w/air and disc brakes has a SE code type O 3.23
with a casting # of 402227 and should be a 28 count spline on the axle shafts
according toSupercars Unlimited.

http://www.supercarsunlimited.com/in...id/diff_id.htm

 

If I recall correctly, the mid sixty cars for some unknown reason had different rear axle codes that correspond with the brake option.

 

Actually, a '70 442 with a 4-speed was not suppose to be available with A/C. The M-21 was not available with gears numerically lower than 3.42, which precluded the A/C option.

There are some rare documented '70 4-speed 442's with A/C though, which have a factory M-21 and 3.23 gears. This was not an issue in '71 since the 442 came with the M-20, which was available with the 3.23 and numerically lower ratios.

There is a Rallye 350 in Florida that allegedly has documentation showing the Rallye was ordered and built with an M-21, 3.42 gears, and A/C.

 

All 69 and 70 O-Types had 28 spline axle shafts. The only non-28 spline axle shafts were the late 67 and 68 HD 31 spline rears that were available in the OAI applications.

 

1970 Oldsmobile options & power teams