Unless I'm reading the shop manual wrong, the '68 4-4-2 came with a 4.33:1 gear ration? THAT would explain the engine revs when cruising down the highway. LOL
I thought it might have been a 3.73 (better highway gearing) but I really think it's the factory ratio if I read the shop manual correctly. Also need to check for the stamp on the housing. I guess I COULD change the ring and pinion to keep the stock differential assembly.

 

For '68, the standard from the factory was a 3.08:1 ratio. Optional ratios were available 3.23, 3.42, 3.73, and a few in the 4s as I recall (4.11, 4.33 and 4.56?, some of which were only dealer-installed), depending upon transmission and options, such as A/C. I believe the Turnpike Cruiser could have come with a 2.73 or a 2.56. Anti-spin was an option with all those gears.


As for revs, I'm always amazed at my '68 with its 3.08 anti-spin. I keep expecting the THM to shift one more time when I'm rolling down the highway, but it doesn't because it is already in high (3rd) gear! I've gotten so conditioned to the newer cars with their 4th gears and overdrives that knock the RPMs down below 2000 at 60-65 MPH that it seems out of the ordinary having RPMs at 2500-2700 for the same speed!


Randy C.

 

If you can find the code on the axle housing, pass side rear, between the pumpkin and the shock mount, it can be decoded. if it is an auto a/c car, most were 3.23's.

 

You left our the 3.91 gears & you grouped the Type O & Type C together.


Type O 3.08 3.23 3.42 3.91 4.33 with dealer 4.66 or 5.00
Type C 3.07 3.31 3.55 3.73

 

Finally got a chance to jack her up and do the rotation count. Seems I have a 3.73 P-Trac.

 

Take a picture of your diff cover. Unless someone swapped out your axle for a Chevy model, it's not a 3.73.

 

If your car was built in Canada it could have a Chevy 12 bolt from the factory. Take a pic of your rear cover and check the code.

 

I believe the guy I bought it from mentioned he and his son installed the 3.73 Chevy differential. I didn't pay that much attention at the time.
12 bolt cover

 

That's why we want a pic. The Olds rear also has a 12 bolt cover, but it looks different.

 

Olds:



Chevy 12 bolt:

 

Well, there is no stamped code on the axle housing that I can see. But there is a lot of undercoating on the differential. According to the above photos, mine is an Oldsmobile. I saw the metal tag on top and removed the bolt to read the tag. Just a warning tag to use the proper differential grease. I was hoping for more identification info. And again, counting the number of turns of the driveshaft with one complete turn of the wheel, I am 99% sure it's 3.73 gearing.

 

That is definitely an Olds 12 bolt. You will only have either 3.42 or 3.91 gears. No 3.73 EVER for Olds 12 bolt!

 

Look on top of the right axle tube for a 2 digit code.

 

Just another case of stump the monkey. LOL
Too much paint and undercoating on the housing.
Brake line laying right across the stamp.
Stamped upside down.
Combine all that with my miscounting the number of driveshaft turns and you have mass confusion.
What I am 100% sure of now is I have an "O" type differential.
Stamped TM, or if you're expecting it to NOT be stamped upside down, a W1. LOL
Since there is no W1 in the service manual, and since I paid a bit more attention to the number of driveshaft turns, I have a 3.42 geared rearend.
Mystery solved.
And I also learned not to believe everything a previous owner says.
It sure "SEEMS" to be a lower gear ration since this baby sounds like she is taching out pretty high at 55mph. I think I'll be adding a tach (tastefully placed of course) just to see.
Thanks again for all of the help and lessons on Oldsmobile!!!

 

TM is the correct code for 3.42 and is usually specific to W-30 and W-31 only. Is your car a W-30? Also, the carrier for the 3.42 is also correct for 3.91, 4.33, 4.66, 5.00 etc. gears and many people changed the gears for more performance.

 

That means....time to service the diff.

 

Don't know.

 

I meant the only way at this point to be 100% sure what you have is to pull the cover and look at the ring gear for the markings. That will tell you the ratio with 0 doubts.

 

Just under 3-1/2 turns of the driveshaft tells me sure enough.

 

But weren't you 99% sure it was 3.73?

 

Good thing I didn't say 100%...especially based on what the previous owner said.
LOL
Yep, I must have not watched my reference point close enough the first time.

 

I'm running 3.73's

Great around town, but useless for highway runs.

Wish I went with 3.42's instead.

 

Anyone could stuff a new gear set into any case so the only way to be 100% is to pull the cover and count the teeth. The tire to drive-shaft rotation count will get you in the ballpark. So EZMAN you likely have a 342 or 323. No 68-70 Olds O type rear axle is considered a 12 bolt. Yes the cover has 12 bolts but the carrier has 10. All 68-70 Olds O type rears are 10 bolts not 12. If it was an Oshawa car it should/could have a Chevy 12 bolt (442s). 12 bolts on the cover 12 bolts holding the ring gear to the carrier assembly.
Some of the BOPs built in Canada got some if not complete Chevy drive trains in BOP bodies or hybrid bodies. Pontiac built the Beaumont and the Parisienne. The Parisienne could have been ordered with a 427 Chevy big block.

 

[QUOTE=droldsmorland;8601
Some of the BOPs built in Canada got some if not complete Chevy drive trains in BOP bodies or hybrid bodies. Pontiac built the Beaumont and the Parisienne. The Parisienne could have been ordered with a 427 Chevy big block.[/QUOTE]

That's a pretty cool little tid-bit, thanks. Are there many survivors?

 

Not BOPs, just Pontiacs. Google Beaumont and Arcadian.

 

Everything you need to know about domestic 442 and Cutlass rear end ratios:

 

Heres a 69 Poncho with a 427. This one had paperwork too. The guy who found it got a folder full of docs from the farmer who was the original owner. One wonders why if he was so meticulous with paperwork why he'd let this gem go?
I have another pic somewhere of a 67 or 68 B Bodied Buick wagon with a Chevy drive train SAID to be factory special ordered with that big block, no proof. I have also seen a 68 4 door Cat with a 427. Didn't see any paperwork on it though. So who knows? Interesting area 51 lore for sure.

 

I have a 70 442 factory 4 speed car that I purchased from John 2blu442. It is a project to say the least. I have been gathering parts for it for some time. It has been frankenstiened with lots of wrong parts so it will never be numbers match. So, I have a 71 455 that had treatment by Joe Mondello and I have been waiting for the car to put it in. I am using a M20 for the better out of the hole feel of the wide ratio trans and the car has the wrong rearend which just so happens to be a 12 bolt Chevy. I was thinking I would change it to a O type and then thought better of it. The 12 bolt Chevy is a good rearend and there is lots of parts available rather cheap. I have decided to go with 3:31 with an eaton posi. That will cost me less than just a posi carrier for the O type.

The only way to tell for sure what gears you have is pull the cover and read the ring gear or count teeth.

 

Chevy powered Pontiacs are the Canadian built ones