Ces

Hello good people of CO,
I have a transitional year 1972 Olds Cutlass Supreme convertible.
I'm having a 455 built at Gotellis Speed Shop.
The engine builder there told me he needs my rear end gear ratio,
to order the correct parts for the build.

I read though the forum here in the hopes of finding info, which I did.
This thread was helpful:

https://classicoldsmobile.com/forums...ou-tell-s.html

It mentions finding build codes on the axle, underneath on the passenger side.
I just spent a half hour scraping gunk off this area, and found no trace of numbers or letters.

I plan on buying an Eaton posi differential gear to go inside my "peg leg" 10 bolt housing.
Eaton Part number 362- 19557- 010
The people at Jegs told me they need my rear end type to sell me the right part. They said "the '72 Oldsmobile Cutlass Supreme is a transitional year and it could have a 28 or 30 spline rear end. Likely it's a 28. 3.08 or 3.23"

I know that my car is built in Lansing in March 1972.
It came with a 350 ci, 4 barrel, single exhaust.
TH350 with console shift.
And a 10 bolt non posi rear.

I don't have the $275 the local shop wants to open up and id my rear end.
Is there any way I can figure this out on my own?
I'd prefer to not have to open it up.
My mechanical skills are few...

I'd like to know:
How to correctly ID my rear end.
what's the standard rear end on cars with these specs.
That'd be a good guess where to start with what I might have.

Where to look for the build codes, or if I'm looking in the wrong place.

Please keep in mind, this is all totally new to me.
I apologize if I left out any crucial information, or if I sound like an idiot.
I'm completely in the dark here, trying to find my way out.
I'm extremely appreciative for any and all info you share on this.

Thank you very much.

Octania

$275 seems a bit steep to do a half hour cover pull and refill with lube.
Maybe that was for axle pulling and spline counting too

Supercars catalog has or used to have visual ID chart:

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

Can you find a local hot rodder at the cruise night, pay them to do the work?

If you don't want to be getting into pulling the cover yourself, then just count turns.

You want to count the driveshaft turns required to obtain one full turn of the RING GEAR.
This requires TWO full turns of ONE rear tire, while the other tire does not move, as can happen when the final drive does not have a positraction unit.

Front wheels chocked
Jack up ONE rear wheel.
Trans in neutral

Does ONE elevated rear wheel turn? Sure it does, w/o posi

Turn the ONE elevated rear wheel until valve stem or your favorite marker is in an obvious position.
or
Mark the tire with chalk or whatnot...
so you or your helper can accurately ascertain the TWO tire turns.

Watch the driveshaft and count ITS turns while turning the ONE rear wheel TWO full turns.
See youtube differential explanation videos and/or other threads here for why this is TWO turns of one tire.

https://classicoldsmobile.com/forums...y-rearend.html

https://classicoldsmobile.com/forums...end-ratio.html

post #13 of
https://classicoldsmobile.com/forums...o-stumped.html

Note that you can easily determine driveshaft turns to the nearest 1/8 turn by the position of the U Joint.

compare to known ratios
Not quite 2 & 3/4 ==> 2.73
Just over 2 & 1/2 ==> 2.56

etc.

Ces

Thanks.
This was suggested by the guy building the motor.

Will this also tell me if it's 28 or 30?
Sounds like I still need to open it.

And,
Yes $275 is incredibly steep.
This is not including pulling the axle.
This is to remove the cover, ID the ratio.
Replace cover (and gasket or silicone seal) and refill with fluid.
I live in the San Francisco Bay Area and prices are usually higher here than most of the country. From gas to houses, everything here often costs more.

jaunty75

What's a "transitional year" Cutlass?

Ces

To my understanding, transitional model products can have different specifications or features than a standard model. As they are built between an established model and a new model. These products can have new features and old. New parts and parts from the previous model.
I know these exist from two Rolex Submariners I've owned.
BTW, "transitional model Cutlass" were the words that Jegs used, not me.
I'm just relaying what was said...


1972 was supposed to be the first year of Colonade body style Cutlass.
Due to UAW strikes, Olds produced the 68-71 body style for one additional year.
Transitional model in this instance means my rear end could have 28 or 30 spline teeth. Where as 64 to 71 does not. That might be 68-71. As I said before, I'm in here for help because my knowledge is very limited.
I'm the wrong person to answer Oldsmobile questions.

Ces

Here's a reference on Wikipedia about a "transitional" model Oldsmobile engine:

http://en.m.wikipedia.org/wiki/Quad_4_engine

jaunty75

Cool.

I've never heard the term "transitional" applied to the '72 Cutlasses. As you say, '72 was supposed to be the year GM introduced the new A-body styling that ended up getting delayed by one year because of the fall 1970 UAW strike at GM. So the '72 models ended up being warmed-over '71s, but the effect was to give us, all these years later, another year of collectible Cutlasses as the '73s and later are by no means as popular.

As far as what rear-end gear ratio you have, the 1972 Olds Chassis Service Manual should be of help. It says that the differential ratio code letters are 1/4" high and are stamped on the "right front inboard side of the axle housing tube."

I would keep looking for these numbers as they are stamped into the metal and should not have worn away unless someone took a metal grinder and ground them off, which would be a weird thing to do.

The first two characters in the code should be, for a Cutlass Supreme, SA, SC, or SR, with these indicating, respectively, 2.73, 3.08, or 3.23 gear ratios. If the car is equipped with an anti-spin differential, the first two characters would be SB, SD, or SS, indicating the same three ratios.

The later characters indicate the manufacturer and the build date.


The gear teeth for the three ratios are, for SA/SB, 41:15; for SC/SD, 40:13, and for SR/SS, 42:13.

The ring gear size for all three is 8.5 inches, and they all have 10-bolt covers.


The above does not apply if the car is a W-30.

jaunty75

True enough, but the Quad 4 was an engine, not a car model, and it was from the late 1980s, not the early 1970s.

Ces

Great info. Ill go find those numbers.
I admit I looked on the bottom of the axle, not the front.
More elbow grease and the right location should yield the codes.


Yes I am aware of that. Having found it and read it before posting the link.
It does show an oldsmobile product being referred to as transitional.
So I thought it might be relevant to support the term being used by Jegs and in reply to your question, respectfully.
No, it is not a direct nor identical example.
Just the best and closest similarity I could find at the time.
Thx

jaunty75

Let us know if you find them.

70cutty

Ces talk to Jim - Monzaz here, he can help you ID the rear end and supply all the parts needed. He helped me and many others, good guy to deal with.
His website.

http://www.jdrace.com

Allan R

Your car really isn't 'transitional' if you want a better example of a transitional year, look to the 1988 production when Cutlass changed from RWD to FWD. 2 completely different offerings of the same brand name. There are a significant number of differences between 71/72 that make the car different, but all of the parts will fit, just not match. Jets needs to better define their benchmark.

You have 28 spline axles. My car was also built at Lansing in April of 72. It had a 2.73:1 ratio. Follow Chris's advice if you can't find the letter code. If you do find it, it will also have the ordinal date when the axle was assembled. That date code stamping is on the top side of the axle, near the vent tube BTW, so it's not going to be all that easy to find and read with the axle in the car.

Octania

talk to Jim - Monzaz here, he can help you ID the rear end and supply all the parts needed. He helped me and many others, good guy to deal with.
His website.

http://www.jdrace.com[/QUOTE]

More specifically:
http://www.jdrace.com/diff_id/10b85.htm

In my limited experience, the Diff code characters are
about 1/4" in size
fwd or aft side of tube
RH = passenger side
upside down, as the frame was assembled upside down
sometimes absent
always rusted beyond any possible reading in MI

Good light and some sandpaper might bring the characters into view for you.

The above site lists the spline count and with that site and looking at your car you should be able to peg it.

If you take the cover off, then you can see the HUGE 3-digit number cast into the carrier where the ring gear mounts- and that will tell any competent diff man what the spline count is, etc.

Ces

Inside the diff housing we found this:
137•138•298

On the ring gear it's stamped
41A15 GM CHYXX 73

On the pinion gear it's stamped
on top:
15A41 GM UU

on bottom:
1285804-18

So we deduced the following:

41 teeth ring gear
X
15 teeth pinion gear
2.73 to 1 ratio
10 bolt
28 spline
8.2" rear end
Looks to be a "GM corporate" aka Chevy rear end that were used in some of these cars.

Please let me know what you think....

Ces

image_zps4c56ab89.jpg

image_zps050b514c.jpg

image_zpsa7649296.jpg

70cutty

I don't know how to decode the numbers but i do know that many so called rear end specialist think that 71/72 rear end is 8.2 and it's not it's 8.5. It's because it is kind of similar to 8.2. When I bought a 71 rear end for my cutlass, the guy I took it to said its 8.2, I talked to Jim and he said take it somewhere else, you don't want that guy working on it.
Whether that's your case, I am not sure, but I don't see why would anybody swap it for a weaker rear end.

Like is said before you do anything do your self a favor and talk to Jim, he can tell you exactly what you have and supply you with good quality parts.

Allan R

Up to this point you were doing fine. 1972 Cutlass models did not use Chevy rears. The 72 is an 8.5" corporate rear.

Ces

My rear end has all the features and dimensions of the 8.2 not the 8.5
Using this picture as reference

image_zpsbf3047ad.jpg

Ces

My cover also has the "irregular" lip feature.
We could find nothing similar to my rear end and the 8.5 pictured

image_zpsbf3047ad.jpg

Ces

My rear end has "slip in axles retained by c clips" and a 1 1/8 pinion nut.

Allan R

Can you post pics of the rear that's on your car? It's entirely possible a PO swapped it out for some reason. But from the factory, it would have been the center differential in your pics. You said the shop didn't pull the axles? How did they ID the spline count then? Did you ask if the axles were bolted in, or whether they were held with C clips?

Here's some pics of my stock 72 8.5 corporate rear cover before I restored it 2 years ago. Does your differential look like this?

Allan R

Ah, you posted while I was typing and inserting pics. Your axle is not an Olds axle, so a PO did some changes before you got it.

Ces

It does look exactly like yours.
BTW, OPGI says they only list and sell parts for 8.2 rear ends on this car.
They have no records of 8.5's in these vehicles.

Looking at the Eaton and Auburn Posi rear end choices for my car,
There are no 30 spline choices for 10 bolts, for 1972.
The only 30 spline choices were for very different years and for 12 bolts.
So with that, and some info from other sources, we deduced it's a 28 spline rear.
No we did not pull the axle.

Thx

Ces

Here's mine. After we put it all back together today...

image_zps81853580.jpg

Ces

image_zpsa33832be.jpg

Ces

image_zpsb5c9f278.jpg

Ces

Unf, we found no sign of numbers or letters on the axle.
We cleaned and looked closely in various locations.
Nothing.
No grind marks either...

Ces

Here's the source for the picture I posted with the three rear ends.
Lots more info on this page:

http://www.crankshaftcoalition.com/w...identification

jaunty75

But didn't Allan establish in this post

that your axle is not an Olds axle?


If so, then anything I said earlier about codes and where to find them is invalid. That info is out of the Olds Chassis Service manual for 1972 and refers only to Oldsmobiles of that year.

Ces

Sorry, haven't really considered or investigated this.
I've been so busy all day under the car and on the phone/net looking up references, I haven't gone there yet.

It very well may be.
I have no idea.
Thx

Allan R

I wouldn't trust their records, and if they say 1972 Olds Cutlass is 8.2 they're flat out wrong.

That's 100% correct - all 72 Olds Corporate 10 bolts c/w 8.5 rings were 28 spline.

Did you pull the rear drum to to see if the axle was a C clip type? I can't see the pin in your pics of the differential. A C clip axle won't have any holes in the hub for undoing bolts that retain a bolt in axle (as below)

Ces

No, we did not.

70cutty

That's a olds 8.5, original to your car.

Ces

Thank you again, 70cutty!
I'll do that if needed.

I think we learned today that a po swapped the rear axle and I seem to have a non-Olds 8.2. Some kind of GM...

Allan R

True, but what if the carrier and axles were changed?? I'm really curious about this now because I thought exactly the same as you when I saw that picture.

Interesting on that cover that the PO changed the rear fluid about every 2 years. Pretty much overkill IMO, especially with an open differential.

Ces

Wow, really? It doesn't have any Olds stamps or codes that we could find.
The dimensions and specs all indicate 8.2 if you review the picture I posted showing three rear ends...

Ces

The second owner had the car from around 2000 to late 2013.
I see he last changed the rear end fluid in 2006!
That didn't seem like every two years to me...

Ces

This indicates 8.2 not 8.5.

Right ?

According to the three rear end picture I posted.

Maybe the picture is wrong

My mechanic measured the pinion nut very carefully, three different times.
It is 1 1/8. Found only on 8.2 rear ends.
True ?

70cutty

Here is a picture of mine. Tell me one thing, does yours have the little square bumps on the casting collar. I would draw a circle around them but kind of hard on the phone.

rearend_zps8b4d0ad3.jpg

Allan R

Take a look under the car (as per this pic) and you'll find the part number of the differential. Should be identical to this.