Aceshigh

My car was a 1970 Olds Cutlass S from the factory.
Got a Rocket 350 / th350.

I upgraded the rims and tires to an 18" rear.
Now the fat *** won't even chirp em on a full stomp 0-60mph run.
It did before , no problem. So I think the rear end needs to be swapped.
I think my rear gearing might be stock which I read , is 2:56

My tires are 285/40/18 so my tire height is now 26.98"
Stock was 225/70/14 tire height 26.40"

What do you guys think would be a good choice ??
I'm probably going to go with a T-56 six speed or 4L80 in the future.

gearheads78

I am running the same rear tire with .62 overdrive and 3.73 and it about perfect for around town and highway cruising. If you have no overdrive about 3.23 is going to be the best compromise gear.

Look for your stamped 2 digit code on the axle tube and one of us here can tell you what it is.

Aceshigh

Well, I want a T-56 but the cost of the conversion will be $3000-$4000+
SO I'm looking at possibly going with a 200-4R for now. 0.67 final ratio.

I'm still undecided if I'm going to just go with an LSx drivetrain eventually or not.
Maybe I should go in between somewhere.....like a 3.42 if I can.
I don't care about drag racing, this is for a family street cruiser for fun.

I am just wondering if any GM 3.42 gears can be pulled out of a 3rd gen or 2nd gen Camaro
out of a junkyard or if I should just buy new.

gearheads78

Do the same thing I did. Find 71/72 Cutlass or Skylark 8.5 rear. 3.42, 3.73 and 4.10 GM gears are everywhere out of late model Chevy trucks.

Aceshigh

I'm wondering if ANY 10 bolt 3.42 will work with this car.

Like any 2nd gen F-body or 3rd gen or anything for that matter.
It's only $150 new.......honestly I have never done this before, so I'm not sure.

http://completeoffroad.com/i-161322-...t-10-bolt.html

gearheads78

Just the rears Pontiac Olds with 8.2 only
http://www.richmondgear.com/07pdfs/RG12.pdf

I personally would rather have good USED GM gears if the option is out there. The 8.5 gears you show above will work in the 72 Cutlass rear in my car. My gears came from a 2000ish Suburban

Aceshigh

So this is an 8.2" differential ???

Crap.......

So that means 8.5" won't work ?? Stupid question, but I have to ask it.
They look like the same size gasket and cover, so I assumed it would.

gearheads78

Take a pic of it. You never know whats been swaped in 39 years

svnt442

The stock rear that should be in your car would be an O type axle which has 12 bolts on the cover ands 10 on the ring gear and bolt in axles.
Don't think strictly about F body gears. You're going to want a A body axle if you want easier swaps. Like Richard said find a 71-72 8.5 axle from a chevelle, skylark, lemans or cutlass. Parts are all over for that and not too expensive.

Aceshigh

Finding one of those around Chicago might prove to take quite a bit of time and a bit of a headache.

Can't you just buy replacement gears and pinions ??
I found some 10 bolt 3.42 gears, but I don't know if they will fit now.

http://www.summitracing.com/parts/RMG-4900821/

Won't this work ?? Do I need this too ??

http://www.summitracing.com/parts/RAT-309K/?image=large

svnt442

No this is what you would need. You would also have to find a 3 series carrier.

http://www.summitracing.com/parts/RMG-4900491/

Aceshigh

^ That link says it's a 8.5" not a 8.2" .......

So I'm assuming that isn't going to work.....correct ??
They have 8.2" options at Summit I found.

I don't know what a 3 series carrier is......like I said, I'm new to this part.

gearheads78

I thought only the performance cars got the 8.5 "O" rearend. Since his started life as a plane Cutlass I figured it would have the 8.2"


Aces you need to figure out what you have for sure. Like I said before snap a quick shot of it. You also need to know what gears are in it before you can change to new gears beacause as was mentioned you may need to switch to a 3 series carrier if the gear in yours now are too high. (numerically lower number like a 2.56)

svnt442

All olds A-bodies got the O axle from 67-70. I had a 70 S that was a 2.56 posi O axle. I have seen numerous 68-69 cars with the O axle that were not
"performance cars". It's just what Olds used.

svnt442

Correct you shouldn't have an 8.2. All Cutlass/F 85/442s got the O axle in 1970.

gearheads78

I would still check to be sure. The 69 Convertible I used to have had the 8.2 B/P axle and a friends 70 Cutlass I worked on also had the 8.2 B/P axle.

Aceshigh

Ahhhh.....so you're saying everything from the base model Cutlass (F85) up to the 442 had the 8.5".

Is there any place I can verify this to be accurate ??

Help me out here in Lamens terms......because I just don't know what you're
talking about here honestly.

What is a 3 series carrier ?? What might I have now ?? maybe a pic with an arrow or something to speed me along here.

gearheads78

You have to know what gears are in it now to know what series carrier you have.

Aceshigh

Okay, so I need to jack the bad boy up and figure it out.

Buddy of mine told me to just jack up the rear end.
Mark a spot on the driveshaft and spin the rear wheels 1 revolution
and see how many times the drive shaft spins.

He said if 1 tire revolution = ~ 2.5 driveshaft spins I'm probably a 2:56 or whatever it is.

svnt442

Also get a pic of the cover. Look on the passenger side tube near the vent, back side of the axle, for a 2 letter code. You may need to scrape off the tube with a steel brush or steel wool to get a good look at it.

svnt442

They didn't come with them.
There is a non O axle in my 442 right now. I know it came with a 3.23 open O axle because it was there when I got the car.
Axles can be swapped out. You just never know.

EDIT: This is from the service manual



OldsreadendIDcodes.jpg

Aceshigh

Can anyone take a pic of an axle and show me exactly where this tag should be ?? I can't find it.

Looks like you were right so far.

Okay, here's the pic of the rear end. 12 bolt.....
Now 6" to the right of the differential housing on the axle tube there is an SA stamped on it.
So I'm guessing according to your information page you posted, I have a limited slip 2:78 rear end.
Unless it's been changed internally.....

Now if I want to go with a Posi 3.42 , what would be a good recommendation??

DSC01808.jpg

oldsdroptop

Aces....I just went out and looked on my 1971 Cutlass drop (442 w-30 recreation car) and I found it immediately on the front part of the right axle tube on the passenger side, my rearend has been sandblasted and is highly detailed (southern car) But I found the letters SC 0151 so my rear gear s a 3.08 according to the guide. I'll check my SX drop its got a 2.56 posi 12 bolt stock and its detailed the same way with sandblasting and a W-27 cover on it. Good luck on your mission. it should be just behnd that right exhaust pipe on the front leading edge of the axle tube. Hope this helps. Oldsdroptop

oldsdroptop

here are 3 pics of my rearend so you can see what I'm talking about as far as the condition of it....let us know if there's anything else we can answer for you.....Oldsdroptop

svnt442

71 will probably be a different code, but I'm unsure of that. They only got the corporate 10 bolt as the O was dropped after 1970.

svnt442

It's actually a standard diff, not a posi (anti-spin) according to the chart.

Get a hold of Brian Trick. He may have something for you. He COLLECTS rear end stuff and knows what he's doing. thetrickfamily@yahoo.com
Very upstanding guy.

gearheads78

x2 Brian sold me the parts to build my axle. I highly recommend him too.

Aceshigh

Thanks,

I was told this axle was only made for 4 years (67-70) so getting parts isn't easy.....or cheap.
I already started hitting up Craigslist looking for 12 bolt differentials for sale.

But I'm going to contact him if this is a cheaper option.

svnt442

A body 12 bolts (chevy axles) are STUPID expensive. figure $500 for a JUNK core and then another $2000 for parts and labor to get is set up.
If Brian has (or can get you) a 3 series and a 3.42 it will be MUCH cheaper to get that installed in your housing.

Aceshigh

Thanks.

I was looking at this one just in case. Not sure if it would work ,
but I assumed it would.....yeah ??

http://chicago.craigslist.org/nwc/pts/1409959720.html

svnt442

That's cheap. I'd jump on that in a min.

Aceshigh

Yeah ???
So that would bolt in no problem ??
I just don't want the 4.11 gear.

I'd rather have 3.42 or 3.73 or I'll never enjoy driving it with a TH350.
So I was thinking I'd have to buy another gear set, pay to have that
done......another $600 -$800 more.....

Otherwise I'd have to put the 200-4R trans in asap.

svnt442

You can compensate with a taller tire until you get the OD trans in.

Aceshigh

Like some Mickey Thompson big a** street stickies ?? LOL

svnt442

If you go with a 275/60/15 it well give you an effective gear of 3.71. The stock tire height for the car is 25.3. The 275/60/15 is 28".

mugzilla

I thought you needed different carriers for dif gear sets, one for low gears another for tall ...

I been giving my stock rear end (3.23) a good work out and it seems pretty durable ...

svnt442

This is true. The size of the pinion determines the "series" of the carrier needed. Different rear ends use slightly different ranges as to where they change so there is no set break to go by.
He would need your carrier in his axle to use a 3.42. His 2.78 carrier would sit too far from the pinion and wouldn't make proper contact.

Using a taller or shorter tire can change the effective gear ratio. But you can loose some of the benefit of the tire you were using depending on the size you go to.

jturkey69

Hmm...I will have to look on my 71 to see if I can find any numbers. Im also contemplating an LSX in the future, but it would have to be a serious budget build with minimal wiring. Im looking at keeping it simple with a LSX/th350 with neck snap shifting, (but not u-joint destroying)