Hi all my fellow Olds guys. I'm wondering, I do have a real 1970 Olds W31. It has the 3:91 gears which as we all know suck on the highway. I want to make if more Highway worthy, with out it costing me a ton of money. Obviously an OD transmission would be best, but expensive now. What are my options with this rear end. The only two ratios it will except are 3:91 and 3:42. with out swapping carriers. Where can I get a new carrier for my car? I thnk this is an O type rear end. I can't remeber. My uncle will do the labor for free, I just have to get the parts. OR does anyone know of a good OD trans that isnt $2200 or more like I've been seeing for a beefer motor. Thanks in advance everyone. I do have the 12 bolt rear and it is a posi rear end.

 

Why not swap the entire rear end assembly?

You can have 3.08 or 2.73 probably w/o much cost.

You can even leave the brakes on the car. Backing plates and all.

 

I talked to my uncle and he said for a rear end it would be about $1100 and would maybe have to motify the driveshaft Is that true? Or are refering to something else?

 

Try "supercars unlimited"....I believe Greg still sells 'o' type posi's that will fit 2:98 to 3:23 gears and he even had 3:42 gears that fit the same carrier.

 

If you use another similar 67-69 12-bolt with 10 bolts.... the driveshaft should be the same. Driveshaft is not all that expensive. Go ahead and price out your various options. From what little internal rear end work I have done, I would way rather swap assemblies. That 3.91:1 final drive you have should be kept as it is. They made millions of non-posi rear ends in more economical gear ratios, there should be some around yet for not too much $. I probably have a dozen of them, but none handy.

 

I agree with Octaina, swap in a complete rear with highway gears and put that one under your workbench. With a car as valuable as a W car any modifications will reduce its value. The 3.91 housing will have a two letter code stamped into it. Once you go messing with the internals that will detract from the originality of your car. I too have several Type O rear ends with highway gears and probably many other members have them as well. In my part of the country they sell for about $100-150, add shipping and your still way under $1,100. If you want a posi that will be more like $500-600 for one with highway gears. That's my 2 cents worth

John

 

Huh, I'm having problems and am unable to edit my post. I realize I didn't finish the thought on the two letter code. There is a two letter code stamped into the passenger side tube that keys out what came in that housing from the factory. I don't remember, but think TM or TO is the 3.91 posi. In addition there is a date casting code in the center pumpkin. If your car is original, like the correct engine and transmission I'd not do anything that would make it less original. Many of these cars lost their original parts years ago, so finding one that still has everything is pretty rare. I'd have no problem putting an overdrive transmission in a Cutlass. But would think twice before modified a 442 or W car. That's my thoughts on keeping your 3.91 under the work bench. Some day... you may decide you want to put it back to original and the easiest way would be to swap the whole assembly.

John

 

However ..... if you really have a W-31, with original engine and original cam, you should not even be considering putting highway gears in it. 3.42 will be tolerable, but anything numerically lower will turn your car into a dog (if it has an automatic transmission) and also make it difficult to drive (if it has a manual transmission). There's a reason the factory made 3.91 gears standard for the W-31.

 

The HD O-Type rears were 31 spline, and my information shows those were the early versions only. For 1970 there were no HD 31 spline rears.

 

Telling the gear ratio is only half the equation. Final drive ratio and cruise rpm are also a function of tire height and cruise speed.

First off slow down. What is the big hurry?

If you are currently running a 26" tall tire on the car then you have the option of going to a 28" tall tire on a 15" rim. This with a gear swap to OEM 3.42 gears will knock the stink off those highway rpm.

Any taller tire or less gear behind a W-31 automatic makes the engine very unhappy. A W-31 engine was meant to rev. If you wanted a lazy highway cruiser you chose the wrong Rocket.

 

I have a few type O 3:08 rearends.

contact me direct

lemoldsnut@aol.com

Or call 8 am to 8 pm mon-sat 541-815-4363 west coast time

 

Thanks for making the corrections. I forgot it was 31 vs 30 and didn't know the 1970 were all 28 spline. I'll edit my post to prevent someone from being led astray!

John

 

Isn't someone making an overdrive that bolts on to the trans. Maybe it replaces the tale part of the trans. You said earlier about the drive shaft wouldn't fit . I had a new drive shaft made for my Omega . All I had was the slip yoke. It cost a couple dollars over 200. Balanced and everything.
Railguy

 

So you are installing a 455 in a real W-31 car? Shaking head. You should have mentioned this earlier.


Anyways if you are going to a 455 then put your 3.91 gears & posi aside & install a 3.08 or 3.23 gear & carrier. The 455 will be fine with a tall tire & low 3 series gears.


Sure hope your trans is up to the TQ of the 455....

 

Yeah, I know it was a tough decision, but I got such a good deal on this 455.. compared to what it would cost to rebuild the non original 350 under the hood. And this trans is built up, so hopfully it should handle it.

 

Ps, what is wrong with the 455 in that car, just curious? As I mentioned, it was a less expensive way to go. I actually may sell my 455 still. I was just broke in and dynoed last week. And of course I still have the 350 sitting there.

 

@Blackgold, Yes sir, it is a real W31, had it authnticated at the GM dealership which used to be an Olds dealer as well. It was bought her new actually. But unfourtunaly it is not the original 350 under the hood

 

There is nothing wrong with using a 455 and a turbo 400 auto.

 

I put a TKO 600 5 speed in my Omega. I think it was about $2,300. the plan was to put a 5 speed in first then later change the gears in the rear. I haven't change the gears yet but it seems to run really well. I have 2.73 gears now with 15 inch tires. it takes around 1400 rpms to do 60 miles an hour. it doesn't have a lot of power in overdrive but its not that bad and it takes off really well. I'm still planning on changing the gears I have a set of 3.43 S with a posi carrier. I'd like to change the gears this winter but I'm planning on going to Ocean City cruise week in the spring. and I don't want the test drive to be the 250 mile trip one way to Ocean City.
Railguy

 

It will work just fine and it is your car so you decide what works.


However....I am sure I am not the only member pained to see a W-31 with 3.91 gears be converted to lazy gears & a 455. That kills the purpose of the W-31 doesn't it. But like I said it is your car so have at it....

 

Non numbers matching w31 Dave.It has 350 that isn't the factory motor nor transmission! If it was a numbers matching i would agree with you Dave.

 

Gear Vendors OD unit (google it). Keep the trans and rearend. You will need a custom length driveshaft, which is not costly if you don't want cut the OEM. This will basically give you a 6 speed out of a TH350 and an 8 speed out of a Muncie and you can keep the 391s

 

Thanks for all the input guys. Keep it real, keep it Olds!

 

Sorry but the loss of the original drivetrain does not mean it is no longer a W-31 car. W-31 cars should stay SBO powered IN MY OPINION. By the same reasoning you would allow the installation of a 350 Olds in a 1970 442 W-30 when the original engine went away....and that too is just wrong.


The only opinion that matters is the owner of the car. Do what you want but I will never agree that it is a good idea to put a BBO in a REAL W-31 car.

 

Oldsmobiledave, I do agree with you, somewhat. But this opportunity for the the 455 came up. I am still considering selling the 1969 455 I have. Its a brand new rebuild, broke in and dynoed. Then I would use that money to rebuild my 350 rocket. The poblem is my car will stay at the shop till march now do to our weather in Grand Forks ND. So I won't even get a chance to try the BB till march.