sixtyfourbeets

Hello forum readers and advisors, I am looking at a local '68 Cutlass Holiday to purchase.

The current owner says it is a non posi rear, when I inquired about the gear he informed me that he does not know what the current ratio is. But gave me an example that when he drives on the highway it cruises along at 2k or so and with a little effort is able to spin the tires.
From what I was told the transmission is a 200 4R and the lock up mechanism for the torque convertor is not hooked up. From the photos the engine is a 350 rocket with a 4 barrel Edelbrock sitting on a fancy lookin intake.

On to my question. First what is the most cost effective way to put a reliable posi unit in? I currently own a '94 Caprice with a G80 GU5 rear which translates into posi with 3.22's. From what I understand the spline count is 30 although I could be completely wrong about that. But I am almost certain that the spline count would not match up to the shafts that are in the '68 now.
So how much of that if any of it can be bolted in to the housing that is in the back of that '68?
If it can be bolted in the current housing is it even worth it? Will the housing be able to stand up to an increase in horsepower down the road?
I am happy with 3.22's in my Caprice which is a heavier car than the '68.

If rear axle is not worth keeping what would be the next best thing to do in order to have a sturdy cost effective posi unit as close to bolt in as possible. I dont want to have a custom drive shaft made yet because eventually down the road I may decide to put something entirely different in the drive train area.

I am planning on putting an F-body rear disk brake setup in and from what I understand the bolt patterns for the backing plate on the A-body's are the same.

Thank you for reading and any advise that you can offer me.

2blu442

Welcome to the site!

You've got a number of options and these options have been discussed before by other members in the same boat your in. I'd encourage you to read through some of the threads in this category to get an idea what you might want to do. Then there's a couple experts on the site, you'll see many posts with them sharing information. 507OLDS and monzaz are the two members I'm referring to.

You should also read the transmission section to learn about the 200R4. I don't know much about them myself, but from what I've read they sound like a good way to go if it was built and setup right.

John

sixtyfourbeets

Thank you.

Ok I will I glanced through some of the posts but it doesnt seem like there is an agreed upon standard. So I figured I would post my question to try to get a specific answer geared towards more of what I am looking to do. Like the G80 GU5 for example.

2blu442

Well, I just surfed through looking for one of the past threads that asked what options were out there for the type O rear ends. That's what's under the 1968. I found several threads that touch on details, but not specifically what I was looking for. You can read through the following threads and probably get a nugget from each. But the bottom line is that the Type O which started in 1966 or 67 but was used exclusively in the 1968-70 (except Canadian built cars in 1968) does not have new parts being made for them except by specialty shops like monzaz's. So its hard to get internal parts for them. You can put rear ends from any 1968-72 A-body under it with some needing different U-joints or drivelines, then the Buicks had some odd stuff that you may want to avoid. One of the simpler swaps would be to install a 1971-72 Cutlass rear end as they have the GM corporate 8.5" internals. Lots of parts available for these as they were used for many years in lots of GM cars, vans and light trucks. Unless you've got a numbers matching car that you want to keep original I'd go with the last option.

John



Here's a few that will comment on what you could put under the 1968

https://classicoldsmobile.com/forums...rear-axle.html

https://classicoldsmobile.com/forums...967-442-a.html

https://classicoldsmobile.com/forums...i-options.html

https://classicoldsmobile.com/forums...utlass-s3.html

https://classicoldsmobile.com/forums...ersions-s.html

sixtyfourbeets

Yes, I saw some of those posts during my search. So it appears that I *may* be able to put that G80 GU5 differential out of my '94 Caprice in to an 8.5 corporate housing.
I believe the '94s had an 8.5 inch rear. My Caprice is an L99 which I believe also had the slightly narrower rear and I cant help but think that if only the attachment points were the same I could bolt it right up to the '68. I dont think it would be economically worthwhile to do any fabrication work to make it be able to bolt up directly.
With all that being said the answer to the question of whether the spline count is correct has yet to be found out. Or if perhaps there are axle shafts that would fit both the housing and have the necessary spline count for the differential I have now.
The unit is a C clip unit which may be obvious to some readers.

sixtyfourbeets

I keep saying 3.22s I mean 3.23

507OLDS

You can take the guts from the Caprice housing,install it into a 71-72 Cutlass/442 8.5" 10-bolt housing,and get new 30-spline axle shafts made for the 30-spline posi unit.The stock 71-72 shafts are 28-spline.When swapping from an O-axle to the 8.5" 10-bolt,you will also need to shorten your driveshaft.

sixtyfourbeets

Would I be able to use the drive shaft from a 71-72 Cutlass with an 8.5"?
Were the 8.5's available only with 442s?
If I use the differential and associated components from the Caprice would that include the pinion and yoke? And would the yoke be interchangeable with the drive shaft from a 71-72 8.5"?

Thank you for any information you can provide me with.

507OLDS

If your 68 has a TH350,then use a shaft from a 71-72 with TH350. ALL of the 71-72 Cutlass/442's came with the 8.5" 10-bolt.They came with the 3R u-joint yoke.

sixtyfourbeets

The particular '68 I am looking at has a 200 4R.
Would I have to have a custom drive shaft made if I put in the 8.5 combination we are talking about? Or would something from a G-body Grand National/442 work?

507OLDS

Custom shaft. With the 2004R,you need a shat about 1/2"-3/4" shorter than the stock TH350 shaft.The 200R4 is a touch longer than a TH350.