Posi Rear end from '65 Lark 4-speed into '65 GS Auto?

[halfmoontrail]

My next questions. I just got my '65 Skylark 4-speed 300 ci V8, as a donor car for my '65 GS convertible automatic.

I'm pretty sure my GS has an open rear end (no tag) (AND one of the rear brake drums is stuck), while the '65 Lark 4-speed has a posi rear end.

Question 1. Is this a direct swap?

I also have another '65 Skylark, currently a 300 with a turbo 350. I'm pretty sure that this was originally an open rear end, but was converted to posi, "8.2 BOP axle 390-1 gears, Auburn Gear pro-series locking differential" description from previous owner.

Question 2. Is this a direct swap?

Question 3. Were the rear ends/axles/differentials different on the GS from the Skylark? I've seen discussion here about the axle bearings.

Question 4. If GS rears were different, can I use the Auburn Gear Posi setup in my GS chunk?

Question 5. What would you do?

Thanks!

Steve

[WkillGS]

The main difference between the standard rear and the GS rear is the wheel bearings. The GS uses the larger RW-507-AR bearing (same as Sportwagon). Std rear uses the RW-507-CR bearing.
The larger bearing has a larger OD, so the housing flares larger at the ends of the axle tubes.

I'm not sure if there are differences in axles on 65's.
In '66, larger dia axles were used and different RW-507-GR bearings.
Gears and posi center sections should be interchangable between all. If someone used Pontiac parts, they may have different size ring gear bolts.

Center sections are made for a particular gear range. One size fits 2.93 to 3.23 gears, the other size fits 3.36 to 3.90 gears.

[Brian]

You can put the entire '65 Skyark rear end with the 3.23 gears and factory posi into your GS--all the complete rear ends you mentioned are complete drop ins for each other.  Only internal differences.  You cannot use the posi carriers out of either of your posi rear ends in your GS if you want to retain the 3.08 gears that are in your automatic GS.  The 3.08 gears take a different carrier that has the ring gear spacing machined differently.  If you used the gears along with the carrier out of one of your posi rear end, then you could put them in the GS rear end housing.  I would recommend using the 3.23 gears.  The 3.91 would not be practical on the highway.

[WkillGS]

  You cannot use the posi carriers out of either of your posi rear ends in your GS if you want to retain the 3.08 gears that are in your automatic GS.  The 3.08 gears take a different carrier that has the ring gear spacing machined differently. 

If the 4 speed Skylark rear has 2.93, 3.08, or 3.23 gears, the posi carrier would fit the GS's 3.08 gears.
But if it has 3.36 or higher gears, the carrier will not fit with 3.08's.

[Brian]

You are correct Walt-I wasn't thinking straight I guess!   The 3.23 posi carrier from the Skylark 4-speed car will work with the 3.08 gears in the GS rear end. 

[halfmoontrail]

Thanks, Brian and Walt. I'm much more comfortable swapping entire rear ends than opening the differential.

Am I likely correct in assuming that my GS has an open rear?

It sounds like either the 4-speed posi or the racing posi complete rear ends will swap right in to my GS, but the 4-speed posi would offer more civilized gearing.

Steve

[WkillGS]

Am I likely correct in assuming that my GS has an open rear?

It could be either. Production reports show more cars in the snow belt were built with posi-traction, so I'd guess back in the day it was touted more as a traction-aid for bad weather, than it was as a performance option. Overall 10-15% of Skylarks had posi's.
My '66 GS 4 speed car came with an open-end rear......now who in their right mind would order a big-block-4-spd car with an open rear????? Even when I bought it in 2004, one rear tire had much more tread than the other.

Brian, what was the standard ratio for 300-V8 Skylark 4 speed cars?
3.36 was std for the 4 speed GS's.

[Brian]

The 300V8 and 225V6 specials/Skylarks with either a 3 speed manual on the column or 4 speed manual came standard with a 3.23 rear gear.  The cars with a 300 V8 and automatic came with a 2.78 rear gear.   V6 cars with an automatic came with a 3.08 rear gear.  The station wagons were different--can't remember the ratios for them off the top of my head.  I do remember that alot of the wagons had automatics with 3.23 rear gears.