Differential Question

I bought a '69 Skylark Custom as a donor car for a pile of goodies. I'm looking at the differentials of the two cars and have some questions. Here are the pics of the pumpkins of the two. Are the ones labeled as '69 a better differential? I don't know how to tell. The '69 differential uses U-bolts with nuts and washers, and the '68 uses shorter caps and bolts to hold in the u-joints. The first two are from my '68, the second two are from the '69. Any knowledge is welcome.

 

Looks like the 68 has an 8.5" rear, which is the better diff. The one labeled 69 looks like the original 8.2". The 68 must have been replaced at some point in its life.

 

seems to me the 68 rear is actually a 71 and up 8.5" rear. the square corners on the bottom are a dead giveaway. The 8.5" will be much cheaper and easier to build.

 

I was looking at the lumps and thinking that I had this backwards. I had best check with my son, who took the pictures, and make sure he got the years right. Pretty sure they are correct, though, since I can see shiny exhaust pipe in the '68 pictures. I'm pleased if I have the better differential in the car already. Seems like it might have not been, considering that most parts stores can't even get me the cover gasket...like it was rare or undesirable, or something.

Thanks for the speedy response, guys.

 

AS stated just to confirm - first 2 pictures are a 10 bolt 8.5 from a 71 72 skylark next to pictures are of the 10 bolt 8.2 BUICK ONLY 68-70 era

Both can be built -10 bolt 8.5 will be easier to find parts and be cheaper to build Plus the center section will be stonger the axles will both be 28 spline so you will always be limited there.

Gaskets are both easy available. 8.5 will use a chevy 8.2 cover so ask for a chevell or camaro from 67-81 same bolt pattern. You will need to trim the gasket to fit the skylarks 3 and 9 o'clock cut out area OR just leave it ...it will only hurt your eyes....
Buick cover is same as GTO 65-72 done...

Jim
J D

 

Thanks, Jim I appreciate the input.

 

I want to convert my 1968 Buick Wildcat Custom 2 Door OEM single wheel (open differential), differential to a GM 1968 OEM Positraction and use my original GM 1968 OEM gears. I need to know what to ask for when contacting junk yards, used-parts dealers, etc., for a used GM 1968 OEM positraction. Example, did the full-size GM 1968 Buick Wildcat positraction differentials come in OEM series, (which used specific gears) like the full-size General Motors 1957-1964 Pontiac/Oldsmobile positractions?

I was old some years that the GM 1968 Buick Wildcat Positraction is the same as the GM 1968 Electra Positraction. Are there other GM models and what GM years that would fit with my GM 1968 OEM gears? What are the identifying numbers, letters, symbols, features, methods to identify the used applicable GM OEM Positraction for 1968 that would fit my 1968 OEM gears?

What is the information source and other contact methods, ex. names and/or phone numbers. What are some possible sources for used applicable GM OEM 1968 Positractions or other models and years that would fit my 1968 GM OEM gears.

 

Welcome aboard! The biggest stash of related info you're looking for is here: http://www.v8buick.com/showthread.php?71740. In short, you will need to find a carrier from a 1967-1970 Buick Electra, Wildcat or Riviera (NOT LeSabre). To date there aren't any other GM brands with compatible carriers that I've heard of.

The carrier you need will be one of two depending on the gearset you will run. In the '67 model year for instance, the ratios available in those cars were 2.56:1, 2.78:1, 3.07:1, 3.42:1, 3.91:1. The first three ratios use one carrier, the last two use a different carrier to put the ring gear closer to the pinion (because the 3.42:1 and 3.91:1 pinion gears have fewer teeth, thus a smaller gear diameter).

Sorry, I don't know the casting numbers on the carriers to help you with identification.

Hope that helps!

Devon

 

Really need to start a NEW thread for this so it can be searched for down the road...

You are very LIMITED on this rear. it was only used from 1966-1970... THAT IS IT. AND.... 1966 posi is all on its own so now you have to narrow it even more to 67-70 BUICK ONLY FULL SIZE CARS. Electra, Wildcat, Riviera, seems to be it...

9 3/8 " I have a Posi for this rear on t he shelf reconditioned and ready to got. It had 3.08 gears on it. Do not know If I still have the gears though. Jim

PICTURED TO HELP YOU IS THE COVER YOU NEED TO LOOK FOR AND THE POSI UNIT WILL LOOK LIKE THAT ALSO. The Driver side (ring gear flange side)carrier bearing will be larger and wider than the passenger carrier bearing also.
J D

 

steve, on the 8.5 there is a code on the passenger side axle housing, facing the seats. you can decode if it's posi and what gear it may be.
the 71 8.5 10 bolt is "The one". that's the rearend I hunted down, powder coated and upgraded with gears, posi and axles. same rear as Larry and Shawn. I'm sure many others. You scored :TU: