Is it likely the rear diff in a 74 Omega is a 8.5? If so one worth adding a posi too. Not yet sure of the ratio. I'll be crawling under tonight anything to look for?

Thanks!

ps thinking about adding my 455 to the Omega.

 

you can never go wrong with a 455 in any olds!

 

If it is stock it is an 8.5"
Look on the right inboard side of the axle housing for the 14" code letters

First two letters are the ratio code
Third letter is the manufacturer
Numbers are build date

Only ratios available for the Omega
JA=2.73 open JM=2.73 Posi
JB=3.08 open JN=3.08 Posi

BTW I installed a 3.73 before I did any engine work and it was like night & day difference...

 

You guys answered my question before I had a chance to ask it.. Thanks!!!! Much appreciated...

 

X2 ^

Can't wait to get home and find out what it is.

 

JA Was hoping for 3.08 and posi of course.

 

IF you are handy with a wrench, hit the local pick and pull yard. Find a truck from the 70s to late 80s. Plenty of 10 bolts. Many came with 342s and some with 373s.

I can tell you how to pull the gears if you need more info.

You can even get lucky and find posi carriers in some too.
Blazers and Jimmys are the best to find them in.

and I agree . . . it will wake up even a tired 350! Gears make a big difference.

 

I'm handy! A walk through is always nice!
Is there a list that anyone has heard of that list what rigs used the 8.5 diff.
Corvette? found a complete housing for 150.

 

Corvettes use 17 splines. Your Olds is 28 splines (or at least the cutlass is). Found that out the hard way I seen a buick site that has a good list.

http://www.buickperformance.com/posi.htm

 

Most trucks came with a gov-lock posi unit.You do NOT want one of those.Check under the 70's A-bodies,70's-80's Camaros/Firebirds,and the late-70's/80's fullsize GM's.

 

Brian
Can you explain a "gov lock" truck posi? I haven't pulled one of these posi carriers. I just get gears from them. The b-bodies in the late 70s and 80s have quit a few posi diffs. The 90s caprice also has posi diffs but I believe they are 31 spline? carriers so they would work if you plan on using aftermarket axles.

These trucks are DEFINITELY a great source for used 342 and 373 and even 411 (410) gears. You would be VERY hard pressed to find a gear any better than 308 in a full size gm or even any A-body car.
Camaros up until 1981 only. These are getting harder to find but I have seen 323 in camaros. But even the 77-81 Z28s usually have 273 in them. Not a good gear unless you want a freeway gear.

 

I've pulled a few sets of 3:23's out of some early-80's V6 LaSabres.The trucks will have a better chance of having steeper gears.Anything 88-up will have 30-spline axles,and they started using Auburn posi units.The gov-lock is the equivalent of having a grenade with the pin missing.

 

Gov lock units AKA (Automatic locking differential )

The unit acts as an open diff untill slippage occurs (gravel, ice snow dirt mud etc.) from ground surface and is different from on tire to the other. The unit senses the difference by a little ramp driven gear and a flywheel mechanism to tell the unit to lock or not lock. Also senses if the rear diff is spinning to fast to lock up ...This is where sometimes the unit will fail...If it locks at a higher torque RPM the unit is doomed. IF they are locked they work quiet well and you can put goobs of power through them...IT is the engagement and disengagement times where you have to watch out.

cars they work great for everyday driving in the snow MUCH better than the cone or performance units did from the factory.

NOW for drag racing and burnouts you want the cone or clutch type performance units for sure.

pictures for reference Gov lock truck unit, 70-80's traclock posi clucth car unit, auburn 90-96 car posi