[cv70chall]

I know it's a stretch.

[Adrian Worman]

Doesn't need to be a beefcake 489 for your 360 Chuck .......unless your gonna perform a lot of slick tyred strip abuse a regular case will do fine mate

[cv70chall]

Adrian-

I obviously want a POSI in that rear end- and the 2.76 gears it currently has I suppose are ok. What about adding POSI to this unit I have and not changing the gears at all?

[cv70chall]

Also, the 360 is .30 over with a beefed up cam and upgraded pistons/ rods.

[dave-r]

Also, the 360 is .30 over with a beefed up cam and upgraded pistons/ rods.

"beefed up cam" usually means higher duration? If it has much higher duration than the stock 360 cam then you would need a higher stall torque converter (otherwise it will pull the engine speed down too low when put into park) and also lower gears in the rear axle as the rpm the engine makes power at will he higher.

This is what we call "matching the parts".

You only need a "suregrip" LSD ("posi" is a GM term) if you are going to be heavy footed. I would use 3.23:1 or 3.55:1 rear gears.

Both can be fitted to your existing diff.

[cv70chall]

Understood.
So, I can try to locate some 3:23 gears and a POSI unit and add them to the rear and I'll be fine.

[dave-r]

Yeah but it is quite a technical thing to fit new gears. Not so much just the LSD unit.

[cv70chall]

Would I be better off just adding the LSD unit to my existing 2.76 gears?

[dave-r]

Probably. Depends how adventurous you are. Or how much you want to learn these things I guess.

I am the "have a go" type of person myself.

[Adrian Worman]

Davemans right Chuck, fitting gears is a lot more involved than just adding an lsd unit.
It involves removing the pinion and that means accurately setting the pinion depth for the correct meshing of the ring gear as well as the pinion bearing crush. a bit daunting if you have'nt done it before.
But then you had'nt done all that restoration work before and you done a fantastic job................read up on it and do the research and talk to a supplier like Dr.Diff and get some advice.

[cv70chall]

My search continues but I might have a solution- if you guys think its a fair price and if ot will work for my application.
I currently have 2:76 gears in my 8.75 489 case. I have been searching for either 3:23 or 3:55 set with POSI for my 8.75 with no luck (unless I want to throw $950-$1150 at one)
I did find a 741 case with a 3:23 gear set and POSI for $550 shipped to my door. I would obviously need to replace the bearings/ seals etc. It's out of a 69 Imperial.
Will this work with my 8.75 rear and is it a good deal for what I want to do?

ps: On the transmission issues, I found a 904 from a guy literally around the corner who gave it to me for $50 - out of a car with 47,000 original miles. Cleaned up nicely and it goes in next week.

[Adrian Worman]

Well Chuck, it's an old diff and case, '69, so it will most likely be a rebuildable SureGrip, the operating components in it are like a wet plate clutch. The only issue I see is that number of diff had a smaller diameter yoke so it would require an adaptor spider, easily available tho
Complete unit or not it will still need breaking down to service the clutch packs and check the condition of the gears