HI, I have been a member of this forum for a lil while and have gotten some very useful info just from reading other peoples threads..... I have a 1980 Cutlass supreme 2 door with a 307 chevy motor out of a '86 cutlass and a rebuilt 700r4 trans. I'm am looking to make this car the ultimate daily driver and am thinking that updating the rearend system would go a long way as far as driveibility. I am wondering what I can do to swap a better rear end in and what key words, names, models of original cars, etc. I should be looking for in order to find one that will basically bolt on..... I also wanna know more about what posi means and whether this would be what I am looking for. ANY HELP WOULD BE APPRECIATED AND THANK YOU FOR YOUR TIME IN READING THIS THREAD.

 

Any 78-88 A/G body is a bolt in. The best factory rears are 8.5" in the 442 and Grand National / T-types but they are in high demand and can be expensive. What are your future plans for it? What gears are in it now? If you are not building it up to make power or race it the 7.5 you have in there now is fine. If you plan on racing in the future or making a lot of power don't wast your time spending a dime on the 7.5
I have broke them with less than 400 hp and sticky tires.

 

the 307 you have is an Olds

Like Gearhead said, it depends on your plans. The "A" body is an "off the shelf" car so you can get performance parts pretty easy.

If it were me, I would do a Ford 9 inch rear

 

If it truly is the Olds motor (307) how can it have a 7004R? Maybe a 200r4?

Does the trans have a removable rear housing? (700)

Now I'm curious...

RT

 

OOO I missed that. Unless he's got an adapter plate

 

The term POSI is a chevy term / nickname for Limited Slip Differential

THis LSD (limited slip differential) IS what make both tires grip and turn a the same speed when power is applied to the rear end. In turns the LSD will let the axles over come the units preload spring systems and LIMITS THE SLIPPAGE enough to make the inside tire turn slower than the further traveling tire on the outside tires travel distance.

Just that simple.

There are many different kinds of LSD units on the market
Cone type (Auburn 64-72 BOP, Borg Warner Chevy 70-72 BOP 70-72)
Clutch type (Trac Lock ford 9" 8.8 , Eaton GM 64-72 GM, Trac Lock GM 70-80
Torsen units (inertial helical worm gear unit Eaton True trac, Zexen Torsen Gleasen unit GM)
Locker units (detroit and power trax examples)
Gov Lock LSD (GM factory Eaton units)

Hope this info is useful

Ultimate driver rear. The best you can do with the 7.5 rear is UPGRADE axle shaft size to 28 from 26 original and then get a good aftermarket true trac or Detroit locker unit with some good aftermarket gears re-bearing it and that will be as strong as you can get. If you are mostly street bound and some track time this will hold as long as you get a GOOD set-up of your rear end components...INSTALL will be the most critical in ANYTHING you buy.

Set your self a realistic budget for your diff and if you PM me I can see what we have on the DEAL shelf...lol. Some times I get stuff in on trade in Summit budget tables etc. Then I can pass on deals to you guys.

TAke care and good luck on the Ultimate Daily Driver project.

JIm Mitschke

 

****.....just learned something new.
I never knew that POSI meant LSD , I thought they were 2 different things.
Dee dee dee.

By the way, your boy is coming this AM.

 

Yea, I had originally shoped the 200r4 but a trans builder in st. louis told me if I ever planed on adding more power, which I do, and still wanted to get good gas mileage with an overdrive that the 700r4 was the better choice. I had to buy an adapter which I found through Summit Racing. My plans are to get body and paint, chassis, electrical restored with the 307 in it for right now and then to probably either buy an LS motor for this car or get another classic to give more power next winter. I def. want the best handling available which is why I though posi was the way to go because the ice and snow here during the winter makes classic car driving dangerous i've found. All the work is being self done and I already have succesfully swaped the original 26 something that was powering the car with the 307 I had originally been told was a 350...

 

Yep, Its a new day and it was a good one. Learn everyday....

Thanks for your help on the diff!

BAck in the day that is pretty much how other car guy knew what you drove by the NAME of the LSD you used... lol.

Anti spin - you were a Olds guy
Safety track you were a Pontiac guy
Sure grip you were a Mopar guy
Twin Grip you were a AMC guy
And so on.

NOW the YOUNG Import guys are using the correct term BUT JUST THE LETTERS OF COURSE ( L S D ) cool dude.... LOL

JIm