Anyone have suggestions to a nice upgrade from stock rear end on a 1971 cutlass Oldsmobile convertible, or where I can buy it

 

Why are you looking to upgrade? I have read from some of the rearend gurus that the Olds bolt-in axle 8.5" 10 bolt rear is very strong and is good for 12s or faster in the quarter mile.

You can swap the original 28 spline axle shafts for aftermarket 30 spline shafts for a strength increase, and I'm sure there are a few other mods that can take that rear faster than 11-12s.

 

Your going to need to be more specific on the upgrading for people to give opionions...do you want better milage better highway cruising better street performance posi...and what engine trans and rear do you currently have to let people know what you have

 

Sorry should have been more specific, I'm really new to cars and don't know much other then what my mechanic tells me, he said if I'm going to do work to my engine to beef it up I'm going to need to change out my rear end., I currently have a 350 engine and trans that I have no idea what year the engine is the car is a 71 cutlass supreme

 

A stock olds 1971,3.73 10 bolt is pretty popular for street strip stuff i'm wondering what you have in there now and what the mechanics intentions are...does he think the axles are bad? You may be jumping the gun a little untill you know what your doing with the engine and what kind of power range you want

 

I just want my car to have some power behind it nothing crazy,at a dead stop I can put pedal to metal and it just takes off with no peel out.... how would I tell what I have in there now?

 

There is a 2 letter code stamped on the rear of the passenger side axle housing. You may need to take a wire brush to it to see them.

 

thanks!

 

The quickest and easiest way is jack up one rear tire turn the tire one complete turn as you are watching the drive shaft turn so if the driveshaft turns 3 1/2 turns for one complete tire revolution you would have 3.55 gears....this should be your first step knowing what equiptment you have

 

I would of said to check the axle code also but i'm fat so its easier to just jack one side up a little

 

Not quite. You have to take into account the differential action if one wheel is on the ground.

 

Worst case is you wold need new gears and a limited slip differential. The rearend will hold up to more than your engine can throw at it.

 

If you do decide to count the driveshaft per tire revolution put the trans in netral and remember safety first it will take you 5 mins

 

Thanks for the help guys! Gonna try and see what's under there soon as it cools off a Lil

 

And of course it gets more complcated because with just checking the ratio with one tire off the ground that wont tell you if you have limited slip diff. You need both tires off the ground to check that if both tires move in the same direction its an open rear if one tire moves forward and the other backward at the same time its limited slip or posi terminology

 

Posi is when both tires spin correct? My car don't have that

 

Yes both will turn only wth posi one forward one backcward

 

The posi had to be be specially ordered or part of a high performance package so its not a surprise your is open, i dont know what the standard open ratio would be for a 71 though

 

My car came with a 2.56 rear. According to the build sheet, that was the "no cost" ratio.

 

I think you have that backwards. The limited slip tries to lock the axle shafts together and keep both wheels moving together.

Also, the wheels will turn opposite directions on any differential if the driveshaft is held in place (as in the trans is in Park or in gear for a MT). Doesn't matter if it's an open diff or an LSD. That's what keeps your car from rolling away when you park it.

 

Turn the wheel 10 times ,count the revs of the driveshaft and then divide by ten. More accurate results. West coast differentials sells a posi unit and gears for the 10 bolt differential. This site times out too soon for me to be more descriptive. good luck. I lost all the info I wrote first time. Good luck.

 

Same thing happened to me just now - typed up a buch o stuff and lost it all.

But again, you need to account for the differential action when counting turns.

10 bolt posi and gears are available from everywhere.

 

The open rear will spin in opposite directions. The poster already indicated both wheels don't spin. The posi unit is a good investment if you plan to upgrade gear ratio anyway because the mechanic is in there anyway so do everything needed while he is at it.

 

I may just copy me post before submitting it and if timed out and have to sign in again just paste to the new window. More than one way to skin a cat. ONE IMPORTANT THING. buy the OEM gears because they don't whine. (that gets old quick). WCD said the OEM gears are not loud.

 

Instead of spending your money on a new rear end, spend it on a good tune-up. A '71 Cutlass with 350 (even a 2-bbl) and no posi should be able to spin its right rear tire all day long.

 

what would a tune up consist of? I supposedly got one, the guy changed wires on spark plugs and new spark plugs also new distributor

 

A new distributor? What type? Maybe the initial timing, advance curve, etc. are not correct.

 

I'm not sure what kind but I know that we bought one for a 1971 olds 350 and it was to short, we ended up getting one that goes in a 1978 and it fit right in.... I'm thinking this car has been messed with big time

 

I just noticed this and thanks for the correction... didnt mean to confuse the question, hope you got the ratio figured out so you can go from there

 

Does anyone have a pic of where to look to find the number stamped on it?

 

this is on my 1969 your will be in the same area (maybe higher) you may need a mirror and wire brush

 

the silver area right to right of the duk tape

 

My differential numbers on my 72 were on the front of the axle housing to the passenger side.

 

Um, the distributor for any '64-up Olds V-8 is interchangeable (Aurora excluded). This means that the "too short" distributor was likely NOT an Oldsmobile distributor at all.

So if you have one for a '78 engine then it is an HEI distributor, and therefore its advance curve is totally different than the '71 points distributor. The HEI will need the initial advance set to ~20º in order for the total to be in the 34º range. HEI also uses different spark plug wires and needs a full 12 Volt power source and not the resistor wire used with the points distributor.

 

As Kenneth said, your timing curve is wrong with the 78 distributor, you've gone backwards in regards to a performance increase. My advise is for you is to find a mechanic that can explain things to you and for you to ask more questions from your mechanic. Make sure you tell the mechanic what exactly what your goals are and have him explain to you what needs to be done and why to achieve those goals.

 

Definitely going to talk to my mechanic, just wanted to get some insight from some real olds guys!