I am looking to put a limited slip in my 74 but I have very limited exp with rear ends, I know I have an 8.5" but thats about it, did 74's come with a standard gear ratio? its an LS with the 350 4bbl option. do the have a standard spline size on the axels and lastly what gearing do you all recomend for street weekend warrior car. thanks

 

I just picked up a 4.10 for my car, it is far from drivable right now though. Do you want to take it on the highway at all? 3.73-4.10 for street, 3.73 and less for highway IMO. You may find it cheaper to find a rear end that is already set up the way you want it used though.

 

Were it mine I'd go with 3:42 to 3:73 gears. The 3:73 for around town or some highway with a small block, and the 3:42 for half and half with either big or small block. Of course this depends on what tranny you will be running too. If by chance you're going for a tranny with an overdrive automatic, or manual with 5th or 6th gear, then I would definitely go with at least the 3:73, or even the 4:10 gear ratio. I'm running 3:42 gears in mine with the big block, and I like that ratio a lot.
No certain gear ratio back in 1974 for that rearend, but you can easily figure out what your's is. Jack up both tires and sit it on jack stands. Move one tire so the valve stem is straight down or up. Mark the drivesaft also. Now turn the driveshaft one turn and count the number of turns the tire makes. That's your ratio. A 3:73 will turn 3 3/4 turns, while a 3:08 will turn just over 3 turns.
You will also see if you have posi doing this, as the tires will turn the same direction with posi, or opposite with open rearend.

 

Oops! Splines are either 28 or 30, but I can't say which you have. You'll need to pull an axle, but that's really easy on a GM 10 bolt.

 

I am fairly certain you spin the tire once, and count the number of times the driveshaft turns. This only works with a posi though, not so much with an open one. I have done a lot of looking it up on the Internet though and there seems to be alot of conflicting methods. Spinning the tire once and counting the driveshaft revolutions worked with my 4.10 posi.

 

Hmm...I thought I said that? And yes, the open rear will work the same, but you need to stop one tire from turning before turning the other or it might not read accurately.

 

You guys are awsome, thanks

 

now ad additional question, i have never worked on a rear end before, is changing the gears and adding a limited slip something i could do myself?

 

oh yeah its got a th350

 

I have watched some threads where someone was going through and doing it, it looks like a very precise thing, I don't think so. I would like to learn how someday though. I recommend really reading up on it, if you can understand it, then go for it, if not, forget about it. I still say you will be money ahead finding one on Craigslist already done, or buying a car with one in it already, swapping rear ends and selling it again.