I have a 1986 Berlinetta that I'm in the process of installing a 383 in. The car currently has a 2.73 open diff in it and I would like to have at least a 3.42 locking diff in it. My head is about to start spinning with all the options there are for doing this swap. I need help in my choice so I don't end up with parts that won't work or end up with inferior parts. What gears and what locker do you guys recommend for me to use with my car. Part #'s or web links would be great.

I know the car to be totally unmolested (till I got it ) so I know the diff is 2.73 open and since it's an 86 I guess it has 26 spline axles. The car has been in my family since new.

thanks in advance for the help
Rod

 

The info in the following link will provide some info and/or food for thought:

https://www.thirdgen.org/forums/tran...-10-bolts.html

BTW, big gear head recommends the Eaton limited slip.

JamesC

 

For ease of parts Im going to recommend a 10 bolt if your on a budget. If your not hammering on it real hard it will survive. If you beat it then u might want to think other rear ends. If you keep the 10 bolt i would get

-28 spline axles
-Eaton Posi (way better than stock)
-3.42 if your going to be driving mainly on the street. Others will tell u 3.73 but thats a bit steep for the auto trans and if you do any driving on the highway it will suck.

If you think you will be hammering the living daylights out of it you might want to save up for a stronger rear end. A 12 bolt or a 9 inch or a factory dana 44 (good luck on that one) would all be good choices. 9 bolts are alright rears as well if properly maintained and reshimmed again. I did it to mine but i dont think i would get another 9 bolt. They are marginally stronger than a 10 bolt but not enough to warrant that change.

 

That's good advice. I was going to say pretty much the same thing.

 

I read all the FAQ b4 I started this thread but that is alot of info to take in.

So are you guys saying that the 26 spline axles in my car won't really hold up and that its not worth upgrading the 26 spline unit? Maybe I would be better off just finding a used posi rear end out of the junk yard???

The only thing I like about the idea of keeping the rear end that is currently in the car is that I know it has seen no abuse at all. You never know what your going to get when you go to the junk yard.

BTW- I don't really plan on drag racing the car. Maybe a few redlight runs to knock the doors off some ***** (foreign car). The plan is to keep the car looking stock and it will be a sleeper. I also have a 700r4 with TCI rebuild kit in it with a 3000 rpm stall TCI converter.

And thanks for the help so far

 

If you get a 26 spline posi and have axle problems then you are going to have to buy a 28 spline posi along with the 28 spline axles. I would upgrade both together and be done with it. You could get a '90 to '92 rear end and use the 28 spline axles in it (if they are not worn) and maybe save some money. A new set of axles is about $220. The Eaton Posi is $440 in 26 or 28 splines. The gears are $165 and you will need an installation kit, which is $92. Axle bearings and seals are $30. That gives you a total of $947 plus shipping in parts. Then you have labor on top of that, unles you are planning on doing this yourself. That's about half of what a new 12 bolt would cost.

 

holy crap.....$1k for parts.....for a 10 bolt. Any ideas what my other options are? If I'm gonna spend $1k I may as well dig a bit deeper and see if there is a better option that I know will not fail. Btw- I won't have to pay labor cause I have a shop/tools/know how. Are there other rear ends that may fit in our 3 gens with some cutting and welding?

Again, thank for the help

 

You can install other rear ends if you want to do all of the design and fabrication work. It's not easy or simple. You can get a bolt in Moser 9 inch housing and axle package for $990 and install a junk yard chunk in it.

 

I believe a 4th gen rear should fit right into it. There is a how-to somewhere on this site. If it can handle the power a LS1 puts down, you should be fine. That said, I would get 3.42 or 3.73 if you are going to be on the highway at all. If its strictly a drag car then 4.11s should do nicely.

My car has an Auburn Diff in it, but it is a stock 3rd gen rear 3.23 gears.

Edit:
here is the link https://www.thirdgen.org/4thgenrear

 

can I buy a junkyard 4th gen rear end and swap the guts (sans axles) into my rear end. Then all I would have to buy is axles. If this is possible I could get by for about $400 - $500.

 

Yes, you can do that. I recommend using a rear end from an LS car because it will have the Torsen differential instead of the Auburn. You never know what you are getting with an Auburn. It might already be worn out and you can not rebuild them.