What rearend with positraction should i look for

by Hs1973 Thu May 26, 2016 1:41 pm

Im looking to Swap out my rearend. It is starting to whine a little at Cruise Night. Anyways i was thinking that i will upgrade and find a positraction rear. And im not that much into rearends, and i was wondering what cars that have a posi rear that will fit our cars without to much changes. I know i could just change the insides of my old rearend, but i would like to refurbish another rear while i drive my car during this summer. Also what to look for in gearing since it is a dayli driver with a Nice 355.

Any input is welcome.

by clanceman427 Thu May 26, 2016 4:15 pm

My stock setup is 3:42 gear with posi and it's great. Rear tire is 275-60 r15 and just yesterday I was buzzing along the highway doing 70mph and it was fine. My tach is inoperative but it doesn't sound like its rpming too high.

by Joe73 Thu May 26, 2016 7:27 pm

clanceman427 wrote:My stock setup is 3:42 gear with posi and it's great. Rear tire is 275-60 r15 and just yesterday I was buzzing along the highway doing 70mph and it was fine. My tach is inoperative but it doesn't sound like its rpming too high.

You would be spinning about 2900 rpm at 70 mph with a 3.42 gear. http://www.advanced-ev.com/Calculators/TireSize/

by clanceman427 Thu May 26, 2016 7:38 pm

Music to my ears. Plus when you stab the throttle at 70 you're in poeerband

by clanceman427 Thu May 26, 2016 7:40 pm

I also have stock exhaust manifolds and stock style dual exhaust so no drone

by SSTOOLMAN Fri May 27, 2016 10:26 am

Joe73 wrote:
clanceman427 wrote:My stock setup is 3:42 gear with posi and it's great. Rear tire is 275-60 r15 and just yesterday I was buzzing along the highway doing 70mph and it was fine. My tach is inoperative but it doesn't sound like its rpming too high.

You would be spinning about 2900 rpm at 70 mph with a 3.42 gear. http://www.advanced-ev.com/Calculators/TireSize/

That's close to what I am seeing with turbo 400 and 3:42's, runs close to 3000 at 65 mph which translates to about 11 mph combined,
I don't know why its so low but it is, what it is. The mpg calculator doesn't lie. When I do a BT it turns both the tires over effortlessly and I can spin them as long as I want, that makes up for the low mpg.

by Hs1973 Fri May 27, 2016 11:54 am

That sounds Nice, i have a lock up 350c trans so mine would be even lower on the highway. So that takes care of the gearing.
But what other model cars can i take a rearend from that would fit without major sugery. Does a something from a newer Caprice or camaro fit or should i buy a new 3erd member and restore my old rear.

A body has a rear from a Monte Carlo for cheap. I could restore that with a new Unit and get it like i want. Or am i better of finding something used. I fear i get something old and worn.

Is it hard and Pricey to buy a new posi Unit for the old Monte rear? And can i use summit parts. And i guess my already restored rear brakes can be moved over, i have 11 inch rear drums and the Monte only 9.

I know its alot of questions but i dont know a whole lot about rearaksels. And Living in Europe its expensive to have parts shipped from us so i better get it right the first time.

Thank you for your time Henrik.

by Joe73 Fri May 27, 2016 12:29 pm

Final gear ratio for muncies, saginaws, turbo 350 and turbo 400 are all 1:1 final. So your rpm will be the same will all these trannys. Thats the benefit of having an overdrive auto or a 5 or 6 speed. Lower final drive which lowers your cruising rpm. The 200r4 and 700r4 have a final drive of about .70:1 which is great for lowering your cruising rpm.

Heres a cool chart with popular trans gear ratios. And how much HP is required to run the trans.
http://www.oldengine.org/unfaq/leadfoot/trans.htm

by 73ss Fri May 27, 2016 3:45 pm

Joe73 wrote: all these trannys.

Joe, We will soon not be able to say this anymore... Razz

Anyways as far as rear ends any 73~77 a body will work. As far as posi, best thing is to jack it up and spin the wheels and see. any ID numbers will be rusty and hard to see. I think some of the guys on here have swapped in later model impala SS/Caprice rears with some bushing mods? Those would be about the only bolt-in swaps without going custom. Do they have any sort of a craigslist in Europe? there are normally at least 2 G3 a bodys on the CL in my area at any time

I went with a 200r4 trans, It was a desirable core from a Monte SS, I had a pro build it and I'm more than happy with the end result. with the convertor locked, I can cruise 75 at 2250 rpm. keeps right up with modern cars. It also knocked 4/10's, half second of my ET due to the lower 1st & second gears and it doesn't rob as much HP over the old turbo 400, however it blows the tires off alot easier now which can be a pain at times.

by Hs1973 Sat May 28, 2016 3:51 pm

We dont have a craigslist here. But there are some places you can find used parts for us cars. But even though 3G parts are not that easy to find. I will look around and see what i can find. Caprice parts are easier to find here. Thank you for all your help.

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What rearend with positraction should i look for

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