Is there a reason NOT to put a posi rear end in my '85? What kinds of junkyard cars should I be looking for as donors? How can the rear end be easiest identified? What kind of gear ratio is most desirable to go with my 350?

Hi Ryan;
Limited Slip also called posi is always a desirable option to any vehicle.
Limited Slip is a factory option which could of been ordered by the customer on a new vehicle.Seeing where you live and if you drive in snowy weather it will be of great help in getting to where you're going.
Are you referring to a 350 engine or auto trans?A favorite rear of many is the 373:1 found in the 85-88 Monte Carlo SS which is a direct bolt in.Also rears out of the Buick Grand Nationals which will cost you alot more.A 373:1 is fine with a Overdrive tranny,But with a 350 tranny it will turn much more RPMs while driving down the highway than what you would like.Every rear has a code stamped on the front of the right axle tube telling the ratio,build date,plant it was built and will have another code if it is Limited Slip.The Monte will have a 2TF code if its a 373,and a 2TH if its a Limited Slip.
The best thing for you to do is buy a book that has all these codes in it.I'm sure another member will be able to recommend a good one.Also just a reminder ,when you change the ratio this will throw the speedometer off .Good luck with your decision.

A favorite rear of many is the 373:1 found in the 85-88 Monte Carlo SS which is a direct bolt in.
Any 78-88 G-body rear will fit in your Elky. Many 5th gen Elkys and Malibu/Regal/Cutlass wagons has 3.08:1 posi rears. Look for any MCSS rear end from 83-88. The 83-84 MCSS came with 3.42:1 gears and the 85-88 MCSS came with 3.73:1 gears. The posi rear ends had a 1x3" metal tag attached to one of the cover bolts. It looks like this:
http://elcaminocentral.com/users/elcamino/pics/poistag.jpg

The G-body Olds and Buick 8.5" rears are getting real pricey. Many sell in the $750 - $1000 range. A 7.625" MCSS posi rear end sells for about $300 and it'll handle the HP from your 350.

Here is some more info on G-body rear ends and axle codes: Rear End FAQ (http://www.geocities.com/malibunirvana/technical/rear_ends/index.html)

I thought the Buick Grand Nasty came with A 342 rear?

I thought the Buick Grand Nasty came with A 342 rear?
They did. The 84-87 GN came with a 3.42:1 rear end. It was an 8.5" ring gear. Those are the pricey rear ends.

Good luck finding one used. You can get a new posi unit from the aftermarket.

A body's 12 bolts with a SSM kit will work too i believe.

-Eric

A body's 12 bolts with a SSM kit will work too i believe. -Eric

:-(
Well, I've got bad news for anyone who wanted to put a 12 bolt A-body rear end into their 5th gen El Camino. South Side Machine is no longer making the conversion kit. Neither Summit Racing or Jegs carry it anymore.

I plugged in the Summit part number (SSM-1328) and Summit says it's no longer available. Jegs says the part number (862-1328) has been discontinued by the part manufacturer.

Oh, and their web site http://southsidemachine.com doesn't work any more either.

I don't know someone said their site was just done due to construction, but anyways..thats ashame if this is the deal.

-Eric

Seems a few years ago someone told me that a posi can be undesirable at high speeds on curves. Is this true? Because my 44 mile round trip to work each day is pretty much nice paved but very curvy country roads.

Secondly, is it easier or cheaper (or even possible) to convert my existing rear end. I figure I would be able to get a posi rear end used for under $500 but if there is a better way to do it I'd go that route for the experience even if it cost more.

you could get a powertrax unit, you don't even have to mess with removing and setting up the gears in you rear. You could check with elkypete i'm pretty sure he has one for his 5th gen.

You could also get an aftermarket posi carrier and aftermarket gears. I don't know if I'd install a powertrax unit and then do lots of city driving. I've heard that they make lots of clunking noises going around corners.

Ryan, Here is a web site that may be of interest to you. http://home.hiwaay.net/~ppatter/tech_rearend_swaps.html It describes some of the possibilities available for G-body rearend swaps. Jon

What the heck is powertrax?

Here ya go :cool: powertrax (http://www.powertrax.com/)

PowerTrax Locking Differentials
First Fully Streetable Locker!
Powertrax's No-Slip provides 100% lock-up under maximum traction output. Provides smooth and quiet operation. Eliminates the noise, harshness and ratcheting-around-turns associated with conventional lockers. No special tools needed for installation or altering ring and pinion set-up. Fits both open and limited-slip differentials. Available for most RWD cars and 2WD/4WD Trucks, SUV's and RV's.


powertrax from jegs (http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1158&prmenbr=361)

I agree that posi comes in handy in snow. I also agree that if you have lots of power, it will help you hook-up better. But, I vote no for posi in a "normal" type daily driver. It's particularly troublesome on wet roads. If you throttle on a little too hard, whether from a stop or from a stomp, both back wheels spin and you go sideways which can be disconcerting, not to mention maybe deathly. I goosed a posi Buick I had back in the early '70's on I-35 in Iowa in the winter at about 75 mph, did a half a dozen donuts, went through the median, into the northbound lane and ended back stuck in the median in the snow. I didn't know about "black ice" at that time. You have the same problem when turning a corner. A little too much throttle and you're sideways in the wrong lane with the attendent unpleasant possibilites. Think very carefully about this decision.

Found out South Side Machine is still up and going and you can still get the kit to put the 12 bolt rear in too. The site address just changed, its kit number 1328.



South Side Machine (http://www.ssmliftbars.com/)

Chris

Found out South Side Machine is still up and going...
It looks like it's a whole new company. I heard a rumor a few months ago that the owner was retiring and non of his kids wanted to run the business. I bet it was sold. I sent them an e-mail to find out. I'll post the reply here.

Anyway, I'm glad the conversion kit is still available. :)

I installed a PowerTrax in the 80's rear end. If I get the time and cash I'll put one in the 76 also. They warn you on the box and in the instructions that it could create some oversteer in some cases. I read an article in PHR about it and was impressed so I figured why not I was going to go for a Posi but this is better actually.

Anyway that is my 2 cents worth.

Oh yeah, its a piece of cake to install takes about 2 hours or less.

Would be nice , but I don't think that for that price to would be worth it.

I had a Powertrax in my Dakota p/u for a couple years, but ended up taking it out. I got tired of the popping and lurching. Might be OK for a weekend car, but not a daily driver IMO. Installation (and removal) is super easy, though.

It looks like it's a whole new company... I sent them an e-mail to find out. I'll post the reply here.
I sent an e-mail to SSMAUTOLIFTBARSL@AOL.COM a week ago asking for information. As of today I have not gotten a reply. I don't think that any reputable company would fail to reply for a request for information about their product. Nor would any professional company use an America On-Line e-mail address. I'd be very careful about doing business with them. I'm going to send them a follow-up e-mail.

I have not received a reply to either of my e-mails to the "NEW" South Side Machine company. I would suggest using caution if you're thinking about doing business with them.