Well I have my 1985 Conquista with a completely redone 305 with some bolt ons, and the stock TH350 tranny. It has the stock slip-posi rear end. I want to have a fully posi rear end.

Coming from a newbie to the automotive world, what rear should work? Whichs ones wont? How do rear ends work? I know they are labels by ratios, like 3:73, 4:11, correct? What does this mean?

I was also thinking of putting disc brakes on, good choice?

I don't think '85 El Caminos came stock with a th350 trans. Most had a light duty metric th200. Anyway a th350 tranny is a three speed. It' better than a th200 if that's really what you have.

The higher the number of the axle ratio the more RPMs the engine will turn at a given speed. Your stock axle ratio is probably 241:1. That's almost like running an overdrive trans. A higher number axle ratio will give you more performance but you will be turning more RPMs on the highway

I never heard of an '85 Elky with a "stock slip-posi rear end". Where are you getting your information?....Doug

My 82 had a TH350c (with lock up) stock.

Does anyone out there have an '85 or later with a stock th350 transmission?

And how about an '85 or later with a stock "slip-posi" rear end?

Does anyone know if a lockup torque convertor be installed in front of any th350 trans if it was replacing a lockup th200?....Doug

Its possible it was replaced, but the rear is defanatly slip-posi, and I am looking for full posi. Which rear end would be most beneficial?

Here read this, it should answer your question http://answers.yahoo.com/question/index?qid=20061001235309AAxS500 As far as which is more beneficial, that would depend more on your intended use of the car. If you have a limited slip rearend, and the intended use of the car is as a daily driver...the limited slip works just fine. One type of setup that is not discussed in the article would be a spool rearend, either mini or full...and I dang sure wouldn't recommend using either of these in a daily driver. You may want to consider a Posi-Trac or maybe even a Detroit Locker in a car that is performance orientated...but not just a daily driver.

My bad on the slip-posi rear end. Did not realize that 85chevycamino was talking about a limited slip posi......Doug

If it's a 4 speed it's a 200r4, if it's a 3 speed it's a 250, not a 350. If you're looking to find out what gears you have, jack up the entire rear of the car , put axle on stands, car in neutral, turn tires forward, if both tires turn in the same direction, you have a posi rear. on to the gears. mark tire on the inside bottom, turn the driveshaft one complete revolution, if the tire goes around a little bit more than 3 times, you have 3:08, if it goes 2 3/4, you'll have 2:73, 3 and 3/4 times you'll have 3:73, got the idea, if it has a virgin ,untouched rear, GM installed a little tag on the rear cover with posi lube recommendations, if no tag is there, you got a one wheel peeler. I own a 84SS, it came with a posi & 3:08 gears. Try and find your build sheet. Most of them were put in the passenger side of your seat, flip your seat forward , unzip the bottom of your seat cover and look up in there. That's where I found mine. that will have all the info on your Els build. mine also had the service parts sticker inside of the glove box mine has 59 3 digit codes, that can be decoded at a dealer . The 3 speed trans that came in the 80"s models were turbo 250s not 350s, that was a M31 code on the build sheet, marked as standard equipment.They look just like a 350 anybody can mistake it for one, they're not built as heavy as a 350, i got all that from the tranny man, and was shown the difference in the parts Any questions, feel free to write back. build sheets don't lie, mine is in front of me as i write this. wow I got babblin on with this one.

if you are thinking about doing disc breaks in the rear, this is always a better setup than drums easier to work on and what no. Also pretty cheap to swap out. but its not really that important unless you are really tricking it out and your car demands more stopping power ex: bigger rims, added weight, or a substantal increase in power. you should be fine with your drum set up, as your car uses 70+% breaking in the front compaired to the 30 or less percent in the rear. So again a drum set up would get the job done just fine there isnt much stopping work for it to do any ways. if you wanted to do any thing to your rear, swap gears and have some fun 3.42's or 3.73's you would really notice a difference. what are your gears now 2.4somthings? hope i helped you out a bit. :) ps..what is a slip posi? is that another word for a "live rearaxle"? if you try and do a burn out does only one tire go? or if you jack up the rear end and try and spin the back tires do both move in the same direction? just never herd of it b4

I mean by slip posi, only one tire pushes the car. If that spins, the other catches to make it posi. But I know sometimes these are faulty and you only have one tire smoking.

The OEM posi units do wear out, I believe they were made by Auburn and are not rebuildable...replacing them with an Eaton or an Auburn HP series (I had one installed in my Z71) would be a good idea...but then again I myself wouldn't put a dime into a 7.5" rearend.

HOTWHEELZDUDE,
you have the right idea just the wrong innie and outtie----with a 3.08 it takes 3.08 turns of the driveshaft to turn the wheel one revolution etc... another thing that might confuse folks is if you have an open rear end (non-posi) if you hold one wheel steady the other will spin twice as fast because of the spider gears in the rear transferring all the motion from the driveshaft to the one wheel....Dan

HEY DAN
Thanks for the correction, :oops: , funny how many folks DON"T notice things of that sort, like on a posi rear both wheels turning the same direction, or an open spool , turn one forward and the other goes reverse, I think I gave a good clue on how to determining what gear set ya got
Rick

It is sad to see people ask questions on that Yahoo site and then get answers by those who don't have a clue. They write as though they know what is going on, so you would assume the poor guy takes it as fact.
This is for you, Cody, if you are still following this thread. First, our cars came from GM with one of two types of rear end. The standard rear, often refered to as a open carrier, and the optional limited slip. Period, no inbetween. GM's option name for the limited slip is Posi traction, which is usually just called Posi. The differential not only turns driveshaft rotation into axle rotation, it also makes it possible for the wheels to turn at different speeds. This is necessary because when you turn, the inside wheel has a shorter path than the outside wheel. A drag race car with a "spool" which locks the axles together has no provision for this. That makes corners difficult and involves some tire sliding. The differential makes this possible by connecting the axles to the carrier with a four gear combination. A gear on the end of each axle and another pair on a shaft that runs through the carrier. This allows the axles to counter rotate. The open carrier will most likely transfer power to the wheel with the least amount of traction and the counter rotating action of the differential gears will keep any power from being applied to the other wheel. Not good. Enter the limited slip. A system of clutches in the center of the carrier will begin to apply when the difference in axle speed becomes too great. As the clutches apply, the power is applied to both axles. In normal driving, the clutches slip, allowing for the counter rotation when cornering. Although different brands of limited slip use different methods, the principal is still the same. Another device mentioned was a locker. This takes the place of the differential gears and connects the axles with a type of one way clutch. They can be thought of as like a ratchet, one axle can turn faster than the carrier but will grab as soon as the carrier turns faster. These work great but some are noisy in the corners as they ratchet. I hope this has answered some of your questions.

Thanks alot for the info. So if I was to go aftermarket, what would be the best option for the setup I have?

Mostly city-intown driving also, not to much highway.

Well Cody, you might think about converting your rear. Although doner cars are out there with posi carriers, sometimes you don't know exactly what you are getting. Converting yours would either be, changing to a posi carrier or going with a locker in your existing carrier. The parts cost is not that far off from one to the other but the labor would higher with the carrier swap. This is because the clearances will need to be set up with the new carrier. The locker on the other hand is a fairly easy swap. If you had any thoughts of changing your axle ratio, this could be done with the carrier swap if you went that route for an extra 200 or so. As Mike mentioned, putting five or six hundred dollars into your rear end might not be wise. With your current set up it would probably do just fine but if you ever were to step up the power, the small rear end can easily fail. See what you can find first in a 8.5" posi rear from a A/G body.

3:73

Found my build sheet, it says 2:41 ratio? Can someone explain this rear to me and whats the story on it?

Not a whole lot to explain, the driveshaft turns 2.41 revolutions for every one revolution the wheel turns, it's an economy rearend, nothing special, great on the highway. Whether or not it's a posi is unknown.

found rpo codes in another forum here if you have g76,g80,or g86 you have a posi/limited slip let us know if it is a posi with 2.41s as i have yet to see any 2.41 geared rears with a posi but it could be :cool:

what is the g76...? Is that on the build sheet because I cannot seem to find it.

It also says I have a 3spd auto. Which tranny is this and what is the story on that?

It also says I have a 3spd auto. Which tranny is this and what is the story on that

this meens your rig came from the factory witha standard three speed automatic transmission most likley a 200 r or th350

the g76 is a posi uint would be on build sheet or the option tag if you look in forum under technical you will see rpo codes there is a link to site that has the codes for just about everything
the 3spd tranny is either th250 or th350 ck bottom of pan if it has metric on it then you have th250 if not it would be a th350 the codes from build sheet or option tag can also tell you what you have
the 200r is a 4th gear overdrive unit like the 700r4

oh also if if you dont have the g76,80 or 86 on the build sheet you most likely don't have posi or limited slip rear unless it was changed over by some one

Hello, The factory style Posi-Traction would be fine for your 305. A locker is overkill unless you plan on a big engine later. Even then the rear end should be upgraded to a 12 bolt or ford 9 inch. As for gears try 3.25:1 or 3.50:1 for the street. The numbers represent the ratio of the driveshaft turning 3.25 times to 1 revolution of the wheel.

get a frickin service manual. I can't tell you exactly what your elky has but for 85 caprices, impalas, monte's and elkys, a 200C, 2004R and a 700R4 were offered. If you had the OFFICIAL service manual that the dealership would have used like me (don't use hanes or chilton they suck unless that's all you can find) you would be able to identify the tranny and rearend and would know exactly what you had. It will tell you where the markings are to identify what you have and what they mean. I cannot believe you lasted this long without one. Buy one tomorrow it will be the most useful tool in your garage. It might be kinda expensive but you won't regret it. Tell you what you do, look in hemmings motor news. They have a website too hmn.com.

Found my build sheet, it says 2:41 ratio? Can someone explain this rear to me and whats the story on it?

This is what I have now. Like the boys said good highway gears bad for performance. think about it this way. Have you ever ridden a ten speed bike. You know the gears people call the easy gears the ones you use to start going with or to go up a hill. These would be the low gears like a 3.73/1. When you start to go faster you have to pedal a lot more to maintain speed. What you have, a 2.41, would be one of the gears on the bicycle that would be really hard to get going with but much easier to maintain a faster speed. hopefully this makes sense. So basically a lower gear ratio, 3.73, will make it easier for your car to take off, but will hurt highway gas mileage because the car has to "pedal harder"