buick electra posi rearend

Hello all I was fortuate enough to find gentleman that was willing to part with the posi out of his 72 buick electra for what I thought of was an unheard of price. He delivered it to me today, posi tag still intact, but I wanted to know to freshen this unit up before it goes into the car what would I need to do. Also could someone tell me how to make sure this is a posi outside of the tag, once it's opened up. The guy says he turned one wheel and the other spent, but I want to make sure I got what I thought I got. Also how can I determine the gear ratio, and once I do could someone tell how that ratio would be a benefit. This thing was heavy as hell, so I would like to do the work myself if it's possible, where it lays. :beer

 

To find out the gear ratio, count the number of teeth on the ring gear (the large one) and then divide that by the number of teeth on the pinion gear (the small one). For example, 41 ring teeth divided by 12 pinion teeth equals a 3.42 gear ratio.

 

Do I need to pull that whole assembly out to count them. Also like a idiot, being so anxious to find out, soon as I pulled the lid off I drained out all the fluid, would it be a good idea to refill the rearend because I probally won't be putting it in the car until the weather breaks again. I'm thinking it's good to fill it so the gears won't get correded during the winter. Also to fill am I just filling it before putting the lid back on, and what's a good rule of thumb for filling. Also before putting this in would should I do to refresh it so it'll be working at it's optimal performance. thanks fatboybuick

 

If it's a posi, you'll see some plates and springs between the smaller internal side gears like this:



To refill the housing, you'll need gear oil and a bottle of positraction additive from your GM dealer.

After you've emptied the old lube, you'll need a new gasket for the front cover. After you've installed the cover, to fill the axle you remove the fill plug on the side of the center section. With the housing flat and level, you add the positraction additive then fill with gear lube through the fill hole until the lube just starts to seep out of the fill hole. Then replace the plug and your done.

Devon

 

Thanks for the fill info devon! To count the teeth on the gears is the best way to pull th whole combo out, I don't really want to because I'm so new at this and I'm affraid I'll replace it wrong, plus I don't know if these bolts has to be torqued or anything. My last question is why are 3.42 such a desirable gear ratio, apposed to the other ratios? Thanks fatboybuick

 

You can count the teeth without taking anything apart. If you're lucky, the tooth count will be stamped on the edge of the ring gear; might look like 41-12.

3.42:1 is a good compromise between good acceleration and good street manners. A healthy engine will do just fine with ratios around 3.07:1 too.

The lower the number, the lower the rpm when cruising the freeway.

Devon

 

So I'm going with a larger wheel tire combo probally around a 22", would I need a lower or higher gear ratio for good performace, on the street and freeway?

 

Are there any number on the gears that would denote what ratio it is?

 

I already mentioned the tooth count being stamped on the edge of the ring gear:

Don't get carried away with planning rim/tire diameter until you know the ratio. With that, we can calculate how rpm will change with tire height.

Devon

 

Ok just opened up the rearend and I don't have plates and springs as shown I'm going to get pictures and guys please don't tell me I've been dupped!!!ou: counted the gears and divided them it comes out that it's a 2.93 though, but I want to make sure it's a posi, getting nervous here.

 

Get us some photos before you get too excited.

Devon

 

The springs in the middle will not look like in the picture Devon posted, there will be an "S" shaped spring in there, not much else.

On the side of the ring gear (the big gear inside the housing) there will be a bunch of numbers/letter stamped, just take a clean rag and wipe it off when you slowly spin it around, once numbers like mentioned above shows up, just divide them. (seems like you have already figured that one out)

Those big wheels you're running will make the gearing seem taller (less bottom end acceleration), but better for the highway (less rpms on the engine). The 2.93 gearing is sort of the middle route, ((tall=2.73) < 2.93 < (low=3.42)).

To make it as driveable as possible, a preferred gear ratio would have been lower, 3.23 / 3.42 to compensate for the large wheels.

 

Ahh, ye ol' "S" spring...then it'll be more like this:

http://image.carcraft.com/f/techart...rd_8.8_rear_end+traction_lok_limited_slip.jpg

Devon

 

Ok sorry it took me so long but I had to load the pics from my phone the digital camera is having issues. What I have is what you guys later mentioned, with the s spring. Just to make sure I'm correct I counted 41 on the large gear, and 14 on the small gear. That gave me 2.928 something and I figured the round up to 2.93. So to get the best performance for what I have I need to run a smaller wheel/tire combo if possible could you guys tell me what the largest size you would recommend running to get the most out of this rear end, because from what I'm seeing to get a good set of 3.42 or 3.23 is kinda unheardof these days. Thanks and please let me know if I'm on the right track.

 

If you don't plan on taking the car to the track, but just cruising around in it, you'll do fine.

I wouldn't take it apart either, it take experienced knowledge in matching up the pinion gear to the ring gear again after it's been out = more $$$. It will be quicker to just pop the cover back on, get some help from your buddies to install the whole new axle, and then test it.

 

Many times you can find out if a differential is a 'posi' or more correct 'limited slip' in a factory GM without disassembling the unit,but by turning one of the axles and the other one should spin the SAME direction. There is an amount of force that will allow the axles to turn in different directions,this is a result of the amount of 'slip' the clutches will allow(depending on ware and the amount of 'slip' the unit was originally designed for). There are 'locking' diffs(never put in electras from the factory as far as I know) these use centrifugal(spelling?) force to lock the unit at a certain axle rpm. With these locking units the axles will turn in opposite directions when tested by hand.
There are 'fully locked' units, usually used in 'race only' applications,these units do have any 'give' like clutches and will cause one tire to spin at a different speed than the car is moving while turning in a corner(no good for street). I would estimate that over 95 percent of the 'posi' units used on the street are of the limited slip variety.
Hope this helps for identifying the 'next one'. Good luck.

 

Here's the pics, thanks everyone for your help.

 

Ok to fill it up, what is recommend brands for gear lube,and posi trac additive? Hopefully I can find this at advance auto parts, or something. Thanks.

 

Don't use any additives other than the GM additive, and don't let the parts store sell you synthetic or synthetic blended gear oil. You want the crude-based regular stuff. Pretty much any brand is fine.

Devon