spun the tire 10 times and the yokes spun 12-3/4 times. what gear ratio does that give me. ?

 

1.275. Something is wrong here. If you spin a tire 10 times with a 3.73 gear it will turn the yoke 37.3 times. You're saying your u joint turned 12.75 times and turned the tire 10 times. That equals 1.275 gear. That can't be right.

NO ONE SAID THERE WOULD BE MATH!!!

 

If he had one tire on the ground it's 1.275*2=2.55 ~> 2.56.

 

AND...

It is not a posi axle. When you only turn one tire while holding the other one fixed, you get a 2:1 reduction through the differential spider gears.

 

I learned something just now. I can rest easy the rest of the day. Didn't know about the double with the pegleg.

 

Go find the youtube video that shows the workings of a differential.
It really helps to understand what you are doing inside the housing.

here I got it for you


and


and


As said so many times before here... you need 1 (or 10, or...) turn of BOTH rear wheels to get one (or 10 or...) turn of the RING GEAR...

Now you can get your two rear wheel turns by turning one wheel two turns [open]
or two wheels each one turn [posi], or
any other combination you like:
1.5 & 0.5
202 & -200
1.25 & 3/4...
as long as you END UP WITH one turn of the RING GEAR.

Ooooooh, ya doesn't have to call me Mr. Johnson!
You can call me Ray, or you can call me RJ, or...

 

Joe, would one know that for certain? A posi has a breakaway torque rating, so it is possible to turn one wheel with the other on the ground - it just takes more force to do it. Seems I remember someone posted the breakaway torque rating was typically in the 50 Ft-Lb range.

I just searched and found that 35 Ft-Lbs is the minimum spec. That would turn fairly easily, and worn clutches would make it even easier to turn.
Higher breakaway torque with new clutches and springs would obviously be much harder (or maybe even impossible) to turn.

 

ok ill try this again . I wire brushed the axel on the pas side all I could see was p2 and it was upside down

 

I don't think there's any doubt you have a 2.56. Unless there's a small metal tag hanging off one of the differential bolts, it's unlikely you have a worn posi - more likely an open differential.

 

I agree. The 2.56 open was the no-cost rear (for 1970 at least). It's amazing now many folks didn't spend a few extra bucks for a posi back then, even on 442s.

 

ok guy maybe this will help in telling me what rearend is in my 1970 cutlass s . its not a posi I pulled the cover and the ring has 41 teeth and the pinon has 16 teeth. theres a marking on the ring gear and it says, 16 then its an A or ^ 41 Gm 70 055 . does this help.

 

Let's do the math.

41 teeth on one gear, 16 on the other.

41/16=2.5625

You have a 2.56 open rear. Like I said twice already.

 

THANK YOU very much no wonder it didn't have much grunt when I took it around the block. had gotton the motor running , wasn't when I bought the car ran smooth but when I did a compression test 7 cyclinders had 100lbs and one had 75lbs. ive pulled the motor out and am planning a rebuild this winter trans was just rebuilt before I bought it.ant suggustions on a different gearing I was thinking 345,s or 355,s Do they sell a set that size and I want a posi.

 

If you have the O-Type 12 bolt rear, there are currently no aftermarket gears being made for them so none of the typical outlets will have any in stock. You may be able to locate a set of original GM gears, or someone may have an aftermarket set in their garage. New posi carriers are available, though. They are machined Ford 8.8 carriers that are made to fit the 3.08-3.23 series O-Type gears (I think).

The easiest and probably cheapest option is to buy a complete '71-'72 10 bolt rear with the ratio you want.

 

Actually Jim (monzaz here) had several different sets for sale. I would contact him and see if they are still available.
His website http://www.jdrace.com

https://classicoldsmobile.com/forums...1-o-gears.html

 

Don't the newer Cars have a number stamped on the housing like the older cars that tells the gear ratio?

 

I would be happy with a 342 rear posi im doing a resto mod so it don't have to be orignal

 

"Newer" and "older" are very subjective terms, especially on this board.

 

I'm sorry since I drive a 65 everything after that is newer. I break down 64-67 as older and everything after as newer and I haven't decided what to call the 80's cars.

 

Junk. Go for the 4.88s for one summer. See how you like the acceleration. I used to run a 4.11. Pin you back.

 

yea but I want to do highway driving also

 

Um, yeah, forget about that then. Liked my 4.11s. Now 3.73 with an overdrive. Best of both worlds. Good luck my friend. I envy you because you are starting out and seeing what this stuff is all about. I was 15 when I dove in. Small block Chevelle. Best times of my life.

 

dude im 54 this ant my first time around the block built many engines in my life ,but there were always stock rebuilds so hipoing a car is new to me. Thats why im asking for help theres a place next to me called transaxle I might just bring it to them and let them handle it.

 

I didn't mean any offense. I was just remembering how much fun it was putting a new bigger cam in my small block. It was too big. The car went slower! LOL! Live and learn. I learn something everyday from this site. You sound like you know more than I do so I may learn from you too. Like I said, no offense intended you old bastard (I'm only 52).

 

LOL that's funny when I was 19 didn't think id make it to 30 and so on and and so on im still here.this will more than likely be my last full rebuild but I want to do it right so I have something to leave my son hes 16 my plans are nothing radical im using a 262 hi energy comp cam and a trick shift kit in my rebuilt 350 trans might go 2000 stall and a 355 rear I want a posi im going to port the heads my self then send the out to the shop and I would like to put a larger intake valve in it and hardend valve seats . borening it out only if it needs it its a 1970 sbo with # 6 heads 64cc going to put 10- 1 pistons in it I have a 4bl stock intake for it but im thinking of going with a rpm airgap intake I have a 1970 qjet # matching all rebuilt and I will put a pointless ingintion in it have a coyles timingchain for it. and headers and a dual exhaust sorry but I like glass pack mufflers not looking for a strip car but I want instent response and goobs of mid range of course the whole motor will be rebuilt.this is my plan but im open to everyones opion on this I want to do this once and get it right also I will be putting new springs in the head and may be go with roller rockers if I left anything out please be free to tear a new hole into me it wont be the 1st time ive heard it.

 

Fix your period button.