Help With Rears

[dave6184]

Ok I have an 85 Monte Carlo SS with the factory 7.5" rear non posi. I want to add an auburn posi unit but Im not sure what series carrier I have or how many splines the axles have.

 

[MonteMan1987]

Ok I have an 85 Monte Carlo SS with the factory 7.5" rear non posi. I want to add an auburn posi unit but Im not sure what series carrier I have or how many splines the axles have.

if its a true SS it should be a 3:73 posi. but your carrier depends on the gear ratio so you need to figure that out first. Just take off the diff cover and look at the numbers on the ring gear for example 41 11 is a 3.73, you just divide the ring gears by the pinion gears.

the two carrier series are 3.08-down and 3.23-up

and the 7.5 came wih 26 spline axles i believe

 

[JESSE]

rears

if the 4th and 5th spots in your vin is gz you have a ss my ss also came with a 3.73 non posi,i think the series system is due to the gear ratio and ring gear thickness 3.73 3 series 4.11 4 series i'am not sure about the axle splines i think there 26 but maybe some one can tell you that knows for sure, you can always call your chevy parts guy 😀 i hope this helps you jesse

 

[megaladon6]

the easiest way to do it may be to get a junkyard or stock replacement posi unit. IIRC mine is an auburn cone type with 28 spline axles and 3.73 gears--87 monte ss.

 

[85_SS]

...if its a true SS it should be a 3:73 posi...

This is incorrect. Posi was an option, and an uncommon one at that. Only about 1/3 of SS's actually had it from the factory. I have owned 3, none of which were posi cars. Most cars were dealer ordered, so they didn't add options that weren't flashy. Also note that 83/84 SS's came with a 3.42 rear (and TH350c trans).

 

[MonteMan1987]

...if its a true SS it should be a 3:73 posi...

This is incorrect. Posi was an option, and an uncommon one at that. Only about 1/3 of SS's actually had it from the factory. I have owned 3, none of which were posi cars. Most cars were dealer ordered, so they didn't add options that weren't flashy. Also note that 83/84 SS's came with a 3.42 rear (and TH350c trans).

Well i just assumed it was a posi because every ss i have owned had a posi rear end, I know not all came with a posi but i thought that was one of the perks of it being an ss was the HO motor and posi rear. and being a 1985 it should of been a 3.73 with the overdrive transmission. but I dont know much about the 7.5" i dont bother with them because they are useless.

 

[megaladon6]

i thought that was one of the perks of it being an ss was the HO motor and posi rear.

you're applying logic to GM, it doesn't work. hell, they made the GN without a posi!!!

 

[MonteMan1987]

i thought that was one of the perks of it being an ss was the HO motor and posi rear.

you're applying logic to GM, it doesn't work. hell, they made the GN without a posi!!!

haha good point.

 

[85_SS]

...one of the perks of it being an ss was the HO motor and posi rear. and being a 1985 it should of been a 3.73 with the overdrive transmission.

Yes, all 85's had a 3.73 and 200-4R, but posi was still an option... and yes, posi should have been a given on the SS/performance models, but we all know how logical GM can be at times 🙂