Does anyone know which spline count rear end they used in 89? my rear end is pretty much shot, the bearings are whirring like crazy, and the posi clutches let go a week ago, so time for a rebuild. i also need to know if since my car came with a 2.73 posi which should be a series 2 carrier if i have to get my auburn pro series posi as the same one or can i switch to 3 series? thanx

 

1989 was the change over year from 26 to 28 splines. Some rears such as the 2:73 may have the 26. Only sure way is to pull one and find out for sure. Nothing else is going help so don't order parts until you are sure.

 

88 was the year of 28 spline change

we cant guess what ratio is in your car

pull the cover or get the code off the pass side axle tube

good luck

 

If i get the code off the axle tube where can i find out what it means? i know my car has a 2.73 posi in it cuz i decifered the RPO code for it. GU2 and G80.

 

You answered your own question on the ratio as long as you have your original rear. GU2=2.73, G80=Posi. The original rear from my 89 RS was 2.73 also, and it had 26 spline axles. I would say probably 80-90 percent of the 89's had the 26 spline axle because they didn't switch to 28 spline until almost the end of that year's production. But like the other guy said, the only way to know for sure is to pull an axle and count the splines. On your other question, yes, you need to order your new posi carrier in the 3 series to run better gears. 2 series=2.73 and 3.08, 3 series=3.23, 3.42, and 3.73. All axle housings are identical whether you have a 2 or 3 series carrier, so either series carrier will fit just fine in your axle housing.

 

89 was the change over year and most were 26 with only a few at the end of the 89 run being 28. the spline count on the axles isn't a big deal. get the carrier you want or need and buy axels to match it.

 

OK well i ordered my gears and posi. Has anyone ever did a comparision on how much faster switching from 2.73's to 3.42's are?. just curious how much faster in the 1/4 my car will be. i was thinking .2-.5 faster E.T's

 

Anyone have a list of the RPO's for the differen't available rear-end gears?

 

hum well i guess the changeover year depended on the vehicle model because i see some models were 26in 88 and some were 26 til 89

http://www.ring-pinion.com/PartsList...b-Differential



for RPo axle ratio codes do a google

there are lots of pages out there listing them,
theres a billion of them

heres a partial listing


GU2 2:73 ratio

GU4 3:08 ratio

GU5 3:23 ratio

GU6 3:42 ratio

GT4 3:73 ratio

GT5 4:10 ratio

GQ1 Open Differential Rear Axle

G80 GOV-LOC Rear Axle


and another:


GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)

HC4 -- AXLE REAR, 4.56 RATIO

and there were billions more such as 2.77 and 3.27 and 2.41 and 2.56 and 2.21 and 3.40 and so on that GM has had over the years

 

A lot of mis-information you posted with regards to 3rd Gen models only.

 

Thanxs for the input guys but this post can be deleted. My rear end is done now i just gotta wait for the weather to break to go drive it.