I have always been under the impression that the SE models had the 4.076 gear ratio from all of the literature that I have ever viewed.

Today however going through the factory parts catalog I found this.

SE 4.076 Through Nov 84
SE 3.909 Dec 84 on.

I have not checked this on my 85 to confirm it though.

 

Weird...

 

Back when I was active here with a 13B GSL, I remember the SE guys throwing around the 3.9 ratio. I never paid a whole lot of attention, but it was definitely 3.9. Sounds like you're onto something.

Maybe now there's a second difference between 84 and 85 models (intake funnel length being the first)

 

The door label says my SE was mfged '04/85', so I guess it has the 3.9, which I like. The tall gear gives a little better MPG and I don't need a stump puller.

 

This is quite interesting... Humm I have to check my born on date.

 

First Ive heard of that one.
It could have been a neccesity thing,maybe they ran out of th 4.07 gearsets during production.It would be easy enough to do since the gears swap right in......I wonder if they just ran the entire GSL unit in those cars,with the better LSD stack?

Ive been into a handful of SE rearends,pretty sure they were both 84 and 85 model cars,and they have all been 4.07 equipped.Not that the switch to 3.90 makes much of a difference (I just went back to 3.90).

 

According to the parts fiche, it is like this:

'81-'83 = 3.909
'84 (non GSL-SE) = 3.933
'84 (GSL-SE) = 4.076
'84.5-'85 (non GSL-SE) = 3.909 (change in May '84)
'85 (GSL-SE) = 3.909 (change in December '84)

I'm not sure why they did the short run with the 3.933 gears for the non-SE. Also, they show no difference between the GSL and GSL-SE LSD packs. There are changes to the carrier over the years. Also, maybe when you compared the LSD packs, perhaps one was an earlier year or something. They also don't show a change to the clutch pack or anything else (except the diff carrier) and the diff carrier was changed at the same time (same part) between the GSL and GSL-SE. Actually, the diff carrier is the same for all models, but they switched in Jan. '85 for GSL/GSL-SE and switched in Feb. '85 for the S/GS models.

My guess is it was a cost issue (make all models the same, also using the same gear sets as earlier models). Also, it looks like the GSL-SE went to the taller 5th gear in July '84. So after December '84, the GSL-SE had both the taller rear (3.909) and the taller 5th gear. My SE is a 01/84, so it has the earlier gear sets.

 

With the 2nd gen N/A transmission that I am running the RPM is much lower than the SE transmission.

At 100 MPH the RPM on my SE is 4400
At 120 MPH the RPM on my SE is 5100

The earlier SE trans 5th gear was 0.758, the later 0.715, the 2nd gen transmission that I am using has a 0.697

 

The '85 brochure does show 4.076 for the rear of the GSL-SE, 3.909 for everything else. However, since '85 models started to roll out in mid-'84 (before the change), that could explain that. Also printed material is usually produced well in advanced of when it is needed, so it could have been actually printed in early '84 or whatever. I guess the only way to know for sure is to crack open some SE rears that were built after Dec. '84 and count the teeth.

 

Very interesting info, thanks for posting guys.