View Full Version : Gears

07-07-09, 09:58 PM
I was just wondering what the gear ratio in my Cadillac is. It's a 1984 Coupe DeVille with the HT4100 and the 2004r Automatic Overdrive. I don't think there was a trailer-towing package in '84. It is the basic 7.5 inch 10-bolt rear axel. I want to put a limited-slip in there when I do my engine swap later this year, and I want the same ratio. :burn: Also, how many splines do my axels have? Thanks for any info.

07-07-09, 10:34 PM
Ratio should be 3.42:1 (unless it came with a factory diesel, then it's 2.93:1) 8.5'' rear axle. And I don't believe anyone made a limited slip with that ratio.

07-08-09, 12:42 AM
The 4100 cars got the smaller 7.5" ring gear rear end. You can confirm the rear end ratio by looking at the "G" codes on the SPID sticker in the trunk (but I also think it is 3.42).'

If you are swapping to something stronger than the mighty 4100, go with a rear end from a 80/81 (if you want highway gears) or the 90-92.

07-08-09, 10:52 PM
If it is a 7.5'', then the closest thing GM made to the right ratio was a 3.23:1 limited slip with 26 splines.

07-09-09, 12:49 PM
I'll look on my mother's 84 FWB SPID. Her's is a 4100. They definitely got the 7.5, so all we need to know is the ratio.

07-09-09, 10:34 PM
Just got off the phone with mom: her 84 with the 7.5 axle is GU6, which is 3.42, as we thought.

07-10-09, 04:47 PM
Thanks for the help guys. It has 26-spline axel-shafts, right? Thanks again, Matt

07-15-09, 02:25 AM
Sorry to dredge this post back up top, but I have can't find my number of axel splines anywhere in the forum. Does anybody know if it has 26 spline axels? Thanks guys!