I just changed my rear end from a 2.73 to a 3.23 and I'm having trouble finding which driven speedometer gear to be used in the rear end change. I was informed to get the brown gear (25513046) for this swap but after installing the new, brown, gear my speedometer now reads approximately 5 higher than my actual speed when going say 45 (actual) my speedometer reads 50. Please help!

 

Remember, you don't always have just one option. Often times, there are two different combinations of drive/driven gears that'll work.

I'm not too familiar with the later VSS cars though. ...on my car you have two gears and a cable! If you have the right gears, it reads right! Nothing else to it!!!!!

 

Here's a calculator off transmission center's site. ...what DRIVE gear do you have???

http://www.bgsoflex.com/speedo1.html

 

How much of a difference did the swap make? more power everywhere in the rpms?

 

You need the red (17 tooth) drive gear and the grey (44 tooth) driven gear.

 

Could someone please tell me which speedometer gear to use on a 1981 Trans Am 4.9L automatic transmission with a 273 rear? What color did you take out of your car Sir?

Thanks,

Tom Colbert
Elkton, MD

 

https://www.thirdgen.org/forums/tran...eedometer.html
try the sticky.
or do something simple:
-check what drive and driven gears you already have
-download a speedo phone app w/ trip
-take a nice cruise. compare the car ODO distance vs the app trip.
-select the ratio to get your ODO (and speedo) on target

i just did this, and posted in an above post when going from 3.08 to 3.42. I'm going from a 42/17 to a 40/15 combo.

 

So if I'm reading this correctly, I went from 2.73s to 3.42s so I'll need the 40/15 gears?

 

Yes.
I independantly confirmed for myself by checking my existing speedo gears, using the ODO and GPS Speedo App, and appying the % change. 40/15 is my perfect pick for 3.42 & 26.0" tall tire. a 25.6" tall tire will be ever so slightly different but 40/15 is still the closest/best choice.

edit: my original reading was off some to start and the verification method also gave the same results as the table to get it spot on instead of assuming it would fix with 40/15

 

Thank you! Another thing on my project list, be glad to get my speedo right.

 

I received mine from amazon yesterday, $45 for drive gear, metal housing, and driven gear shipped. cheaper than parts or kits on ebay. If you have a plastic housing i believe you need to upgrade to the aluminum housing. I won't have it installed for a week or two as I have other home/car projects I need to work on.