Huy guys, I've never swapped a rear-end before. But I just took out my Borg-Warner 9-bolt 2.77 posi rear and threw in a B/W 9-bolt 3.27 posi. On the freeway I felt like I was goin about 60mph, but my speedometer read 80mph. Am I supposed to go to my Chevy Dealer and get something to fix that? Thanks for the replies.

 

Since you have changed the gear ratio, now your driveshaft (and engine) turn over more revolutions per one rotation of the tire. You car was set for the 2.77 ratio and tire size. Now that you changed gears your speedo and odometer are reading way fast.

I have an 87 and just swapped 3.08's for 3.42's. I have a 9 tooth drive gear and a 22 tooth driven gear. I needed to go to a 7 tooth drive gear, and stay with the 22 driven gear. But, to change the drive gear I would have had to pull the back of my T5 off to change the gear. Not fun. So this morning I had a speedometer shop make up a gear reduction box that corrected my speedo error. I'm now within 1 mph of being exactly on for speedometer reading. Cost me $75 with installation and calibration before and after the gear box was put on.

I believe about 1990 and newer cars had electric speedo pickups (at least that's what one person on this board told me) If this is true, you have to have the gear ratio, and tires size handy, then you go to the dealer and pick up a new module to correct your speedo. The guy at the speedo shop told me to have anyone with the electric speedos contact Instrument Sales and Service in Seattle, WA. (Best price and they know what they are doing) Their phone is 800-333-7976. I've also been told there might be a problem with the computer doing a gear change like this. I'm not having any problem with mine, but with an automatic I can see there might be a problem with the TC lockup. It's probably best to ask about potential computer problems in the DIY prom forum.

Hope this helps.

 

I see, so what you're basically saying is, "If it ain't broke, dont fix it!" Thanks alot alloy, that helps alot. I'm getting my transmission rebuilt this week (700R4) so I'll just tell the guy to get that part for me as well. Thanks

 

No, you should fix it. Just go to a local speedometer shop and they'll change the gear and calibrate it for you. I did this when I jumped from 2.77 to 3.45 gears and from 16 x 8 rims to 18 x 9.5 rims. Cost me $30 for parts and another $30 for labor.