I just recently changed from my stock 3.23 ring and pinion to a 3.73 and now my speedometer is off. I called my local Chevrolet dealer and he said 3.42 was the max combo they had. I know there is a way to have accurate readings without changing my rear tire size. Please help!
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1990 Firebird Formula 350 speed density TPI; K&N, air foil, throttlebody coolant bypass, underdrive pullies, MSD 6AL, MSD HEI coil, 8.8mm wires, adjustable fuel pressure regulator, Hypertech Thermomaster chip, 160* thermostat, fan switch, B&M stage 2 shift kit, Edelbrock 1&5/8 headers, gutted dual cats, Flowmaster 80 series muffler, stock 3.27 posi rear end
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1990 Firebird Formula 350 speed density TPI; K&N, air foil, throttlebody coolant bypass, underdrive pullies, MSD 6AL, MSD HEI coil, 8.8mm wires, adjustable fuel pressure regulator, Hypertech Thermomaster chip, 160* thermostat, fan switch, B&M stage 2 shift kit, Edelbrock 1&5/8 headers, gutted dual cats, Flowmaster 80 series muffler, stock 3.27 posi rear end
TGO Supporter
If you have an automatic, GM has a speedo gear combo that works for 3.73s: 44 tooth Driven/15 tooth Drive.
It isn't listed as being for 3.73s (as 3.73s were not offered with automatics) but the combo exists.
Your tire size has to 25.5-26" overall height for this to work. That is the height of the 245/50/16s or 225/60/15.
It isn't listed as being for 3.73s (as 3.73s were not offered with automatics) but the combo exists.
Your tire size has to 25.5-26" overall height for this to work. That is the height of the 245/50/16s or 225/60/15.
Kevin91Z
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Mar 23, 2026
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Hey Glenn, you can get a 3.73 with an automatic in the 84 L69 HO cars. That was the only year I believe. But I'm not sure if the mechanical speedo gears from an 84 will fit the electronic speedo gears from a 90.
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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-
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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-
TGO Supporter
Thanks Kevin. I knew GM offered 3.73s with the HO L69 but I was unsure about the automatic. The combo I am talking about works for VSS and uses the a combination of Drive and Driven gears for the automatic in 1991 (and any automatic with VSS).
One of the gears (can't remember which) is not available as a "single" part for dealerships but as a package of 5, so a lot of dealerships MAY SAY "Discontinued" when they really don't want to sell just 1 and have 4 sitting in inventory. I think it is the 15 tooth drive gear as it is only used on automatics with 215/65/15 tires and 3.23 rears. All other combinations in 1991 (2.73 & 3.23) used the 17 tooth Drive Gear, so the 15 tooth Drive gear is the tough one to find.
If anyone is having problems finding that gear, let me know and I will contact the dealership that got me mine. They probably still have the other 4 in inventory. With the cheap Canadian dollar, it should be cheap. I think it was around $15 Canadian when I got it (almost 2 years ago).
One of the gears (can't remember which) is not available as a "single" part for dealerships but as a package of 5, so a lot of dealerships MAY SAY "Discontinued" when they really don't want to sell just 1 and have 4 sitting in inventory. I think it is the 15 tooth drive gear as it is only used on automatics with 215/65/15 tires and 3.23 rears. All other combinations in 1991 (2.73 & 3.23) used the 17 tooth Drive Gear, so the 15 tooth Drive gear is the tough one to find.
If anyone is having problems finding that gear, let me know and I will contact the dealership that got me mine. They probably still have the other 4 in inventory. With the cheap Canadian dollar, it should be cheap. I think it was around $15 Canadian when I got it (almost 2 years ago).