speedometer drive gear question
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Melting Slicks
Joined: Nov 2004
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St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
speedometer drive gear question
I'm going to change my early '63 coupe diff. from a 3:70 to a 3:08.
Can I change just the speedometer driven gear or do I have to change the drive gear as well. Borg Warner 4 speed tran.
TIA, Larry.
Can I change just the speedometer driven gear or do I have to change the drive gear as well. Borg Warner 4 speed tran.
TIA, Larry.
Burning Brakes
Joined: Dec 2006
Posts: 965
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From: St. Charles/Cave Creek IL/AZ
i'm no expert on driven gear selections, but there is another way.
It is possible to have these adaptors made with gears that will compensate for speedometer inaccuracies. On my '67 GTO I drove exactly 30 miles on I-88 and discovered that it was 41% off.
Gave the numbers to United Speedometer Service in California (Riverside?) and they sent me a 90 degree unit that perfectly compensates. No messing with the drive OR driven gears at all.
Thread Starter
Melting Slicks
Joined: Nov 2004
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St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
In order to reduce wear on the speedo cable, I use a 90 degree adaptor at the trans.
It is possible to have these adaptors made with gears that will compensate for speedometer inaccuracies. On my '67 GTO I drove exactly 30 miles on I-88 and discovered that it was 41% off.
Gave the numbers to United Speedometer Service in California (Riverside?) and they sent me a 90 degree unit that perfectly compensates. No messing with the drive OR driven gears at all.
It is possible to have these adaptors made with gears that will compensate for speedometer inaccuracies. On my '67 GTO I drove exactly 30 miles on I-88 and discovered that it was 41% off.
Gave the numbers to United Speedometer Service in California (Riverside?) and they sent me a 90 degree unit that perfectly compensates. No messing with the drive OR driven gears at all.
I did not know such an item was available. Thanks for the help.
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
With a 3.70, you should have a 22-tooth silver driven gear; if so, that's in the "small" driven gear family (which uses the "large" DRIVE gear), and you can replace it with an 18-tooth brown driven gear to match the 3.08 axle.
If it has a 22-tooth green driven gear, that's in the "large" driven gear family (which uses the "small" DRIVE gear), and there are no driven gears available in that "family" for any axle ratios lower numerically than a 3.70. If that's the case, you'll either have to pull the trans and change the DRIVE gear to the "large" one so you can use the 18-tooth brown driven gear, or have a ratio adapter box made calibrated for the 3.08 axle.
3.70 was the only ratio that had a speedo driven gear in both "families".
If it has a 22-tooth green driven gear, that's in the "large" driven gear family (which uses the "small" DRIVE gear), and there are no driven gears available in that "family" for any axle ratios lower numerically than a 3.70. If that's the case, you'll either have to pull the trans and change the DRIVE gear to the "large" one so you can use the 18-tooth brown driven gear, or have a ratio adapter box made calibrated for the 3.08 axle.
3.70 was the only ratio that had a speedo driven gear in both "families".
Thread Starter
Melting Slicks
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St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
JohnZ, thank you for the very detailed reply. If I have the "silver" gear I will change it out. If not I will go with one of the adapters CaveCreekChump mentioned.
I noticed Corvette Central shows the 2 different 22 tooth gears as you mentioned.
Thanks alot for the info, Larry.
I noticed Corvette Central shows the 2 different 22 tooth gears as you mentioned.
Thanks alot for the info, Larry.
Thread Starter
Melting Slicks
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St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
