85 vette speedotomer reading wrong
Thread Starter
Instructor
Joined: Jul 2005
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From: henderson nevada
85 vette speedotomer reading wrong
my speed reading is showing the wrong speed. It is showing 50 if I am doing 40. Showing 5-6 as I stop then goes down. Any reason for this and how to fix it??? Do the 85's shift smoothly into gear (automatic) or jerk as you shift??? Had the jerking but Mech tighten throttle cable and changed govenor gear. It shifts smoother but still does not feel right. After he did that that is when speed starting reading wrong. Any Idea's??
Race Director
Joined: Feb 2004
Posts: 12,518
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If the origional trans was changed, you may have the wrong grer or gears in the trans. There is a drive gear and a driven gear. Mixing and matching different tooth counts will allow for any gear ratio up to 3.73. If you know what gear ratio is in the car, we can tell you what tooth count will be needed for a proper match. Then you can verify this. Gears are cheap and not terribly difficult for a pro to install.
Thread Starter
Instructor
Joined: Jul 2005
Posts: 202
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From: henderson nevada
Originally Posted by Pete K
If the origional trans was changed, you may have the wrong grer or gears in the trans. There is a drive gear and a driven gear. Mixing and matching different tooth counts will allow for any gear ratio up to 3.73. If you know what gear ratio is in the car, we can tell you what tooth count will be needed for a proper match. Then you can verify this. Gears are cheap and not terribly difficult for a pro to install.
Drifting
Joined: Nov 2001
Posts: 1,783
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From: Latham NY
There are two different sets of "gears" in the 700R4 transmission. The governor gear which affects shifting and the VSS (vehicle speed sensor) gears.
You need to check the colors of the VSS gears. On is on the VSS and the other in on the tail shaft. As mentioned above, if the transmission was swapped and the correct gears weren't installed, you will have a problem. It could also be the VSS itself that is faulty.
You need to check the colors of the VSS gears. On is on the VSS and the other in on the tail shaft. As mentioned above, if the transmission was swapped and the correct gears weren't installed, you will have a problem. It could also be the VSS itself that is faulty.
