Speedo problem - 62 is actually 70
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 3,252
Likes: 6
From: The Colony Tx
Speedo problem - 62 is actually 70
I had my transmission replaced this week and when this was done the 'green' speedo gear was pulled out of the one going into the car and the old gear was put in. On the trip home I was keeping up with what I thought was really slow traffic and showing 62. Looking at the tach I was showing 1700 which is normally 70 in my car. I called the person following me and asked how fast they were going and it was 70.
If the proper gear was put into the rebuilt trans, what would cause the difference in speed display?
I did use the search and couldn't find anything that I thought covered this problem.
If the proper gear was put into the rebuilt trans, what would cause the difference in speed display?
I did use the search and couldn't find anything that I thought covered this problem.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
There are two gears that determine speedometer accuracy, one is the driven gear that you changed the other is the drive gear that is on the output shaft of the trans. If the original drive gear was different than the replacement trans that is likely the culprit.
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 3,252
Likes: 6
From: The Colony Tx
I am pretty sure that the car the tranny came out of was a 3:07.
I looked again this afternoon and it looks like the gear on the side of the trans was purple not green.
From what you said it sounds like I am going to have to replace the second gear. Does this involve getting inside the output shaft to change?
I looked again this afternoon and it looks like the gear on the side of the trans was purple not green.
From what you said it sounds like I am going to have to replace the second gear. Does this involve getting inside the output shaft to change?
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
I am pretty sure that the car the tranny came out of was a 3:07.
I looked again this afternoon and it looks like the gear on the side of the trans was purple not green.
From what you said it sounds like I am going to have to replace the second gear. Does this involve getting inside the output shaft to change?
I looked again this afternoon and it looks like the gear on the side of the trans was purple not green.
From what you said it sounds like I am going to have to replace the second gear. Does this involve getting inside the output shaft to change?
Here is a calculator that will help you determine if you have the right drive gear, good luck.
http://webpages.charter.net/khasting...peedocalc.html
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Your GPS can help tremendously. With the GPS establish an error percentage. Record the speedometer display at maybe 5 GPS displays.
I'd do maybe 40, 50, 60 and 70 MPH. Once the percentage of error is established it might be very easy to correct the error with maybe just a driven gear (side of trans) replacement.
You didn't mention which transmission is in your car or the year. I'm guessing it's an '88 from your "user ID"! Maybe NOT!
Which?
The donor transmission was from what MY? It looks to me like all of the transmission builds through '88 used a 17 tooth "drive" (internal) gear. It doesn't matter if it's an A4 or a 4+. You could be very fortunate!
Don't rely on "colors" - remove the driven (side of trans) and count the number of teeth!!
I'd do maybe 40, 50, 60 and 70 MPH. Once the percentage of error is established it might be very easy to correct the error with maybe just a driven gear (side of trans) replacement.
You didn't mention which transmission is in your car or the year. I'm guessing it's an '88 from your "user ID"! Maybe NOT!
Which?
The donor transmission was from what MY? It looks to me like all of the transmission builds through '88 used a 17 tooth "drive" (internal) gear. It doesn't matter if it's an A4 or a 4+. You could be very fortunate!
Don't rely on "colors" - remove the driven (side of trans) and count the number of teeth!!
Last edited by WVZR-1; Jul 11, 2010 at 08:48 PM.
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 3,252
Likes: 6
From: The Colony Tx
Yes the car is an 88, I have never been accused of being creative. The car is an A4 and the donor was an 85 that was supposed to have 25K but turned out to be junk. I won't go into how it happened, but I got it rebuilt at a transmission shop for $200 and installed in the car for $200. So I now have a rebuilt 85 A4 in the car for $950. It had a shift kit in the 85 when I got it and it was a huge suprise the other day when it chirpped the tires going in 2nd at about 3/4 throttle.
I am going to pick up a GPS tonight and will see what shows up at different speeds.
I am going to pick up a GPS tonight and will see what shows up at different speeds.
