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speedometer drive gear

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william View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote william Quote  Post ReplyReply Direct Link To This Post Topic: speedometer drive gear
    Posted: Jan/08/2009 at 8:52am
Can anyone tell me where to get speedometer drive gears...I am changing the rear end gears...and need to correct the speedo drive  Thanks   e-mail  wkulis@mottcorp.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 11:22am
I need that info too. I think my SC/Rambler ended up with a six cylinder cable when the cable was replaced from a donor car and it now tells me I can go 70 MPH in first gear!
Dan Curtis, AZ AMC Collector Quality Restorations & Parts - amcmusclecars.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 1:40pm
Which trans? Different trannies use different gears.  Kennedy had some of the driven (cable) gears for the M-11/M-12.  Some are no longer available.  There are also 7, 8, and 9 tooth drive (inside tranny) gears. 

My problem was that my AMX came with 3.15 gears and a 23 tooth driven gear (the biggest).  When I went to 3.73s, my speedo read almost 20 MPH high.  Since I have the biggest driven gear, the only option will be to replace the drive gear.  I assume I have a 7 tooth, and need an 8 or 9 (which would have to come from a used tranny).

I contacted these guys, and they said they could set me up with a reduction box and new cable for about $200.  http://www.transmissioncenter.org/

So far, I've just been living with it.  One of the things on my "to do" list this winter.

Bob
tufcj


Edited by tufcj - Jan/08/2009 at 1:42pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 1:53pm
Some info here if TorqueFlite
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 5:17pm
If using a T10, or Borg Warner auto, the speedo gears from just about any Ford transmission will work. Toploader, T-5, C-4, C-6, FMX, they are all the same. The oddball is some of the AOD gears, they won't work. If the AMC parts vendors don't have what you need, & the Ford dealer doesn't have what you need, check ebay. There are lots of people selling the Ford gears.
 
Here's the easy way to figure out what driven gear you need.  First you need to find out how far off the speedo is with the current gear. Cruise at an indicated 60MPH & compare that to a known accurate speedo. Or GPS systems give you MPH, in my area we have side of the road radar that shows how fast you're going. Let's say indicated is 60, actual is 70.   60 divided by 7 = .85, or, the speedo is 15% slow. Pull the speedo gear, count the teeth. Let's say it has 20 teeth. You need a gear with 15% less teeth. 20 X .85 = 17. Try a 17 tooth gear & the speedo should be accurate, as accurate as a 38 year old speedo head can be.
 
Another example: Indicated 60, actual 55. 60 divided by 55 = 1.0909, or 10% fast. You need to slow the speedo down, so you need to add teeth. 20 tooth gear, 20 X 1.10 = 22 tooth gear needed.     Scott


Edited by scott - Jan/08/2009 at 5:23pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote whizkidder Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 5:25pm
Originally posted by tufcj tufcj wrote:

My problem was that my AMX came with 3.15 gears and a 23 tooth driven gear (the biggest).  When I went to 3.73s, my speedo read almost 20 MPH high.  Since I have the biggest driven gear, the only option will be to replace the drive gear.  I assume I have a 7 tooth, and need an 8 or 9 (which would have to come from a used tranny).
 
Bob:  Are you sure?  Seems like an 8 or 9 tooth trans gear would spin your cable even faster, and push your indicated speed even higher.  I'd think you'd need less teeth on the trans gear...
 
at 800 tire revs/mile, and 1000 rpm cable speed @ 60mph indicated, 3.15 gears would require:
 
7/17.6 (18 tooth cable gear)
8/20.16 (20 tooth cable gear)
9/22.68 (23 tooth cable gear)
 
Swap to 3.73 gears:
 
7/20.888 (21 tooth)
8/23.872 (24 tooth not avaliable?)
9/26.856 (27 tooth not available?)
 
If your speedo was close to correct with your 3.15 gears, I'd guess you had a 9 tooth/23 tooth combo, and now need an 8/23 combo to get close.


Edited by whizkidder - Jan/08/2009 at 5:42pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mramc Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 6:00pm
I have a similar problem as my 69 AMX has a 727 type transmission in it and I've found the speedometer is reading some thing like 15 MPH low. So, I did a lot of research on the internet and found the out fit with the web address below and saved it for future reference. I have not contacted them yet , but they seem to pretty much be "Speedometer Gears R' US" If don't have it I don't think any one else will. They have a very extensive list of speedometer gears. LRDaum
http://www.transmissioncenter.net/speedometer_calibration_______va.htm
LRDaum
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2009 at 7:24pm
Understanding is if a speedometer is off, it is off by a percentage, the faster one goes, the farther it is off.  For example if off by 10%, would be off by 1 MPH at 10mph, off by 10 MPH at 100mph.  It does give the "target' Revs Per Mile in the TSM doesn't it ?  Oh, ok, just looked, it gives the Revs Per Mile for the TIRE, not the speedometer cable.  Have in my head from somewhere the speedometer cable should spin 1000 revs per mile, but that might be incorrect.  Guess I could do some math based on the TSM info.  About 1000 Revs Per Mile for the Speedometer cable is what I get using the info in the TSM.  Your mileage may vary Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Jan/09/2009 at 10:29am
Originally posted by whizkidder whizkidder wrote:

 
Bob:  Are you sure?  Seems like an 8 or 9 tooth trans gear would spin your cable even faster, and push your indicated speed even higher.  I'd think you'd need less teeth on the trans gear...
 


I haven't looked inside the tranny.  I knew it would be off from my years of gear/tire size changes in 4x4s.  But you are right, I probably have a 9 tooth gear, and need a 7 or 8, I was thinking backwards (which happens more often as I age). Wink

Bob
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you'll eventually pay for it...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/09/2009 at 12:59pm
Link to a Ford Speedometer gear info web page, not sure if it's any help or not,
but may be if the Borg Warner's use Ford style speedometer gears
which should be available from your local Ford dealership.
 
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