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Borg Warner M12 Automatic speedometer drive gear |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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Posted: Jan/07/2016 at 11:23am |
I was wondering if someone could check their M-12 Borg Warner automtic and let me know how many teeth are on the speeometer drive gear mounted on the tranny output shaft inside the rear housing? The guys at PATC can supply different speedometer gears, but need to have 7 teeth on the gear in the transmission to work. I was hoping somone might have theirs apart and could give me the teeth count.
Or maybe someone has the BW auto with 3.54 rear gears and has found a soultion to calibrating the speeometer with that rear axel ratio?
PATC can figure out how many teeth are needed on the cable gear, once they verify the teeth on the driven gear.
Steve
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sidewinder
Moderator Group Joined: Oct/07/2007 Location: Niagara Falls, Status: Offline Points: 6665 |
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Try giving AMARK a call...he makes replacement gears and may know what you need.
http://www.amarkamc.com/ Chuck Page |
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Chuck Page ,AKA Sidewinder
1968 "BLACK CHERRY" Javelin Previous owner of 2013 Heritage Cup winner 1970 BBO AMX |
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amxdreamer
AMC Addicted Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8511 |
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The TSM lists all the gears for what rear ratio is used.
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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Tony:
I'll check my Technical service manual tonight. I did not realizre that info was there. As far as you know the number of teeth on the inner gear or drive gear doesn't matter if you change the speedo cable gear?
The ones AMark lists are exacaly like the ones that Permormance Automatic Transmission show on their web site.
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scott
AMC Addicted Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3502 |
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There were 2 different drive gears, they differed according to the rear end ratio. The driven gear also differs according to the rear end ratio.
The M12 uses the same driven gear as just about any Ford application from the 60's into the 80's. |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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Scott:
So if I give them the number of teeth on the driven gear they can match the one for the speedo cable for a 3.54 rear axel that I should be able to get from the Tech Ser Manual?
Have you ever changed out the driven gear? I know I can get the rear housing off the tranny, but didn't check at that time how to remove the driven gear.
Steve
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scott
AMC Addicted Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3502 |
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The best thing to do is drive your car at the MPH you want the speedo to be most accurate, let's say 60 MPH. Have a GPS in the car, & see how far off you are at that speed. Let's say speedo shows 60 MPH, GPS shows 72 MPH. That is roughly a 20% error, speedo reading slow. Pull your driven gear, count the teeth. Let's say it has 20 teeth. You need a gear with 20% less teeth to get the speedo close to accurate at 60 MPH. 20 X .8 = 16 teeth.
You do the opposite, add teeth, if the speedo is reading faster than actual. If you can't get a driven gear that will correct the error, then you may need to change the drive gear. I've never had to do that, I guess I've been lucky. I've heard that anything under a 5% error is considered very good. I know the truck I drive at work, a 2013, is about 10% off at 60 MPH, but it becomes slightly more accurate as the speed increases. maybe at 100 its dead accurate. I'm not the greatest at math, so be sure to double check my calculations!! |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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Scott: I have 23 teeth on the speedo cable gear and I was told that the speedo was reading 10 mph under what I was actually going. This was on a friends dyno. As the speed increases the error is bigger. So using your formula 23 x.8 would give me a speedo cable drive gear at 18.4. AMark and PATC have 18, and 19 tooth gears. I'm thinking try both and see what's the closest. The guy at PATC said to verify if the driven gear on the output shaft has 7 teeth. The best I could count with my finger was 6, but I'm thinking that it could be 7 as I couldn't really get a good feel. Wish someone would have first hand info on this set up. I can get the gear and install it on another cable and see if it spins without binding. Then it should work on the road? No specs in the factory TSM. Steve
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amxdreamer
AMC Addicted Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8511 |
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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71 Javelin AMX O.O.
AMC Addicted Joined: Aug/29/2008 Location: Minnesota Status: Offline Points: 655 |
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Tony:
What section did you find this chart? I can look in my 1971 TSM again. It didn't have any kind of this info in the transmission or rear axel sections. I'm pretty sure that the driven gear has 7 teeth and the cable gear has 23. This set up was for a go pac 401 autiomatic with A/C I beleive the stock set up would have used a 3.15 ratio in the rear posi unit. CATC said to get the speedometer to read more actuatly I would need a 20 tooth cable gear, which they are sending me. He calulated it out by giving him the E-60 15 Polyglas tire diameter of 25".
Steve
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