Need to complete 4.10 gear swap....

[jtstang89]

Is the 23-tooth speedo gear enough?

OK, here's my question:
I'm getting 4.10s put in by a local guy who does this kinda thing on the weekend, but he hasn't ever fixed a speedo after a gear swap...I bought the 23 tooth speedo gear for the swap, but I've heard some say that it won't work! What else do I need to get my speedo working right? I've heard people say that the 23 tooth will work..just not fully accurate. I can live with that, but I might freak out if I'm off by like 30mph! Any input?

 

[DropTopR]

With 4.10's, you may have to change the gear on the output shaft too. I think that there is a part number from Ford for that. My friends car with 4.10's and the "right" speedo gear still reads a bit too much off I think. Like, 8-15 mph off, depending on speed.

 

[jtstang89]

With 4.10's, you may have to change the gear on the output shaft too.QUOTE]
Is this also known as a 23-tooth speedometer gear?

 

[DropTopR]

not sure what it is, but it's something different. Give a call to D&D Performance. THey should be able to help

 

[blk92stangg]

Changing the gear on the output shaft is not a weekend warrior job, btw...the tranny needs to come out of the car.

 

[goldbomb79]

the highest speedo gear change that is accurate is for 3.73's but if you change the gear on the output shaft and get the right speedo gear then you can get it more accurate for the 4.10's. i would use the 23 tooth and just see how far it is off at the speed limit where you live and just go by that because it's a pita to change the gear on the output shaft for what it's worth.

 

[omnecide]

i thought that you only have to change the output shafts on autos after 1990 when they went to the 8 tooth drive instead of 7
http://www.geocities.com/mgnedell/notchback/tech/speedo.html
according to that you should just need the 4.10 Gear Ratio / White 23 Speedo Gear

 

[Michael Yount]

Check out the site - it should help. The output shaft gear (drive gear) comes in 6, 7 and 8 teeth. The speedo cable gear (driven gear) comes in 16, 17, 18, 19 and 21 teeth if I'm remembering correctly. Technically I believe the 23 tooth piece was actually for a Chrylser/Jeep application, but some have used it. If you want your speedo accurate, you need to know what two gears you have now, and how far off you are -- use Interstate mile markers to check accuracy. If you're say 25% off now (you're going 50 and it reads 62.5 mph for example), then you need to change the ratio of the 2 gears you have in there now by the same percentage that you want to adjust the speedo by - in my example, change the ratio of drive gear to driven gear by 25%.

http://www.geocities.com/mgnedell/notchback/tech/speedo.html