Speedo gears

[BILL BOWMAN1]

Finally got a functioning speedometer in my 65 Catalina. Only issue is that it is off a tad. I measured out an exact mile with 2 other vehicles, they were right on, the Catalina is at 9/10th's of a mile in that same distance. I know I have to take it apart and find out what gear is in it now, but would I go more teeth or less? And, roughly how many teeth difference for 1/10 mile difference?
Thanks.

[stevep]

You need 10% LESS teeth on your driven gear. If you have a 38 tooth gear, you would need a 35 or 36 tooth.

[Heybuck]

Finally got a functioning speedometer in my 65 Catalina. Only issue is that it is off a tad. I measured out an exact mile with 2 other vehicles, they were right on, the Catalina is at 9/10th's of a mile in that same distance. I know I have to take it apart and find out what gear is in it now, but would I go more teeth or less? And, roughly how many teeth difference for 1/10 mile difference?
Thanks.

The gear drive is in the transmission, not in the speedo head. You don't have to pull the speedo out of the car again, just pull the cable off the transmission and the gear is right there.

I think there are various colours denoting the number of teeth? Not so sure about that part??

Of course another possibility is your tyre size?? Larger diameter tyres will reduce the shown MPH on the speedo.

Ian

[BILL BOWMAN1]

Thanks!!

[Deadhead]

WARNING: You can not just swap any of the colored gears into the Trans. There are certain groups that will fit your Trans. I forget exactly how this works, but similar to or same as the rear, there are certain families that you can swap between. If the gear you need is not in that family, you have to change the drive gear in the Trans. Steve P should be able to flesh this out, but if you try to use a gear not in the family, you will destroy the plastic gear. IIRC there is a # on the trans where the gear goes in that lets you know the family you are working with. Or you use the Tranny code to determine. You can also buy am adapter thingy to go on the trans, but it is a lot neater to swap the gear if you can. Pretty sure all this is in the Chassis Manual.

[BILL BOWMAN1]

WARNING: You can not just swap any of the colored gears into the Trans. There are certain groups that will fit your Trans. I forget exactly how this works, but similar to or same as the rear, there are certain families that you can swap between. If the gear you need is not in that family, you have to change the drive gear in the Trans. Steve P should be able to flesh this out, but if you try to use a gear not in the family, you will destroy the plastic gear. IIRC there is a # on the trans where the gear goes in that lets you know the family you are working with. Or you use the Tranny code to determine. You can also buy am adapter thingy to go on the trans, but it is a lot neater to swap the gear if you can. Pretty sure all this is in the Chassis Manual.

UGH!! Never anything easy. But thanks for the heads up on this.

[Deadhead]

The good news is - if you check the chart and you can use the gear you want with what you currently have in the tranny - just put a pan under where the cable goes into the TH400, remove cable, the retainer & gear. Let the fluid pour into pan while you swap and then refill after you reassemble. That part is EASY!

Numerous E-Bay sellers have the gears. I think I got mine from a place called the Gearbox, which I initially found on there. Great people to deal with.

In my case, I remember that when I changed from a 2.73 to a 3.08 rear, I got very lucky and the black 3.08 plastic gear was the lowest allowed in the family I was working with. When you get in there, you will see why it is like this. Hopefully you can just swap the gears.

4 Spd is same deal. I have changed the drive and driven gears on those. You have to take it completely apart to change the drive gear on that.

[BILL BOWMAN1]

I did forget to mention this is a 4spd car. 3.73 gear, 225/75/14 tires, roughly 26.5 tall.
If it's not a simple gear change, it may stay 10% off for a while.

[Deadhead]

Worth a check. The 3.90 plastic gear or the 3.55 should be readily available and likely in the same family (not sure which 10% direction you would go). Someone in the 'Street' section should know the delineation of the gear groups for a Muncie.

[BILL BOWMAN1]

Ok, determined today I have a red 21 tooth gear. According to Stevep, I need 10% less teeth.. 10% of 21 is 2.1, so I will go with a 19 tooth gear.
This sound correct?

[stevep]

Yes. Try this place. https://transmissioncenter.net/shop/

[GpFreak]

What about a calibration box?