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Early A Speedometer Gear Source?
https://slantsix.org/forum/viewtopic.php?t=56839		 Page 1 of 2
Author:  63Valiant [ Thu Jan 01, 2015 8:12 pm ]
Post subject:  Early A Speedometer Gear Source?
Looking for 'em for my '63. Online searches are not yielding much; mostly later model stuff.
TIA!
Author:  Danarchy [ Fri Jan 02, 2015 6:29 am ]
Post subject: 
Here are a few places I have used in the past with Good Results!
http://www.imperialservices.net/Aparts.html
http://www.texasindustrialelectric.com/speedo.asp
http://www.zepco.com/Products6.asp
Author:  Doctor Dodge [ Fri Jan 02, 2015 6:47 am ]
Post subject: 
I have some good used ones...
What tooth count do you need?
DD
Author:  63Valiant [ Fri Jan 02, 2015 3:40 pm ]
Post subject: 
Quote:
I have some good used ones...
What tooth count do you need?
DD
If this chart is accurate: http://www.drivinithome.com/mopar-speedo-gear-chart/ I need the 32 tooth gear.

Only reason I question its accuracy is that I do not know if the tooth count per MPH was changed between the old and new design and I'm assuming that chart is for the newer design. Maybe I'm over thinking it...

Thanks!
Author:  65 dartman [ Fri Jan 02, 2015 4:46 pm ]
Post subject: 
Quote:
Quote:
I have some good used ones...
What tooth count do you need?
DD
If this chart is accurate: http://www.drivinithome.com/mopar-speedo-gear-chart/ I need the 32 tooth gear.

Only reason I question its accuracy is that I do not know if the tooth count per MPH was changed between the old and new design and I'm assuming that chart is for the newer design. Maybe I'm over thinking it...

Thanks!
That's for the newer style gears. The style you're looking for had at the most about 20 or 21 teeth.
Author:  63Valiant [ Fri Jan 02, 2015 5:34 pm ]
Post subject: 
Thanks! That's what I was afraid of. :( Is there a calculation for the older style? I have a 2.93 rear and I just measured my tires, they're smaller than I originally thought, 22" diameter.
Quote:
Quote:
Quote:
I have some good used ones...
What tooth count do you need?
DD
If this chart is accurate: http://www.drivinithome.com/mopar-speedo-gear-chart/ I need the 32 tooth gear.

Only reason I question its accuracy is that I do not know if the tooth count per MPH was changed between the old and new design and I'm assuming that chart is for the newer design. Maybe I'm over thinking it...

Thanks!
That's for the newer style gears. The style you're looking for had at the most about 20 or 21 teeth.
Author:  Doctor Dodge [ Fri Jan 02, 2015 6:17 pm ]
Post subject: 
17 tooth was used for the taller (24.5 inch) factory tire so I would guess that an 18 tooth is about right.
DD
Author:  63Valiant [ Fri Jan 02, 2015 6:52 pm ]
Post subject: 
Quote:
17 tooth was used for the taller (24.5 inch) factory tire so I would guess that an 18 tooth is about right.
DD
TY! Do you have an 18 tooth available?


Just some history on this, car was factory 170 and the manual shows a 3:55 rear. I've long since scrapped the rear and the 170 is in a wood shed. It has a 225 now.

I've been running a 7 1/4 rear from a '66 V8 Valiant that has the 2.93s for many years, but the speedo is way off; I'm talking 10+ mph off.

Wanting to get it right now, or at least close to it.

I hadn't realized 205/60-13s were so much shorter than the 6.50-13's. A tire site shows the 205's as being 27.5", but obviously mine measure much shorter. Of course tire manufactures don't always use the same dimensions....

LOL, I remember when my Dad was running 7.00-13's on this thing over 30 years ago and had to switch to the 'new' tire sizing C-78-13. :P
Author:  emsvitil [ Fri Jan 02, 2015 7:19 pm ]
Post subject: 
24.5/22 * 17 = 18.93

So a 19 tooth



205/60 13 = 22.7"
Author:  63Valiant [ Fri Jan 02, 2015 7:31 pm ]
Post subject: 
Thanks Ed, so if I understand correctly with the 205's that math works out to 17.54 so that confirms that I want the 18 tooth for my tires? The 19 would have been for the stock size?

You're measurement of the 205/60 series is a heck of a lot closer to reality than the 27.5 that tire site was showing. :lol:
Author:  nm9stheham [ Sat Jan 03, 2015 7:49 am ]
Post subject: 
Just ot add to the confusion.....!

Your smallish tires are going to turn the driveshaft faster so you need a higher pinion tooth count to slow the speedo back down. And keep in mind that rolling diameter is a bit smaller than most published diameters (unless they explicitly publish rolling diameter; I have seen both).

Just as a reference, my 26 diameter tires and 3.31 rear gear uses a 19 tooth old-style gear which is pretty close in speed indications (it may be a bit low so I might need a 18T gear someday). With your 22" tires and 2.96 gear, I get 20.1 using my gearing and tires as a reference.

I am not sure using my car as a reference is the best idea, but it looks like the math ought to be re-worked a few times; 18T sounds like it is going the wrong way. 19T sounds closer.
Author:  63Valiant [ Sat Jan 03, 2015 8:32 am ]
Post subject: 
Okay, sounds like I'll need to do a little more research; so to give me a starting point I'll pull my gear and count the teeth and then do another speed comparison with my GPS vs speedometer.
I had checked it against the GPS before, but cannot remember specifically what the numbers were.
Thanks guys!
Author:  emsvitil [ Sat Jan 03, 2015 3:55 pm ]
Post subject: 
Here's the basic math........

Find a combo that's correct.

Say 25" tire, 3.00 rear-end, 20 teeth is correct.


Changing just the tire:

25/(new tire diameter) * 20 = new gear size.


Changing just the rear-end

(new rear ratio) / 3.00 * 20 = new gear size


Changing both, do both of above.



If your speedo is consistently 10% high

(old speedo gear) * (1 + .10) = new speedo gear


10% low

(old speedo gear) / (1+ .10) = new speedo gear
Author:  nm9stheham [ Sat Jan 03, 2015 4:10 pm ]
Post subject: 
That is how I backed into calculating his needed gear teeth from from my car, EMSVitil.

If 63 Valiant is still working on this in few days with no better answer, I can get to my car and doublecheck the tire rolling diameter and maybe measure how close the speedo really is. (I know it has a 19 tooth pinion gear and a 3.31 rear gear.....) I'll keep checking to see if you have a better answer before Tuesday.

BTW, have you had your gear out? You could just pull, it count the teeth and increase the tooth count by the percentage that your speedo is reading high. That is your best bet. You'll probably have to drain some fluid or have a pan ready under the tailshaft. Pull it out gingerly and straight; I snagged and broke mine the last time. (Found a way to repair the nylon gear.....)

Also, there is a small oring-like seal up inside of the gear that keeps the trannie fluid from running down into the speedo cable and making a mess so keep an eye on that. It comes out with the gear.
Author:  emsvitil [ Sat Jan 03, 2015 4:23 pm ]
Post subject: 
I went to tirerack and looked up a few tire specs.


They give you diameter and revs/mile, so I figured out the revs/mile with given tire diameter and found.....



that the difference was 3%... i.e. the tire acts as if it's 3% smaller than it's actual diameter (or it spins 3% more times than you would calculate out)
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