Speedometer Pinion Gear Size?

[Fast_68_440]

I am looking in the 68 Service manual and the section about the speedometer pinion gear on the transmission says see the chart for the correct size, only problem is I cannot find the chart.  Does anyboyd know the proper size or have the chart for the 68?  I am running a 355 rear end with N50-15 pro-trac tires.  What size gear do I need and where can I buy it?  I also don't have a speedometer cable yet.  Also I have the gauge cluster out right now so it should be an easy install for the cable, but what size screws are needed to hold the gauge cluster to the dash?

[A383Wing]

I got a chart..I'll post it when I get home

Or you can look here and copy the info for yourself

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150306897415&ssPageName=STRK:MEWA:IT&ih=005

[Mick70RR]

There's a chart here.

http://www.mymopar.com/speedometer.htm

[A383Wing]

Here....more options

[Fast_68_440]

Well I measured my tire diameter and it seems like it is 26.5" and my rear end is a Dana 3.55 so based on the charts it looks like I will need 36 teeth.  Just curious, how many teeth did the gear have on a stock 68? 

[A383Wing]

Depends on what tire it had and what rear gear it had....look in the above chart to determine what gear you had originally

[John_Kunkel]

With a 26.5" tire and a 3.54 gear you need a 35 tooth pinion, orange in color. P/N is 52068157

[dspaulding70]

I have spent an hour trying to find the old link that had the formula to calculate the pinion gear but could not.

I just changed the gears and need to get the new pinion gear.

I have 255x60x15 on the rear which I understand is 27" diameter.

Gears are 3.50 (not 3.55, because the shop that did the change are idiots!!!!)

My guess is that it should be a 34 tooth gear. 

Can anyone give me a confirmation?

[70 Charger RT]

Once you determine your pinion gear size and install it, take a GPS on the road with you to determine actual speed and compare with your speedo.  It's a good way to check.

[John_Kunkel]

My guess is that it should be a 34 tooth gear. 

Can anyone give me a confirmation?

Correct, actual math is 33.87

[A383Wing]

GPS is a good test....remember, one tooth difference on the speedo gear is about 5 MPH on the speedometer in hte car