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Old 06-29-2011, 09:49 PM
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Need help with speedometere

Hi again everyone, Been enjoying my ride but just recently lost my speedometer.
My 62 impala which had a strait 6 235 with a 3 speed manual trans underwent the transformation to a SB350 with a TH350 tranny. Initially
the speedometer worked at first but was short lived. I did replace the cable but can only get the speedo to work with a drill. Therefore it leads me to believe that the drive gear in the trans is gone bad. The driven gear looks okay but until I remove the tail of the trans I don't know what I need for the drive gear. I would like to have a new one in hand before I open this up.
My dilemma is I don't know what I have for a gear ratio in th meatball.
Anyone know what it may be given the original power train I mentioned above? Or is there an easy solution into figuring this out.
I'm not looking for dead accurate, I'm mostly concerned with the odometer reading so I can keep track for maintenance.
From what I've found out so far there are about 5 different drive gears for this transmission from 7 teeth to like 12 teeth. The driven gear is gray in color which I think is 22 teeth. I didn't know to count them when I had it out.
So anyway with all that said, is there a simple easy solution?

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Old 06-30-2011, 06:29 AM
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The gear vender should have the information you need, keep in mind the tire size comes into play as well.
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Old 06-30-2011, 07:51 AM
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I'll post a speedo calc. TCI had a great one and of course took it off their website. This one is okay even though its a Ford site.

I dont know if you have a 7 or 8 tooth drive gear, and you cant just count the 'threads.' You have to lay them flat on their face to count them.

So If it was me, I would calculate for both and then pick a driven gear thats between both answers.

You'll need your tire height, rear axle ratio and 7 or 8 tooth for a drive gear
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Old 06-30-2011, 08:03 AM
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I've used a GPS unit instead of a speedometer. It also keeps track of how far I've driven just like having a working odometer.

It doesn't work to well in tunnels.
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Old 06-30-2011, 02:31 PM
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Geeees. Since CompCams took over they've been redoing the TCI site. Leave it to the Bone Heads to screw up a perfectly good working site, can't find squat on there now.

Good sites for TH350 gears:

If your Rear Diff is Open/Non-Posi.
Jack up 1 wheel and spin 2 revolutions, count the Driveshaft revolutions.

For Posi.
Jack up Rear and spin both wheels 1 Rev and count DS Revs.
= Rear Diff Ratio
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