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Need help with speedometere

7K views 4 replies 5 participants last post by  SSedan64 
#1 ·
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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#3 ·
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

http://www.moldyrabbit.com/liquid/speedo_gear.html
 
#5 ·
Geeees. :rolleyes: 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. :mad:

Good sites for TH350 gears:
http://novaresource.org/speedo.htm
http://www.transmissioncenter.net/speedometer_calibration_______va.htm#350

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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