Tire Size / Gear Ratio

[the hamiltons]

Emery,

I assume you mean 16" tires. That was useful information.

Our transmissions use a 31 tooth speedometer plastic driven gear and all
the checking I've done resulted in finding that the 31 tooth is the largest
available for a 425. There are 29 tooth, 28 tooth, etc. which is going the
wrong way. We need more teeth to slow the speedometer down when a lower
ratio final drive is added.

The small box attached to the speedometer cable is the only way to correct
the speedometer that I could find.

Al Hamilton

 

[kara m kosier]

Al,
I have all the gears for the Stewart-Warner speedo cable gearbox.
Obviously then, I can regear the boxes to correct almost any
combination of gearing and tire size.
When traveling on the freeways, I occupy my time by checking
odometer error by using the mile markers. If you use an even ten
miles, then each tenth of a mile error is one per cent. Then correct
it with the gearbox. If the odometer is correct, then the speedo
should be right on. If you habitually exceed the posted limits, as we
do, it's nice to know where you are. Fun and games!
Gary Kosier
- ----- Original Message -----
From:
To:
Sent: Wednesday, January 26, 2000 10:53 AM
Subject: Re: GMC: Tire Size / Gear Ratio

 

[the hamiltons]

Emery & Gary,

I was refering to GM Dealer-available speedometer driven gears that I'm
fairly certain are not made with more than 31 teeth for a 425. I've seen a
few of the fixed ratio boxes, but the changeable-gear type sounds
interesting. Is there a part number for the Stewart-Warner speedo cable gear
box and it's various gears?

Al Hamilton