After Rear End change..Speedometer

[BigRed]

Ive got the plan layed out for the 3:73 gear change however I am I little fuzzy regarding what to do about the speedometer.

Ecklers has a little computer dohickey for 200 bucks that will compensate but is that required? Also Ive heard about the Hypertech programmer but ($$Ouch)

What about the Speedometer gear? (Ive never worked on transmissions like this so bare with me) Is there a cable going to the trans on my 4+3? Can I simply change the gear? Where do I get it?

Thanks guys

 

[JonM]

Call Jeff Kopp at superior chevrolet ...He is the wholesale parts manager...tell him you spoke to me...he will help you out...

800-728-8267 913-384-3115

He too has an 85 (red) he just compleated....

http://home.att.net/~red85vette/vette/vette.html

 

[BigRed]

Hey thanks alot bud I got that copied down!

 

[-=Jeff=-]

The General never made a driven gear and a Drive gear for the 3.73 ratio.

Here is how to determine the new drive driven gears..
Let's assume you have the 3.07 rear gear now:
The drive gear is 17 teeth and the driven is 42 teeth
Info found here:
http://www.corvetteforum.net/c4/vettenuts//SpeedometerGearshtm.shtml

Okay first equation is Current gear/new gear (3.07/3.73) = 82.3%

The 82.3% is the goal for the next equation

(New Drive Gear/Current Drive Gear)x(Current Driven Gear/New Driven Gear) or (New Drive/17) x (42/New Driven)
Lets try 15 tooth for the drive and 45 for driven

So (15/17=.882) x (42/45=.933) = .8229 or 82.29%

So if you have the 3.07 here are the GM Part Number's you will need:
8642620 = 15 tooth drive
25513052 = 45 tooth driven

And also the hypertech will not work in your App.
As for the Ecklers box, you can do it, but I think swapping the mechanical gears is the better alternative

 

[JT ZR-Won]

I had an '85 vette that I did a gear swap in and I remember purchasing the two small speedo gears for around $30 through Summit Racing. I had a transmission specialist instal them for around $100. Never had a problem. That was around 6 years ago though, so I'm not sure if the price from Summit is still the same. But it might be worth a shot.

Jay

 

[BigRed]

Hey ya that sounds better and cheaper ZR!

I read something about having to tear apart the tranny and that scared me a little but if its only around the 100-200$ mark to get installed hell ya thats ok with me!


Thanks guys