4.3 and speedo change
 

I'm getting my 90 vert back this week I hope, with the 4.3 Lsd. Now my speedo will be off by ten percent, and if my thinking is right it will read higher than I am actually going, which may help me avoid a ticket some day. I can live with this but would rather have it accurate. I'm not familiar enough to know, is the speedo cable gear thingy easily accessable, and If I can do this easily wear can I buy the gear? Thanks in advance. Ron

There are small gear boxes that go between the tranny & the speedometer cable to compensate for final drive ratio errors.
Custom big wheel trucks have this issue also.
A custom truck shop, or a tire shop may be able to get you the right one.

For an accurate speed check, borrow a handheld GPS.

Yes the speedo gear is accesable, just put the car on jack stands, and you should have no problem. And as far as what you need to get the speedo correct, find a place that sells speedo gears, I believe that mazdatrix does, not sure though. You could probably find one on the forum as well.

I've read here on this site, that there is a different colored plastic speedometer drive gear for each rear-end ratio. Can't remember the color code, though.

here is how to figure out what gear you will need:
http://members.ij.net/mrmazda/speedo.html

Is the speedo gear prone to failure? I still haven't figured out my erratic speedometer.

No, probably a bad speedo cable

Thanks Icemark you are the man.

I suppose I could've called Mazdatrix first and not even started this thread, but for the benefit of all:
You just need these three parts-
TRANS SPEEDO GEAR 86-92 FOR 4.375 R&P 17-441A-1011 $20.64
TRANS SPEEDO GEAR 86-92 ROLL PIN 20-2140-9922 $1.09
TRANS SPEEDO GEAR 86-92 SLEEVE 4.375 17-442A-1011 $17.84

Geoff Barton
Mazdatrix
2730 Gundry Ave
Signal Hill, CA 90755
www.mazdatrix.com
geoff@mazdatrix.com

found my own answer
 

I suppose I could've called Mazdatrix first and not even started this thread, but for the benefit of all:
"You just need these three parts-
TRANS SPEEDO GEAR 86-92 FOR 4.375 R&P 17-441A-1011 $20.64
TRANS SPEEDO GEAR 86-92 ROLL PIN 20-2140-9922 $1.09
TRANS SPEEDO GEAR 86-92 SLEEVE 4.375 17-442A-1011 $17.84

Geoff Barton
Mazdatrix
2730 Gundry Ave
Signal Hill, CA 90755
www.mazdatrix.com
geoff@mazdatrix.com"

Thanks again to all!

You should be able to get it from the dealership, just tell them you have a 89 or 90 GTUs.