[RRGTO]

Where can I get the correct speedometer gear to recalibrate my speedo to my non stock rear end gears?

[RRGTO]

Where can I get the correct speedometer gear to recalibrate my speedo to my non stock rear end gears?

[Colorado Bill]

You can get gears and some adapters from GM. Search the Street Performance forum for "speedometer" and you'll get some how-to information and links to part numbers. Know your part #s when you go, because the parts guys probably won't have much interest in helping you figure out what you need. That's the low-budget option. You could also just take the car to a speedometer shop.

Bill

[Rocky Rotella]

What year GTO? What was the stock rear gear? What is new rear gear? What is the current tire size? What tranny?

I'll see if I can do some cross referencing with my Master Parts Catalogs

[goathead68]

Rocky,

As long as this is posted, I'll ask you. '68 GTO, Turbo 400, original gear 2.93, now 3.23, 225R70-14 Radial T/As, 26" tall. What speedo drive gears do I need?

Thanks.

Ken

[RRGTO]

Rocky, It's a '68. It originally came with a 2.78 10 bolt. I now have a 3.73 12 bolt. It has a T400. The tire diameter is about 25. I don't want anything custom for the tire diameter as that may change. Just a stock gear probably from a chevy with a 3.73. I appreciate any info
Thanks.

[ April 15, 2002: Message edited by: RRGTO ]</p>

[Rocky Rotella]

I'll check my MPC tonight and try to cross reference. I'm on a trip in Jackson, MS but as soon as I get home, I'll look into it.

[Colorado Bill]

Goathead68,

Yours should be easy. Go to http://fteufert1.home.att.net/speedo/speedo.htm and click on 68 GTO. The chart will show you the rearend ratios, gear combinations, tire sizes, and trans codes you need. Your tires are the same as the original 225Rx14 on the chart. All you need to do is find out which trans you have, which will tell you what drive (output shaft) gear you have. Then you can use the chart to pick the right driven (speedo cable) gear for a 3.23 rear and that same trans. The trans code is 2 letters, on a metal tag riveted to one side of the trans, I can't remember which side. Be careful cleaning the tag, because I think the trans code is painted on rather than stamped.

RRGTO,

Your situation is a little more complicated. Look at the topic linked below, and I'll do some more checking when I get time.
http://performanceyears.com/cgi-bin/...10&t=000079&p=

[Rocky Rotella]

Colorado Bill beat me to the punch! Great site.

I was goin gto suggest #9775187 45 tooth blue gear for the 3.73 geared car and #1362048 40 tooth black gear for the 3.23 geared rear end.

Either way, all tranny's show to have the same drive gear inside the tranny.

[RRGTO]

Thanks for the info guys. I'll try that# for the 3:73.

[Colorado Bill]

RRGTO,

I just did some figuring about your speedo gears. If I'm right, you will still read about 12 mph fast with the 45 tooth side gear. To be accurate, you'd need even more teeth than that, but 45 is the highest GM makes. You also need a different sleeve for that gear, about $20 plus $7 for the gear.

I'm assuming you want to correct the speedo without taking the tailshaft off the trans and changing the driven gear inside. You could get the speedometer to read only 3-4 mph fast with a .7333 reduction adapter for $48. I used that with my stock 2.93 trans gears when I changed to a 4.10. The adapter just screws in between the speedo cable and the trans. That ratio was available a year ago, part #3932220, listed for a 70s Vette. Good luck. I know it's a pain to have the speedo bouncing around 85 when you're doing 60.

[Colorado Bill]

[ April 21, 2002, 04:02 PM: Message edited by: Colorado Bill ]

[goathead68]

Thanks for your help, guys!

I did a little math while driving the car on a long ride last year (it was a long ride!)to figure out how many percent the speedo was off. The number I came up with was 13%. After looking at the charts on the speedo gear link posted earlier, the 40-tooth 'Black' gear, part # 1362048, will put me within .5% of being exactly accurate.

Oh yeah, 225/70R/14 Radial T/As are 26.5" tall, not 26", as I had posted earlier.

Thanks again.



[ April 20, 2002, 11:45 AM: Message edited by: goathead68 ]

[RRGTO]

Thanks for all the info guys. I'll run with it.

[goathead68]

FYI,

I ordered driven gear #1359273 (Brown, 39-tooth) yesterday from my local Chevy dealer-it arrived today and cost a total of $3.99 (including tax).
It's hard to believe that some of these parts are still available!