# 70 GTO Odometer Gear



## GTO JUDGE (May 14, 2005)

I need some help locating the correct or as close to correct as possible the plastic odometer gear for my 70.

Here is the scenario:

The Transmission is correct for the car.. 3 speed Turbo automatic.
The car has a 12 bolt Posi rear. I have discovered it has 4.10 gears. For whatever reason that particular rear was installed, I dunno, but that's what I got.

My speed is off by 18 mph at 60 miles per hour. It is progressive though, at the slower speeds it seems ok but the faster I go the more off the speedo is. I removed the gear and housing. The gear has 40 teeth. On the aluminum housing there is the number: 1362077. I believe this housing will accommodate a gear with 40,41,42,43 teeth, as those numbers are also stamped on the housing. 

I called my GM dealer and am told that part is no longer available but I got a part number of 8623311 which may be the correct gear however there is no way to confirm this. 

I went to my local speedo specialist and am told they can make an adapter that will correct the 18mph difference but then I will be off at the lower speeds. I am further told that the problem may be in the cluster, they want 400.00 to calibrate it. 

I am running 245-60-14 tires on 14x7 rims. Now I realize the size of the tires will throw off the mph so I don't expect the correct gear to solve this problem but I would like to get the mph close. I am putting undue miles on the odometer the way this is going. The car was like this when the previous owner purchased it 14 years ago so this has been going on for quite some time.

Any help would be GRRRRRRRRRRRRRRRRRRRRRRRRReatly appreciated.

Vic


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## Rukee (Feb 8, 2007)

4.10`s?? Is that stock?? It must scream going down the highway. I would swap out the rear gear, not only would that help with the RPMs, but the speedo will correct itself too (or get closer) with a taller gear or tire.


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## 05GTO (Oct 6, 2004)

My 67 has a chevy 12 bolt that had a 4.11 when I purchased the car a few years ago, I changed the ring and pinion to 3.42 which helped the highway speeds and corrected the speed-o. 

I purchased the R&P from Randy's ring and pinion,


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## GTO JUDGE (May 14, 2005)

I don't have the $$ to swap out the gears right now. I been going through $$ like a drunkin sailor. The rear is not stock. I believe 12 bolts were offered on the 455's mine is a 400 but for whatever reason this rear was installed. Worse case scenario would be to let it alone for now and in the future change out the gears. I was hoping just to find a gear with the correct or close to correct teeth. 

It does get up and go in a hurry. I don't plan on doing much highway driving with it. Maybe the person who installed it used it for short jaunts I dunno. The previous owner had no issues with it. It tachs about 3K or just over it at 60 mph.

If I can't find a happy medium right now maybe a 3.55 or the 3.42 gear would be on the horizon down the road.


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## Rukee (Feb 8, 2007)

The rear gear swap would pay for itself in gas saving alone in a few short road trips.


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## GTO JUDGE (May 14, 2005)

Rukee said:


> The rear gear swap would pay for itself in gas saving alone in a few short road trips.


Whats a ball park figure on swapping out say for a 3.55?


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## Rukee (Feb 8, 2007)

Gear sets start out at about $200 and an install kit runs about another hundred. Call Randy`s with your specs. :cheers


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## 68greengoat (Sep 15, 2005)

Who's this Randy everyone keeps talking about? Does he have a website? Does he carry complete rearends? Judging(no pun intended, but not bad) by 05GTO Randy's response it's not him....


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## GTO JUDGE (May 14, 2005)

Well I was able to find a speedo drive gear with 43 teeth. Ordered it and will install it. Although it won't get me where I need to be it should reduce me 7.5% or 6 mph. I dunno what my 245 tires are throwing me off but I am figuring a few mph. I should be at about 9-10 mph off now at 60 mph. 

I book marked Randy's R&P for future reference.


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## Rukee (Feb 8, 2007)

Randy's Ring & Pinion


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## ppurfield001 (Jan 21, 2008)

GTO JUDGE said:


> I don't have the $$ to swap out the gears right now. I been going through $$ like a drunkin sailor. The rear is not stock. I believe 12 bolts were offered on the 455's mine is a 400 but for whatever reason this rear was installed. Worse case scenario would be to let it alone for now and in the future change out the gears. I was hoping just to find a gear with the correct or close to correct teeth.
> 
> It does get up and go in a hurry. I don't plan on doing much highway driving with it. Maybe the person who installed it used it for short jaunts I dunno. The previous owner had no issues with it. It tachs about 3K or just over it at 60 mph.
> 
> If I can't find a happy medium right now maybe a 3.55 or the 3.42 gear would be on the horizon down the road.



Judge, I feel your pain about the "drunken sailor" spending. I'm in the same boat nowadays. I just had 3.55 gears installed and your post reminded me to ensure that the speedo is recalibrated. Good luck and thanks. Regards, Paul.


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## 68greengoat (Sep 15, 2005)

Rukee said:


> Randy's Ring & Pinion



Thanks Rukee.........


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## GTO JUDGE (May 14, 2005)

ppurfield001 said:


> Judge, I feel your pain about the "drunken sailor" spending. I'm in the same boat nowadays. I just had 3.55 gears installed and your post reminded me to ensure that the speedo is recalibrated. Good luck and thanks. Regards, Paul.


I am only doing so much this season. Next winter I have some plans, the RA 3 goes in for one, the gearing wasn't figured in. 400 for a calibration is not in the plans either. :willy:


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## geeteeohguy (Feb 2, 2008)

_ would verify the gear ratio. 3ooo RPM at 60 mph sounds more like 3:55 gears to me. 4:10s with your tires should be at about 3400 RPM at 60. With 27.5 inch tires, my 3.36 geared '65 turns about 2800-2900 rpm's around 70 MPH._


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## geeteeohguy (Feb 2, 2008)

Just did the calculations: with 245 60 14 tires (25.5 inches in diameter) at a true 60mph at 3000 rpm, you have a 3.73 gear. If you have a 4.10 rear gear, at 3000 rpm with your tires, you'd be crawling along at 54 mph. I woould put some 27.5 inch tall 15" tires on the back of it if I were driving it!


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## 68greengoat (Sep 15, 2005)

Isn't Randy's R&P site great? You can calculate what your rpm's will be at any given speed by punching in different tire sizes and gear ratios. I think it's a great help figuring out a setup that will suit an individuals needs.


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