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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> 3.42 gears, what speedo gear do I need ?
Post Info TOPIC: 3.42 gears, what speedo gear do I need ?
ABC123


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3.42 gears, what speedo gear do I need ?
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On the white Parisienne, it came advertised as having an updated gear of 3.42

The speedo is way off of course.

The buick guy seem to suggest 42 teeth 

Speedometer gears for a 3.42 TH400 | V8buick.com

What do you guys think ?

 



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4SPEED427


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Do you know what drive gear is in the TH400?


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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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4SPEED427


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Oh, and tire size too please? Either tire diameter or tire size.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
ABC123


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Tire size is 245/60/15 but I can't find info on the drive gear.

I have been looking up 1969 Impala.

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seventy2plus2


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We'll need to know what drive is presently in the tranny, if your speedo is reading high or low, and by how much.

Many years ago I was grabbing speedo drive gears from Turbo 400's and have a small selection of them.



-- Edited by seventy2plus2 on Wednesday 31st of July 2024 12:31:21 PM

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ABC123


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GPS in hand.

Road trip !



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beaumontguru


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This TCI calculator works fantastic,  and they have a list of all the plastic gears and # of teeth too.

https://www.tciauto.com/speedometer-gear-calculator



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Beaumontguru

MY BEAUMONT HAS 4 STUDDED TIRES AND 2 BLOCKHEATERS......AND LOTS OF OIL UNDERNEATH.  The other one has a longer roof.
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ABC123


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I just got back.

Changed the GPS into miles.

At 50 miles an hour on the speedo, the GPS read 44 miles an hour.

So, it looks like 12% over or showing other words 12% too fast.

I was just reading up on 400s and they say jack from the rear to prevent excess fluid leaks.

I might pull this apart tonight to count.

I'll bet it's a 38 tooth.



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4SPEED427


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So you need to reduce it 12%. 

If it's a 38 now, you should try about a 42 tooth. However, from the little I know about TH400 speedometer gears and sleeves, I think you will need to change sleeves to go to a bigger gear. I think the sleeve your gear fits into now is only made to go up to 38 or 39 teeth. I think the 40 and up, maybe even 39 and up use a different sleeve.



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
4SPEED427


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And I just found the answer in a parts book. 

Look at the bottom of the left column.

t6.jpg



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
ABC123


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Found a decent video.

This is what I have,

35 teeth, so by my calculations, I need 39.77 .

A 40 tooth would be perfect.

I think after seeing the video, I will go with 39 teeth and call it a day !

002a.jpg

No fluid loss, I will check the level later.

008a.jpg

 



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seventy2plus2


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39 tooth is brown, part # 1359273.
40 tooth is black.

I seem to have every color except brown.



-- Edited by seventy2plus2 on Wednesday 31st of July 2024 08:07:07 PM

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ABC123


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I took the advice of all above and I went off to see the guy who first rebuilt a transmission for me 30 years ago.

It took him seconds to pull out what I needed.

004a.jpg

You have to wonder if brown is rare.

Like Clint, no brown but black and the proper case too !

Hard to count black teeth but I confirmed 40.

I traded him some parts and off I went.

Minutes to install and road test.

I am now just under 50 MPH on the speedometer when the GPS shows 50 MPH.

Problem solved !

 



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seventy2plus2


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Excellent!!

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