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Old 01-16-2008, 06:45 PM
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700r4 Speedometer correction help

it's simple, I have a 700r4 from a v6 car, which I don't know what gear ratio it had. It's currently in a v8 monte carlo ss with 3.73 gears, and 235/60r15 tires. My speedometer is off, right now I'm going to install a new autometer speedometer and would like it to read correctly. I know I have to change some gears in the tail. I actually never have done this before, so I would like to know how to do this (maybe a link) and what gears I must install.

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Old 01-16-2008, 06:51 PM
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Here is a chart that will help you decide the correct gears to correct the speedometer

http://www.tciauto.com/Products/Tech...eedo_gears.asp



Here is a cut away photo of the 700R4 speedometer drive set up. You remove the speedometer cable, then the bullet. Remove the tail housing and there is a clip that holds the big gear to the shaft. Change the gear ... change to gear in the bullet. Reinstall everything.

Simple
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Old 01-16-2008, 06:53 PM
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So, I must change both, I've seen somewhere that it was possible to change the small one only (driven), am I wrong??
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Old 01-16-2008, 06:55 PM
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Also...if the closest gears available still leave it very slightly off, you can get a "speedometer adapter" in almost any possible correction percentage. It's a small gearbox that attaches quickly between the trans and the cable. Look on ebay motors; some sellers offer custom ratios.
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Old 01-16-2008, 07:19 PM
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Quote:
Originally Posted by chevy_power427
So, I must change both, I've seen somewhere that it was possible to change the small one only (driven), am I wrong??

well , yes and no.... you have not indicated if the speed-O is off by 7 mph or 27 mph , high or low


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Old 01-16-2008, 07:20 PM
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my speedo always reads faster than im driving, lets say around 15kmh for 50kmh approx.
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Old 01-16-2008, 07:52 PM
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Quote:
Originally Posted by chevy_power427
So, I must change both, I've seen somewhere that it was possible to change the small one only (driven), am I wrong??
It depends ...

Use the chart I posted and put in your drive gear number of teeth in the equation.


Drive Gear

The drive gears are colored coded. Gray = 15 teeth, Red is 17 teeth, Blue is 18 teeth and Yellow is 19 teeth. You may be close enough to just change the driven gear. Pull the bullet and driven gear out and LOOK see which driven gear you have in the 700R4 now.


Driven Gear
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Old 01-16-2008, 08:03 PM
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DEUCE, You do a really good job and definitely deserve to be a moderator. I am not a tranny expert so correct me if I am wrong, but isn't there a range off about 3 numbers corresponding to the gear teeth that the bullet will accept? I changed one on a friends 57 chevy with a 700R4 and I seem to remember this.
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Old 01-16-2008, 08:12 PM
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Quote:
Originally Posted by speedydeedy
Isn't there a range off about 3 numbers corresponding to the gear teeth that the bullet will accept? I changed one on a friends 57 chevy with a 700R4 and I seem to remember this.
There are two bullets listed by Chevrolet ...



One goes from 34 tooth to 39 tooth,
and the other goes from 40 tooth to 45 tooth.

All the drive gears and driven gears, in addition to the bullets are still available from Chevrolet at your local Chevrolet dealer. Finding a parts man smart enough or willing to order them ... NOW ... that migh be a different story
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Old 01-16-2008, 08:16 PM
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Thanks Deuce, I went to a local tranny repair shop and they gave me one.
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Old 01-16-2008, 08:36 PM
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ok, good, that makes the thinks more clear. As for the parts, I just discovered a good transmission component distributor which I guess I'll be able to find whatsoever I need. I'll start by taking the bullet off and identifying the drive gear, from there I'll see in what direction to go. Thanks!
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Old 01-16-2008, 08:41 PM
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If your speedo reads faster you need a driven gear with more teeth to slow it down.
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Old 01-16-2008, 08:50 PM
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Quote:
Originally Posted by speedydeedy
Thanks Deuce, I went to a local tranny repair shop and they gave me one.
I used to go to my friends transmission shop and rob his old 700R4 cores ... but the pickings got thin and most of the stuff was just plain high mileage or worn out. Most had the RED 17 Tooth drive gear ... The little seal in the bullet would leak or the driven gear would have a wore spot and allow leaks ...

The Chevrolet dealer is just down the highway and I eat lunch with a couple of those parts guys once or twice a week ... a couple of them are actually smart enough to order the parts ...
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Old 01-16-2008, 08:54 PM
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Bowtie Overdrives website has the calculator and any and all parts you would ever need to make the swap.

They were who I went with for the info and then the parts.

You would need to know the size of your tires, and gears in your axle to make the calculations correct, and when you figure out what the needs are to correct the speedometer, the numbers coincide with the drive/driven gears and the correct bullet to make everything work out to what you need.

Somewhere in the Knowledge Base I have all the math and numbers work already done for the TH-700R4 for speedometer corrections. It's only been a couple years since I've even seen that article.

OH YEAH, it's only about a 15-20 minute swap from one speedo gear set to another if everything works out right, for someone like me that's only taken one apart to date.
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Old 01-16-2008, 08:58 PM
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I found a website that has an application that gives the gears needed.
http://www.bgsoflex.com/speedo1.html
It's somewhat similar to the one offered by Tci.
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