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Speedometer Inaccurate

Grease Monkey

Grease Monkey

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I just got done fixing my speedometer so it will actually move now with a new cable, and realized that it is way off on my speed. I can be going 45ish and it'll only show 15mph :confused: Someone in the past converted my 1/2 ton to a 4-speed. I dont know if that would throw it off or not? Is there a way to correct this problem? Thanks, Cody
 
speedo drive gear teeth number

GP 4.337
http://chevy.oldcarmanualproject.com/1929_54chevyparts/04/276.HTM

Shows the different drive gears.
And further down, what was in the 3 speed versus the 4 speed.

As you can see tire size is a factor too.

Find your speedo part # (far left column) for your 3 speed and part # for your 4 speed.

Then look at the beginning of GP 4.337 for those part numbers and you will see the difference in gear teeth.
 
Keystoner said:
GP 4.337
http://chevy.oldcarmanualproject.com/1929_54chevyparts/04/276.HTM

Shows the different drive gears.
And further down, what was in the 3 speed versus the 4 speed.

As you can see tire size is a factor too.

Find your speedo part # (far left column) for your 3 speed and part # for your 4 speed.

Then look at the beginning of GP 4.337 for those part numbers and you will see the difference in gear teeth.
Click to expand...


Thank you for the link! I was wondering how I would figure out what was different and which size i needed.
 
Finally ;

Now that you've done all that and know what gear you need , go to the Chevy Duty catalog and order up the one you need , they're color coded and in the catalog .
 
Hi vwnate1, I'm facing the same problem as Grease Monkey. In your post you mention the Chevy Duty catalog. I've tried to call their web page, but it is not working. Do you know any other supplier/internet page for those parts?

Thanks

Mike
 
Thanks & sorry, did not know this, just joined the forum. I was browsing the web page but could not find the parts. I got a 1953 4-gear Chevy Truck 3100. Can you help me find them on the page?
 
Catalog

yebozobi said:
Thanks & sorry, did not know this, just joined the forum. I was browsing the web page but could not find the parts. I got a 1953 4-gear Chevy Truck 3100. Can you help me find them on the page?
Click to expand...

When you're reading this reply , somewhere along the top of the page , will be a link to the host site , then you can search for a " request catalog " button or link to click on .

I'm not a computer whiz so that's the best I can tell you but it IS in here somewhere , you just have to be patient and keep looking & clicking on things until you find the catalog button .

They have an OnLine catalog but I always prefer the paper ones .

BTW : WELCOME !
 
Here's a handy formula to get it close if your using a non-stock rear end or actually any rear end. Driven gear (on end of speedo cable) ='s drive gear (inside trans) x rear end ratio x revolutions per mile and divide this by 1000. Get revolutions per mile by multiplying tire height by pi (3.14) and dividing this by 12 to change inches into feet. Now divide this into 5280 to get revs per mile.
Example:
Drive gear (inside trans) has 8 teeth
Rear end is 3.25 to 1
Tire height is 28 inches (28 x 3.14 divided by 12 = 7.33 and 5280 divided by 7.33 =720 revolutions per mile.

Plugging all into the formula; 8 x 3.25 x 720 divided by 1000 = 18.7 driven teeth. This means to chose a driven gear with 18 or 19 teeth.
Now use your gps, or borrow one, and see what your speedometer reads when the gps shows 60mph. Say it reads 68 then that is a 9% error. If speedo reads fast then driven gear needs MORE teeth, in this case 1.6 more teeth ( 18 x .09) but the closest you can get is 2 more teeth. I'd go one more since it's better to read a fraction fast when it comes to school zones and such. On trips I go strictly by the gps since it always shows the posted speed limit as well as ones exact speed.
 
Thank you. This really helps.

Do you know a good shop where I can order the gear?

I've tried to find the part for the last two months. It seems Classic parts does not have it in his catalog. As shown on the photo the plastic gear points slightly to the right and has 11 theeth. I guess it is not the right gear, the speedometer did not work anymore when I bought the car - since the part was worn out.
 

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Your drive gear is machined onto the yoke so you stuck with driven gear changes which are limited. Two places I use are TCI and D&L Transmission. They probably don't have much for you but could maybe direct you to someone that does. Google "speedometer gears" and a bunch of suppliers come up. Neil, "Brit 50" on this site needed the plug since he'd lost his (clumsy oaf) so I sent him one. All this leads to maybe--just maybe he has his old driven gear which a warm pint could deal him out of.
 
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