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I Paid for this sh!t
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675 Posts
Discussion Starter #1
How accurate are the stock guages in our vehicles, Especially after 20 years?

Specifically the Tach, im trying to find out what rear end gear i have, and need a good tach reading) thanks
 

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710 Posts
reading the tach won't give you an accurate reading of your rear end... just pop the cover and count the teeth, that's the only way to know it for sure!

as far as the gauges go, I'd call them accurate enough to get you in the ballpark of what's going on with your truck, but no way would I bet money that they are what they say they are.
 

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Kitteh Commandaar!
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4,191 Posts
Accuracy and stock gauges shouldn't be in the same sentence. :haha

At least for everything but the speedometer and maybe a tach. I'm going to say the tach is ok. Not as accurate as an aftermarket, but good enough to know where your about to redline ;)

KC
 

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Redneck Romeo
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1,810 Posts
The worst factory gauges are the temp and oil pressure. They're essentially idiot lights with needles on them -- the senders aren't all that accurate, and even if they were, there aren't any numbers on the gauges. What's Hot? Cold? High oil pressure? Low oil pressure?

But to answer the OP's question: The factory tachs are generally pretty close.

Easiest way to check your gear ratios (without dropping the diff covers) is to jack the truck up, put a piece of tape or a longitudinal mark on the driveshaft and a mark on your tire. Rotate the tire one full turn and count the number of turns that the driveshaft makes. If you have an open diff, only jack up one side of the truck. If the DS turns a little over 3.5 times, you have 3.55s. A little over 4 = 4.10. You get the idea.
 

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I Paid for this sh!t
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Discussion Starter #5
well according to my tach im running at 2100 rpm at 70mph on 31" tires, with a .71 OD and a 1:1 transfer case, that equates to 4.10 gears. yet the truck had 3.55 according to vin code
 

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I Paid for this sh!t
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675 Posts
Discussion Starter #7
hmm, that would explain the lack of a axle tag on either pumpkin. Would the fact it has a trailer hitch mean anything??
 

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Satyr of the Midwest
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Did you use the ACTUAL tire diameter in your calculation, or did you just use 31 inches? This will make some difference.

I wouldn't completely trust the tachometer, at least not to the resolution of 100 revs/min. What looks like 2000 rev/min might be 1800 to 2200 or so, through experience.

The only absolute way to know the ratio is to pop the cover off and count the ring & pinion teeth.
 

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I Paid for this sh!t
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675 Posts
Discussion Starter #10
ok well i was planing on redoing all the fluids to synthetic anyways, so ill be able to figure this out when i do that
 

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my old gears and new gears all had the ratio stamped on the ring gear. easier than counting all those teeth
 

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Satyr of the Midwest
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my old gears and new gears all had the ratio stamped on the ring gear. easier than counting all those teeth
You take ALL the fun out of it! :rofl:

Introducing the concept behind gear ratios was my original intent. Knowledge is power. :beer
 
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