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Old 01-06-2013, 09:25 AM
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Speedometer off speed

Hey everyone. I have a question. Im grtting ready to install my manual transmission today. Hope the weather holds out for me. My transmission is the nv3500 its replacing my 4l60e in my 94 c1500. I know my speedometer is going to be off but I dont know by how much though. Its an electronic speedometer and the rear is a 3:08. Im running the stock size tires and wheels. 235/75 r15s is the stock size tire if I remember correctly. Havent drove it since August when the auto took a dump. Reason im switching to a manual. Anyways now that ove given a little background on the truck, can anybody tell me how much my spedometter will be off?

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Old 01-06-2013, 12:37 PM
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What is the tooth count on the auto trans speedo drive gear and the tooth count on the manual trans speedo drive gear?
As long as they are the same, and you run the same driven gear tooth count , it should be the same.
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Old 01-06-2013, 07:59 PM
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Im not sure on the spedo sensors magnetic pickup tooth count on either to be honest. I do know that the manual transmissions final drive gear, 5th, is faster than the one in the automatic, 4th 4l60e, . Usually lower gearwd rearends arw put behind manual transmissions and higher geared rears are behind automatics. I do know that my truck is going to be running faster than what will be showing on the speedo. The manual is an nv3500 and is between an 88-90 modle and the auto is a 4l60e and is a 94 model. The spedo sending units arent the same but use the same electrical connector.
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Old 01-06-2013, 08:53 PM
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Originally Posted by mh1984 View Post
Im not sure on the spedo sensors magnetic pickup tooth count on either to be honest. I do know that the manual transmissions final drive gear, 5th, is faster than the one in the automatic, 4th 4l60e, .
Gearing INSIDE the transmission has no bearing whatsoever on which speedo gears that you use. Tire size, rear end ratio, & speedo tooth count are the only issues needed to get correct dash output.
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Old 01-06-2013, 09:54 PM
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The transmission is geared higher in my 5sp than my 4l60e. The lower geared rears are behind the manuals for pulling and the higher 5th gear is for compensation for the lower gearing of the rear. Trucks like the 07 chevy dualies have a 6spd for fuel economy and low gear compensation for the rearend which is like a 4:10 or a 4:11 im not sure on the rear ratio. If the rear in the truck was a lets say 3:73 rear (just and example) it would run much faster than what it is showing on the speedo. The truck was designed to have a certain rear gearing to work with the 6spd efficiently. If I was to put a t56 in my truck the thing would fly cause of the higher gearing in the trans. Its final gear 6th is higher than the final 5th in the nv3500. Another example, my brother put an engine and transmission into a mazda pickup that has a 4:08. It turns high rpm going down the road. Lets say if it were a 5or 6spd with the same rear it would drop the rpm of the engine. It originaly had a 5spd in it but with no engine. The automatic in it is a 4spd. A4LD. Now do you see my point. If nessesary I can get my brother who is a certified mechanic and a truck driver so he knows more about gearing than what may would think. Transmission ratios and rearend ratios play a part in rhe speed and rpms of a vehicle. I also have an elderly friend who is also a certified deisel mechanic.
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Old 01-07-2013, 06:59 AM
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spedo off

what brand of electronic spedo do u have.. i have auto meter and u put in a switch and drive it cal it to what u are running. it don't care what gears u are running
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Old 01-07-2013, 07:57 AM
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The speedometer is the factory gm one. Im wanting to maintain the stock cluster setup for now. Later on I may build my own cluster with a classic muscle car looking setup. Right now its looking like its going to be a collor changing cluster and the tach is going to light up red when the engine reaches tach out same with speedo. When it reaches top speed or starts getting close itll turn red also
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Old 01-08-2013, 02:04 AM
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Originally Posted by mh1984 View Post
Transmission ratios and rearend ratios play a part in rhe speed and rpms of a vehicle. I also have an elderly friend who is also a certified deisel mechanic.
Transmission ratios do play a MAJOR part in the engine RPMs, but play ABSOLUTELY NO PART in the SPEEDOMETER GEARING.
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Old 01-08-2013, 06:06 AM
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The speedometer works by magnetic induction. The nv3500 has an inductor ring on the output shaft. The 4L60E i think has a worm drive on the output shaft that turns an inductor ring that the magnetic speed sensor picks up. If ii had the same geared rear under my truck that came under whatever vehicle the manual came out of im pretty sure the spedometer would be on cue.
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