Put in new gears! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

84Stepper · 11-20-2003, 11:14 AM

Got my truck back last nite. Had new Eaton Posi 3:73 put in. Wow!!! What a difference. Question? My speedo seems to be reading higher than normal. Did having that done change my speedo or am I just going faster!

God I love these gears!

gldevall · 11-20-2003, 11:21 AM

You will have to re-calibrate it. But on mine with a 27" tire in the back my speed is double the RPM. So at 3000 RPM, I know I am going about 60 MPH.

**N2TRUX** · 11-20-2003, 11:22 AM

What gears did you have before? Yes, those 3:73's will bring you truck to life. They will also make a difference in you speedo. Here's a calculator that will tell you how much...
Calculator page

84Stepper · 11-20-2003, 09:35 PM

I used to have 2:something in there. 2:46 maybe? What happened was when I went to pull away from the house a real loud pop came out of the rear. The truck just kept rolling back. Even in park. Had it towed to a shop and he called to tell me the news. He said it looked like little car gears in there all mashed up. I think the motor probably overpowered them. It used to have a 305 in it. So that's why I made the upgrade.

What do I need to get to fix the speedo, is it the little gear at the end of a cable that goes into the tranny? Do I get a part at say Autozone to get the speedo right or do I have to take it back into a shop? Thanks for any info you guys can give me. I was hoping I could fix it myself this weekend. Also I don't have a tach yet. But it's on the short list.

dwjack · 11-21-2003, 01:21 AM

I had the same problem with mine when I put a different rear end on. I went to a dealer with the gear at the end of the speedo cable and they told me that they could sell me another gear but only to fix it a small amount, 5 or 6 mph if I remember right. If it is more than that you have to replace the gear inside the tranny. So knowing that if was off about 12mph at 55 they figured out which gears I needed. (you also need to know how many teeth are on the other gear.) All you have to do is drop the driveshaft and unbolt the housing at the back of the transmission. I can't remember exactly what held the gear in there, some kind of C clip I think. Not hard to do, the parts are cheap at least.

11-20-2003, 11:14 AM	#1
84Stepper Registered User Join Date: Feb 2003 Location: Edmond, Oklahoma Posts: 425	Put in new gears! Got my truck back last nite. Had new Eaton Posi 3:73 put in. Wow!!! What a difference. Question? My speedo seems to be reading higher than normal. Did having that done change my speedo or am I just going faster! God I love these gears! __________________ 84 Chevy Stepside, 350, TH350, 268h Comp cam, Hooker headers, MSD Pro Billet, Edelbrock Performer manifold and 1604 carb, 40 Series Flowmasters dumped, and Western Chassis 3/5 drop w/ c notch. New 3:73 Eaton Posi

11-20-2003, 11:21 AM	#2
gldevall Registered User Join Date: Mar 2003 Location: Walker, LA Posts: 2,925	You will have to re-calibrate it. But on mine with a 27" tire in the back my speed is double the RPM. So at 3000 RPM, I know I am going about 60 MPH. __________________ Gary -1986 SWB: lowered 4/6, SOLD!!! -Best 1/4 mile: 14.51 @ 91.01 MPH -2001 Pewter Tahoe, billet grill, Corsa Sport Cat-back, K&N FIPK SOLD!!! -2004 Z-71 Extended cab with a flowmaster, BDS 6.5", 3" BL, 35x12.5x18 Trail Grapplers on Pro-Comp 18x9 wheels

11-20-2003, 11:22 AM	#3
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	What gears did you have before? Yes, those 3:73's will bring you truck to life. They will also make a difference in you speedo. Here's a calculator that will tell you how much... Calculator page __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

11-20-2003, 09:35 PM	#4
84Stepper Registered User Join Date: Feb 2003 Location: Edmond, Oklahoma Posts: 425	I used to have 2:something in there. 2:46 maybe? What happened was when I went to pull away from the house a real loud pop came out of the rear. The truck just kept rolling back. Even in park. Had it towed to a shop and he called to tell me the news. He said it looked like little car gears in there all mashed up. I think the motor probably overpowered them. It used to have a 305 in it. So that's why I made the upgrade. What do I need to get to fix the speedo, is it the little gear at the end of a cable that goes into the tranny? Do I get a part at say Autozone to get the speedo right or do I have to take it back into a shop? Thanks for any info you guys can give me. I was hoping I could fix it myself this weekend. Also I don't have a tach yet. But it's on the short list. __________________ 84 Chevy Stepside, 350, TH350, 268h Comp cam, Hooker headers, MSD Pro Billet, Edelbrock Performer manifold and 1604 carb, 40 Series Flowmasters dumped, and Western Chassis 3/5 drop w/ c notch. New 3:73 Eaton Posi

11-21-2003, 01:21 AM	#5
dwjack Registered User Join Date: Sep 2003 Location: Alaska Posts: 35	I had the same problem with mine when I put a different rear end on. I went to a dealer with the gear at the end of the speedo cable and they told me that they could sell me another gear but only to fix it a small amount, 5 or 6 mph if I remember right. If it is more than that you have to replace the gear inside the tranny. So knowing that if was off about 12mph at 55 they figured out which gears I needed. (you also need to know how many teeth are on the other gear.) All you have to do is drop the driveshaft and unbolt the housing at the back of the transmission. I can't remember exactly what held the gear in there, some kind of C clip I think. Not hard to do, the parts are cheap at least. __________________ 1984 Silverado C10 GM Goodwrench 350 Edelbrock Intake/Carb Hedman Hedders 700R4 Transmission 12 Bolt out of an 81 275/60/15 Centerlines



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