WTB Speedometer ratio box - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**zeusflash** · 10-19-2008, 08:18 PM

My 72 GMC 3/4 ton 4x4 is missing the speedometer ratio box. The gear ratio in my truck is 4.56. Any help will be greatly appreciated. Thanks in advance.

low'n slow · 10-19-2008, 09:39 PM

How far is it off? I have a few laying around and would part with one if it would work for you. Go down the road for 5 - 10 miles and match your odometer against the mileage markers.

Get the correction ratio and post it here.

va_tlc · 10-20-2008, 08:13 AM

low and slow, is this the little metal looking box that the speedometer line screws into to? if so after zeusflash is taken care of , i need one for a 3.73 auto truck, thanks alot.thanks alot.

**zeusflash** · 10-20-2008, 08:31 PM

va_tic,what I need is the little metal box that attaches to the transfer case and the speedo cable attaches to. On 4x4s there was only one speedo drive gear available in the transfercase so the ratio box is used to syncronize the drive gear to the speedometer head for different gear ratios. The ratio box has two gears in it to either speed up or slow down the speedo cable as needed. As to how much mine off....the box is missing completely!

low'n slow · 10-20-2008, 09:14 PM

Still need to know the ratio of correction. I have 4 of them.

**zeusflash** · 10-20-2008, 09:34 PM

Sorry low'n slow, I didn't understand what you were asking for. Probably will not get a chance to do this until next weekend...I still have to change the speedo cable.

va_tlc · 10-21-2008, 07:45 AM

mines not even on the road yet, but mine is leaking gear oil outa it, thats kinda why i wanted one.so if you do have a extra one after zueusflash, keep me in mind thanks

**zeusflash** · 10-26-2008, 07:20 PM

Did the road test yesterday,had my wife pace me in her Suburban,did the math and it didn't seem right. I installed a ratio box I had laying around(1.202 ratio). Redid the pace test,did the math an got the same answer. Looks like I need a ratio box right around .877. Let me know what you come up with.

low'n slow · 10-26-2008, 08:53 PM

I have 1 that is 1:0.9, should slow it down almost 10%. That is about as close as I can come. PM me if you want it.

msgross · 10-26-2008, 08:58 PM

if you know someone that has a GPS you can use the speedo on it as well...

Tire size will change your ratio as well...

10-19-2008, 08:18 PM	#1
zeusflash Senior Member Join Date: Feb 2005 Location: Post Falls,Idaho Posts: 691	WTB Speedometer ratio box My 72 GMC 3/4 ton 4x4 is missing the speedometer ratio box. The gear ratio in my truck is 4.56. Any help will be greatly appreciated. Thanks in advance. __________________ '69 3/4 ton 427 CST Pickup '71 CST Blazer '72 GMC 3/4 4x4

10-19-2008, 09:39 PM	#2
low'n slow Too Dumb To Know Better Join Date: Nov 2005 Location: Texas Posts: 882	Re: WTB Speedometer ratio box How far is it off? I have a few laying around and would part with one if it would work for you. Go down the road for 5 - 10 miles and match your odometer against the mileage markers. Get the correction ratio and post it here.

10-20-2008, 08:13 AM	#3
va_tlc Registered User Join Date: Nov 2005 Location: VIRGINIA Posts: 905	Re: WTB Speedometer ratio box low and slow, is this the little metal looking box that the speedometer line screws into to? if so after zeusflash is taken care of , i need one for a 3.73 auto truck, thanks alot.thanks alot. __________________ 1969 rs 1966fastback 1969swbc/10 2006gt 1972swb4x4

10-20-2008, 08:31 PM	#4
zeusflash Senior Member Join Date: Feb 2005 Location: Post Falls,Idaho Posts: 691	Re: WTB Speedometer ratio box va_tic,what I need is the little metal box that attaches to the transfer case and the speedo cable attaches to. On 4x4s there was only one speedo drive gear available in the transfercase so the ratio box is used to syncronize the drive gear to the speedometer head for different gear ratios. The ratio box has two gears in it to either speed up or slow down the speedo cable as needed. As to how much mine off....the box is missing completely! __________________ '69 3/4 ton 427 CST Pickup '71 CST Blazer '72 GMC 3/4 4x4

10-20-2008, 09:14 PM	#5
low'n slow Too Dumb To Know Better Join Date: Nov 2005 Location: Texas Posts: 882	Re: WTB Speedometer ratio box Still need to know the ratio of correction. I have 4 of them.

10-20-2008, 09:34 PM	#6
zeusflash Senior Member Join Date: Feb 2005 Location: Post Falls,Idaho Posts: 691	Re: WTB Speedometer ratio box Sorry low'n slow, I didn't understand what you were asking for. Probably will not get a chance to do this until next weekend...I still have to change the speedo cable. __________________ '69 3/4 ton 427 CST Pickup '71 CST Blazer '72 GMC 3/4 4x4

10-21-2008, 07:45 AM	#7
va_tlc Registered User Join Date: Nov 2005 Location: VIRGINIA Posts: 905	Re: WTB Speedometer ratio box mines not even on the road yet, but mine is leaking gear oil outa it, thats kinda why i wanted one.so if you do have a extra one after zueusflash, keep me in mind thanks __________________ 1969 rs 1966fastback 1969swbc/10 2006gt 1972swb4x4

10-26-2008, 07:20 PM	#8
zeusflash Senior Member Join Date: Feb 2005 Location: Post Falls,Idaho Posts: 691	Re: WTB Speedometer ratio box Did the road test yesterday,had my wife pace me in her Suburban,did the math and it didn't seem right. I installed a ratio box I had laying around(1.202 ratio). Redid the pace test,did the math an got the same answer. Looks like I need a ratio box right around .877. Let me know what you come up with. __________________ '69 3/4 ton 427 CST Pickup '71 CST Blazer '72 GMC 3/4 4x4

10-26-2008, 08:53 PM	#9
low'n slow Too Dumb To Know Better Join Date: Nov 2005 Location: Texas Posts: 882	Re: WTB Speedometer ratio box I have 1 that is 1:0.9, should slow it down almost 10%. That is about as close as I can come. PM me if you want it. Last edited by low'n slow; 10-26-2008 at 08:56 PM.

10-26-2008, 08:58 PM	#10
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: WTB Speedometer ratio box if you know someone that has a GPS you can use the speedo on it as well... Tire size will change your ratio as well... __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

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