55.2-59 speedo question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**old Rusty C10** · 07-15-2020, 12:23 PM

can i use a standard speedo cable on this speedometer to a TH 350 trans from like a square body truck? Im building a custom truck and am hoping to use an older round speedo with that trans

Wrenchbender Ret · 07-15-2020, 03:51 PM

If it fits it will work. All the old mechanical speedos are calibrated 1,000 revs per mile.
George

**mr48chev** · 07-16-2020, 12:29 AM

You have to have a cable housing that matches both the speedometer and transmission speedometer drive housing. As long as the transmission has the right piece to drive a speedometer cable.

It's just a parts house item if you don't have one. The main issue with cables is at the speedometer rather than the trans. later cables got away from the nut on the end of the cable that screws on the speedometer and has the push on end held on by a tab on the speedometer.

This is saying that the same speedometer cable will work from 37 to 72 https://www.classicparts.com/1939-72...ctinfo/24-574/ Including automatics. It might be a tad short for a 350 trans swapped into a TF though.

Parts houses also an extension cable that is about 15 inches long to use on Chevy trucks that need a longer cable.

You still have to figure out your tire height and rear axle gear ratio to calibrate the speedometer.
Or cheat and take the truck for a drive and use a GPS to check the speedometer at a set speed like 60 and figure the percentage it is off and then adjust the drive and driven gears in the trans to correct it.

1project2many · 07-16-2020, 07:32 AM

If you have a nearby road with milemarkers you can drive between markers to figure out how far off the speedometer is. If you drive two miles and the odometer registers 1.5 miles then speedometer reading is low by 1.5/2 or 75%. I used to make charts for people that listed speedometer reading and actual speed. Guys would tape them to the dash instead of paying to fix the speedometer.

burnin oil · 07-17-2020, 09:45 AM

I used to drive by tach in my old blazer. A given rpm was X mph in 4th gear. It was a manual though. You brought back some memories there.

07-15-2020, 12:23 PM	#1
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,310	speedo question can i use a standard speedo cable on this speedometer to a TH 350 trans from like a square body truck? Im building a custom truck and am hoping to use an older round speedo with that trans __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

07-15-2020, 03:51 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: speedo question If it fits it will work. All the old mechanical speedos are calibrated 1,000 revs per mile. George

07-16-2020, 12:29 AM	#3
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,705	Re: speedo question You have to have a cable housing that matches both the speedometer and transmission speedometer drive housing. As long as the transmission has the right piece to drive a speedometer cable. It's just a parts house item if you don't have one. The main issue with cables is at the speedometer rather than the trans. later cables got away from the nut on the end of the cable that screws on the speedometer and has the push on end held on by a tab on the speedometer. This is saying that the same speedometer cable will work from 37 to 72 https://www.classicparts.com/1939-72...ctinfo/24-574/ Including automatics. It might be a tad short for a 350 trans swapped into a TF though. Parts houses also an extension cable that is about 15 inches long to use on Chevy trucks that need a longer cable. You still have to figure out your tire height and rear axle gear ratio to calibrate the speedometer. Or cheat and take the truck for a drive and use a GPS to check the speedometer at a set speed like 60 and figure the percentage it is off and then adjust the drive and driven gears in the trans to correct it. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around. Last edited by mr48chev; 07-16-2020 at 12:38 AM.

07-16-2020, 07:32 AM	#4
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,200	Re: speedo question If you have a nearby road with milemarkers you can drive between markers to figure out how far off the speedometer is. If you drive two miles and the odometer registers 1.5 miles then speedometer reading is low by 1.5/2 or 75%. I used to make charts for people that listed speedometer reading and actual speed. Guys would tape them to the dash instead of paying to fix the speedometer.

07-17-2020, 09:45 AM	#5
burnin oil Registered User Join Date: Jan 2013 Location: Eastern TN Posts: 1,921	Re: speedo question I used to drive by tach in my old blazer. A given rpm was X mph in 4th gear. It was a manual though. You brought back some memories there.



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