What is the thing behind the speedo?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

craig32 · 04-07-2012, 09:24 AM

Greetings! I just bought another gauge set for my 56 (from a 59), and when I got it there was some sort of gadget screwed on to the back of the speedo and the cable screws into it. It has a vacuum line coming out of it. Any idea what this thing is?

Rude Dude · 04-07-2012, 09:30 AM

Post a pic maybe it will help, If line is metal might be temp sender

mr48chev · 04-07-2012, 10:05 AM

It is probably part of a governor off a bigger truck.

_Ogre · 04-07-2012, 11:37 AM

That would be a 2speed adapter for use with a 2speed axle.
I had a 56 bus/ camper that had the 2speed vacume actuated axle.
Vacuum shifted the axle and speedo
Posted via Mobile Device

mr48chev · 04-07-2012, 12:00 PM

I didn't think of that one or how it worked. I got the big truck part right though

craig32 · 04-07-2012, 12:03 PM

Is that so it would turn the speedo at a different rate with a different axle gear? Kinda like changing the speedo gear in the transmission, only on the fly?

mr48chev · 04-07-2012, 02:19 PM

Quote:

Originally Posted by craig32

Is that so it would turn the speedo at a different rate with a different axle gear? Kinda like changing the speedo gear in the transmission, only on the fly?

It was so that it would correct the speedometer to match either high or low range that the rear axle was in. When you flipped the lever/button to change ranges in the rear axle the valve also switched that box on the back of the speedometer to correct the readings.

04-07-2012, 09:24 AM	#1
craig32 Registered User Join Date: Apr 2011 Location: PA Posts: 56	What is the thing behind the speedo?? Greetings! I just bought another gauge set for my 56 (from a 59), and when I got it there was some sort of gadget screwed on to the back of the speedo and the cable screws into it. It has a vacuum line coming out of it. Any idea what this thing is?

04-07-2012, 09:30 AM	#2
Rude Dude Registered User Join Date: Sep 2005 Location: Glendale Arizona Posts: 1,188	Re: What is the thing behind the speedo?? Post a pic maybe it will help, If line is metal might be temp sender __________________ http://67-72chevytrucks.com/vboard/s...d.php?t=436442

04-07-2012, 10:05 AM	#3
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,392	Re: What is the thing behind the speedo?? It is probably part of a governor off a bigger truck.

04-07-2012, 11:37 AM	#4
_Ogre Registered User Join Date: Jan 2012 Location: Motown Posts: 7,677	Re: What is the thing behind the speedo?? That would be a 2speed adapter for use with a 2speed axle. I had a 56 bus/ camper that had the 2speed vacume actuated axle. Vacuum shifted the axle and speedo Posted via Mobile Device __________________ cool, an ogre smiley Ogre's 58 Truk build how to put your truck year and build thread into your signature shop air compressor timer

04-07-2012, 12:00 PM	#5
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,392	Re: What is the thing behind the speedo?? I didn't think of that one or how it worked. I got the big truck part right though

04-07-2012, 12:03 PM	#6
craig32 Registered User Join Date: Apr 2011 Location: PA Posts: 56	Re: What is the thing behind the speedo?? Is that so it would turn the speedo at a different rate with a different axle gear? Kinda like changing the speedo gear in the transmission, only on the fly?



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