Lingle Posted June 25, 2020 Report Share Posted June 25, 2020 (edited) I purchased a replacement cab and sheetmetal last fall and finally got around to disassembling the cab so I can start mocking up the new powertrain(see my build thread for more info) and when I removed the speedometer, it is very different from my 1951 speedo originally in the truck. I know the cab is a 51-53 given the gauge cluster layout but the part on the back of the speedo is different. It appears to have a oil(maybe air) line feeding a linkage on the back of the speedo. The original speedo I have the cable screws directly into the back, whereas on this one, the cable screws into the back of whatever has the steel line coming out off it. I looked in the parts catalog and didnt find anything special here, so maybe it was aftermarket? Sorry for the grainy photos, iPhone lens was cloudy due to excess humidity this morning here in Iowa. Thoughts? Edited June 25, 2020 by Lingle Added photos Quote Link to comment Share on other sites More sharing options...
Young Ed Posted June 25, 2020 Report Share Posted June 25, 2020 I believe that would be a speedometer from a truck with a 2 speed rear end. Quote Link to comment Share on other sites More sharing options...
Lingle Posted June 25, 2020 Author Report Share Posted June 25, 2020 22 minutes ago, Young Ed said: I believe that would be a speedometer from a truck with a 2 speed rear end. that would make sense that somehow the rear diff/vacuum may feed into the speedometer sender since the transmission output would stay the same speed, but the rear axle would change speeds and need to compensate for the change, thanks! I still need to figure out how to adapt, when the time come, the NV4500 speedometer output to the factory speedo, but I have some time to do that. May need to see how ggdad1951 does his when he gets closer on his project. Quote Link to comment Share on other sites More sharing options...
wallytoo Posted June 25, 2020 Report Share Posted June 25, 2020 (edited) it IS a two-speed adapter, to allow the speedo to read close to correct when shifting the rear end. the tube is a vacuum line that runs from the control switch mounted on the upper firewall, directing vacuum to the rear axle diaphragm (on/off). this is the switch (note the small tube running directly from the unit into the firewall, which leads to the back of the speedo unit): Edited June 25, 2020 by wallytoo Quote Link to comment Share on other sites More sharing options...
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