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48 f6 with two speed rear the speedometer does not work at all. After further inspection there is no vacuum line hooked to it where should this go? Would that alone be the problem?
IIRC, it should go to the switching valve on the engine side of the firewall. When you pull the cable on the dash to shift the axle to high, the vacuum valve on the firewall should pull a vacuum on the speedometer changer on the speedometer and shift the speedometer. If your speedometer is not working at all, you either have a broken speedometer cable or the speedometer changer is stuck in neutral.
48 f6 with two speed rear the speedometer does not work at all. After further inspection there is no vacuum line hooked to it where should this go? Would that alone be the problem?
Thanks
There is no neutral in the vacuum switch. If your two-speed rear end is shifting ok, then all is good with the switch. Your problem could be with either the little two-speed transmission connected to the rear of the speedometer, or the speedometer / cable itself. There is a tiny 1/16" square drive pin between the speedometer and speedometer transmission that could break also. So far mine is all good (knock on wood).
To test if its the guage or transmission cable I can just unscrew the cable from guage and drive the truck and see if cable spins? I have no vacuum line going to the speedometer at all where exactly should that line hook to on the switch on the firewall?
To test if its the guage or transmission cable I can just unscrew the cable from guage and drive the truck and see if cable spins? I have no vacuum line going to the speedometer at all where exactly should that line hook to on the switch on the firewall?
That's one way to do it. There should be a 1/2" steel vacuum line running across the outside of the firewall. This supplies a vacuum source for the two-speed axle shift and the Hydrovac brakes. Do you have a little two-speed transmission connected to the back of your speedometer? I'll take a pic of mine tonight.
There is a hose barb on the backside of the switching valve that should be directly in front of a hole in the firewall. That's where the small vacuum line connects.
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