I just bought a 87 ford f250 4x4 with the 5.0l and a manual 4 speed tranny. i have only had it for 2 days and the speedometer just started bouncing above 40 mph. it bounces from 45-90. Is this a cable driven speedo? If so where does the cable hook up ( tranny or transfer case)? i havent been able to crawl under it today to look but i would like to find out before i dig in tonight.

 

Yes, cable driven. Attaches to transfer case rear output shaft housing.

 

I recently had this issue on my 90 f150. The little keeper that holds the VSS in place was missing allowing the cable to move in and out, hence causing the bouncing speedometer.
Luckily it's a fairly simple item to replace, good luck!

 

Thanks i checked it out today and the clip on the cable where it attaches to the t case was gone so i replaced it and hopefully that will fix it. but on the way home i noticed that the truck wasnt heating up past the lowest line in the normal range. so i swapped out the radiator cap and no change and i had to fill up for the first time and the rear tank wont let me put any fuel in it and its bone dry and the front will let me fuel up but i have to hold the fuel pump slow so it takes about 15 minutes to fill. Any suggestions? im starting to think i bought a lemon.

 

temp gauge is not very accurate. if it has heat, don't worry about it reading low.
the rear tank may be blocked off due to bad selector switch. as for the slow fill, try driving up on a 6 inch block next time. that is what i have to do to fill my 88 diesel.
it has something to due with the tank vents.