Trod8812 Posted August 26, 2016 Report Share Posted August 26, 2016 My speedometer says 20mph when I am around 33, what can cause that. All of the gauges work so I'm not sure is the cable is bad and where the cable is located. Quote Link to comment
datzenmike Posted August 26, 2016 Report Share Posted August 26, 2016 Is the reading steady? or jump around?? What size tires do you have on your 620 Have you replaced the transmission? Or differential?? What year of truck?? Fill out your profile with year of truck Quote Link to comment
Trod8812 Posted August 26, 2016 Author Report Share Posted August 26, 2016 The reading is stable They are 195/70/r14 the previous owner had 18 inch Rims It's a 1979 And no I have not replaced the transmission or differential but the pervious owner said he rebuilt the 5th gear. Quote Link to comment
datzenmike Posted August 26, 2016 Report Share Posted August 26, 2016 The '79 was an odd year for the 620. It's the one year when a 4.11 differential was used rather than a 4.375. If it had an earlier transmission the speedometer pinion gear would be turning 6.5% slower. You are out over 30% I can't account for that much. If you remove the speedometer pinion it should have a White plastic 19 tooth gear. A Red 20 tooth gear is for a 4.375 and will turn the speedometer slower, but only 6.5% slower. That's 2 MPH at 33. This much out must be the speedometer itself. Quote Link to comment
Trod8812 Posted August 26, 2016 Author Report Share Posted August 26, 2016 Ok well when I bought the truck the guy gave me an extra guage assembly, would you recommend me putting that in? And how would I go about installing it? Quote Link to comment
flatcat19 Posted August 26, 2016 Report Share Posted August 26, 2016 Rebuilt 5 speed...what if truck never came with 5 speed? Or he rebuilt a different 5 speed then installed. Never know what's happened in the last 40+ years with these things. Quote Link to comment
hobospyder Posted August 26, 2016 Report Share Posted August 26, 2016 Gps speedo on your phone or buy speed hut gps speedo Came with 14x6 bias ply tires, modern equivalent doesn't quite match up, and like flat said, who knows what's happened in 40 years Quote Link to comment
datzenmike Posted August 26, 2016 Report Share Posted August 26, 2016 Reach up under the dash and unscrew the speedometer cable. Remove the cigar lighter, radio knobs, (I forget the rest) you'll see anyway. There is a large round 10-12 pin connector on the back of the gauge cluster that just needs unplugging. Quote Link to comment
Trod8812 Posted August 27, 2016 Author Report Share Posted August 27, 2016 Where is the speedometer cable on the transmission? Quote Link to comment
datzenmike Posted August 27, 2016 Report Share Posted August 27, 2016 Passenger side at the rear. It's the round thing on the bottom. This is the pinion sleeve. It mounts on the tail of the transmission and is gear driven. The speedometer cable screws onto it. Top is the speedometer pinion. Below it is the cable end. Quote Link to comment
Trod8812 Posted August 27, 2016 Author Report Share Posted August 27, 2016 Ok so I don't have any way to jack up my truck at the moment but I can reach the cable, do you know what size wrench it is or the best tool to get the cable off? Quote Link to comment
datzenmike Posted August 27, 2016 Report Share Posted August 27, 2016 A careful squeeze on a pair of vice grips will usually loosen it so it can be turned by hand. You'll see there are flat faces that an adjustable wrench can get a good hold on. Generally it is not on very tight. Quote Link to comment
Trod8812 Posted August 27, 2016 Author Report Share Posted August 27, 2016 I really appreciate all of the help, always looking to make the truck mint. This is when I first got it. And this is it today Quote Link to comment
datzenmike Posted August 27, 2016 Report Share Posted August 27, 2016 Vast rim improvement. Quote Link to comment
flatcat19 Posted August 27, 2016 Report Share Posted August 27, 2016 All trucks eventually go black. Quote Link to comment
sebpv Posted August 27, 2016 Report Share Posted August 27, 2016 can you show me other angles now that its painted please. I was planning on painting it black but it only looks better in my head... Quote Link to comment
Trod8812 Posted August 28, 2016 Author Report Share Posted August 28, 2016 Passenger side at the rear. It's the round thing on the bottom. This is the pinion sleeve. It mounts on the tail of the transmission and is gear driven. The speedometer cable screws onto it. Top is the speedometer pinion. Below it is the cable end. What is the part called that the speedometer Cable screws into? Quote Link to comment
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