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1st Gen. Ram - All TopicsDiscussion for all Dodge Rams prior to 1994. This includes engine, drivetrain and non-drivetrain discussions. Anything prior to 1994 should go in here.
A couple weeks ago I started the truck and all the gauges were bouncing around and going erratic. Turned it off and restarted and everything seemed fine.
Except, now my speedometer reads about 10-15 mph faster that actual. Odo works but haven't checked it against mileposts yet. I think the speedo reads exponentially higher but not positive.
Anybody have an idea what could cause this? Isn't the speedo mechanically driven? Everything else seems to be working correctly.
The speedo is electrically driven by the VSS (vehicle speed sensor) which is a pulse generator on the transfer case. The VSS is driven through several gears. The drive gear on the shaft inside the transfer case, the driven gear which is your connection on the outside, your ratio adapter which corrects for gearing and tire size, then the VSS.
The ratio adapters can sometimes wear out and fail, I've seen pics of the square hole wallowing out. Or perhaps the VSS is failing and sending a weak or corrupted signal, or the pig til wiring to the VSS has a tendency to break over time as well.
Sounds like you had a voltage spike. My 2005 Lesabre did that on a trip. Fuel gauge is above the temp. The needles got into a sword fight. Everything went nuts. Temp gauge went back to normal a day later. 4 months later the speedo went whacky. Sometimes is reads 165mph just by turning the key on. I use the digital read out to read things about the fuel. Lately using the Waze app for my speed as the tack is whack.
I've always thought that contraption looked pretty Rube Goldberg to me...
Crawled back under today and wiggled things around/tighten-up/reconnected. We'll see if that makes any difference. Last time I drove it I was doing 90mph at about 45mph. Everything else seems to work fine.
Anybody know if any of those plethora of pieces are still available? I've not started searching yet.
Anybody know if any of those plethora of pieces are still available? I've not started searching yet.
It's 3 separate pieces. With the suggestion the vss is still available, the rest is just old-school mechanical speedo drive stuff used in the 70s and 80s. Should be available.
I'll compare my VSS to the ones RA lists. It shows several different variations, all for the same truck. Hopefully I'll have some time this weekend to mess with it...
The speedo is electrically driven by the VSS (vehicle speed sensor) which is a pulse generator on the transfer case. The VSS is driven through several gears. The drive gear on the shaft inside the transfer case, the driven gear which is your connection on the outside, your ratio adapter which corrects for gearing and tire size, then the VSS.
Took mine apart and all the gears look ok and functioning. Mine is missing the plastic nut that secures it to the output from the tailshaft. Also missing that hold down clamp or what ever it is on the upper right. And the metal piece above the yellow gear, whatever that is? Looks like gravity has been holding it in so far.
I'll get a new VSS and see if that gets my speedo back. Then work on getting the rest of the parts to make it secure.
I believe the 3 pieces on the left of the pic are for 4x4 and the 2 on the right are for 2wd
The lower piece on the left is probably for the np205. The 2 upper left pieces are used for both 2wd or 4wd. Pieces on the right are what's on my np241.
06-30-2023, 07:17 AM
