Speedometer reads high?
#1
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Thread Starter
Speedometer reads high?
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.
Many thanks,
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.
Many thanks,
#3
Registered User
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.
#4
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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.
#5
Registered User
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.
#6
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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.
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.
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#8
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#9
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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...
#10
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Thread Starter
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.
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.
#11
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I believe the 3 pieces on the left of the pic are for 4x4 and the 2 on the right are for 2wd
#13
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#14
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Thread Starter
Interesting. I didn't realize the CTD1st Gens used two different transfercases. I thought they were all 205s no? Or was the 241 for half tons?