Hello everyone, I’m hoping to get some help. My speedometer shows I’m going faster than actual speed, gets further off the faster I go. I’m pretty sure there is some mild slippage. Looked it up on the internet and find that all this could possibly be caused by speed sensor. I’ve replaced the speed sensor on the transmission which apparently is the output sensor located in the drivers side near the rear of the transmission near the transfer case, that didn’t fix the issue. There is also an input sensor I didn’t know about. I have no idea where the input sensor is located. I’ve looked it up on internet and also looked in an old chilton manual I have and I still can’t find where it goes.
Speedometer issues
- Thread starter Marchie
- Start date
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The speed sensor for the speedometer would be at the output of the transfer case, not the transmission.
In any event, I'd be surprised that a fast-reading speedo had anything to do with the sensor. My guess is that it's in whatever circuit-board is involved in processing the signal that comes from the sensor.
On my '88, that's the DRAC in the instrument cluster. The DRAC reduces the number of pulses from the sensor into something the speedo, odometer, cruise control, ABS, and computer can manage.
On later vehicles, the DRAC moved out of the instrument cluster and into a stand-alone box near the computer, or maybe into the computer itself.
www.udmodule.com/drac/
You need to download the service manual set for your vehicle, and look at the schematics for the speed sensor and the associated support circuitry.
In any event, I'd be surprised that a fast-reading speedo had anything to do with the sensor. My guess is that it's in whatever circuit-board is involved in processing the signal that comes from the sensor.
On my '88, that's the DRAC in the instrument cluster. The DRAC reduces the number of pulses from the sensor into something the speedo, odometer, cruise control, ABS, and computer can manage.
On later vehicles, the DRAC moved out of the instrument cluster and into a stand-alone box near the computer, or maybe into the computer itself.
www.udmodule.com/drac/
GM DRAC Module GM VSSB Module Replacement and Speedo Calibration TBI VSSB Speedometer Buffer
DRAC VSSB GM Speedometer Module Replacement and Calibration 1989-2002 Mixed applications 6.2L Diesel, 6.5L Diesel, TBI Gas. Digital Ratio Adapter Calibrator, Vehicle Speed Sensor Buffer, TBI VSSB Module, TBI DRAC Module
www.udmodule.com
You need to download the service manual set for your vehicle, and look at the schematics for the speed sensor and the associated support circuitry.
Not all "same size" tires are the same size. Fast forward to the three minute mark.
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Speedometer indicates mph right. Time is constant, velocity changes. You said the change is greater the faster you go? If your GPS steady speed is 65 mph but your truck speedometer indicates 72-73 that's a 10% high error, as if you had smaller tires than stock. The inverse would be larger than stock GPS indicates 65 but speedometer indicates 57-58. Since velocity changes faster or slower, the change is a percentage of speed. Therefore the change is different at each speed. 10% of 30 = 3, 10% of 65 = 6.5
Are you sure your ECM/ PCM has the right tire size loaded?
Your condition is what occurs with tire size changes, and not updating the ECM/PCM.
Are you sure your ECM/ PCM has the right tire size loaded?
Your condition is what occurs with tire size changes, and not updating the ECM/PCM.
It's best practice to mount same brand, same size on Duals. Same practice on same axle. The width may variance, but diameter has to be correct or all speedometers would be inaccurate, infraction liability issues.
Twice he uses mounted on " Tandem ", he should have said " mounted in Dual "
Codes are fine, but nobody has all them memorized. He failed to show the most basic, the block stating " maximum PSI at maximum load single or dual mounted " in plain English.
My Mustang's speedometer has been off by 4 mph at 60 since it was new. Have you heard of any "infraction liability"? I haven't. Unless a city is revenueing on speeding tickets, a judge isn't likely to look favorably on a police officer who routinely brings in speeding tickets for less than 5 mph.
So there's a different max PSI for single and dual? I didn't know that. Tandem, dual, eh. You missed that I called Roscoe a "dually" when I meant that it's a one-ton.
I did get a speeding ticket, on I-5 , I exited onto H-12 , at the stop to turn left there was a cal HP. I turned left onto 12. In mirror I see him pull out with reds and blues, ( must got a call ). I pull over let him blast by. No eff way. He pulls in behind me. (I made full stop at stop sign, there was traffic. WTH )
Drivers license, blah, blah. Sir, you were being tracked by aircraft doing 74, you do know the speed limit is 70.
Sigh. Here signature press hard 3 copies.
I bought new, 86 Toyo, 4x4. The dealer had installed , old sizing , 10 L 15 desert duelers on western centerlines. Way taller than stock.
I thought as indicated on speedo between 65-70, varies for traffic and passing. I had know idea.
We actually had a shop in town that used rebuild mechanical tachometers, and could do speedometer calibration, mechanical drive, if anybody remembers. He the truck. Yep here install this at the transmission output , and $70 later all good.
Go to court, innocent your honor. "Go ahead," bought truck, dealer installed, unknown problem. Got citation, corrected and certified.
Excellent Sir, dismissed, have a great day. If there had been any other reasons I still would have dismissed it. The law states, " at 5 mph and greater " , again thank you for correcting it. Clerk please draft a memo to xxxx CHP reminding them of that fact."
Next!
This is a perfect example of " my bread always falls butter side down."
So yes, I agree.
.
Drivers license, blah, blah. Sir, you were being tracked by aircraft doing 74, you do know the speed limit is 70.
Sigh. Here signature press hard 3 copies.
I bought new, 86 Toyo, 4x4. The dealer had installed , old sizing , 10 L 15 desert duelers on western centerlines. Way taller than stock.
I thought as indicated on speedo between 65-70, varies for traffic and passing. I had know idea.
We actually had a shop in town that used rebuild mechanical tachometers, and could do speedometer calibration, mechanical drive, if anybody remembers. He the truck. Yep here install this at the transmission output , and $70 later all good.
Go to court, innocent your honor. "Go ahead," bought truck, dealer installed, unknown problem. Got citation, corrected and certified.
Excellent Sir, dismissed, have a great day. If there had been any other reasons I still would have dismissed it. The law states, " at 5 mph and greater " , again thank you for correcting it. Clerk please draft a memo to xxxx CHP reminding them of that fact."
Next!
This is a perfect example of " my bread always falls butter side down."
So yes, I agree.
.
Oklahoma used to have an anti-speedtrap law that said the police couldn't write tickets for anything less than 10 mph over. Back in the '90s there were several cities that ignored it and would write you a $100 fine for 1 mph over. They usually had a busy street or highway though their town. When the national 55 mph speed limit got removed, Oklahoma raised the turnpike speed limits to 70 mph, but removed the 10 mph restriction for tickets. Since then they've passed a law that cities can't raise more than half their revenue from tickets. That finally nipped the problem.
HALF (!!!) their revenue from SCREWING the motorists driving through town?
Time to sign up with the National Motorists Association. They're the ONLY group fighting for the rights of all motor-vehicle owners/operators.
www.motorists.org
STRONGLY recommended, I've been a member for decades.
Time to sign up with the National Motorists Association. They're the ONLY group fighting for the rights of all motor-vehicle owners/operators.
www.motorists.org
STRONGLY recommended, I've been a member for decades.
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