Speedo reading off
#1
Registered User
Thread Starter
Speedo reading off
At 35mph on the gps the speedo read 30, at 75mph on gps the speedo says 65mph. Its 15% off. I havent changed any parts and its never been off before. It doesnt bounce and the cruise works fine. Im a bit perplexed as to why. Thoughts?
#4
Registered User
Is it possible for the GPS to be skewed?...I ask because I often get delivery drivers on my street who can't figure out how their GPS took them somewhere completely off their route...Can you verify it another way?...For instance a cop buddy with radar?......Ben
#5
Registered User
When I got my truck the speedometer ran backwards. It took me a while to realize the reverse/ratio adapter was missing. I found a new one online and "miracle" it agreed with the GPS.
After you check the speedo independently of the GPS you can look into whether the gear is missing/wrong at the trans pickup. I really doubt the GPS is off though.
Edwin
#6
Registered User
Thread Starter
The gps matched the gps on my phone. 2 gps's agree. Also at 2250 rpm=75 mph.
How does the speed sensor work? Does it have zource voltage OR dors it develope its own?
How does the speed sensor work? Does it have zource voltage OR dors it develope its own?
#7
Registered User
2WD or 4WD?
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#9
Registered User
It is pulse driven.
I remember hearing about failures where there appeared to be an error that was a constant ratio, such as yours, surprisingly due to a stripped drive tang or socket slipping at a somewhat constant rate. I would check obvious mechanical failure first, but I would then check to see if the odometer is off the same percentage as the speedometer. They are driven by separate IC outputs, and I believe it is possible for the odometer step motor to work properly, while the amplifier that puts out the voltage signal for the speedometer is failing . . .
I remember hearing about failures where there appeared to be an error that was a constant ratio, such as yours, surprisingly due to a stripped drive tang or socket slipping at a somewhat constant rate. I would check obvious mechanical failure first, but I would then check to see if the odometer is off the same percentage as the speedometer. They are driven by separate IC outputs, and I believe it is possible for the odometer step motor to work properly, while the amplifier that puts out the voltage signal for the speedometer is failing . . .
#10
Registered User
Thread Starter
So strange it went from bouncing to steady, but now 15% off. Eventually Ill get that speedo figured out. For now I have more mystery leaks. No cowl cracks, fixed floor vent, new cab light seals, bed light seal, new door seals, new steering shaft to firewall seal. Next is windshield gasket.
#11
Registered User
If the floor gets wet, pull the mats and let it dry out, rather than have wet smelly carpet rust out your floor boards. It is also nice if you want to wash out the rig.
Maybe it is a tiny bit louder, but trying to quiet down an old 1st gen Cummins is like telling the college kids to quite down their graduation keg party. You just get stressed out with little results.
Have you checked the vent window seals?
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#12
Registered User
Thread Starter
The vent seals seem decent unless you powerwash it. Water just seems to magically appear where the door, floorpan and kick panel meet, its just that corner. Its not coming from kickpan seal. Theres no vertical water drops etc. Wonder if water could be coming through door area and getting past the seal? Or windshield gasket.
#13
Registered User
The vent seals seem decent unless you powerwash it. Water just seems to magically appear where the door, floorpan and kick panel meet, its just that corner. Its not coming from kickpan seal. Theres no vertical water drops etc. Wonder if water could be coming through door area and getting past the seal? Or windshield gasket.
Edwin
#14
Administrator
Don't forget that there is a factory set bias on the speedos that read 10-15% over, it is a liability thing. It isn't constant through the speed range, it widens the faster you go, pretty close at slow speeds and pretty far off at speed...Mark I just did some googling and the bias is generally 4% and it varies by manufacturer...