Question on RPMs
Cargo Master
Joined: Jan 2001
Posts: 2,726
Likes: 5
From: Slatington, PA
Sorry if you posted this already, but what size tires do you have on the truck? Stock is LT265/75/R16. If it had larger tires on it at some point, the speedo might have been recalibrated for them.
Gone, but not forgotten
Joined: Oct 2005
Posts: 5,026
Likes: 2
From: Charlotte-Fairbanks-Bflo
I've been mulling this one over and if he did my instructions to a tee, your guess is probably a good one. It makes no sense to me, other than maybe slippage in the tranny, but they don't slip for long and keep on going. The Energizer bunny they ain't.
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Junior User
Joined: Jan 2008
Posts: 60
Likes: 0
From: Chehalis, WA
It has the stock wheel/tire on it LT265/75/R16. I had it in the shop for an oil change at the beginning of the year before I started changing my own. Asked about the speedo and they flashed the PCM a couple times with the same results. Yes, it is dropping into overdrive.
Gone, but not forgotten
Joined: Oct 2005
Posts: 5,026
Likes: 2
From: Charlotte-Fairbanks-Bflo
Well then, if it is nothing mechanical or electrical in you systems then either your tach or speedometer is off. Another simple do it yourself test. Stopwatch, measured mile, perfect 60 mph for the entire mile. How many seconds? If it is not EXACTLY 60, something is wrong with your speedometer.
Go Bills !
Joined: Jan 2008
Posts: 2,778
Likes: 65
From: Buffalo, NY
How does the rpm gauge gets its signal? I Borrowed a scangauge and it told me the RPM and it matched what the gauge was telling me.
62 @ 2000. RPM. Sure does sound like 4:10. I know you mechanically checked it but it still seems like 4:10. OR how ever it gets the rpm signal is screwed up.
I would believe your GPS. mine is dead on.
Could someone swap out the gears and not the tag?
For me. And checked it again today.
373 gears 265 tires bald.
70=2100
68=2000
65=1900
62 @ 2000. RPM. Sure does sound like 4:10. I know you mechanically checked it but it still seems like 4:10. OR how ever it gets the rpm signal is screwed up.
I would believe your GPS. mine is dead on.
Could someone swap out the gears and not the tag?
For me. And checked it again today.
373 gears 265 tires bald.
70=2100
68=2000
65=1900
Gone, but not forgotten
Joined: Oct 2005
Posts: 5,026
Likes: 2
From: Charlotte-Fairbanks-Bflo
How does the rpm gauge gets its signal? I Borrowed a scangauge and it told me the RPM and it matched what the gauge was telling me.
62 @ 2000. RPM. Sure does sound like 4:10. I know you mechanically checked it but it still seems like 4:10. OR how ever it gets the rpm signal is screwed up.
I would believe your GPS. mine is dead on.
Could someone swap out the gears and not the tag?
For me. And checked it again today.
373 gears 265 tires bald.
70=2100
68=2000
65=1900
62 @ 2000. RPM. Sure does sound like 4:10. I know you mechanically checked it but it still seems like 4:10. OR how ever it gets the rpm signal is screwed up.
I would believe your GPS. mine is dead on.
Could someone swap out the gears and not the tag?
For me. And checked it again today.
373 gears 265 tires bald.
70=2100
68=2000
65=1900
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Gone, but not forgotten
Joined: Oct 2005
Posts: 5,026
Likes: 2
From: Charlotte-Fairbanks-Bflo
I don't know where the tach pickup is, but if I were to guess I would say the CPS. If you were to take off your serpentine belt and see if the tach still works that would pretty much tell you that's where it is.
Senior User
Joined: Mar 2007
Posts: 473
Likes: 3
From: Issaquah, WA
Pretty good claculator. It's all mechanical linkages, so it can be exactly determined. Check what you are seeing against calculated values.
4R100 w/3.73: 2000 RPM = 71 MPH
Gear Ratio Calculator
4R100 w/3.73: 2000 RPM = 71 MPH
Gear Ratio Calculator
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