Help! Many questions on my 12 valve!
07-15-2018, 08:58 PM
#1
Help! Many questions on my 12 valve!
Okay so I purchased this 12 valve a few days ago, it’s my second one but I’ve have 3 24v’s since.
Anyways first thing, it’s a 1997 3500 5 speed 2wd.
So the first question, I’m running about 2750 ish rpms going 75 mph, by the time I’m going 80 mph I’m right at the redline. It’s got 4.0/4.1 Axel Ratio. What could be causing this? I’ve never seen one run so hard? Also trans is fairly new.
Second is the speedometer just goes straight to 20 mph as soon as you turn the key on and doesn’t move ever until you turn it off. Same with the odometer it doesn’t turn over at all. Also have a question about the fuel gauge, itll go from full and slowly work it’s way down to empty and then go back to full?? If anyone has any suggestions on where to start looking and repairing that would be amazing! My biggest deal really is the rpms running so high in 5th gear or “overdrive gear”. Thanks again
Anyways first thing, it’s a 1997 3500 5 speed 2wd.
So the first question, I’m running about 2750 ish rpms going 75 mph, by the time I’m going 80 mph I’m right at the redline. It’s got 4.0/4.1 Axel Ratio. What could be causing this? I’ve never seen one run so hard? Also trans is fairly new.
Second is the speedometer just goes straight to 20 mph as soon as you turn the key on and doesn’t move ever until you turn it off. Same with the odometer it doesn’t turn over at all. Also have a question about the fuel gauge, itll go from full and slowly work it’s way down to empty and then go back to full?? If anyone has any suggestions on where to start looking and repairing that would be amazing! My biggest deal really is the rpms running so high in 5th gear or “overdrive gear”. Thanks again
07-15-2018, 09:42 PM
#2
Administrator
For the speed, I did the gear ratio calculations and I think whatever else is affecting your instrument cluster is affecting your tachometer too.
I don't know your tire size so I went with a common size E rated tire, 285/75 R16. Tires larger in diameter than that will bring your engine RPM's down for the same road speed. Using that tire size, your axle ratio, and transmission gear ratios I have the following data:
*Factory 12 valve redline is 3,000 RPM*
4th gear at 70 MPH is 2,937 RPM, 5th gear at 70 is 2,203 RPM
5th gear road speed to engine RPM:
70 - 2,203 RPM
75 - 2,360 RPM
80 - 2,518 RPM
Max speed in 5th gear (engine running at 3,000 RPM) will be 95 MPH.
If this were my truck, and knowing I had questionable information from my gauges, I would use a GPS for my road speed.
I don't know your tire size so I went with a common size E rated tire, 285/75 R16. Tires larger in diameter than that will bring your engine RPM's down for the same road speed. Using that tire size, your axle ratio, and transmission gear ratios I have the following data:
*Factory 12 valve redline is 3,000 RPM*
4th gear at 70 MPH is 2,937 RPM, 5th gear at 70 is 2,203 RPM
5th gear road speed to engine RPM:
70 - 2,203 RPM
75 - 2,360 RPM
80 - 2,518 RPM
Max speed in 5th gear (engine running at 3,000 RPM) will be 95 MPH.
If this were my truck, and knowing I had questionable information from my gauges, I would use a GPS for my road speed.
07-15-2018, 11:08 PM
#3
I have 235/85/16 on it. So what would be the best place to start looking? I can do the mechanical part of these truck but the computer and electronic part I’m no bueno.
07-16-2018, 11:22 AM
#4
Registered User
Small tires, like you have and those 4.10 gears will get you that.
4,10 gears is for heavy hauling around town if you ask me.
For doing 80 down the road AND getting good MPG, you really need 3.54 gears.
You can improve it with larger tires. I run 37s on my '85 crew cab with that size tire and can cruise the highway freely.
37 inch tires on a 2wd will be a tough fit though.
What do you use the truck for?
4,10 gears is for heavy hauling around town if you ask me.
For doing 80 down the road AND getting good MPG, you really need 3.54 gears.
You can improve it with larger tires. I run 37s on my '85 crew cab with that size tire and can cruise the highway freely.
37 inch tires on a 2wd will be a tough fit though.
What do you use the truck for?
07-16-2018, 12:15 PM
#5
I pull a large horse trailer around a lot, but it’s not just around town it’s long hauls. Like 7 hours sometimes, it sucks traveling when I’m only going 55 mph at 2000+ rpms. How hard is it to get re geared?
07-16-2018, 12:22 PM
#6
Registered User
Swapping axles is the easiest way unless you do axle re-gears for a living.
I swapped the 4.10s out of my '95 dually for the same reason.
They are 3.54s in there now.
I swapped front and rear as it was a 4x4.
I swapped the 4.10s out of my '95 dually for the same reason.
They are 3.54s in there now.
I swapped front and rear as it was a 4x4.
07-16-2018, 12:44 PM
#7
Does it all work nice? I know a shop would rape me to re gear it so maybe I better look for a new rear end. Do you have any suggestions on the speedometer and odometer? And fuel gauge?
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07-16-2018, 02:58 PM
#8
Registered User
It is my tow rig and year round daily driver.
Yeah it works nice.
I have a few rear axles here if you need one. I am in VT.
Where are you?
The fuel level might be acting funny due to in tank interference, or bad wiring most likely.
Search the forum for tips on the other gauge issues, there is lots of free info. here if you search for it.
Yeah it works nice.
I have a few rear axles here if you need one. I am in VT.
Where are you?
The fuel level might be acting funny due to in tank interference, or bad wiring most likely.
Search the forum for tips on the other gauge issues, there is lots of free info. here if you search for it.
07-17-2018, 04:41 PM
#9
Registered User
Fuel sending units on these trucks are known to become troublesome with age/miles. If you verify that the sender is the problem, there is a very cheap fix or two for the sender...
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The following 2 users liked this post by texasprd:
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