Question about gear ratios...
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Freshman User
Joined: Oct 2004
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From: Waldwick, NJ
Question about gear ratios...
Hello all... I am the proud new owner of a 2000 Excursion 4x4 PSD! I have a question about RPM's and speed. It seems like the engine is at rather high RPM's when only going 65-70 (around 3000 RPM's). I wanted to know if that was normal or not. I was told the truck used to have a lift in it, and I suspect the gears were changed, and I was going to drop one of the diff covers, and count the teeth. I just figured I might save some time if this is to be expected!
What should the correct gear ratio be for a stock 2000 4x4 psd? 3.73?
Thanks!
Dave
What should the correct gear ratio be for a stock 2000 4x4 psd? 3.73?
Thanks!
Dave
Post Fiend
Joined: Oct 2002
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Congrats NJ !!!
And welcome to FTE !!!!!
All Ex's stock have 3.73 gears....
If the previous owner put a lift and LARGE tires, he may have dropped in 4.10's to get the effective gear ratio up...
Can you call the previous owner ? It will be listed on your title... or maybe use the VIN number to run an oasis report at the dealer....
And welcome to FTE !!!!!
All Ex's stock have 3.73 gears....
If the previous owner put a lift and LARGE tires, he may have dropped in 4.10's to get the effective gear ratio up...
Can you call the previous owner ? It will be listed on your title... or maybe use the VIN number to run an oasis report at the dealer....
Elder User
Joined: Feb 2002
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From: Portage Twp, PA
There's a bunch of conversion calculators over on supermotors.org, and one of them deals with speed, gear ratios, tire size, etc. NJ...if you're turning 3000 RPM at 70 MPH in overdrive with 32" tall tires (the rough diameter of a 265/75-16 tire), it looks like you have a gear ratio somewhere in the 5.43:1 neighborhood, which is obviously way too short for highway use. For reference, my dad's '00 X V-10 has 4.30 gears (a pretty steep gear itself), and it turns around 2400 RPM at 70 MPH.
The gears you'd want to buy to get your engine RPM down to a more tolerable level depend on what you do with your X. If you only occasionally tow or never tow at all, a 3.55 or 3.73 ratio would probably be good. If you do a fair amount of towing, then I'd go with a 4.10 gear...IMO, a 4.30 is a little steep, although I towed a 9000-lb boat and rarely had to shift out of OD in the PA hills.
Hope this helps...
Pat
The gears you'd want to buy to get your engine RPM down to a more tolerable level depend on what you do with your X. If you only occasionally tow or never tow at all, a 3.55 or 3.73 ratio would probably be good. If you do a fair amount of towing, then I'd go with a 4.10 gear...IMO, a 4.30 is a little steep, although I towed a 9000-lb boat and rarely had to shift out of OD in the PA hills.
Hope this helps...
Pat
Last edited by PatsPOS; Nov 1, 2004 at 10:33 PM. Reason: typo
Thread Starter
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Freshman User
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From: Waldwick, NJ
Well that makes a lot of sense! Thanks so much for the reply. I have no plans to tow, so I will probably just drop 3.73's in the diffs. When I swap the gears out back to stock, do I need to re-calibrate the speed sensor in the diff, or does it figure it out on it's own? If I need to do it, how is it done?
Thanks,
Dave
Thanks,
Dave
Senior User
Joined: Nov 2003
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From: NH
Originally Posted by jdadamsjr
Congrats NJ !!!
And welcome to FTE !!!!!
All Ex's stock have 3.73 gears....
...
And welcome to FTE !!!!!
All Ex's stock have 3.73 gears....
...
Sit. Stay.
Joined: Oct 2001
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From: Washington State
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Tuned
Joined: Apr 2003
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From: SEVA
Just jack-up the rear, place it on jackstands, put a chalk-mark on the driveshaft & another on a tire, then count how many times the shaft revolves during one revolution of a rear wheel (turn the wheel by hand).
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Freshman User
Joined: Oct 2004
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From: Waldwick, NJ
Ok, so I got 2 quotes to change the front and rear diff gears, one was $1875, and one was $2000. That is for the gears, bearings/seals, and labor. Is this right for pricing? It sounds kind of high to me... Anyone else changed gears recently, and for less?
Senior User
Joined: Apr 2004
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From: Los Angeles
Gentleman,
I got a 6 in lift with 35 x 12.5 x 16.5 BFG's all terrains. My speed @ 2000 rpm is 60mph. If I got to 65 mph it goes to 2200, then to 70mph it goets to about 2350 RPM. What gear ratio do you think I have. Also, my front dana 50 has a tag that reads 4.30. I assume the rear is the same. Please correct me on this.
p.s. i really love this site, i'm on this more than I'm on my wife....j/k
I got a 6 in lift with 35 x 12.5 x 16.5 BFG's all terrains. My speed @ 2000 rpm is 60mph. If I got to 65 mph it goes to 2200, then to 70mph it goets to about 2350 RPM. What gear ratio do you think I have. Also, my front dana 50 has a tag that reads 4.30. I assume the rear is the same. Please correct me on this.
p.s. i really love this site, i'm on this more than I'm on my wife....j/k
Sit. Stay.
Joined: Oct 2001
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From: Washington State
Originally Posted by njfirefighter15
Ok, so I got 2 quotes to change the front and rear diff gears, one was $1875, and one was $2000. That is for the gears, bearings/seals, and labor. Is this right for pricing? It sounds kind of high to me... Anyone else changed gears recently, and for less?
To what gear ratio are you changing it to?
I suspect that you are running 5.38s since I've never heard of 5.43's being a ratio that is available.
The guy who owned the truck before you musta been running 39+" tires to justify 5.38s! Or he got a great deal.
Before you go to a shop to buy gears I would check around to see if anyone wants to swap 'em for you, Maybe a shop knows of someone who wants to lift thier Super Duty and you guys could work out some kind of deal that'll save everyone money and still put some $$ in the installer's pocket.
I would also verify before doing anything that the Torque Converter is locking properly and the high RPM is not a slipping transmission or unlocked TC.
I would record and post a constant rate of speed for each gear. ie 1st gear at 20mph, 2nd at 40 mph etc. etc.
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Freshman User
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From: Waldwick, NJ
OK - thanks for the insight. I'll keep an eye on the speedo tonight at the shift points and post later... The truck does have a Banks TransCommand module, which seems to tighten up the shifts nicely, and I believe I remember feeling all four gears shift... I'll pay closer attention tonight! I'm looking to go back to the factory 3.73's... I have no need to tow anything, this is mostly to survive the insane amount of miles I drive... Also, the better fuel economy would be great, at the current cost of diesel. With a tank of Exxon diesel, no additive, I was getting between 10 and 11 mpg on the lie-o-meter. After hearing BP does the additive pre-mixed, I filled up a tank of that, and im getting between 12 and 13 mpg! Made me a believer fast! As soon as I get the gears swapped, I might actually be seeing better milage than my other truck!
Thanks!
Dave
Thanks!
Dave
Last edited by njfirefighter15; Nov 4, 2004 at 05:05 PM.