GEAR info needed
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Elder User
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GEAR info needed
I currently have the 3.73 LS gears in my 2004 Fx4 SCrew and with the 6" Suspension lift and 3" Body lift I will be upgrading to Pro Comp XTerrain 37x13.50R18's very soon. I tow a 12 ft trailer 3-4 days a week and I am wondering how it will pull with the 3.73's. A buddy suggested 4.56 but the Truck shop suggests 4.10's. So I have NO clue which to upgrade to and do both the front and rear need to be upgraded?
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Joined: Oct 2002
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From: MA
Yes, you must upgrade both front and rear. The 3.73s will not only make the driving experience pure garbage, but your mileage will drop significantly. You have to maintain the mechanical advantage the stock setup had. 4.56 are a good gear for 35"s. I might even venture you can jump down to a 4.88 if you really wanted to (those are some massive meats you will be tucking in those fenders). You might want to ask the guys in the 4x4 forum too. I am sure they will have a few opinions for you.
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Way outa my league (37's) ... but I added a couple extra columns to my sheet of calculations that I did to help me decide what gears to go to: http://tycreek.com/p/f150/gears.htm No guarantee on accuracy ... But, I drove my truck for its first run with the new gears tonight and it checked out pretty close to what I calculated. Just a needle over 2k at 65mph on the GPS … speedo is still way off … waiting on a tuner (in shipment) to help with that.
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Estimate $600-700 per diff, half each parts & labor. I didn't have LS so I had one put in at the same time and it with the special bearing kit (not originally calculated for) was about $700. I did find a couple places that quoted less ... but I went with a place that had a proven reputation for this sort of specialty. Ford said about $2k for 4.10's without LS and wouldn't/couldn't do 4.56 + ... go figure.
Performance difference? Hum ... guess that depends on the rest of the equation ... uses ... etc...?
As you gear low (up numerically in ratio number) the contact surface and strength is reduced. Noise potential goes up. Without compensating tire diameter rotational balances become of increasing concern.
Performance difference? Hum ... guess that depends on the rest of the equation ... uses ... etc...?
As you gear low (up numerically in ratio number) the contact surface and strength is reduced. Noise potential goes up. Without compensating tire diameter rotational balances become of increasing concern.
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New User
Joined: Mar 2005
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I'm Pretty New To This Whole Gear World, But I Bought A 2004 Ford F-150 Fx4 It Has The 5.4 But It Has A Gear Ratio Of 3:55 I Put On A Set Of Toyo 325/50r-22 Open Country A/t. When I Purchased The Vehicke I Knew Nothing About Gears, Now I Learned The Hard Way. I Noticed A Clicking Sound Coming From The Tires, My Friend Told Me I Need At Least To A 4:10 I'm Trying To Find The Best Of Both Worlds, Better Gears, And Decent Mpg
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Joined: Aug 2004
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From: Orlando, FL
DEFINITELY 4.88s or even 5.12s!! Look into Precision Gear for gear brand. I have 4.56s with only 305/55R20s (33s) to improve towing over stock. The stock 3.73s are horrible with even the stock 32" tall 4WD tires. My truck accelerates much better now and drives like it should have from the factory. I get around 15 mpg on the highway, 75 mph, and 13.5 mpg in town.....but I have a heavy foot, so MPGs aren't much worse than stock 4WD trucks.
Elder User
Joined: Apr 2004
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Hi guys. Ifound this really good gear chart. Maybe it will help your decisions. http://www.proficientperformance.com...ing-pinion.php Good luck and keep us updated.
Senior User
Joined: Oct 2004
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From: South ALABAMA
First, find out what the biggest( tallest ) gear you can put in the FRONT. A lot of times they'll make a 4.88 ( for example ) for the rear but won't make one for the 8.8 IFS in the front. If you're ride is an automatic go a little steeper than recommend. The power loss is a little more with an auto than with a 5 speed. For those 37's, I'd stuff 4.88's by Percision Gear in there. I have used PG before and they or super quiet compared to Richmond Gear. Those gears will kill your top end, but pull like hell.
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Ok, the 4.56 gears and the Diablo tuner (Predator) to get things back in sync are a point of celebration for me tonight! Holy #$%# batman! Complete new truck! Wow! A good scratching of both my 33’s in 2nd is quite the kick!
No vibes or noses yet either!
No vibes or noses yet either!
Junior User
Joined: Aug 2004
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From: Orlando, FL
Ok, the 4.56 gears and the Diablo tuner (Predator) to get things back in sync are a point of celebration for me tonight! Holy #$%# batman! Complete new truck! Wow! A good scratching of both my 33’s in 2nd is quite the kick!
No vibes or noses yet either!
No vibes or noses yet either!
One thing that surprises me....your Predator corrected your speedo??? I was very upset with mine when I discovered it didn't correct the speedo after the 4.56s went in. I had to have Diablosport send me a custom tune because of an "oooops, there's a glitch" in the programming. Anyway, the custom tune works great....just annoying to have to deal with since the product was advertised to correct for gear and tire changes. Besides scratching 2nd gear, you should also probably leave about 4 foot strips by stabbing the throttle from a stop
Senior User
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Predator out of the box wouldn't correct for gears with a message: "parameters are not available for this vehicle/transmission combination.(2)" No big deal ... sort of expected that as I just had a new PCM loaded. Updated to the recent r85b code and everything works just fine now ... It took me 4 adjustments away from published tire specs for rotations/mile but the speedo dialed in right smack dab on the money!
I’ve got a CAI on order (Volant w/ram) and can’t decide on what cat backs … Corsa$ or Magnaflow is where I’m at right now. Maybe even my local shop? Hum…
Anyway … Makes a serious kick in the pants change! And Oh, the freeway at 75 was fine … not wound out at all … quite and smooth for an easy cruise.
I’ve got a CAI on order (Volant w/ram) and can’t decide on what cat backs … Corsa$ or Magnaflow is where I’m at right now. Maybe even my local shop? Hum…
Anyway … Makes a serious kick in the pants change! And Oh, the freeway at 75 was fine … not wound out at all … quite and smooth for an easy cruise.
Junior User
Joined: Aug 2004
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From: Orlando, FL
Which adjustments did you go on tire revs/mile? Up or down? Are your WOT shift points also working where you set them on the predator? I may have to get that update and try it without the custom tune.