twurl

My truck is currently running the stock tires and has the 3.73 gear ratio. I plan to be lifting my truck 8 in and run 37 in. tires in the next 3-4 months and need all the info I can get. What about the 4.88 or 5.29 gear ratios? Will they fit in the front and rear axles?

driver444

The 37" tire's rolling diameter is about 12% bigger than the stock 32" tire. So I would go with a gear ratio that's a little more than 12% lower than what you have to make up for the added circumfrence of the tire, plus the added weight.

You have 3.73's now, so 12% lower would be 4.18. So add a little for weight and that put's you at a 4.30 as I said earlier. 4.30 is a starting point. It would be a great gear for highway driving with those tires, and would have reasonable power. But to add a little more power (acceleration) and a lower crawl ratio, I'd go with the 4.56's.

4.88's and 5.29's are waaaaaay too low (in my opinion) to do anything but off road and rock crawl. Total overkill. They belong in Massey Fergusons and John Deeres.

twurl

Thanks for the advice. This will help me alot when I get the work done on my truck.

TFX4

Thanks for the helpful thread! I determined i have a 9.75 rear in my FX4 (pretty sure thats factory anyway lol)

henry4rd

How can I find out which axles were in which models/years... ???

Why does the factory use two different axle sizes for 4wd 1/2 ton trucks...???

It would seem to me that they would all be the same...

I ask because I am going to sell my 2wd 7700 and get either a 2004-2008 4wd or 2009 4wd... and figuring that unless I get an 09 fx4 I will likely get either a Truetrac or e-locker... maybe even both...

So I am trying to plan ahead and make good decisions but not familiar with 4wd trucks...

I have done lots of 4-whln in my Rhinos...they have spooled rear and electric 2wd/4wd/4wd-locked...

So I know very well the value of having ALL the options...being able to fully lock only the rear in 2wd as well as being able to fully lock all four makes a huge difference when it matters most... lol...

Anyway... it would help me a lot to have a clue which models have which axles and why...so I can cross reference which lockers are available for what ever vehicle I am considering getting into...gotta be able to sort them out from home if you guys know what I mean...

TheJMC

For the F-150 from 1997 to present all the V6 trucks have the 8.8 31 spline rear axle.
All of the 4x4 trucks have the 8.8 reverse cut 28 spline 8.8 front axle. All of the less than 7700# trucks with 5.4 have the 9.75 34 spline rear axle and with 4.6 have 8.8 31 spline rear axle. All of the 7700# trucks (includes the F-250 Light Duty) have the 10.25 rear axle. All of the rear axles are semi floating.

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henry4rd

Thank you very much...

Now I can take a closer look at the Eaton Truetrac and Elockers as well as gearing options...

twurl

What do you mean by 7700 # trucks?

So if I have the 4.6L 3.73 rear end, I have the 8.8 reverse cut 28 spline front axles and a 8.8 31 spline rear axles. Right?

06fordf150

i have a full locker in the rear of my 89 and never been stuck yet!!

driver444

I have the Truetrac in the rear of my '08, (love it), and a detroit locker in my '96 F-350 (love that too).

The Truetrac is as close to a locker as you can get without actually having one, meaning there are very few instances where you will spin only one tire. 99% of the time, both wheels get power, and you'll never know it's there until you need it. Great for snow and most off-road situations.

The advantage of the detroit locker is that is does offer 100% lockup, cornering capability, and you don't have to think about anything. No hoses, no wires, no switches. Just cast iron and steel. It's there, it works, and it doesn't require any input from me to function. Many times with selectable lockers, people will wait until there stuck or almost stuck to engage it. By then it's too late. It handles just fine on the road too. Mine has yet to bang and clang. As long as you don't drive like a squirrel, there won't be any problems with premature tire wear or handling. Though I wouldn't put one of these in the front axle, If I had to do it again in my F-350, I would.

Pretty much all differential options are available for all of the differentials Ford uses. but the 9.75 is still relatively new (compared to the other 2), and certain easy lockers and such aren't available yet.

So my suggestion, For 99% of off road, and total on-road drivability, put TrueTracs in front and rear. I always said that if you get stuck with Truetracs, you'd probably be stuck with a locker too! Nevertheless, If you want something a little more radical, Truetrac front, and Detroit Rear.

P.S., Not to confuse the question, but I have a friend that has a 2003 supercrew with a 4.6, and it has a 10.25". (I know, sounds strange) I think the 9.75 is basically the replacement for the 10.25 in ALL the newer trucks (2006 and up I think), and the 10.25 will be only in the F150HD's.