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Originally Posted by Larry_Loo
Ray, I thought about regearing my F-150's transmission after we purchased our TM trailer. We purchased our truck from an individual who had won it in a drawing. It came with only 300+ miles on it and at a bargain price. Of course, it wasn't equipped with some of the options that I wanted, like power windows. Its low axle ratio and lack of a tow package never bothered me - until after we got our TM. Then I thought about having someone install higher ratio rear axle gears in it, but, never did it. I'm a dunce when it comes to vehicle engines and transmissions. Just out of curiosity, how difficult and complicated was your truck's rear axle modification?
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Just to clarify things for everyone, the regearing is not done in the transmission but rather in the differential. (Or differentials if you have 4WD). Regearing is fundamentally just replacement of the
Ring & Pinion Gears with a set of R&P gears that have a different tooth ratio. For instance, on my truck, the stock axle ratio was 3.91 which Toyota achieved by using a Ring Gear with 43 teeth and a Pinion Gear with 11 teeth. I replaced that set with a R&P set that had a 4.30 ratio; I believe that was achieved by a 43 tooth Ring Gear and a 10 tooth Pinion Gear.
Although fundamentally simple, the devil (as usual) is in the details. First, these gears have to be precisely machined together as a pair and they have to be made from extremely hardened steel. Therefore expect to pay as much as $600 per R&P set for OEM gears or as little as about $185 for aftermarket gears. Secondly, regearing always requires new Pinion shaft bearings, seals, and the use of spacers and shims which typically are bundled into an "Install Kit". Install kits typically cost around $200. And finally, there's quite a bit of skilled labor involved to not only remove/replace the so called "third member" but also to precisely (to the nearest 10000th of an inch) set the backlash and tooth contact area between the Ring & Pinion. This is a job that should
only be done by an experienced differential shop. Accordingly labor will usually run about $300 to $500 for the rear axle and sometimes as much as $800 for a front differential in a 4WD that has independent front suspension (most do).
For your Ford, you should expect a total charge of around $550 to $750 for just the rear (if 2WD) or around $1100 to $1700 if it's a 4WD.
IMO, the gains are more than worth the expense, especially if you tow on hilly/mountainous roads and/or at high altitude. I'm getting a 10% change increase in usable torque across the board and more like a 15% to 20% torque increase at preferred towing speed because the engine will be into its peak torque RPM band. If your truck has something like a 3.30 or 3.5 "economy" axle ratio and you jump that up to something like a 4.10 ratio, you would experience more like a whopping 30% to 40% in usable torque because of both gear multiplication and moving the engine into its peak torque band. That's about the same as going from a small V8 to the biggest one the manufacturer sells.
Technical Note on choosing the correct axle ratio: For towing purposes, the ideal goal of regearing would be to install an axle ratio that allows the engine to turn at the RPM that provides maximum torque at the highway speed you want to tow at. If you look at the torque curve of most modern engines, it climbs quite steeply with increasing RPM until the engine is turning somewhere around 3400 to 3800 RPM and then it pretty much flattens out. You want an axle ratio that brings the engine to just about the RPM where the curve flattens when driving at your normal towing speed. In my case, the goal RPM was 3200 and the speed was about 65 mph...to reach that I needed a 10% increase in ratio to 4.30.
The major concern that people have about regearing to much lower gears (higher numeric ratio) is they will take a huge hit on gas mileage. This is
mostly a false worry. According to an article I read in a recent issue of either
Trailer Life or the Good Sam Club's
Highways, apparently the effect on mileage is not big...typically about 1/4 to 1/3 mpg for each 10% increase in ratio. I can testify that my mileage change on the one highway trip I've taken since regearing was minimal...I got about the same 19 mpg for that combo of city/highway driving that I was getting before. And actually I might be getting a tad better mileage since the tranny doesn't have to downshift out of OD (non towing) on the hills as much.
The only real deleterious effect that I've seen so far is that there was a small, but noticeable increase in engine noise at highway speed.
The bottom line is regearing to something around a 4.10 to 4.30 ratio will make a huge, huge improvement in your truck's towing capability. It won't have much effect on fuel mileage (maybe 1 mpg) and only slightly increase cabin noise. It may help extend your transmission's life because it cuts down on downshifts under load. But it does involve a moderately to fairly hefty upfront expense.
Hope I answered your question.