I tow 7000 lb camping trailer. I thinking about changing front and rear gear ratio to 4.10 or 4.56. Would this void the warranty. I only have 9300 miles on it. The tires 35x13.5x18 with leveling kit. I'm looking towards going with 4.10. I take the tires off for winter. Factory gears are 3.73s, 5.4 engine 4x4.

 

Well no, it won't void the WHOLE warranty. But it would void any warranty related to the new gears. And the warranty would no longer cover any problem that results from the new gears or the work done to install them.

But replacing gears is a pretty simple task for a competent shop to perform. Usually the new gears will come with their own warranty. And the shop that installs them will usually warranty their work for a period of time. So, all of this being said, a gear swap is a fairly safe thing to do with regard to warranty issues. Just be sure you have the work done by a reputible shop.

 

It will only void the warranty on the rear end. If the dealership does it, then it is covered. 4.56's are pretty steep. 4.10s will be ok.

Here is a real quick formula to decide what your new RPM's will be

(new gear x rpm)/(old gear)=new RPM

You can use rpm at any speed and that will give you your new rpm at the same speed. No dealing with tire size, etc, etc.

For my truck:
(4.10 x 2000)/3.55=2309
So if I change from a 3.55 to a 4.10 I would gain about 300 rpm. It would be a little less of an RPM gain for a 3.73 truck. If you have the same size tires/rims, you would see about the same RPM.
For 4.56
(4.56x2000)/3.55=2659
That is a little bit steep IMO. BTW I think those are my RPM figures for 75mph and reading with the needle on the spedo and tach (no test mode).

You will have to calibrate the spedo as well, or drive around by gps.

 

I originally had 3.55's in my truck and decided to upgrade to 4.10s after I installed my 35" tires to get back some of the power I lost. I decided to go with 4.10s because I do a lot of hwy driving and didnt want to loose a lot of mpg. When I am on the hwy my rpms are @ 70mph-2000rpms
@80 mph-2250rpms. The deciding factors between the 4.10s and 4.56s for you should be: how much do you tow your trailer and how much hwy driving do you do.
Doug

 

I tow my travel trailer to different campgrounds about once or twice a month. Some campgrounds are 2 hours away. As of highway driving without the camper not whole lot. I use company vehicle for work.

 

I think that you will have a lot better chance of staying in OD with the gears. If you do decide to go through with it, let us know what you think.

 

If I decide to change the gears it won't be until spring. I'm going to posts some pictures of my truck in spring. 35"s tires are off for winter. there are awesome pictures on here.