changing rear end gears

I plan on buying a travel trailer and I currently have an 8.8 in rear with 3.31 gear set. I am thinking of changing the gears to 3.73 to more easily pull the trailer. I have seen Ford Racing sets for mustangs which includes an install kit (bearings, seals, gasket, etc.). Would this fit in the Expedition? Also, what would be a reasonalbe cost for installation? Should I install a transmission cooler or might this already be on the truck. I know I need to install a 7 pin connector and brake unit under the dash (I have seen the connection for it). Hope someone can help. Thanks!

Just find a rear axle out of a wrecked expy with the towing package.

F&P's answer is the certainly the quickest answer.. and depending on yard prices the cheapest.

Its an average of $500 per axle for gear supplies and labor depends on where you are. I live in a rural area of the midwest, so our labor costs are generally a bit cheaper. Rear gearing an axle costs about $300 for labor.


Considering that LKQ Orlando charges only $90 plus core for an axle complete brake backer to backer.
LKQ Self Service Auto Parts - Orlando | LKQ Self Service

Is your truck a 4x4 or 4x2

The truck is 4X2. I am pretty handy but have never put in rear end gears and I have read that it can be tricky if not correctly shimmed. Also, I guess you would need a gear puller which I do not have. It seems it would be easier to do with independent rear suspension as the shafts from the differential to the wheels can be unbolted although I could be wrong. I believe I would need it reprogrammed to correct the speedo.

if you dont have the right tools this will be next to impossible too do , you must set the backlash right or the rearend will come apart

FordandPolaris said:

Just find a rear axle out of a wrecked expy with the towing package.

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1up on this

for the cost and whatnot, getting a complete rear end is going to be the cheapest way to go. Also, like was mentioned, if you don't have the right tools, you will ruin a set of gears in a matter of miles. I paid around $1000 to have gears put into my truck for front and rear. So, you can plan on spending about $500-600 to have the gears in the rear of your truck done.

Thermo, while researching this on my vehicle in the past, I learned that I have the NON limited slip differential 3:31. Wouldn't it behoove him to get a LIMITED slip diff rear end if he's going to spend this kind of money? If not for his own money, for the value add when he sells it.


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That depends on which route he is going... If he is going for a JY rear end, it might not make any difference. I find alot of JY rears with LS are worn and the clutches don't engage correctly. If he finds one and its in good condition...sure. But if it was me, I sure wouldn't not get a regular one if the price was right.

If I was going for new parts and was getting a new carrier anyway, I would more than likely get the LS carrier. The pricing will be close and might as well add the option.

Thanks for the info. Since I live in Florida, I probably will not upgrade to LS. Most likely, I will opt for the gears only and replace the bearings, seals, etc. I have seen pretty good pricing for the ford racing gears but always are listed for mustangs. Will they be acceptable for the expedition?

Even if its just wet out you might like having a limited slip diff. It is actually really nice to have while towing. I love mine when I am taking a boat out of the lake. Never need 4wd because the rear end turns both wheels with power. Only short coming is off road when one wheel gets up in the air.

you are probably right regarding the limited slip. Does anyone know if I can use the ford racing parts for the mustang (i.e. cobra, gt, etc.). Seems I can pick up these fairly cheap online. Would they be an exact fit given I currently do not have a LS rear end? Also, anyone know the cost of having it reprogrammed for the speedo? Thank you

The Ford Racing gears will work. 8.8 is 8.8 is 8.8. You might call the dealer to see if they can reprogram your speedo. If not you'll have to invest in a hand held tuner.

Captain, me personally, I can not see owning a truck without some sort of traction device in the rear. It makes a world of a difference as I see it. If for no other reason than when it rains, you have 2 tires pushing you around and when you feel the rear end start to chatter, you know you are getting close to your traction limit and you need to ease up on the gas just a little bit. I know my LS rear end has helped way more than I care to admit to. The only "downside" that I can give to an LS rear end is that when you break the rear end loose on a turn, you are going to spin in a heartbeat. But, like I mentioned, you pay attention to the rear end chatter, you will be golden.

Thx, yeah I got the NON limited according to the door tag ID.

I'll crawl under there and try to read the pumpkin\axles to verify.

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Thermo said:

The only "downside" that I can give to an LS rear end is that when you break the rear end loose on a turn, you are going to spin in a heartbeat. But, like I mentioned, you pay attention to the rear end chatter, you will be golden.

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This is what worries me.... especially with folks that aren't used to the behavior of a LS...

Now.. I have had a DD with LS for 17 of the last 19 years and a full auto locker the other 2, so I am used to it. But I don't like my 16 year old driving a LS equipped vehicle in the wet weather as she doesn't have much experience.

The other downside to LS operation is when you are in a low traction situation and you need more. Like someone mentioned lifting a wheel off-road.

I wonder if someone creating a write-up page here about the differences between an open, LS and locker might be worth it. Seems like the folks here come from a pretty varied background and might gain some insight.

whowey, I can understand what your worries are with a 16 year old and the truck with an axle like that. But, how do you trust her to drive the truck and not run over cars? Simple, you taught her how to drive and you observed how she drives. This is just one more part of that training for how to drive. The same can be said about driving a high power car or even an underpowered Geo Metro. Every vehicle has different characteristics and the driver must know and understand them.

As for your question about knowing the differences between the various types of lockers, here you go, here is a short and sweet summation of the different types of traction control out there. This is not manufacturer specific, so, use this information to understand how the systems work and then learn what each vehicle that you have is equipped with.

Open differential: The most basic of differentials. Power comes in via the drive shaft, goes to a ring gear and then through a gear assembly, applies power to the wheel that is spinning the fastest. If both wheels are spinning at the same rate, then it will apply power fairly equally. But, once a wheel starts to slip, all the power gets transferred to the slipping wheel, resulting in complete loss of traction.

LImited Slip: As the name implies, it limits the slip between the two wheels. This is normally done through a small gear assembly and a clutch pack. When both wheels are spinning at the same rate, the clutch plates are barely touching (ie, not being squeezed together) and like an open differential, most of the power is going to 1 wheel. As the powered wheel starts to slip, the gear assembly starts applying pressure to the clutch assembly. This causes the speed difference between the wheels to be limited since some of the power going to the slipping wheel is now being forced over to the non-slipping wheel. As the power is being transferred and the spinning wheel is being robbed of power (and being slowed down), the clutches will engage more and less, resulting in a vibration/chatter. The harshness of the chatter is directly related to how much traction the non-slipping tire has and how much gas is being used.

Locker: These come in a few different flavors. You have full time lockers, cable selectable (you route a pull cable to where you want to activate the locker from), electronic selectable (uses a solenoid to engage the locker), and then you have air lockers (uses compressed air to engage the locker). On the selectable lockers, they have 2 different modes they can run in, open differential (see above) and locked. When locked, both wheels are physically locked together and forced to spin at the same rate. So, as one wheel is loosing traction, the power is seamlessly transferred to the wheel with traction. The locked differential is perpetually in the locked mode. This system is great for low traction conditions or when running on a surface that gives a lot (dirt/gravel roads). But, on dry pavement, this system (when locked) can lead to high stress loads on the drivetrain while turning as you are now forcing the tires to spin at the same rate when they are actually spinning at different rates. This normally results in the locked axle "hopping" as the tires are breaking traction to keep them spinning at the same rate. If the tires do not hop, then this can lead to axle breakage or other driveline problems.

Trac-loc: While this is a brand name, the concept needs to be explained. This is a differential that automatically goes between an open differential and a locked differential. It is essentially a limited slip differential on steroids. It allows for a small amount of slip (like a limited slip). But, when it senses too much slip, it engages and becomes a locked differential. This engagement can be rather harsh if done under load. This gives a bigger one time bump than the limited slip vibrations, but once locked, it is locked. This bump transfers a lot of force to the non-slipping wheel and can lead to it breaking loose during engagement.

Computer controlled traction: Every manufacturer has a name for this type of system. This is normally what is found in cars and the higher end luxury trucks. The system works by having a wheel speed sensor in each wheel. A computer then monitors each wheel to make sure that it is spinning at the same rate as the other 3. When a wheel is sensed to be slipping, the spinning wheel is controlled by applying the brake caliper to the slipping wheel and/or limiting the engine's power. When 2 or more wheels are slipping, normally the engine's power is limited to keep the vehicle controllable. This system is sometimes used in conjunction with one of the above lockers to provide a more seamless system that does not rely on limiting engine power.

As always, if you want more info, just ask. This is a big picture view and did not go into the specifics of how each brand does the job. They all have a twist on the same idea to make the "bigger, better mouse trap". As you can see, each one has pros and cons. The question then becomes, what is the best system for what you need?

Can you re post this with some animations and graphics illustrating the concepts for each application you explained, in color with interactive pop-outs in Flash when you hover the cursor over the paragraph? Some cool numbers for torque on lb\ft would also be great and maybe change the color to red where the potentials for breaking occur?







naaaaaahhh I'm just kidding, great post! Should be sticky'd.




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Captain, do not tempt me. LMAO.