I have an 18 SCREW with an 8.8 3.31 rear axle. I am wanting to change to a 3.73 9.75 axle. I look on car-part and see that there are many choices. Could someone explain what the actual difference is in the axles? Is it just a different bracket or something that is welded the the axle. I am not talking about the gear ratio, locker or size. but why would a 2.7 and a 5.0 have a different axle, difference between normal payload heavey payload and max payload.. I believe I should be able to bolt in a 9.75 with no issue but was wandering if anyone has run into this.
Thanx

 

is your truck 4wd? if so you have to do the front as well

 

The difference is the duty cycle. 5.0's and 3.5 eco's get more GVWR and Tow capacity than 2.7's and 3.3's.

In addition to anything else, if you switch from a super 8.8 rear to a 9.75, you are going to have to get the shorter prop-shaft.

You can get 3.73's for the super 8.8, if you didn't know.

 

im not saying they are or aren’t different (I’d like to know if a 9.75 out of a 2.7 is the same as a 5.0) but I do know that when I was trying to find a XLT seat for my STX they wouldn’t give me prices since I didn’t own an XLT, they basically refused to sell me a seat. I think they make you select your exact configuration regardless of whether a different part will work to avoid return claims and issues.

 

A 9.75 is a 9.75.... the variants from that being the HD axle for MaxTow/HDPP, the wider axle for Raptors, and the new 3/4 float axle for MaxTow/HDPP..

 

The 8.8 has electric parking brakes.

The gawr maxes at 3800 for the 8.8.

The gawr for the 9.75 starts at 3800 and stops in the 4000s, I think 4800.

The hdpp 9.75 has different wheel bearings.

The early 9.75 had manual parking brakes.

The driveshaft lengths are not off enough to need to change.

If it has the same parking brakes they are easily interchangeable. I am about to do a project like this and will post it up once done.

 

You might possibly be better off finding an 8.8 3.73 with your current parking brake setup at a salvage yard. It would certainly simplify the swap. If you are doing even light duty towing the ratio swap would be well worth it. If you don't have the E locker currently a 3.73 ring and pinion swap with a limited slip in your 8.8 might be a consideration.

 

I keep seeing the parking brake mentioned…my 2020 with the 8.8 had an electronic parking brake and my 2019 with a 9.75 has an electronic parking brake. Was that new for 19?

 

2018 9.75" had an electric parking brake.

Something to consider. Finding a 3.73 8.8" is going to be very difficult, as the vast majority of trucks with a 3.73 also had 9.75". Not sure, but I believe you could only get an 8.8" and 3.73 with the base V6 in 2018.

Just my opinion: Best would be a gear swap, and skip the 3.73 and go to 4.11 (or whatever you can get close). I have a 3.73 and like it, and wouldn't even consider less gear, but would still gladly take a lower ratio if available. The 3.37 is just good enough to make me lose my motivation to go to all the trouble for what I'd really like. 9.75" isn't enough of an upgrade to bother.
2n'd choice if really wanting to swap diffs without messing with gears would be to find whatever parking brake configuration you have in a 9.75" truck with ELD and take everything including the drive shaft. 9.75" 3.73 trucks are much easier to find than 8.8.

 

It's not just good enough, super 8.8 internals are nearly all the same as the 9.75, most can be swapped between the two. The difference is suspension load capacity. The super 8.8 has a lower max GAWR, but weighs less.

I read somewhere the super 8.8 is officially rated at 800lb-ft. It goes into the GT500, putting out over 800hp and running 10's. The case size and shaft diameters are up to the task.

If I was going to run slicks at the track, I'd look at swapping to a 9.75. Otherwise, doesn't make sense to drop the lighter 8.8. If I needed the 9.75 for why the 9.75 goes into some trucks... higher load capacity, better heat handling for towing, I'd want a truck with the higher ratings.