brulaz

Where did that 4500# number come from?

The source book for 2011-2014 says 4100# for the limited slip axle rating (4800# for HD payload). But guess something drops that to 4050# in my MaxTow's rGAWR .

I'm a hundred and some over that axle rating, but under the GVWR, so would love it if you could show me that it really is 4500#.

5.0GN tow

It is what Ford states that the maximum rating GAWR for the axle itself is. The application may limit the rating in a vehicle, but I found it by looking up just the axle assembly itself and how it's built and rated. Ford rates it for max continous torque of 1500 lbs and max peak torque of 6100lbs. It was built to be as tough as a Dana 60 semi float. Found lots of articles including one written my University of Northwest Ohio Instructors(one of the best diesel and auto tech colleges in the US). They really like the axle even though it's rated for 500lbs less GAWR than the 60, but rated for more torque and uses better grade components than the Dana unit.

brulaz

Would still like to see the docs on that.
Attached is a screenshot from the "2013 Source Book".
Pretty clear that the 9.75" ring gear rear axles are either 4100# or 4800# (p.96). The rear Leaf 3+1 springs are rated separately as either 4220# or 4800# (p.99).

5.0GN tow

Must not be entirely accurate as I have a 3850lb rated 9.75 with 3.55 gears. My truck is a 13 Supercab 4x4 5.0. Could be they were talking about the 5 lug axles being 4500lb rated as the one they were working on was on an older 97-04 style truck. Like I stated before I think spring pack has more to do with the rating than the axle itself which is much stronger than its rated for. I would guess north of 5500lbs since ford is rating at 4800 in a half ton truck.

smurfs_of_war

Yes, the spring pack, mounts, frame tail- all of that goes into the GAWR on a vehicle. So the axle as a stand alone unit may be rated to a higher number that it is in the real world application simply because there is another component limiting the overall rating.

5.0GN tow

Agreed, the axles are all rated the same, from what I can gather for the most part so are the frames. The big difference is the spring packs which are listed as being different. The wheels are different too. The standard aluminum 18s and 20s are rated at 2025 for the 09 to 14 trucks, while the HD steel 17s are rated 2400. So looks like wheels and spring packs limit the axles since 3850 is one spring pack option. The next highest is 4100 which just a hair over the wheel ratings for the max tow trucks, while 4800 was for the HD payload trucks with the steel wheels.

The funny thing is the HD payload trucks got thicker frames with a lower strength rating. The strength rating of the standard frame was 49K+ and the HD was 36kand change. That one surprised me a little. The sectional modulus is higher on the HD frames, but the RBM which is the true test of truck frames in use would be very close. So for all real practical purposes the frames are pretty equal.

smurfs_of_war

Thats telling me that the frames of either truck are way under rated on paper and the HD frame is more about rigidity, no?

5.0GN tow

They are underrated for sure, in one way, but calculatedly so, because of fatigue cycles and usage cycles. I design weapons components, and we do the same thing in my line of work. You purposely over build so that the fatigue life of the part is as close to infinite you can make it.

In the case of the trucks, both frames would be almost equally rigid. On shorter sections (short wheelbase) builders spec for strength on longer wheel base it's more for deflection hence slight thickness increase.

RBM (resistance bending moment) is calculated by multiplying sectional modulus by yield strength. This is the true rigidity measure of a frame. For the 09 to 14 trucks the supercab 4x4 145wb trucks have a RBM of 281,010
The HD trucks have an RBM of 259,200. Both of those measurents are in inch pounds. Both are very rigid, but it is interesting that the supercab or shorter WB trucks rate higher. All this makes me feel even better about my supercab and towing my gooseneck.

Even more interestingly I used the source book for the 13 SD and calcated the RBM of the SD frames and it certainly shocked me that it was lower than either of the 150 frames it also has fewer cross members. It's RBM is 241200. They have either 5 or 6 cross members vs 7 on the 09-14 150s.

11screw50

Your wheels are probably only rated for 2025 each...that is what the book lists for most of the wheels anyway. Axle rating will take into account the axle itself, springs, wheels and tires...lowest rated component dictates the assembly rating.

brulaz

That is correct as I don't have the HD Payload package (2400# per wheel). So despite the spring rating of 4220#, axle rating of 4100#, the double wheel rating of 4050# gives me the rear GAWR on my door jamb.

I have upgraded the springs and could upgrade the wheels but then I would be limited by the 4100# axle rating, unless what 5.0GNTow says is correct: that the axle is really rated at 4500#.