Here is what I did about my diesel bottoming out.

[Mash5]

I have a 21 diesel Sport. I was looking for a better solution for the front suspension. I use it for touring with five people. I don't daily drive it, so it is all about long highway miles followed by a few days on trails or in the woods and then back home on the highway. The vehicle's max rated weight is 6350#, but it has been as high as 6860# fully loaded for a trip. I have a bed cap on the back and a large RTT on that, so I don't really want to lift it. Mileage is also a significant consideration. I have air helpers in the rear that make all that weight work fine back there, but the front performs poorly. It dives under braking and bottoms out on any kind of trail. I am on my second set of front stock shocks at 18k miles, so it needs a bit more support up front. I would also like to add a bumper and winch, but it is out of the question with the way it is now. I would just be riding on my bump stops.

While I normally believe bump stops primarily protect the spring from over-compression damage, people on this forum say these diesels have longer bump stops than the gas JTs. That leads me to believe that the bump stops are actually set to prevent some other interference and that therefore I may be able to lift the front a bit without the corresponding bump stop pads without the risk of over-compressing the spring in order to improve up-travel.

I was going to try just adding a 1.5-inch spacer above the spring until I Claytons your SKU: COR-1509150 springs. Clayton lists them as 1.5 inches, but the drawing calls them 2.5 inches. I think 1.5 would be just about right, but 2.5 would maybe be too much. I reached out to James at Clayton and after a few back and forths, we determined that the COR-1508250 might give me the leveling and up-travel that I was looking for better than the 150s. Based on James's estimates of stock spring rate and the known Clayton rate they should also be about 40% stiffer than stock. James also estimated that they might net about an inch of lift. Perfect!

I placed the order and got them installed.

Here are the old and new springs side by side. You can see the new one is about an inch longer than stock at free length and that the bar of the spring is noticeably thinker. The old springs have 8.5 coils and the new one is about 11 coils. I will be getting numbers on this and doing some spring rate calculations based on spring geometry soon. I will report that here.

At the same time, I also added TeraFlex 1959200 Bump Stop and I think it is fairly clear why these are going to work a lot better. With the spring out it was clear that there had been significant metal-to-metal contact at the bump stop. The stock one only protruded from the tube about half an inch. I'd like to talk to the engineer (or his bean counter overload) that signed off on that.

Initially, after putting the springs in and putting the truck weight on the axle, I could not even get it to come down enough to get the shocks connected and I had a moment of panic. I put the wheels back on and with it full sitting on its own weight it settled in better. I then had to push the shocks in about an inch to get them in position.

Down travel is clearly being limited by the stock shocks but I think that is how the stock setup was as well so it’s just doing it a lot sooner now. Up-travel is noticeably better. I hit a local pothole at speed and it just soaked it up. Before that would have been a crazy hard bottom event. Flex seems to be less than before. Again, I think the shocks are the problem here. The compressed spring is still partly open and the new bump stop is just kissing the pad. The uncompressed spring seems like it has a bit more to give. the bottom control arm was sloping up a bit from the frame to the axle and now it slopes down a bit. The steering was a little off the driver's side and now it is almost perfect. The ride is noticeably different with no load but I think it will be better once I get it loaded.

I have a trip to Death Valley scheduled for next weekend and I will report here on how it goes. I’m very optimistic that it will be a lot closer to what I need from my setup. I think with some stiffer, longer travel shocks I will be right where I need to be.

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[Mash5]

Before and after

 

[Free2roam]

What's the part numbers on your stock springs? Curious if they are the same as mine. I have a Sport S Ecodiesel 21. Ordered in March of 21 and picked up end of April 21.

 

[Mash5]

What's the part numbers on your stock springs?

That is a fair question. I should look and see if I can read the tags. Stand by.
Looks like the one I have a picture of says 6377AA.

 

[Free2roam]

Both sides same numbers. When was yours built?

 

[Mash5]

Both sides same numbers. When was yours built?

The springs are at home, so I'll have to look tonight after work. I just pulled that number from a picture I had. My build date was March 12, 2021

 

[Mash5]

Both sides same numbers.

I did confirm that on the old springs, both sides are the same 6377AA number.

I have about 100 miles or so on the road now with the truck mostly packed for our trip including the RTT and I am still feeling like this has been the right move. Handling is way better. It does not have excessive body roll. The diving sensation under breaking is gone completely. I still need to add four people and their personal gear and then get some offroad miles under her to make a final assessment.

The back end seems to be sitting a bit lower than the front for now. I am at 55 in the airbags in this picture. I may add another 10 and see how she does.

Stand by for Death Valley pictures!

 

[Mash5]

Death Valley was a good test of the suspension and overall I am very, please. We spend all of the first two days on rough corrugated roads or worse and parts of the third and fourth day. I ran 24 psi for a lot of it and dropped down to 14 for parts as well. At no point did I feel the suspension bottom out. Compared to before where any rough road, paved or dirt would result in multiple hard bottoms.

Shocks limiting down travel did not seem to be a noticeable problem. I do still feel the truck is substantially under damped and I will be looking for some upgraded shocks.

I also lost an airbag. The night before the trip as I was checking the air in the bags and one was at near zero. As I tried to air it up I could hear a leak from the top of the spring. I ended up running the entire trip with only one bag. It resulted in a bit of wonky handling. I'm running the Firestone bags that have Schrader valves in the top of the bag and then a hose that connects to that. I think it is that connection that is leaking. I am going to try the Airlift bags as they have a barb fitting on the bag which seems like a more permanent connection that hopefully won't vibrate loose.

I think I will also hit up Clayton to see what they recommend for a matching set of rear springs. Maybe I am asking too much from these airbags and stiffer springs are in order too.

 

[Mash5]

Update:
I added Bilstein B8 5100 - Shock Absorbers
Part Number:bilstein 33-304847 Position: Front -For Front Lifted Height: 0-1.5" Collapsed Length (IN)15.75 Extended Length (IN)24.73
Part Number:bilstein 33-304854 Position: Rear -For Front Lifted Height: 0-1.5" Collapsed Length (IN)17.22 Extended Length (IN)25.87

Magic! It no longer feels under-damped. The ride is more sure off-road. Maybe it's a bit on the harsh side on pavement, but the handling feels better. Body roll is markedly better as well. She is no sports car but handing no longer feels sketchy.

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