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Discussion Starter #1 (Edited)
So I pulled out the secondary springs on my 2018 ProMaster 3500, but much like @World Trekker's experience, I was not happy with the result. It sits level (or maybe a hair too low) but also sits hard on the factory bumpstops.

I thought about adding Sumo Springs, but if I was sitting hard on the short factory bump stops, then it would be sitting really hard on the taller Sumo Springs.

I also just thought about putting the original secondary springs in, but the 3500 sits so tail-high that my shower pan was not draining right.

So I found a local set of used springs from a 1500 136" low top van:

63442


But the van they came off (VIN 3C6TRVAG8EE108917 ) had 283K miles so as you can see in the picture above the rear spring bushings are shot.

So it looks like I need a Mopar part 68334682AA which goes from $39.95 to $76.05 at local dealers (no stock) and $27 on internet dealers.

After measuring the 1500 springs and looking at this site:
Fits Fiat Ducato Peugeot Boxer Citroen 40mm Leaf Spring Shackle Bush 2006 Onwards

I think the Fiat part number is 1304640080, that led me to this part:

Which is apparently a Febest FTAB-002 or FAST Original FT18312.

Those look like what I knocked out of the old springs, so I ordered 4 from Amazon (at the price of one Mopar part from a dealer) and we will see if they are correct.

@RnR I chatted with a polyurethane suspension parts place . . . . but they were unable (or more likely unwilling) to cross it. For the used 2014 RAM Promaster 136 low roof spring that I purchased from the junkyard, here are the approximate dimensions that would be needed for a polyurethane bushing:
  • Outer Tube Length: 70mm (width of spring)
  • Inner Sleeve Length: 80mm (length of metal tube)
  • Fastener Bolt Diameter: 16mm (hole in the metal tube)
  • Bushing Outer Diameter: 40mm (diameter of the hole in spring)
I have the old rear bushings knocked out of the springs, disassembled them, power wire brushed them and primed them. I plan to paint them with undercoat since I have undercoating handy and do not want to mess with mixing and spraying enamel.

The nylon spacers / insulators / bumpers between the springs are predictably shot, not compatible with the ones in the 2019 Promaster, and not listed on the Mopar parts site. However, it looks like there are some Dorman stock parts that should work:

Dorman 924-070
https://www.napaonline.com/en/p/NDP7356845

Dorman 31067
https://www.napaonline.com/en/p/NDP6501118

I'll try to post progress and results here.
 

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Discussion Starter #2
The spacers or insulators or isolators in the spring pack of the 2014 low top 1500 (white ones in the photo below) were severely worn. The best one on the left is maybe serviceable. The one on the mid-right is worn paper-thin and completely through in a few spots.

The black ones are Dorman 924-070 that I got at Napa which I will try as replacements.

They are sitting on a wire-brushed and primed spring.

63453



The 2019 3500 spring spacers have an oval plug (anti-rotation perhaps?) and nubs - which I imagine are intended to hold grease -- and they were greased (these were removed at ~400 miles):


63452
 

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So I pulled out the secondary springs on my 2018 ProMaster 3500, but much like @World Trekker's experience, I was not happy with the result. It sits level (or maybe a hair too low) but also sits hard on the factory bumpstops.

I thought about adding Sumo Springs, but if I was sitting hard on the short factory bump stops, then it would be sitting really hard on the taller Sumo Springs.

I also just thought about putting the original secondary springs in, but the 3500 sits so tail-high that my shower pan was not draining right.

So I found a local set of used springs from a 1500 136" low top van:

View attachment 63442

But the van they came off (VIN 3C6TRVAG8EE108917 ) had 283K miles so as you can see in the picture above the rear spring bushings are shot.

So it looks like I need a Mopar part 68334682AA which goes from $39.95 to $76.05 at local dealers (no stock) and $27 on internet dealers.

After measuring the 1500 springs and looking at this site:
Fits Fiat Ducato Peugeot Boxer Citroen 40mm Leaf Spring Shackle Bush 2006 Onwards

I think the Fiat part number is 1304640080, that led me to this part:

Which is apparently a Febest FTAB-002 or FAST Original FT18312.

Those look like what I knocked out of the old springs, so I ordered 4 from Amazon (at the price of one Mopar part from a dealer) and we will see if they are correct.

@RnR I chatted with a polyurethane suspension parts place . . . . but they were unable (or more likely unwilling) to cross it. For the used 2014 RAM Promaster 136 low roof spring that I purchased from the junkyard, here are the approximate dimensions that would be needed for a polyurethane bushing:
  • Outer Tube Length: 70mm (width of spring)
  • Inner Sleeve Length: 80mm (length of metal tube)
  • Fastener Bolt Diameter: 16mm (hole in the metal tube)
  • Bushing Outer Diameter: 40mm (diameter of the hole in spring)
I have the old rear bushings knocked out of the springs, disassembled them, power wire brushed them and primed them. I plan to paint them with undercoat since I have undercoating handy and do not want to mess with mixing and spraying enamel.

The nylon spacers / insulators / bumpers between the springs are predictably shot, not compatible with the ones in the 2019 Promaster, and not listed on the Mopar parts site. However, it looks like there are some Dorman stock parts that should work:

Dorman 924-070
https://www.napaonline.com/en/p/NDP7356845

Dorman 31067
https://www.napaonline.com/en/p/NDP6501118

I'll try to post progress and results here.
Air bags are the only way to go. Don't waste time and money on cheap solutions that don't work properly
 

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Discussion Starter #6 (Edited)
Air bags are the only way to go. . . .
I have not ruled out adding airbags. In my mind, for airbags to be useful you need to have the vehicle setting somewhat low to start with so the airbags will have some base pressure in them. As high as the 3500 rides, you have to do something to the springs to get it low enough that the airbags can raise it to the target. Pulling the helper spring makes it ride so low that I decided to look for an alternate solution with the used 1500 springs.

The cons of airbags are expense ($500 to $1000), complexity, and reliability. I'm not saying any of these are insurmountable, but they are much more complex than dumb old springs and bolts. I do like the idea that airbags would allow some leveling abilities. I will say that @keeponvaning's dissatisfaction with airbags is affecting my willingness to go that direction.

The full air suspension looks way fun, but these appear to be $5000 to $7000.

Did you weigh your van to determine front and rear axle loads? Just curious how your van compares to 1500 and 3500 PM suspension/spring ratings.
No. I do not have a convenient place to weigh around here. The closest is a garbage transfer station and you have to pay the minimum dump fee.

If I am super ambitious, I might stick the 3500 helper leaf springs back in temporarily and take photos & measurements. But no promises on that.
 

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.....cut....

No. I do not have a convenient place to weigh around here. The closest is a garbage transfer station and you have to pay the minimum dump fee.

If I am super ambitious, I might stick the 3500 helper leaf springs back in temporarily and take photos & measurements. But no promises on that.
I’m also curious if the “helper springs” of the 1500 are different enough in stiffness, yet shaped/curved/arched the same, so they could be combined with 3500 primary to make a spring pack in the middle. Have you measured length and thicknesses or compared side by side? Not suggesting you install them, just wondering what spring differences are.
 

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Discussion Starter #8
I thought I read somewhere that all the FCA helper springs were the same, and only the main spring is different.

I'll take the caliper to it and see if there is a difference. Also: 5 years heavy use on the 1500's springs (283K miles) and the 1500's springs were not obviously marked as "Mexico" where the 3500's springs are marked as "Mexico".

Here are the spring options listed for the 2014 (vin 3C6TRVAG8EE108917 ):
63474


Here are the spring options listed for the 2019 (vin 3C6URVJG8KE510923 ):
63475


But unless you have some decoder for the sales codes or part numbers it is all useless. @LaneC is that information available?
 

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Baxsie, you're on the right track with finding the right spring rate.
There are a lot of aftermarket add-ons and Band-Aids for suspensions out there. I see a lot of it in the pickup world, especially when it comes to the towing world. It's amazing how many people just make assumptions on what's okay to do and just go ahead and do silly crap to their vehicles.
The first and best choice is always to have the proper springs for the load. 2nd is the right shock absorber.
99/100 times, if you get that combo right, there's no need for any add-ons.
I've seen a lot of pickup owners that use under powered and under sprung trucks to tow an overweight load and think it's ok just to add airbags. When realistically, they need a 3/4 ton truck with heavier springs, more power and bigger brakes.
Using the sumo springs is an easier and cheaper way to dampen body roll than an anti roll bar. But I wouldn't depend on them for much more than that.
I think air bags are completely unnecessary for a camper conversion and unnecessarily expensive. (Much like a lift kit).
Get the springs right and go from there. You won't need anything else if the springs and shocks are right.
If you were going to spend any money at all, I'd have a spring shop make custom springs, before doing something like airbags.
 

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The 3500 comes with a beefy anti-roll bar.
Sometime, could you measure the diameter of your 3500's anti-roll bar for me? Because "why not", I factory ordered the optional HD version which measures 1". I've always wondered if it's any different from the standard one.
 

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Discussion Starter #14
Sometime, could you measure the diameter of your 3500's anti-roll bar for me? Because "why not", I factory ordered the optional HD version which measures 1". I've always wondered if it's any different from the standard one.
Our ProMaster has:
Premium Heavy–Duty Suspension Rear Heavy–Duty Stabilizer Bar $185
Listed on the window sticker -- so probably the same.
 

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Discussion Starter #15
I thought I read somewhere that all the FCA helper springs were the same, and only the main spring is different. . . .
I think that is a "nope".

I measured the thickness of the helper leaf springs and charted them:

63484


This indicates that the helper springs on the 2014 1500 are considerably lighter than the ones on the 2019 3500.

Raw data in an XLS here:

Notes:
2014 springs were power wire brushed to bare metal and then primed before measuring.
2019 springs were removed at ~400 miles, measured with factory paint and perhaps some stray undercoat here and there.
 

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Discussion Starter #17
Sometime, could you measure the diameter of your 3500's anti-roll bar for me?
Looks like 26.2 mm -- a little over an inch.

63486


Bonus: You can see my 1/2" copper propane line and the sender wire in the background. I wrapped the line with rubber electrical tape, to protect it from minor impact, rubbing or rattling.

I finished prepping (power wire brush), priming, and "painting" with undercoat. Here is a progress shot:

63488


The two colors of primer are because that was what was available in the various spray cans littering the shop's shelves.

What about the arch? Are they close if you hold them over each other?

A picture would be cool.
Well . . . just let me run out to the shop and take that photo for you! :)

They appear to have the same substantially the same arch. I took photos of them both on the floor more or less lined up with the camera.

63487
 

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Thanks Baxsie. I’ll have to remember that replacing the 2nd leaf with one less stiff from a 1500 van may be worth trying depending on overall rear axle weight; if I ever get to that point.
 

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Discussion Starter #20 (Edited)
E24 External Torx Socket for ProMaster Rear Shocks and Springs

@Baxsie - Need to buy a socket, could you tell me the size of the torx socket . . .
I'm waiting on my bushings, so I have not gotten that far yet. I think someone in the other thread said that you can find a 6-point socket that will work - - that was my plan. If I can't make that work I'll have to search around.

These posts mention "E24" in passing:


Amazon has many:


I ordered this set -- supposedly to arrive the same day as the bushings :)


It will match my other specialty socket rails screwed above the bench [cough]tool sl*t[cough].
 
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