Air Ride - Rear Shock Replacement Options

[rpr]

So after a lot of research it appears only Chrysler and Monroe offer a direct replacement for the OEM rear shock on the air ride trucks. Fox, Bilstein, and Rancho do not list any shocks as being compatible with the air ride suspension. However, I want something that performs better than the Chrysler and Monroe offerings so I manually tried to match something up. This is what I came up with.

The OEM shock is:
- 23.44” extended
- 16.44” compressed
- LS43 mounts top and bottom

The closest match out there is the Rancho RS9000XL RS999262:
- 23.83” extended
- 15.28” compressed
- LS47 mounts top and bottom

The two primary issues are not overextending the air bags and not bottoming out the shock. The Rancho will not bottom out as it has a smaller compressed length than the OEM shock. The Rancho shock will allow the air bags to expand approx. 3/8” more than the OEM shock based on the published specs though. However, if I pull on the fully extended OEM shock it actually expands beyond the 23.44 published spec and then retracts back when I let go. So since the OEM shock has some give and it’s apparently designed to overextend a bit, the extended length of the two shocks are essentially identical.

Based on the above, I see no issues with the fully compressed and fully extended lengths of the Rancho RS999262 for the air ride trucks.

However, the mounts on the Ranch shocks are LS47 which are slightly different than the LS43 mounts on the OEM shocks. This translates to the bushing on the Rancho being 0.2875 mm wider. This is so slight I don’t think it will be a problem. Based on how the OEM shocks came out of the mounts (easy) I’m sure the 1/4 mm wider bushing on the Rancho will fit fine in the mount without any need for prying.

The other difference is the inner diameter of the sleeve on the Rancho is 1/16” larger than the sleeve on the OEM shock. That doesn’t sound like much and it also arguably wouldn’t be a problem after properly torquing it but that worries me a bit more.

So I’m thinking the best option would be to replace the OEM 14mm bolt (which is designed for the OEM LS43 mount) with a slightly larger 9/16” bolt (which is designed for the Rancho’s LS47 sleeve). Hopefully the slightly larger 9/16” bolt will slide through the OEM shock mount holes on the frame/axle without any need to enlarge them, but a 1/16” difference is fairly significant. I highly prefer not to enlarge the factory shock mount holes so I may see if a 9/16” bolt will fit before purchasing the shocks.

There’s such a slight difference between the OEM LS43 mounts and the Rancho LS47 mounts that I probably don’t need to change anything and can reuse the 14mm OEM bolts. But before I leap into this I figured I would post the Rancho shock specs and model number here as there are several posters who have wanted to change their OEM shocks on their air ride trucks and felt they had no aftermarket options, and to see if anyone had any thoughts on any of this.

 

[rpr]

Ok, I found a much better option than the above Rancho which doesn’t get very good reviews. I spoke to Fox today and they found a “match” that I missed somehow:

Fox IFP 2.0 Part #985-24-071
- 23.72” extended
- 15.00” compressed

Should work perfect with a sleeve for the bushing to reduce the 0.75” ID to 14mm. Fox has two sleeves, neither exactly perfect but either should work:

- FRS-213-28-007-B
- FRS-213-28-001-B

The Fox shocks are available in multiple locations and Summit has the Fox sleeves. Any local 4x4 shop should also have bushing sleeves that would work.

Fox said this shock was originally designed for the Toyota Hilux truck (essentially an overseas version of the Tacoma) so they thought the valving would be fine for the Ram. However, the curb weight of the Ram does appear to be quite a bit heavier than the Hilux (anywhere between 200lbs and 975lbs based on the trim level). But since my Laramie Limited runs too stiff and I’m looking to slightly soften the ride, I’m thinking (hoping) the valving on these shocks will be about perfect.

Everything is on order and I should have them installed in a week or so. I’ll let you all know how it goes.

 

[rpr]

I got everything installed today. No significant issues with the install and I feel the Fox 2.0 is a significant upgrade over the OEM shock.

Getting to that upper bolt was a real pain but I got it done with a 21mm crows foot and some ingenuity. You’ll be able to get the crows foot on the upper nut but it’s sunk in a shroud so you can’t get a ratchet extension on it. It will jamb itself as you tighten the bolt up to 100 ft lbs but then you can’t get it out. I was able to place a stubby flat head screwdriver between the crows foot and the shroud as I tightened it up. Then just pull the screwdriver out and you’ll be able to remove the crows foot.

Even though the Fox shock has a slightly longer published extended length than the OEM shock the Fox shock has a hard stop at it’s published extended length. In contrast, the OEM shock gets pulled out a bit further than it’s published spec and even a bit further than the Fox’ published spec when there’s weight on it (i.e.: in full droop position). I not sure if that’s by design or not. I think the OEM shocks are either just really crappy or mine were just worn even though I only have 52K mikes on the truck. So the Fox will not over extend the air bags, at least not in contrast to my OEM shocks.

Both of the bushing sleeves I listed above work. I prefer the slightly longer FRS-213-28-001-B. You can’t remove the bushing sleeve from the OEM bushing. The OEM bushing can be pressed out of the shock but the bushing is glued to the sleeve.

This is subjective but the rear suspension now feels more compliant and less harsh. Well worth the time, effort and cost IMHO.

Hope this helps some of you if you feel the rear suspension on your air ride truck is too harsh and you want to upgrade the OEM rear shocks. The Fox IFP 2.0 #985-24-071 works and it’s a significant upgrade.

 

[mgr1001]

Hi RPR

Thank you for the very thorough discussion on the rear shocks. I have a similar situation with my 2016 laramie SRW 6.7 diesel.

I have gone ahead and ordered replacement Bilstein shocks for the front, but was stumped on the rear shocks (because of the air leveling suspension).

I will probably go the same route as you did with FOX shocks in the rear.

Do you, by chance, have the name of a person or department at FOX that I can talk to? Although my situation is very close to yours, I doubt that it is identical.

Also, I was wondering how you managed to find all the specs for the OEM shocks?

Any pointers will also be greatly appreciated. Are you still happy with your setup?

mgr1001

 

[rpr]

I can’t remember the name of the fellow I spoke to at Fox, I just called their main tech support number. Very helpful, just don’t expect them to give you a part number for your truck, there is no supported Fox rear shocks for our truck, you need to check to make sure the fully compressed length is not longer than OEM and the fully extended length is essentially identical to the OEM (as the shock is used to control full droop and you don’t want to over extend the air bags).

Monroe lists a rear shock for our trucks and I confirmed the fully compressed and fully extended lengths of my OEM shocks matched the specs for that shock.

Good luck!

 

[rpr]

And yes, I’m very happy with the performance of the Fox shocks.

 

[mgr1001]

Muchas Gracias amigo

 

[Got 1]

You can also check on BDS Suspension's site. Their 4" lift kit for air ride comes with FOX shocks.

 

[rpr]

Just don’t try to use those Fox shocks listed in the BDS kit without the kit. They have a fully extended length that’s approx. 3” longer than OEM, so they will over extend the air bags without the kit.