Duramax IFS Suspension

[fl0w3n]

I like to overthink things, and my most recent victim is shocks and the Dmax ifs.

I’m getting ready to order the Fox 2.0 model 980-24-663 but then I got thinking.

This is the table of the shocks applicable. What I’m not understanding is with most if not all drop down lift kits for these trucks, it’s just that, a drop down kit. The geometry
for the most part doesn’t change, AFAIK.
I can understand needing different collapsed and extended length, but why does the travel change significantly between them all? How can a drop kit pull more travel without getting wider or changing the shock location?

Does anyone have actual travel numbers of stock ifs? I feel like 5.1” is pretty pathetic, but I don’t really want to go with a lift kit again (I kind of “had to” when I built my 06).

I would be much happier if I could massage the 980-24-658 into the truck without a lift and actually use the travel. On my 06 with the Cognito 4-6 ntbd I had it massaged to stock height/leveled height, and that truck didn’t have UCA droop stops, it just beat up the 5100s in drop out conditions. So, with that, I feel like the limiting factor is the UCA stops. In my head it seems “easy enough” to cut them out, mount a limit strap to the LCA shock hole, and gain a couple inches of down travel. I didn’t have any trouble with ball joints or CVs on my 06 and using the 5100s that came in the 4-6 kit as a limit.

​

Front Shocks
Part#	Lift Height	Travel (compressed-extended)
980-24-663	0-1"	10.95-16.05"
980-24-658	4-6"	13.85"-21.45"
980-24-962	7-9"	14.95-24.05"

 

[Chevy1925]

Most you will ever get from a stock 4wd front end is 12”s before cv bind occurres and even then, don’t crank the wheel to full lock while at full droop and punch it.

Shock travel will increase with suspension drop kits because the frame mount is not moving down with the arm. Shock mfg will not just keep the shock shaft or body one length and then lengthen the other end, doesnt allow it to work on multiple applications then.

You also have what’s called a motion ratio. Basically, the stock lower arm puts the shock at a 2:1 ratio with the tire. For every 2” the tire moves, the shock moves 1”.

100% stock suspension only pulls 6” of wheel travel on 01-10 trucks (think the 11-19 gain an inch or two, have not measured them) and adding upper arms and shocks that give full travel up that to 9-10” wheel travel iirc.

To gain reliable travel, you need more range of motion from the upper ball joint and a shock that does not limit down travel or up travel. The stock upper ball joint ain’t got the range and the arm won’t allow as much droop as the aftermarket arms allow. I wanna say you can get up to 7-8” wheel travel with stock arms and different shocks.

What ever you do, you don’t want hard parts limiting droop or bump as you stated. Limit straps and bump stops are there for that.

 

[fl0w3n]

That’s exactly what I was looking for. Even at a measly 6” of stock travel, that 980-24-663 shock would limit it with only 5.1” of travel.

I’d be amazed at pulling 12” out of a stock front end, without even considering tire size.

I get that some kits only move the lower arm down, but I still don’t understand- even if the top arm and bottom arm were ten feet apart, the location on the arc that the shock is mounted to on both the top and bottom doesn’t change, and the lower arm doesn’t get longer, so I don’t see how that 2:1 would change. What am I missing? I see your compressed and extended measurements would change, but I dnot see how the difference between those two measurements is changing.
Unless you’re saying the travel isn’t changing, just the shock measurements are to accommodate the bigger distance, but the lift kit isn’t using any more or less of of the travel?

I want to go with the Camburg upper arm and the uniball should have more than enough range to not be the limit. I suspect the UCA frame stop will quickly become the down travel limit, especially after I crank it up to clear 35s. Have you found or seen a good way to attach a limit strap to the lower arm?

 

[fl0w3n]

I just realized... it’s all in the spindle, isn’t it? I forgot about lift kits using a different spindle. That would change the distance between the upper and lower arm and then change the motion ratio like you said.

If that’s the case, can I fit a Cognito 4-6 spindle on an otherwise stock front end, and would I gain motion ratio and increased travel?

 

[N2BRK]

Just my $0.02 on Fox 2.0 Res. 2yrs and 20K miles of pure pavement and one was terribly blown out and another was weeping. Fox says that's normal service life and I should expect to rebuild them annually. They're still sitting in the corner of my garage. When new they rode very plush but bobbed around on the highway more than I'd like. If they'd hold more than a couple years, I'd revalve and rebuild them... but f- this annual rebuild crap. https://www.duramaxdiesels.com/forum/threads/no-more-fox-for-me.83073/#post-1138798

 

[Chevy1925]

That’s exactly what I was looking for. Even at a measly 6” of stock travel, that 980-24-663 shock would limit it with only 5.1” of travel.

I’d be amazed at pulling 12” out of a stock front end, without even considering tire size.

I get that some kits only move the lower arm down, but I still don’t understand- even if the top arm and bottom arm were ten feet apart, the location on the arc that the shock is mounted to on both the top and bottom doesn’t change, and the lower arm doesn’t get longer, so I don’t see how that 2:1 would change. What am I missing? I see your compressed and extended measurements would change, but I dnot see how the difference between those two measurements is changing.
Unless you’re saying the travel isn’t changing, just the shock measurements are to accommodate the bigger distance, but the lift kit isn’t using any more or less of of the travel?

I want to go with the Camburg upper arm and the uniball should have more than enough range to not be the limit. I suspect the UCA frame stop will quickly become the down travel limit, especially after I crank it up to clear 35s. Have you found or seen a good way to attach a limit strap to the lower arm?

this to an extent. if your lift comes with different upper arms, you will gain some travel as the uca will allow more down travel. the lift kit is only going to use factory travel or a slightly more if it has aftermarket uca and aftermarket shocks. your biggest hurdle is getting a shock that moves enough on a stock truck to net you 12" of wheel travel, thats the only benefit a lift kit can net you OR if you make your own frame mount for the shock.

I just realized... it’s all in the spindle, isn’t it? I forgot about lift kits using a different spindle. That would change the distance between the upper and lower arm and then change the motion ratio like you said.

If that’s the case, can I fit a Cognito 4-6 spindle on an otherwise stock front end, and would I gain motion ratio and increased travel?

The knuckle affects the cycling of the arms and what camber/caster/toe change happens through it, it wont add more travel. No, a 4-6" knuckle on a stock truck is not a good idea. it will throw proper suspension geometry out the window lol.

camburg arms should give you enough motion in the arm to net 12" of wheel travel but i have not verified them. Just make sure there is enough shock travel range to fit your extended and compressed lengths.

 

[Chevy1925]

Just my $0.02 on Fox 2.0 Res. 2yrs and 20K miles of pure pavement and one was terribly blown out and another was weeping. Fox says that's normal service life and I should expect to rebuild them annually. They're still sitting in the corner of my garage. When new they rode very plush but bobbed around on the highway more than I'd like. If they'd hold more than a couple years, I'd revalve and rebuild them... but f- this annual rebuild crap. https://www.duramaxdiesels.com/forum/threads/no-more-fox-for-me.83073/#post-1138798

he has another thread we discussed about this issue. the silver body shocks are not nearly as good as their steel body counterparts used for racing. without taking one of those apart to see how they designed it, i couldnt say how long it will last after a rebuild.

these will far outlast the cheapies

Smooth Body

With racing in its DNA and good times in its blood, FOX has enjoyed 50 years of going fast and taking chances. From twisting throttles to spinning pedals, we love all things on wheels. Buy your official FOX Factory suspension, apparel and accessories. Free delivery on orders above $99.

www.ridefox.com

 

[N2BRK]

I hope so, though I have to say that when I see "race" I think made for regular breakdown and refreshing throughout the season

 

[Chevy1925]

I hope so, though I have to say that when I see "race" I think made for regular breakdown and refreshing throughout the season

being how many shocks ive rebuilt and ran from fox, king and sway away, i know where those stand over the chinese silver 2.0's. you get a double sealed seal head, larger bearing in the seal head, option of 7/8 shaft on some 2.0 shocks (better for low motion ration vehicles), better flowing piston with more options as far as bleeds and usually tapped for bleeds off the bat, good surface area on the wear bands for the IFP and piston, steel body's and FK uni-ball's in the ends. you also get a higher quality seal (usually viton, not buna) and better oil.

i had fox 2.5 coilovers on my old truck, ran them for 3-4 years before anthony bought it and never touched them other than checking nitrogen once a year. The SAW's on my tracker had a hell of a time holding nitrogen and after a complete rebuild, have 20k on them and no issue. The rear foxes on it have 20k with no issues and we are talking about a rig that see's far more dirt time than it does street time. the sand cars front shocks have not been touched other than nitrogen in 6 year, no problems. rear shocks only come apart for valving testing, same with the tracker.

"race" is a better quality shock, it does not mean more work. you are not working these shocks to the point of needing a rebuild after every race.

there are 2 major issues with shocks that you need to watch for on any nitrogen charged shock. 1st, ANY kind of damage to the shock shaft. if there is any dings, chips or large scratches in it, it will take out the seal head in a hurry. this is caused by rocks or installer not paying attention or working on something around them and they get hit. 2nd is nitrogen level. you let that fall off and cavitation starts to happen to the piston, seals start to fail as air is drawn through them along with dirt which then kills the seal and you loose all your dampening.

 

[fl0w3n]

Just my $0.02 on Fox 2.0 Res. 2yrs and 20K miles of pure pavement and one was terribly blown out and another was weeping. Fox says that's normal service life and I should expect to rebuild them annually. They're still sitting in the corner of my garage. When new they rode very plush but bobbed around on the highway more than I'd like. If they'd hold more than a couple years, I'd revalve and rebuild them... but f- this annual rebuild crap. https://www.duramaxdiesels.com/forum/threads/no-more-fox-for-me.83073/#post-1138798

Interesting, thank you for the input. I kind of am planning on having these as "temporary" while I budget to go bigger one day, but I don't know when that day will come.

Can you elaborate on bobbing? Do you mean when the rear end gets kind of light and hops/skips around on a bump/turn? Or do you mean bouncing like a low rider after hitting a whoop?

 

[fl0w3n]

this to an extent. if your lift comes with different upper arms, you will gain some travel as the uca will allow more down travel. the lift kit is only going to use factory travel or a slightly more if it has aftermarket uca and aftermarket shocks. your biggest hurdle is getting a shock that moves enough on a stock truck to net you 12" of wheel travel, thats the only benefit a lift kit can net you OR if you make your own frame mount for the shock.



The knuckle affects the cycling of the arms and what camber/caster/toe change happens through it, it wont add more travel. No, a 4-6" knuckle on a stock truck is not a good idea. it will throw proper suspension geometry out the window lol.

camburg arms should give you enough motion in the arm to net 12" of wheel travel but i have not verified them. Just make sure there is enough shock travel range to fit your extended and compressed lengths.

I think I'm still missing something because I don't see how the shock is the biggest hurdle on pulling the travel.

I can see if the Camburg or other UCA has a curve to it on the vertical plane that it can avoid contacting the frame until later in the cycle, but that looks like maybe 1" between the UCA and frame stop and at a 2:1 ratio that would give you 2" if you removed the shock as the limit (in this photo). Which, as I type out, I'm realize gaining 2" by just changing out shocks is a big difference.

I plan on pulling a torsion bar and a shock and doing some cycling and measuring before I order.

 

[fl0w3n]

he has another thread we discussed about this issue. the silver body shocks are not nearly as good as their steel body counterparts used for racing. without taking one of those apart to see how they designed it, i couldnt say how long it will last after a rebuild.

these will far outlast the cheapies

Smooth Body

With racing in its DNA and good times in its blood, FOX has enjoyed 50 years of going fast and taking chances. From twisting throttles to spinning pedals, we love all things on wheels. Buy your official FOX Factory suspension, apparel and accessories. Free delivery on orders above $99.

www.ridefox.com

I was looking for that chart the other day that has all the collapsed and extended lengths.

Unfortunately those are kind of out of the budget right now, like I mentioned in another thread. I think it's more important to get a base platform to build off of right now, meaning I'm shooting for at least front/rear shocks, a deaver mini-pack and probably a re-arch, and wheel tire package to last me a year or two. The race series shocks without the deavers or wheel/tire package would be kinda silly. I was thinking of keeping the UCA for a later date, but after this discussion I'm seeing it as more critical to happen at the same time as the shocks...especially if I go with something bigger than the 980-24-663 for "0-1" of lift

Long term I imagine stepping up the shock package and going to a full deaver pack, and maybe even converting the front to coils from torsion. Or...using the cad files from Pirate and doing a SAS with an 05+ SD60

 

[N2BRK]

Interesting, thank you for the input. I kind of am planning on having these as "temporary" while I budget to go bigger one day, but I don't know when that day will come.

Can you elaborate on bobbing? Do you mean when the rear end gets kind of light and hops/skips around on a bump/turn? Or do you mean bouncing like a low rider after hitting a whoop?

I think it’s in the low speed compression; seems too soft. So it would bob around on the freeway with small imperfections.

 

[N2BRK]

""race" is a better quality shock, it does not mean more work. you are not working these shocks to the point of needing a rebuild after every race. "

Obviously, you have about the most experience here with these. I was tongue-in-cheek about hearing race and thinking regularly rebuilt, because the racing goal is usually perfection and zero stiction and not longevity beyond race day when it gets refreshed If they're better and last longer, then great! Win/Win.

 

[Chevy1925]

I think I'm still missing something because I don't see how the shock is the biggest hurdle on pulling the travel.

I can see if the Camburg or other UCA has a curve to it on the vertical plane that it can avoid contacting the frame until later in the cycle, but that looks like maybe 1" between the UCA and frame stop and at a 2:1 ratio that would give you 2" if you removed the shock as the limit (in this photo). Which, as I type out, I'm realize gaining 2" by just changing out shocks is a big difference.

I plan on pulling a torsion bar and a shock and doing some cycling and measuring before I order.


View attachment 104480

if you are at stock height, and it measures 14" from frame mount to lca for a shock, then you compress the suspension to full droop and measure again and get 3", you will never find a shock that fits those measurements because you would need some kind of extendable shock body, no such thing. so you either run a shock that has a collapsed measurement of 3" or an extended measurement of 14", then limit the opposite end. the pic above is a good rendition of "limit droop to allow full compression". This is an extreme variation of what you normally find but its not far off from what i have seen before. If you HAVE to stay in the confines of stock parameters, the shock limits your travel. on a stock truck, i believe a 5" stroke shock works but you will be limited on your up travel or "bump" area. 3.5" is just too short.

when you lift the truck with an actual lift kit, you open up that distance between frame mount and LCA letting you run a shock with more stroke without the worry of the body being too long.

 

[fl0w3n]

Okay yes now I understand.

I think my best bet is to pull a torsion bar and shock and start cycling and getting measurements. Unfortunately I’d kinda need an aftermarket uca in there to really get the right shock measurements.

it looks like Cognitio already offers a limit strap for the truck, I’m guessing it just mounts off the lca shock tab ? Probably not a great long term solution but good to start

 

[fl0w3n]

I thought I had a torsion key puller but I either misplaced it or returned it.

but even still, my concerns were confirmed when I cycled the front with out the shock, sway bar, or bump stop.
I got 17” extended length even with the stock UCA.
So going with the 980-24-663 with even a stock UCA would be limiting down travel.

I got 14” compressed but that’s kinda irrelevant because the torsion was still in there and started to lift the truck at one point instead of cycling. So, unless there’s less than 3/16” of up travel left, if I went with the 980-24-658 I am risking blowing the top off the shock by using it as the bump stop.

 

[fl0w3n]

@Chevy1925 what do you think about this idea...I’m probably way over complicating things here... but this is what I’m mocking up in my head.

Ballistic Fab (& others) sell a eyelet conversion for the earlier Dodges.


If I just got an extra large step bit and hogged the stud hole on the Duramax out to pass a 2.0 or maybe even a 2.5 through, and then welded or bolted the eyelet conversion on top of the stock tower, I should gain 3.5” of available shock length.
I then for sure would be able to select a shock that would not limit the travel, and at that point (after UCA & limit straps) I’m sure my limit would be what I could stuff in the stock fenders

 

[fl0w3n]

Well, for $80 I figured I'd see if that Ballistic tower is even close to fitting so I ordered it up. I'm thinking if it is close to fitting, like maybe with the "legs" bent in a little more, then hogging a hole into the top of the stock shock tower and welding the Ballistic tower on top is still easier than a custom shock tower.

The Ballistic tower is 3.5" from mounting surface to CL of shock bolt, so the 17" I measured + 3.5" gives me at least 20.5" extended length and that's with the stock UCA. The big question is what do I need for compressed then. I'll need to find/get a torsion key puller to know, but I'm thinking maybe I could get 13.8" to work.

With all that being said... seems like a lot of work overall for 8" of travel ha. Maybe I should have just gotten into F250's instead and bolt on a Carli kit and be done with it...


Edit: going with the smallest collapsed number I can find for a factory application of front shocks, I'm seeing 10.70". So if I assume that's safe and most up travel number I've seen, if I add the 3.5" for the Ballistic tower to that, that's 14.2". Those 8.5" might even be able to work in there.

 

[Chevy1925]

8” stroke shock is over kill. 6” is plenty. Remember, 2:1 motion ratio. 6” shock = 12” wheel travel.

Btw, those “should” have a 1” spacer under under piston. You can remove that for more down travel with no hurt against full bump. I’m not 100% confident the 2.0 6.5” stroke 5/8 shaft shock will have that size spacer or one at all but they usually do to help keep leverage off the shaft at full droop so the shaft doesn’t bend but in your case, you won’t have that extreme amount of angle.

Until you find full bump, your kinda pissing in the wind on what may work. I have notes at work but I think full bump is around 12.75”. I’ll check if I have time tomorrow.

As for the towers, add braces down the edges of the stock frame mount so it grabs more of the vertical side of the frame. Your adding leverage and a good hit where the shock bottoms before the arm due to a mis measurement or something moving that shouldn’t will bend that mount. Street truck, no worries, off road she needs it