Sprinter 4WD Conversion Idea, GMT-800 IFS.

[luthj]

Contorted my arms into the engine bay, and took some measurements of the rack input shaft. Its miles better than the E series engine bays, but still lots of crap in the way. Turns out I have more clearance than I thought. The rack is now rotated back about 20 degrees from its factory orientation. So I get a bonus 3/8" of clearance at the diff! The original lines may even clear, which is even better. Some of it depends on what angle I need the pinion at. It may need to come up another 1-2 degrees to line up with the Tcase.




This is where the magic is happening. About half the head scratching on this project was getting these 4 parts close, but not too close. Rack, diff, oilpan, and subframe brackets.

 

[luthj]

The risks of working with rough models, and measuring on your back, are translation errors. In this case I forgot to include the offset of my skid plate (used as a reference from the LCA pivot).



Just a little bit of interference there. So the diff needs to come down. I need to triple check my measurements before I do all that work though. I can drop the diff a bit, and then lower the entire subframe some. I am trying to avoid the bro-dozer lift. Currently its about ~2" from stock, but that will need to increase some. Should be a pretty easy set of changes, assuming I didn't screw up and use the wrong references for my sketches...

 

[luthj]

Well that was fairly painless. Added an inch to the subframe height, dropping everything down.



Looks good, but a lot depends on pinion angle and the draft angle on the casting. Pretty impossible to measure in-situ currently. Worst case I need to do a bit of clearance grinding on the Diff. I could shift the diff to the DS by 3/8". I may need CV spacers anyways, so that would be pretty simple to work out.

 

[b dkw1]

Nice shock tower!

Might want to put clearance hole for the bolt through the outer webs. If the bolt gets stuck it can be a pain to get out without them.

 

[luthj]

I won't likely be incorporating this, but a lift knuckle and tubular control arm would likely allow using a fox 2.5 factory series coilover. The shock tower would be right at the top of the wheel well (depending on lift needs).

 

[b dkw1]

You would not regret going to a 2.5 in the long run. You may however regret sticking with the 2.0.

 

[luthj]

You would not regret going to a 2.5 in the long run. You may however regret sticking with the 2.0.

Important considerations. Part of my initial design scope was to keep costs minimal, reduce chassis mods, and avoid custom parts where possible. The 2.5 would probably require removal of significant portions of the fender wall, and a tube UCA.

Considering that many (most?) owners running 2500 GM trucks have ~2" shocks, I don't see the need, at least for my application. I don't flog my rig enough to justify the cost and difficulty.

Now, if someone wants to go the 2.5" shock route, I could likely make it work, though it may require another 1" of lift.

 

[luthj]

I am on the road for a, so the mockup with diff/rack/LCA will need to wait a bit.

I decided to use a combination of a spacer/shim and a slot for the rack positioning. This allows me plus/mins 0.2" to dial in the bump steer, and plus/minus 0.125" for diff clearance.



Still refining the detail work. Taking the time to educate myself on various high level fuctions in solidworks. Configuration management, linked features etc. Because a good number of the nested cut-outs are non-normal to the sheetmetal face, I will need to go through and convert solids to sheetmetal, and perform adjusted normal cuts. The lases/plasma cutting process can only cut normal (perpendicular) to the sheetmetal surface, so any non normal surfaces will mess up the profiles I will send to shop.

 

[b dkw1]

Considering that many (most?) owners running 2500 GM trucks have ~2" shocks, I don't see the need, at least for my application.

99.9% of those are not coilovers either.

 

[Len.Barron]

99.9% of those are not coilovers either.

I'm going to agree with the idea of using the 2.5 and tubular upper, both are really in-keeping with your desire to first be reliable/durable, second to be easily maintainable(since you're drifting from stock with the coilover to begin with). The 2.5 will be dramatically more durable, and, on the odd occasion of a complete shock failure it will take no more time/effort to get it/change it than the 2.0. The tubular uppers are not wear items themselves, they typically come with bolt in grease-able ball joints and easily replaced urethane bushings, those parts are very easy to get and wouldn't be a particular burden even if you wanted to keep a spare set. Changing bushings on a factory UCA is an absolute PITA and the reason most just buy new arms... I'd also offer that as many times as I've built 4wd vehicles and told myself "I'm only going to run a 33" tire!" I inevitably end up with 35-37" tires a few years later. I'd build in the ability to drop the differential another 1.5", even if you don't use it, when you re-sell it, it will be a huge selling point.

 

[Raul]

"I'm only going to run a 33" tire!"

I LOL.

Luthj. I am loving this project

 

[luthj]

I appreciate the feedback. The primary issue with the 2.5" shock is length. The cabin floor limits total shock length to ~15.5" at max bump. Because of the ~4.2" diameter of the coil The lower eyelet needs an extension to clear the axle shaft. About 1.5" taller than the short eyelet that's standard on most 2.5s.





The universal 2.5" is available in 6" stroke.
Fox 983-02-101 ext:19.5" Comp:13.55" 13.55"+1.5= 15.05
With DSC 983-06-101 These are $650 each, plus springs and new lower eyelet. Obviously they would need tuned by someone who knows there S&*$t.

So it will just barely fit. I would need to remove the entirety of the MB strut support. Which would take the kit past bolt-on, into permanent mod territory. I would also need to increase the tower height by 4", which would require a fair bit more support. I am having trouble finding specs on a tubular UCA. BDS supposedly has one for their coil kit, but if it has a weird offset/angle it may not work with the factory knuckle. The factory UCA might work with some light modification. Not ideal though.

Fox also sells a variety of 2.5" units for the aftermarket (application specific). Most seem to have a 2-3" extended eyelet. So I could drop 1-1.5" with an eyelet swap. Of course these come with a spring that would likely be wrong.

883-06-093 EXT: 21.19 Comp: 16.10 Trvl: 5.09"


Here are the fox eyelets. Looks like 1" increments.

Fox 7/8" Coilover Shock Shaft Eyelet | POLY PERFORMANCE

Fox 7/8" Coilover Shock Shaft Eyelet

www.polyperformance.com

Part # Shaft Length
213-01-237-A 1.950"
213-01-235-A 2.950"
213-01-337-A 3.950"
213-01-330-A 5.260"


So it seems possible, expensive comparatively, but possible. To be clear, there is no catastrophe waiting from using a 2.0. The factory coilovers used on the 1500 trucks (08+?) are 2" or smaller.

 

[b dkw1]

If you went King's (bro), they have an over the body top cap which reduces the body length by an inch or so. You can also get a longer shaft with a welded eyelet that will clear the axle.

If your going custom on the shocks, Kings take about half the time to get over Fox's.

I believe JD fab makes a upper arm for those, might be worth a call. Jesse has done more Cheby 4X kits than he can remember.

 

[luthj]

Thanks for the info. Looking at Kings options (scattered about the web, terrible really). The over-body top cap is only available on the 8-12" travel units. Also kings travel numbers on the coilovers do not count the spring plate thickness. So there are some complications to building a shorter 6" travel coilover.

Looks like both fox and king offer a raised lower spring plate. About 1-1.5" extra on the king, fox has 2-3 options from 0.6-2.6" rise. I need to check spring binding heights, but a fox 2.5x6" unit with 1.5" riser would let the spring clear the axle. Fox P/N 23400239A is 1.4" rise, which is just about perfect. Though the perch might need light clearancing. This would mean no riser eyelet, so no increase in shock height. I could always machine a custom riser, but I want to avoid if possible.



For the curious, here is a comparison of a 2.5 and 2.0" shock piston.

 

[luthj]

It looks like Icon sells a 01-10 2500 UCA. $800 a pair... I guess it does have the high angle spherical. They may require larger wheels, which is undesirable.


The 2011-2018 GM 2500 UCA looks promising. Its much lower profile, and made of cast steel. Is the BJ the same taper/length? If not, can it be swapped for the earlier version? Assuming its roughly the same overall length/width, I can adapt my model to accommodate it. The late style looks to be narrower between the bushings. For 60$ it might be worth ordering one just to measure.



Here is the early UCA, its formed/welded steel sheet.


The early ball joint taper/shaft looks pretty similar to the later style. It looks like the later upper BJ is not replaceable?