Sprinter 4WD Conversion Idea, GMT-800 IFS.

[Pinnacle Campers]

If I had a decent shop, and a CNC plasma cutter,

How about working a deal with someone (like VanCompass?) to fab this and potentially sell as a in shop install/or DIY kit for the masses?

 

[Paddy]

I frequently have laser cutting done right down the street and I’m a pro welder with shop. I’d be interested in helping this project along.

 

[luthj]

How about working a deal with someone (like VanCompass?) to fab this and potentially sell as a in shop install/or DIY kit for the masses?

The early sprinter just isn't common enough, plus most folks aren't interested in the investment on a 14+ year old van. Though if they were interested, I wouldn't say no to a royalty on every sale... I focused on making the design easy for me to assemble/fabricate. So it would need some significant tweaks to be cost effective for someone who pays market rate for labor.

I frequently have laser cutting done right down the street and I’m a pro welder with shop. I’d be interested in helping this project along.

Thanks for the offer. I have a few contacts for getting metal cut (not for free sadly). I need to get some alone time with a disassembled sprinter, which is the major hangup getting the design ready for prime time. I will hopefully be starting work again in a month or so. While that means less free time, I will be able to acquire a place to work on the van (as I will no longer be living in it!).


On the shock front, I snagged a fox 2.5 coilover model and modified it to approximate the 2.0 coilover. It depends on spring OD (depends on rate), but it looks pretty good. The factory UCA has a little bit of contact at full droop. Easy enough to rectify with a die grinder and welder.



The factory bumpstop has to go. So I will just make one integral to the shock.



Just a little contact at full bump. Looks like about .2-.35" needs removed from the fillet/edge area.

 

[Pinnacle Campers]

The early sprinter just isn't common enough, plus most folks aren't interested in the investment on a 14+ year old van. Though if they were interested, I wouldn't say no to a royalty on every sale... I focused on making the design easy for me to assemble/fabricate. So it would need some significant tweaks to be cost effective for someone who pays market rate for labor.

I had/have confidence in your ability to (with significant tweaks) apply everything to the NCV3 (2wd) Sprinter.

 

[luthj]

I had/have confidence in your ability to (with significant tweaks) apply everything to the NCV3 (2wd) Sprinter.

Thanks for the vote of confidence. I would enjoy going that route, maybe when I have a proof of concept?


Repackaged the GM bumpstop. Not quite what GM intended, but should do the trick.



I shifted the shock to nearly vertical in the front plane. I also moved the UCA forwards to get the caster back into spec. Good news, no more interference with the UCA. Now obviously there is a fair bit of camber adjustment built in, so at max (GM allowed) camber adjustment, the UCAs would need trimmed. That should only be necessary at low ride height, or if I totally screwed up some measurements somewhere.

 

[b dkw1]

You would be much better off moving the lower shock mount out and making a new shock tower to fit a longer shock. Your motion ratio is pretty close to 2-1. This will be really hard on the shock. Also with springs that heavy you will run into coil bind issues. 2.0's witth that much load on them will also have a short life, rebuilds will be frequent. 1.5-1 is the sweet spot.

 

[luthj]

You would be much better off moving the lower shock mount out and making a new shock tower to fit a longer shock. Your motion ratio is pretty close to 2-1. This will be really hard on the shock. Also with springs that heavy you will run into coil bind issues. 2.0's witth that much load on them will also have a short life, rebuilds will be frequent. 1.5-1 is the sweet spot.

I agree, the best choice would be a lower motion ratio, and a 14-16" spring. I could possibly package a 6.5" travel shock. I don't see any simple way to move the shock farther outboard. I could maybe get another 1/2", but any farther would require a custom LCA.

My motion ratio is 0.596:1 or 1.67:1 So not quite 2:1. I could get that down to maybe 1.6 without major changes. Not ideal but GM thought it was an acceptable trade off for on-road usage.

I was looking at springs in the 700-800lb/in range. With silicon alloy wire, the solid height for a 2.5"x12" spring is about ~6". I need 4.55" of shock for 8 at the wheel. With .75" of preload, that leaves 6-4.55-.75 =0.7" before solid. With decent thrust bearings would binding be an issue on a coilover (non strut)?


I will give the 6.5" fox coilovers a look. They cost about the same, so I don't mind trying to fit them. I would need to remove most of the MB strut tower lower brace, but thats just spot welds and adhesive.

 

[luthj]

I was looking at the fox 2.5 factory series. They might fit with an offset lower mount bracket. Height is cutting it close. They would probably need a high clearance UCA. BDS makes them for its coilover kits, so they do exist, but are likely quite expensive.

 

[Len.Barron]

Just for ideas on using stock control arms:

 

[luthj]

Finally retrieved my spare steering rack. I should have everything I need to mockup the rack/diff and LCA positioning.



Here is what the 2500 lower shock mount looks like. It is a lot more friendly than the 1500 mount for coilovers. A slightly beefier version from 0.25" plate would do the trick I think.

 

[luthj]

Updating the steering rack in the model. Looking good thus far. My initial measurements were fairly accurate. The rack end spacers are about 1.25" long now. That will allow using the GM tie-rod without any modifications.



There may be some interference between the rack bushings and the diff. Since I am attaching the rack from the opposite side, I can trim down the bushing if needed for more clearance. The hard lines are my major concern, as they run along the back. I will mock up the rack today possibly, to see how it fits against the diff. Its 20F currently, so my motivation is low.

I dream of a heated/cooled garage with 11ft door...

 

[luthj]

After spending some quality time with the steering rack, and doing some rough FEA and math on the rack end spacers, I don't think they are a good option. On the PS side the offset spacer would be okay, as there is a beefy bushing, but on the DS there is just the pinion and preload spacer. My math puts the racks power assist at ~750lbs. Assuming dynamic loading will be 2.5 times that creates 170ft-lbs of torque on the rack gear. The pinion just isn't made for that. I could make a support bushing, but I don't see it having OEM level reliability. Part of this is due to the offset. I had to go to 1" of offset due to the larger 18mm thread GM used (there is a grease bore down the middle).



So I am stuck with whatever ackerman my rack placement allows. The good news is with the GM LCA angle, my ackerman is 60% at full lock. 100% ackerman would be 5.8 degrees, and I am at 3.5 degrees. Not ideal, but will be tolerable.



The MB rack is a bit narrower than ideal for bump steer. So I will still be using a rack-end spacer (around 1.5-2") but without the offset. This will allow using the GM tie rods. I will need to source a boot for the rack ends though. I might be able to modify the MB boots and machine a collar into the spacer. Shouldn't be hard.

The MB rack with MB tie rods has 6.5" of travel. I don't think the outer CVs will tolerate more than 6", but I will check before I make a limiting spacer. The GM tie rods are pretty thin, MBs are 5mm thicker (they are a bit longer).

I have the bump stop aligned pretty close as well.


I will likely get the diff and rack mocked up this week. If everything goes to plan, I can move on to the rack mounts.

The fox 2.0 5" travel units are looking pretty good. The will allow 8" of wheel travel, and should be up to medium duty service. There are some cheaper double tube coilovers, such as the DS701 etc, which could be used by the budget conscious. I would love fox 2.5s but perfect can be the enemy of good. If I need to rebuild the shocks every 30-40k miles, I think thats an acceptable trade off. I have beat the crap out of my current set of fox 2.0s, currently at 60k miles. Other than a bit of oil seep, at one, and a few failed bushings, they still work great.

One issue is that the 5" travel unit is only available in 5/8" shaft. Am I going to regret the 5/8" vs 7/8" shaft? The shock is only 17" long or so.

When it warms up I will pull measure the MB wheel speed sensors. If they will fit on the diff flanges, I will work up some tone wheels. Either weld on, or bolt on. Then I can move on to brake fittings/lines, etc.

A friend says he can get me the Tcase adapter housing, and a Jeep NAG1 main case. So I will hopefully see those in the mail in a month! Once I have some free funds, I will put a big order in for other parts. Bushings, UCAs, bearings, brakes, trans overhaul kit, shocks etc. That way I can do final measurements of everything before I pull the van apart.

 

[b dkw1]

Ackerman is good for driving around the parking lot.

You will be fine with what you have.

 

[luthj]

Did a quick model with 245/75R16s. Clearance looks good.



With 6" of rack travel, I may have some light rubbing at full lock and full droop. This is with a ~40mm ET wheel. Track width would be ~67".






I think the GM factory wheel is ~ET25.

 

[luthj]

The sun came out for a bit, so I got to hacking on the Diff and rack. The rack will fit where I need it to go. One of the bushings/bosses needs trimmed about 0.5". The cylinder lines don't clear around the input shaft. So either new lines need flared/bent, or the existing lines need a significant tweak. I may see if I can source some rubber lines with elbow fittings? These look like brake line with a DIN flare, and metric nuts. Should be easy enough to source some copper/nickle tubing and flare tool.

I am still trying to dial in my bumpsteer. The last round of changes screwed it up (almost 1.5 deg in bump).