Sprinter 4WD Conversion Idea, GMT-800 IFS.

luthj

Adventurer
Greetings and happy new year.


After pursuing several other avenues, I have narrowed in on a 4WD conversion approach for my 2004 T1N sprinter. The Sprinter presents some unique challenges. It is a unibody, and uses McPherson strut front end. Instead of coil springs, it uses a transverse leaf spring built into the subframe.

My goals were as follows.
  • Easy to source parts strong enough for a 9klb vehicle
  • Minimal or no modifications to the unibody
  • No custom wear parts
  • Minimal machining work
  • Stock handling and ride
Having had good success with GMT-800 (GM trucks/SUV from 1999-2006) vehicles, I zeroed in on them due to similar specs to the sprinter, and torsion bar springs. The 2500 series front ends are roughly the same track width, and have beefy enough diff/axles, bearings, etc for our sprinters 3,600lb front end.

I have done some initial rough modeling, and it is looking quite promising. I will use laser/plasma cut steel plate to fabricate a bolt-on subframe. This will accept a complete GM front suspension (without upper A-arm and shock).

Subframe Rough Iso.jpg
Subframe Rough.jpg

Ride height will be 2" taller than stock. The sprinter steering rack will be retained, and moved up and forward. Tie rods will be custom, or use adapters for the GM joints.



What about the upper A-arm? Well I am planning on modifying the GM spindle/knuckle to bolt to the sprinters strut. The upper BJ stub will be cut off, and a bracket with camber adjustment and standoff studs will be welded on.

Spindle Cut.jpg

The GM IFS has a smaller distance between the wheel mounting flanges than the sprinter. So there should be enough room for a wheel adapter to the sprinters bolt pattern without changing the track width much from the ~65".

As far as gear ratios my sprinter is 3.725, the common GM 3.73 gears should work great. The other common sprinter ratio is 4.11, which is also common on GMT-800s.

I plan on using the GM torsion bars, and aft torsion bar member. Riser brackets will be used to attach the torsion bar anchor to the sprinter.


For the Tcase I am looking at a married NP242 or similar. The sprinter uses the NAG1/WA580 trans. My plan is to swap the sprinter internals to a jeep main case and adapter housing. (same as 2012+ wranglers).


Other random changes. The fuel tank will like need to move back 6" or a bit more. New tone rings/bands will likely need to be made and attached to the inner CVs. The sprinter uses 44 tooth rings. I think the GM hubs use 55 tooth, but have not confirmed.
 

mgmetalworks

Explorer
Would it be less work to fabricate the knuckle and use the Sprinter's unit bearing? Not sure what you'd have to do to adapt the axle but maybe you'd get lucky. This will be interesting to follow. I've been through a lot of the challenges you're working through right now while designing our Transit 4x4.
 

broncobowsher

Adventurer
If you used the Sprinter unibearing you would need the Sprinter outer CV to match the splines. At this point you can probably just get custom shafts made to marry the GM inners to the sprinter outers. Nothing a stack of $100 bills won't fix. Now figure how tall of a stack you would need.
 

Len.Barron

Observer
starting with a donor that had a lift on it would be helpful, using the bolt on drop cradle and torsion bar relocators could reduce fabrication quite a bit. I'd stay with the entire stock GM spindle, unit bearing ect... and just solve the tone ring issue. you have the room for wheel adapters so no reason not to use them..
 

luthj

Adventurer
cool project...way to blaze a new trail! with the extra weight the 4.10 gears would definitely be a blessing..
The NAG1 has a .833 5th, and I am running 31" tires. With the diesel I find driveability to be good. If I went with a larger Tire would likely switch gears. With the GM vehicles having a center axle disconnect, I have the option of 2WD low range. I think this is a great feature, as it keeps trans temps and stress down with low speed driving.

Would it be less work to fabricate the knuckle and use the Sprinter's unit bearing? Not sure what you'd have to do to adapt the axle but maybe you'd get lucky. This will be interesting to follow. I've been through a lot of the challenges you're working through right now while designing our Transit 4x4.
If you used the Sprinter unibearing you would need the Sprinter outer CV to match the splines. At this point you can probably just get custom shafts made to marry the GM inners to the sprinter outers. Nothing a stack of $100 bills won't fix. Now figure how tall of a stack you would need.
4WD early sprinters were never sold in north america. Even if I could get the parts from europe, I would still need to lift the van significantly to clear the transverse leaf spring at the diff. That leaf spring takes up a lot of space that a diff needs.

I considered custom knuckles, as that would allow bolting on the sprinter strut. The cost of machining some would be pretty significant. I figure I can CNC plasma cut a set of brackets that I could weld to the GM knuckles in 30 minutes.


starting with a donor that had a lift on it would be helpful, using the bolt on drop cradle and torsion bar relocators could reduce fabrication quite a bit. I'd stay with the entire stock GM spindle, unit bearing ect... and just solve the tone ring issue. you have the room for wheel adapters so no reason not to use them..
Initially I thought a lift bracket set for the GM would be a good place to start. However, I need to mount the diff and sprinters steering rack. The GM vehicles mount all that to the frame rails. Once all the mods to attach those were finished, It would be easier just to fab from scratch.

The tone ring needs are definitely solvable. I could laser cut a band with windows, and wrap the inner/outer CV body with it. Then place the sprinters speed sensor on a bracket perpendicular to the axle.


I think a 1500 series front end would be adequate (and much easier to source). However I only want to do this once. So a 2500/3500 front end is much heavier built. 9.25 diff vs 8.25", heavier A-arms, much beefier hub/bearing assembly.

The real advantage of this approach is that parts are dirt cheap, easy to source, and mods/aftermarket is good. This includes lockers and LSD diffs if desired. Heavier CVs, etc.

I am basically at the point where I need to find a donor. I don't have the space to park a donor right now, and the local yards just don't buy 2500 series trucks.
 

luthj

Adventurer
Continued refining the model. Everything should fit pretty well. The two main areas that will be challenging are the rear cross-over and engine mounts. The drivers side diff mount is pretty low, so the crossover may need dropped, or the mount incorporated into it.

The engine mounts are farther back than the front crossover, and will be tight with the steering rack mounts. Both will be a bit complicated to model I think. The copper colored A-arm is the factory A-arm as it sits on my van (2" lift from stock).

My goal is to allow the diff to be dropped without removing the subframe.


Revised 4.jpg

1546463884571.png
 

Len.Barron

Observer
while I didn't look closely into it, the GMT-900 front diff is reported to be a much easier to retro-fit design and allows more clearance at the driver-side mount, it might fit your desire for drop out capability better..
 

luthj

Adventurer
while I didn't look closely into it, the GMT-900 front diff is reported to be a much easier to retro-fit design and allows more clearance at the driver-side mount, it might fit your desire for drop out capability better..
Interesting. I did notice that many GMT900 parts crossed over. brakes, knuckles, etc are all very similar. I will see what the 9.25" diff looks like on the 07+ 900s.
 

luthj

Adventurer
Here is a side view of the 9.25 diff. Best I can tell without pulling up the OEM parts catalog, GMT-900 and 800 2500/3500 both use the same diff. The CAD actuators are different though.

 

luthj

Adventurer
Thanks, totally missed that. That may be easier to work with. Maybe a U shaped inverted cradle type thing? At least I have options. Though the 900 parts are harder to find used.
 

Len.Barron

Observer
Thanks, totally missed that. That may be easier to work with. Maybe a U shaped inverted cradle type thing? At least I have options. Though the 900 parts are harder to find used.
yeah, a little easier to fab to that design...diff case would be a one time purchase and there are just as many of them on the road now as the older ones...if it was a wear item I'd probably be more critical..
 

luthj

Adventurer
Got some better measurements. Interestingly GM uses a non-parallel lower control arm pivot. Its angled inwards about 2 degrees.

The Diff looks like its going to clear without issue.



The upper driver's side mount is going to be hard to pick up. I was looking at GM lift kits, and they cut the mounting boss off, and bolt on a lowering bracket. The brackets aren't expensive, so that is one route to get everything lined up.



The rear/lower mount is roughly centered in the cross over. So I am going to incorporate it in to the cross over. Possibly make the cross over bolt on.

The donor search continues...
 
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