Sprinter 4WD Conversion Idea, GMT-800 IFS.

[luthj]

I got a line on a local 1 man shop ( its a big steel building in his back yard) who does shafts locally. Going to get over there when I have some time.

I put about 200 miles on the van, I think I am ready to make adjustments this weekend. Some of the vague steering is bump steer. The body roll causes a bit of counter steer initially. So I need to adjust the steering rack a small mount. Even 1/8" can dramatically effect bumpsteer, so I planned for this.

I need more caster. Maybe another degree or two if possible. I am not sure I have enough camber adjustment to compensate. So I may end up doing a bit of light rework on the UCA spacers. I need about 0.2" of aft shift per degree of caster. This will help with the rubbing I am getting at the front of the wheel well. I need to do some light rework on both front wheel well areas. It should be easy enough to correct in all future versions.

A issue I notice a consistent gear noise. Its almost like loud mud tires, but its only on the drivers side. I believe its the diff gears in the ARB locker. I will connect the front axle disconnect to see if it goes away. Its quite noticeable.

The fox coilovers are great. Combined with the anti dive there is very little nose dive even during heavy braking. Rebound is well controlled. There is a bit of body roll until the sway bar grabs, but its very predictable. The best part is the van just eats speed humps. No bottoming, barely anything transmitted to the cab (comparatively).

I have narrowed my ESP/ABS/ASR activation issue. Its definitely only ASR (anti skid/anti oversteer). Its only at specific speeds (40-55mph). And only on right hand turns. This tells me two things. First, my steering sensor needs calibrated to the left a couple degrees. Second, the tire size difference and 54/55 tone teeth is just enough to make the ASR think the rear wheels are slipping when I am on the throttle.

 

[luthj]

Put my 2 wheel alignment tool to use. Front caster calculates to 1.6-1.8 degrees. I think 4 degrees is a good number, that requires a fair bit of adjustment though. I might just barely do it with the hardware I have on there. Gm specifies a minimum of 2.7 degrees. MB was using abour 4-5 degrees on their strut setup, so that jives.

Next step is experimenting with bumpsteer. Just need to adjust the rack up and down, and see which direction improves feel.

 

[luthj]

Sorry for the lack of pictures, nothing much photo worthy happening right now.

Caster is now ~4 degrees. Much better centering than before. Camber is just a tad bit positive, maybe 0.2 deg or so. I think it will get better as I put some miles on the BJs, as they are brand new and a little stiff.

I measured clearance at the trans mount. Its going to be tight with a 1350cv. 1310 should fit fine with a 2" shaft. Total length is about 21.75 C-C. Looks like there might be a few wrangler rear shafts which are the right length (designed for SYE setups). The local shop is only manned 9-4:30 weekdays, so I need to take an hour off to drop by. I wan't to talk through my options, given its a custom setup. I did some quick math, and I think a 1310 high strength (solid UJ) will work.
1310 breaking strength is about 1500lb-ft. Front axle max weigh (adjusting for a weight transfer backing up a hill) is 4500lb. Best case traction would by about 0.7Cf, so 0.7 * 4500 = 3150 Traction loading. With 30" tires, that's 1.2ft *3150lb = 3,780ft-lb 3,780/3.73 = 1,013lb-ft on the driveshaft. That gives me a good margin for peak loads as well.

The brakes feel like they are dragging slightly. I think its just the head pressure of the brake fluid (about 2-2.5ft) which pushes the pistons out slightly at rest. I have a set of fittings in the mail so I can bench bleed the new MC, should get that in next weekend.

 

[mountainhick]

Are you getting the 3500 master cylinder?

I'll be interested to hear how the volume is relative to the 2500. I am concerned that once I have both front and rear GM calipers I'll need higher volume MC.

 

[luthj]

Are you getting the 3500 master cylinder?

I'll be interested to hear how the volume is relative to the 2500. I am concerned that once I have both front and rear GM calipers I'll need higher volume MC.

The 3500 mc is supposedly ~10% larger volume. Though whether thats just the rear cylinder or the front cylinder both I cannot say. Since the front and rear have their own dedicated circuit/cylinder section, changing the rear shouldn't impact the front much at all. Based on my current observations, you should be fine with the 2500MC. My van still stops great, less pedal effort than before. More travel though. Of course that could be a failed MC, We will find out when I change it. Good news is that 3500MCs are cheap enough that it isn't a big deal when you have the system open to do the conversion.

 

[mountainhick]

The 3500 mc is supposedly ~10% larger volume. Though whether thats just the rear cylinder or the front cylinder both I cannot say. Since the front and rear have their own dedicated circuit/cylinder section, changing the rear shouldn't impact the front much at all. Based on my current observations, you should be fine with the 2500MC. My van still stops great, less pedal effort than before. More travel though. Of course that could be a failed MC, We will find out when I change it. Good news is that 3500MCs are cheap enough that it isn't a big deal when you have the system open to do the conversion.

Now if I could just get back to work on it...

 

[luthj]

Now if I could just get back to work on it...

Indeed, rooting for you. I have revised the subframe design for more caster, and made a few small tweaks. At this point, it may be easier to have everything re-cut if you are concerned about time.

 

[mountainhick]

Sent you an email to catch up.

 

[luthj]

Taking the afternoon to fiddle with the skid plates.





Looks like I can line the front parts up parallel, and use a piece of bar stock to tie them together with the existing bolt holes.



The rear looks like it will line up fine. I will need to drill new mounting holes. I haven't decided if I will use rivnuts, or weld on tabs at the trans support.



I put 1/2" spacers between the Tcase and the trans mount. That gives me more clearance between the mount and the driveshaft.

 

[luthj]

Making progress. Got the tabs welded on and some carriage bolts to attach.

 

[TantoTrailers]

Are you welding that seam between the two skid plates?

 

[luthj]

Are you welding that seam between the two skid plates?

Thats a no-go. The front part is steel, the back is aluminum. I may end up adding another strap in the middle Regardless that plate is very stiff. I could jack near the middle and it probably wouldn't deform.

 

[TantoTrailers]

My only concern would be if you hit something that dented the top plate in a bit and caught on the bottom plate since they are independent. If you weld a lip to the bottom plate on the back end overlapping the top plate even without it being mechanically attached it would prevent the top plate from being able bend behind the bottom plate without the bottom plate bending as well. Just a thought of a possible scenario, say a log that jumps up and hits right in that laser cut spot.

Pardon my paint

 

[luthj]

My only concern would be if you hit something that dented the top plate in a bit and caught on the bottom plate since they are independent. If you weld a lip to the bottom plate on the back end overlapping the top plate even without it being mechanically attached it would prevent the top plate from being able bend behind the bottom plate without the bottom plate bending as well. Just a thought of a possible scenario, say a log that jumps up and hits right in that laser cut spot.

Pardon my paint
View attachment 575242

Not a bad Idea as well. I don't really wheel my van, but extra protection can't hurt. The skids are mostly for flying rocks, brush, and the ever present wild animals.

 

[luthj]

Got the plates bolted up. I used rivnuts at the trans support.







Waiting for some stuff to happen before I commit to buying a rear axle for the swap. If the local junkyard is open, I will drop by to measure a couple to work out springs, driveshaft compatibility, etc.