1993 Chevrolet C3500 Crew Cab Restoration/Cummins Build

Had a chance to get some more work done, one of the more challenging things I've had to do thusfar. The speedometer.

Knowing i was going to be using the Dakota Digital SGI-5E speedometer interface, i needed to see what signals i was working with. The SGI5-E can convert/modify a ton of different signals so i called them, clarified what i needed to do and proceeded onward.



Did some research.

(May not be the same for all years - Mine is for the 92-94 model years, many things changed from DRAC to VSSB between the years so double check for your own applications)

The 47Re uses a three wire sensor sends 8000 ppm output square wave signal to the speedometer gauge on the Dodge,

Three wires,
Orange: 5v Supply
White/Orange - VSS Signal
Blue/Black - Ground



The GM 4L80E sensor uses two wire sensor that sends a 128,000 ppm output sine wave signal to the VSSB.

purple/green wires that plugs into the VSS.



The wires then feed into the VSSB (Vehicle speed sensor buffer: pictured below)



The VSSB then transmits the signals accordingly and sends them to each application.



Plug #824 sends vehicle speed to speedo: (4000 ppm signal) - Light blue / black wire
Plug #437 sends vehicle speed to PCM: (signal unknown) - brown wire
Plug #821 (purple/white) vehicle speed input from VSS sensor (green/black) - 128,000ppm input signal to VSSB (one of #821/#822 is a low high SINEWAVE signal)
Plug #250 12 volt ignition - brown wire
Plug #696 goes to the rear wheel ABS (128000 ppm signal) - dark blue wire
Plug #450: ground - black/white wire
Plug #822 vehicle speed input from VSS sensor (green/black) - 128,000ppm input signal to VSSB (one of #821/#822 is a low high SINEWAVE signal)
Plug #818 goes to cruise: (2000 ppm signal) - red/white wire



Basically after discovering all of this, i called the Dakota digital guys. I tried to use #7 on the Dakota digital instructions to convert the 8000 ppm signal from the dodge VSS to a 128,000 ppm speedo for the GM VSS wires (Purple/white & Green and black) - former VSS wires.

I was unable to get the speedometer gauge to move even a little.

So i reverted to mode #4 on the Dakota digital. Figured i would use the 4000 ppm output to the speedometer gauge and the 2000ppm output to the cruise. I did not not worry about ABS since it's just rear wheel ABS that i don't even think hardly does anything.

So essentially what I've done is used the SGI-5E as the new VSS buffer, and ran the dodge VSS wires into the SGI-5E (located in the glovebox) as the new VSS using the original VSS wires. Basically I've replaced the VSS with a programmable VSS that i can easily tune or change based on gear/tire sizes.

This weekend i will use a Ulysses GPS Speedometer on my phone to dial in the SGI-5E.

I'm not saying that the SGI-E cannot transmit the signal into the purple/green GM VSS wires.. i just could not figure out how to do it. and found this to be fairly simple and relatively harmless.

Had a chance to finish up the speedometer wiring at least to some degree in order to get everything working.

Pulled the glove box, unplugged and removed the VSSB. Spliced in the VSSB wires and extended them.



Then mounted the SGI-5E into the glovebox. Figured that would be a good safe place to mount it. All the wires i ran through loom behind the dash. Probably didn't need the loom, but oh well.




Also found out some bad news on the GM factory match gauges. The LED's are built into the circuit boards, so you can't change the colors. Going to try some green headlight film hoping i can match them.

I'm way too OCD to let something like that fly. Not sure where i'm going to mount them. Still need to order the matching boost/EGT gauge if i can find a way to make them match to the lighting of the factory cluster. Font and needles on these gauges are a perfect match IMO. Even better than the GMT800's that they were intended for.



And i threw it all back together for a really good first drive. Put about 50-70 miles on it this weekend.

Runs really well, drives smooth. had one small fuel leak and a power steering leak from a blown hose line. Didn't replace the low pressure because i assumed it was fine, and of course it blows. Oh well, would rather go over everything now. The truck isn't going to let me not replace everything.

Also the front caliper is sticking from what i assume is just a year and a half of sitting. Was going to replace brakes anyways along with the entire front end so everything is new.

Overall i'm really happy though. Truck moves around pretty good.



Now that the conversion is done and the truck runs and drives, on to the front suspension, blown steering lines, brakes, paint and body work....

Bit of an update... Been driving the Cummins sporadically. it's not quite done, still needs some paint and body work, but I've been driving it and I've been nothing but impressed. It runs and drives so smooth, does 80mph on the highway no problem.



Haven't towed any trailers with it, but did load the bed with firewood and you can't even tell. I can't wait to get a hitch and rear bumper on it... and yet that's what this update is mostly about.

Found a DMI bumper local, that while rusty, is solid enough to where it can be sandlblasted/powdercoated...





Rear bumpers are pretty expensive, and given that this truck does have a 2" body lift, i don't want a hitch or rear bumper gap.

I've always liked the look of DMI bumpers however don't want the actual DMI hitch. I made a bumper for my old 97, and plan to make a more sturdy tougher version for this truck.






Now at first sight. it's way too wide for the truck. This did come off an 89 C2500 so it's for a GMT400, but it's way too wide. So i plan to cut and narrow it down to the width of the bed.

Then i plan on putting the hitch on, and raising the bumper up to the height of the bed. That way it sits like a bumper should right above the hitch with no gap. Since this isn't a stock bumper i wont have to worry about any exact body lines.

And also, this is a very thick bumper. So it should make for something i wont have to worry about little dings and knicks.

Plan on having it powdercoated semi gloss black.

JScott23 said:

Bit of an update... Been driving the Cummins sporadically. it's not quite done, still needs some paint and body work, but I've been driving it and I've been nothing but impressed. It runs and drives so smooth, does 80mph on the highway no problem.

You must be registered for see images attach

Haven't towed any trailers with it, but did load the bed with firewood and you can't even tell. I can't wait to get a hitch and rear bumper on it... and yet that's what this update is mostly about.

Found a DMI bumper local, that while rusty, is solid enough to where it can be sandlblasted/powdercoated...

You must be registered for see images attach

You must be registered for see images attach

Rear bumpers are pretty expensive, and given that this truck does have a 2" body lift, i don't want a hitch or rear bumper gap.

I've always liked the look of DMI bumpers however don't want the actual DMI hitch. I made a bumper for my old 97, and plan to make a more sturdy tougher version for this truck.

You must be registered for see images attach

You must be registered for see images attach

Now at first sight. it's way too wide for the truck. This did come off an 89 C2500 so it's for a GMT400, but it's way too wide. So i plan to cut and narrow it down to the width of the bed.

Then i plan on putting the hitch on, and raising the bumper up to the height of the bed. That way it sits like a bumper should right above the hitch with no gap. Since this isn't a stock bumper i wont have to worry about any exact body lines.

And also, this is a very thick bumper. So it should make for something i wont have to worry about little dings and knicks.

Plan on having it powdercoated semi gloss black.

Click to expand...

you should cut that top peice off and make the top of the bumper even with the lower body line. glad to see it getting out and about finally!

Biggershaft96 said:

you should cut that top peice off and make the top of the bumper even with the lower body line. glad to see it getting out and about finally!

Click to expand...

yep that's what i'm doing.

This is the height and width i'm going for. (my old 97)

JScott23 said:

yep that's what i'm doing.

This is the height and width i'm going for. (my old 97)

You must be registered for see images attach

Click to expand...

I need me a bumper like that.

Update for this thing. Another slow moving build, had a lot going on and unfortunately just haven't been able to really make the kinda progress i'd have liked to on this thing ether...

But here's the update.

Cut down that DMI bumper making it narrower fitting the truck better. Then i welded and plated the license plate pocket and boxed in the ends. I'm going to make some custom brackets so it sits as it does here in this picture. The bumper isn't really perfect, but it'll work for a truck that's going to do some work. I don't mind sandblasting and having Line-X (or whomever) do the bumper when they bed-line the truck.





Then i tackled one of the things i'd been dreading. The rockers. The panels for the 4 door trucks were a bit pricy, so i used two regular cab rocker panels with good results.

Before:



After:



Then once i sealed those up, i began tackling the body work. Cab was pretty rough starting out. It's a truck that spent 20+ years in the midwest and for the last 10 used as a blue collar work-truck.

Since the factory paint didn't adhere to the primer i had to take it down to bare metal.




Once i stripped the cab, i pretty quickly got the truck to a buddy for primer for the first of two coats.




While it turned out pretty good, it still needs quite a bit of body work. I've got a couple buddies who do bodywork so they'll likely take over from here. The rust free bed from my 94 is in great shape so it really doesn't need much other than sanding/primer.



Hoping to have this thing painted by next summer. Since I can't really drive this truck in the winter, i'll probably spend most of this winter getting the crew cab short bed chassis ready for my 94 cab and then paint this thing next spring/summer.

Excellent thread/build. I particularly enjoyed the detailed descriptions and ample picture posting. By far the best gmt400 12v swap build I've seen on the net. will be referencing it often in the near future as I am preparing to undertake this swap myself. Thanks for sharing

Appreciate the time and effort posting your journey!

Nice thread.

Way late to your party but be glad you stepped away from the 4L80E. Not that it isnt a good transmission, but any minor mods to the Cummins and its more than a 4L80 can handle (well "stock"). I ate 4L80s and flywheels on my first Cummins swap(2011) bigger turbo and injectors. But it wasnt as difficult as it seems to run one. I said Im done with the 4L80 in 2013 and went to an Allison 5spd. Best thing I ever did. After the body of that truck was beyond help without a full insane resto (was a 92 CCLB C3500 who was rough when I got it did some resto work). I got a 99 K3500 Classic CCLB in early 2015 who got the other Cummins and Allison(4×4) sitting in the garage. On the 2wd didnt have to body lift. For the Allison 4x4 I had to body lift 2 inches. (Yes the old truck was gutted before going to scrap, we are currently still deciding on the home for that one.....Express 3500 swap or Cummins only(then backed by allison manual) in to the 2000 K3500 Classic dually. Decisions decisions, lol.