Couple of videos of my 88 C1500 Swap

DAVe3283

Heavy & Slow
Sep 3, 2009
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Boise, ID, USA
Cool that you have the stock dash almost completely working. Hopefully you can figure out the tach, it would be cooler to have the stock tach than an aftermarket one. Thanks for sharing the videos!

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weazel

Member
Oct 5, 2011
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Thanks guys!

I'm hoping it's just a bad tach in the cluster, and I can just swap it out for another. Maybe I can find a cluster with high MPHs lol. Didn't realize it only went to 85 till my son showed me haha.

And hmmm, not a bad idea! Watch out farm truck, here I come! Lol jk jk...
 

SmokeShow

Well-known member
Nov 30, 2006
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Very cool.

Any oil pan clearance or trans tunnel clearance issues? I guess the shifting detents in that original steering column worked just fine for operating the allison?
 

wilrob

Back in the Motherland
Sep 14, 2016
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Dallas, TX
Did you reinforce the frame at all? General consensus on most of the older GM truck forums when doing a diesel swap is that you should from what I've seen.
 

Novak

SQUIRREL TRYN TO GET A NUT
Jun 15, 2015
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Cloud 9, IDAHO
Personally I think it take a lot more know how to swap a Duramax vs a Cummins swap. Cool truck!


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weazel

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Oct 5, 2011
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The oil pan in this truck is pretty close on the drivers side, Kind of toward the front. But it doesn't rub, luckily. The trans, same, close, but not touching. I didn't have to use a block of wood to clearance anything, which I was pretty pleased about.

The shifter rod, I had to do a little engineering to get it to shift the Allison correctly. I had asked around for a shift cable to hook the stock column to the Allison, but no luck. So went ahead and welded some stuff together to make it work.

No reinforcing of the frame yet. Seems to be holding fine so far. But, the rear is so light that all I get is either tire spin or horrible axle hop lol

Thanks Novak! I originally wanted to cummins swap, but the duramax was new and exciting to me. Got lucky and picked up the engine for a decent price and decided to give it a whirl. Had some help from a couple guys here on the forum, a couple of buddies around here troubleshooting the bad gremlins I had at first, and a LOT of research on wiring schematics.

It's kinda cool when someone stops and takes a double take thinking it's a 6.5 at first, but then I pop the hood and some get a huge smile across their face and others kind of get a spaced out look like they have no idea what they're looking at lol.
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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If you're interested, I can build you a custom cluster. Theres a place that will make you a custom overlay, and I've got the tools to calibrate the cluster. It's not cheap as they quoted me $125 for one of there overlays, but you can have it set up to whatever ranges you want. As to your tach, did you get it hooked to the alternator to the stator output? Do you have the correct pulley on it? The calibration resistors in these clusters do fail, and when they do, they start by reading higher than actual. The air cores themselves that move the needles rarely fail, but the resistors do fail semi often.
 

weazel

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Oct 5, 2011
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Hey Ferm, I may hit you up on that!

I ran the rpm signal straight from the ecm to the tach in the dash. It would read semi correct until about 1100-1200rpm, but then get super lazy and max at 1500. I have an edge cs and also my v2 that I have used to verify rpm differences.
I purchased an adjustable signal convertor thinking it would correct the issue, but it did not.
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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Are you using a gasser cluster? If so the ecm outputs a 4 cylinder signal. You will also have to install a 4.7k ohm pull up resistor to get the tach to stay online. The ecm putputs a 5v pulse for a low voltage tach, and a coil driven tach needs at least 11 volts to work at all rpm's, so you have to wire in a pull up resistor to positive for it to work properly. Some get away with a 10k ohm resistor, but most have to step up to the 4.7k ohm resistor.
 

weazel

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Oct 5, 2011
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Yes it's from a v8 gasser.

So I'll need a 4.7k resistor, wire it to switched 12v, then to the tach wire? Am I understanding correctly?

Or will I be able to use the 4.7k or 10k wired from ecm to tach wire?
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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Yes it's from a v8 gasser.

So I'll need a 4.7k resistor, wire it to switched 12v, then to the tach wire? Am I understanding correctly?

Or will I be able to use the 4.7k or 10k wired from ecm to tach wire?

You take the tach wire that runs from your ecm to the tach, anywhere along it you T into it, you connect one side of your resistor to the tach wire where you Teed into it, and the other side to a 12 V+ switched source. It's that simple except this will leave you with a 4 cylinder 2 pulse per crank revolution tach signal. So you either have to recalibrate your tach, or get a tach adapter to double the signal. The good news is the lb7 ecm outputs the same tach signal as a stock LS ecm, and theres alot of boxesout there to correct there tach signals. Unfortunately we can't correct it in the tuning like they can.
 

weazel

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Oct 5, 2011
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Thanks Ferm! I'll grab some resistors and wire them in and see what it does.
I do have a box that should correct that signal, so hopefully this will cure the issue with the tach. Thanks again sir!