89 GMC Cummins conversion
 

Here is my 1989 GMC CC SRW 4x4 build. It had a 6.2 liter diesel and a TH400 transmission. I am putting in a 24 Valve Cummins and a 4L80 transmission. Over the last two weeks I have managed to pull the old running gear and put in the new running gear. One unexpected hurdle I ran into was that the NP205 transfer case would not bolt up to the 4L80 due to the longer transmission pan making contact with the transfer case. I had to order an adapter that spaced them a little over 1/2" apart. Just to be safe I also grinded a bit on both the transmission and transfer case just to give it a little extra room.

I ordered a 6" lift kit to ensure that the new crossmember did not contact the front differential and was surprised when it increased the ride height by 7" in the front and 7 1/2" in the rear. I was told it would settle a bit once I get a few miles on it.

Here are a few pictures for now.

Re: 89 GMC Cummins conversion
 

Here is a few more pictures.

Re: 89 GMC Cummins conversion
 

Slow progress on my project. It sure is nice to have friends with a large heated garage, overhead crane and a pit to use when your doing one of these projects. I got the suspension lift almost done, just need to build some brackets to secure the metal brake line extensions. I am waiting on my driveshafts to come back, since I had to shorten the rear and lengthen the front. In the meantime I am working on the wiring and trying to figure out what to do about the Dodge radiator not having a transmission cooler built in to it. I am leaning towards a 6.0 liter Ford diesel trans. cooler. I have plenty of room behind the grille since I mounted the intercooler on the back side of the radiator support.


I didn't start this build like most showing you pictures of what I started with so here you go.

Re: 89 GMC Cummins conversion
 

Here are some interior pics.

Re: 89 GMC Cummins conversion
 

I found a used seat and a dual headlight radiator support and parts to eventually get rid of the large single headlight.

Re: 89 GMC Cummins conversion
 

Well I decided to just run an auxiliary transmission cooler with a fan and a deeper transmission pan. I ordered them last night and they should be here by the end of the week or first part of next week. If it doesn't cool it down enough Plan B will be to go back with the GM radiator when I switch out to the new radiator support to install the newer dual headlight front end. I will post more pictures when I have it ready to start up.

Re: 89 GMC Cummins conversion
 

Cool build! :metal:

Re: 89 GMC Cummins conversion
 

i actually like the single lights in the 88-91 trucks dont see many fixed up with that set up

Re: 89 GMC Cummins conversion
 

Greenlee - Thanks for the acknowledgement! I wasn't sure if everyone was tired of another CC Cummins conversion build thread.

Re: 89 GMC Cummins conversion
 

I will probably leave the singles for a little while. My first 1981 C20 had the single lights and I thought about leaving it that way, but once I had to do the lift kit for the cross member clearance the build kind of changed directions. I know some people may think it is actually a Chevrolet because of the Grill and tailgate but it is a GMC. I am looking for a GMC grille and tailgate. And it might be kind of fun to leave the old 6.2 Litre emblem on the tailgate.

Re: 89 GMC Cummins conversion
 

I actually bought a rad support and grill like that for my 86 RCSB c10, it is painted black, you don't see many of them thats why i got it, I think they look good! Oh BTW Nice truck! What size/kind of tires do you plan on running?

Re: 89 GMC Cummins conversion
 

when i do a dmax one prob next year im going to try and find a diesel gate and grill emblem off an old 5.7 olds powered truck if i can. i love the singles in the early 80s trucks never liked the stacked lights as good.

Re: 89 GMC Cummins conversion
 

Not sure yet. If I wouldn't have had to lift it then I would have stuck with the stock tire and wheel combo with the dog dish hubcaps. Now, I am leaning toward 33" or 35"s. Still not sure on the wheels though.

Re: 89 GMC Cummins conversion
 

Hankster - read your build thread and I hope you are getting better. Thanks for your compliment on my new project truck. I like seeing that a person your age is interested in these trucks instead of something newer that everyone has. Good luck with your build.

A week before I bought this truck I traded a Honda 300EX for a 1978 GMC CCSRW K30 with no motor. Trading is the way to go if you can do it. Oh the guy also threw in an extra front D60 and FF14 rear axle in the deal.

Re: 89 GMC Cummins conversion
 

Slow progress in the last week. I got my new TCI deep transmission pan and finally got it installed. In order to drop the old pan I had to remove the cross member and mount. While I was at I went ahead and replaced the mount with a new one. The last two days have been frustrating trying to modify the transfer case shifter lever to work now that the transmission has been moved back 4 1/4" due to the 4L80 being longer than the TH400. After numerous failed attempts and countless hours wasted at trying to make the shifter work in the original location, I finally decided to move the hole in the floorboard over. I am attaching pictures of the before and after pictures of the TC shifter lever. My drive shafts came back from the shop and I got the rear ones installed. I was waiting to finish the TC shift lever done before installing the front shaft.

Re: 89 GMC Cummins conversion
 

Well my truck may not be running yet but I think this new valve cover is worth a few extra horsepower.

Re: 89 GMC Cummins conversion
 

Well I made some progress with the build, but I am still waiting on my Transmission Cooler. I was given an expected delivery date of 1/20 and when I called them on the 24th I was told that the new expected delivery date is now 1/30. I did however put on the new valve cover, mount the radiator and shroud, connect the transmission linkage, install the new shift lever indicator with the Overdrive, started running the wiring and building the mount for the PCS transmission controller. I am hoping to have it fired up and running in the next two weeks.

Re: 89 GMC Cummins conversion
 

I forgot to mention that I had to order a different transmission dip stick and while I was at it ordered a transmission temperature gauge.

Re: 89 GMC Cummins conversion
 

a few more pics.

Re: 89 GMC Cummins conversion
 

Looks like you are making some progress. That valve cover looks sharp! :metal:

Re: 89 GMC Cummins conversion
 

Thanks! It was a little pricey but I wanted to remove the Dodge lettering from the valve cover and add a little bling under the hood.

Re: 89 GMC Cummins conversion
 

Yeah, having it say "Dodge" under the hood just ain't right. :lol:

Re: 89 GMC Cummins conversion
 

Subscribed

Re: 89 GMC Cummins conversion
 

Lol that aint no ****!

Re: 89 GMC Cummins conversion
 

Lol that aint no ****! I hate seeing cummins swaps on this forum with the dodge cover