1972 K20 LQ4/4L80E Swap

[pilotXC]

I'm in the process and beginning stages of doing an LQ4/4L80E swap into my 1972 K20. I bought the truck about 3.5 years ago and thought it was in good shape when I got it. Has a GM crate engine, 350, from 1994 with a TH350 behind it and NP205 transfer case. Seemed to run strong and well in general. I had to fix some wiring issues, replace the steering box, tie rod ends, get an alignment, new seat cover and fix some rust under the rear window seal from a very leaky sliding rear window within the first few months of buying it. I had a couple years of trouble free driving overall then went to replace the master cylinder and had a hell of a time getting the lines bled, had to replace the proportioning valve that turned out to be faulty, then had to do it all again... Noticed a radiator leak at the same time so pulled the radiator and it was shot, so had it rebuilt and realized that the cooling system was a lot worse than I thought it was. Ran tons of water through it to try to clean it out, finally thought it was good and put it all back together... A few months ago out of no where I got a very loud "ping" start and took me a while to figure out what was going on. Finally found out I had no compression in #3 and #5, air was passing between the two cylinders. I pulled the head and the gasket was blown. Thought that's all it was, then a buddy noticed a hairline crack between the cylinder walls that was very difficult to spot. That immediately threw everything into a tail spin. Obviously I could find a new 350 block and swap everything over, which wouldn't be terrible, but the more I started reading and talking to the same friend (he has done a couple 5.3L swaps into Jeep's) I decided if I was pulling the engine, I'd much rather have a modern power plant. Started looking for a donor and found the combo I have now. It's been such a puzzle to try to find info for what I'm doing and there are obviously different ways to go about the swap, but wanted to try to consolidate all my learnings into one place in hopes it might help someone else on their project, so here goes...

Transmission:
This is the biggest issue I've run into. Trying to marry the 4L80E with my NP205. I found 2 viable options that I was planning to choose from originally:

1. Advance Adapters - They make what looks like a great package of the adapter that will bolt to the trans side 6 bolt pattern and an input shaft to swap in the transfer case. You also have to have the housing machined to accept the 90mm bearing for the larger 32 spline input shaft. If you have a 4wd 4L80E you also have the output shaft swapped to a 2wd shaft and have the rear relucter ring installed if your donor trans is 1997 or later. You're probably looking at minimum $1000 just to get the existing 27 spline NP205 to work. That doesn't include the speedometer sensor in the tail housing of the transfer case either.
https://www.advanceadapters.com/prod...h350-or-sm465/

2. Offroad Designs - I did some calling around and when I looked at what they had online and talked to them, this was the route I was planning to go. They offer a similar kit that AA does, but they build it to work with a 4wd 4L80E so you DO NOT have to swap the trans output shaft. You would also need to machine the input housing for the 90mm bearing. They also offer a service to machine the NP205 tail housing to accept the donor VSS for $195, plus shipping both ways. Pretty sweet package and they were super cool and told me, if you find a TH400 adapter for an NP205 and can get it machined down 1/16 you will accomplish exactly what we offer for that portion. Still would have to do the input shaft, but still, very cool of a company to tell you exactly what they do so you can do it yourself if you are capable.
http://offroaddesign.com/catalog/Tra...seAdapters.htm
http://offroaddesign.com/catalog/NP205VSS.htm

Ok, so I was pretty convinced that was my plan, but then my friend said, doesn't a NP241 or an NP208 bolt right onto a 4L80E? Good question. I called Offroad Designs back the next morning and asked, they said, yes, will bolt right up. Change of plans. I started looking around for one of these instead. I'm not building anything crazy, just a driver so these would be totally fine options. I found a NP208 locally for a good deal with linkage, shifter, and even a slip yoke driveline, so I grabbed that to throw in... Problem hopefully solved.

Next is the speedo. How to get a mechanical gauge work with VSS tech. The guy doing my harness told me about Dakota Digital pass through pulse generators and said I can program your PCM on the rear speed sensor for the 8 pulse output from the pulse generator so your speedo will work and transmission will shift correctly. He said he's used it a few times and seems to work great and it's $42 on Summit. That problem solved too, hopefully.
https://www.summitracing.com/parts/dak-sen-01-4160

For motor mounts, I went with Dirty Dingo's cross member and motor mount combo. I haven't pulled it out of the box yet, but looks pretty cool and I love the ability to access the pan if needed. The stock cross member won't come out without some serious negotiating with the engine mounts at best I learned... How often will I need to drop the pan? Hopefully rarely if ever, but I like having the option. I read you can modify the stock cross member and haven't seen a lot builds where people call out this being an issue, but when I called Dirty Dingo, they said the engine will not fit unless you do this cross member change...
https://www.dirtydingo.com/shop/prod...oducts_id=1408

So far, I'm putting new gaskets and seals on the engine, having the transmission given a once over just to make sure it's going to be good once it's in. Figured I'd rather do it now when it's out and easy to get to it than wait and see what happens, even though the place I got if said it's fine and it shifted smooth. Just want the piece of mind... As I started doing the gaskets, I got trapped in the rabbit hole that's so easy to go down. I got a water pump and oil pump and knew I wanted to do those, but once I got it a part I decided since it's a part and the cover is off, I should do the timing chain and power steering pump. Also heard to replace the oil galley barbell when I do the rear main seal and rear cover gasket. I didn't want to or plan to do all of this, but it's one of those things that once you start looking at things and thinking about it, you might as well do it since you have it a part and the engine is out. Again, I would prefer to have the piece of mind to know these things are new not having the repair history on the engine.

My truck has 3 tanks currently as well, stock behind the seat and the dealer option saddle tanks. I wanted to get rid of the behind the seat tank anyway to free up the space and not listen to gas slosh around anymore, and found out I can do a 6 port selector valve and 2 in tank pumps wired up to a switch in the cab. Then decided, with some pushing from my buddy, maybe I won't need 2 tanks and I can add the selector valve and switch later if I want and save myself one more headache to try to get done with the swap.

Still trying to figure out things like if I want to pay for electric fans now or just go with mechanical to get it going and make that switch later? What to do for trans cooler lines to the stock radiator, radiator hoses, if I should or need to swap the battery from the passenger side to the driver side, etc.
No pictures to share really at this point, nothing much has been done yet, just been trying to line everything up. The next few weeks should ramp up and I'll try to post some follow up on how everything works out. Hope some of this is helpful to have it consolidated in one post.

[prodjay10]

I bought a Ford Taurus 2 speed fan with the Volvo relay. $45 for a spectra on rock auto. Easy to setup and cheap. Used the plastic mounts that go through the radiator.

Battery - I left it on passenger side. I used both positive battery cables and did the following. Original positive cable from battery to starter. Donor positive battery cable to starter as well on the same stud. That cable comes around the bottom to the little box on the driver side with the wire that goes to the alternator. Cut the rest of the battery cable that comes out the top of that boxthat would have gone to the battery on the driver side.

I already did the trans cooler but I’ll redo like this. Get a larger after market one with the barbed ends. Run rubber hose to it. Maybe mount using the same plastic mounts that go through the radiator I used on the e fan.

[mongocanfly]

You've got the t-case covered but yes ,,in 91 the 3/4t suburbans had a 4l80/np241 pass side drop...hard to find...I had one and sold it...

[pilotXC]

Originally Posted by prodjay10

I bought a Ford Taurus 2 speed fan with the Volvo relay. $45 for a spectra on rock auto. Easy to setup and cheap. Used the plastic mounts that go through the radiator.

Battery - I left it on passenger side. I used both positive battery cables and did the following. Original positive cable from battery to starter. Donor positive battery cable to starter as well on the same stud. That cable comes around the bottom to the little box on the driver side with the wire that goes to the alternator. Cut the rest of the battery cable that comes out the top of that boxthat would have gone to the battery on the driver side.

I already did the trans cooler but I’ll redo like this. Get a larger after market one with the barbed ends. Run rubber hose to it. Maybe mount using the same plastic mounts that go through the radiator I used on the e fan.

Thanks for the info, I'll definitely come back to this when I get to that stage!

[pilotXC]

Originally Posted by mongocanfly

You've got the t-case covered but yes ,,in 91 the 3/4t suburbans had a 4l80/np241 pass side drop...hard to find...I had one and sold it...

I tried to find one also, and was considering doing the machine work to add the VSS into whatever transfer case I went with, but according to the guy doing my harness, I'd have to buy a converter to go behind the dash to run my stock speedo and it's significantly more expensive than the pulse generator on the transfer case. Or, buy digital gauges, which is even more than the converter... Maybe down the road some day? For now, just want to get it swapped and running!

[mongocanfly]

Yeah ,I'm running the Dakota digital pulse to cable converter box...

[suburban99]

I have a 72K10 that I did a 6.0LS swap on as well. I used the dirty dingo cross member and mounts. I did not move the TH350 or NP205 as truck drove great at highway speeds and I didn't want to mess with the driveshafts. I used the dakota digital to pulse the ECM. I recently added electric fans from a windstar that I got from the auto recycler for around $40.00...I had a mechanical fan up until then. No issues just sounds better without the mechanical fan noise. And warms up quicker. Truck runs and drive great.

[derotoreut]

I'm in the process of doing a 5.3L LM7 swap on my 1970 K10 right now. I'm using Pacific Fabrications front cross member. You are correct that the engine will not fit unless you change this cross member on the 4WD's. Also, my engine is sitting back really, really close to the firewall. I also did not want to move my NP205 forward and mess with drive shaft lengths (same as Suburban99). That's why I elected to go with the 5.3, 4L60E/NP205 combo. Everything fit right in. I'm using the Advanced Adapters PN 50-5311, which adapts the 4L60E to the 10-spline NP205. I relocated my fuel tank to the rear by using a Ricks Tank. I'm going with Dakota Digital gauges and getting away from the stock gauges.

Pacific Fabs 4WD cross member

[pilotXC]

I'm finally getting going on the actual swap part, hope to have some pictures soon...

Anyone know a powersteering pump/reservoir that fits with the stock bracket that only has 1 return line? I tried a Tahoe version and it doesn't work...

[mongocanfly]

I assume your referring to a hydroboost pump...you can simply cap off the unused return ...use quality line cap though...

[pilotXC]

I am referring to the hydroboost return... Was hoping to just get a pump without 2 returns that fits, but if there's not another way, a cap will be fine.

Picture of the engine sans power steering & water pump. Not going to win any awards, but should drive well and hopefully is all sealed and has no leaks anymore.

[pilotXC]

Got the engine out today and started to assemble the Dirty Dingo cross member...

[pilotXC]

Cross member is in finally. Was more challenging than I expected it to be and since my truck is not completely disassembled, the brake lines were in the way of their design, so had to take them out and re-route. Maybe should have done more research prior and gone with something like the Pacific Fabs cross member that looks like it mounts to the stock cross member holes, but I liked the idea of being able to drop the cross member if I needed. Also seems pretty tight to the front differential, not a ton of clearance, I didn't measure, but 3-4 inches at most. Not planning any big gnarly off road trips, so should be fine.

Got the behind the seat gas tank out as well thanks to the help of my dad. Next I'll connect the rebuilt 4L80E to the engine and drop it in to figure out trans cross member placement, hopefully won't have to move it, but not sure yet.

[pilotXC]

Originally Posted by suburban99

I have a 72K10 that I did a 6.0LS swap on as well. I used the dirty dingo cross member and mounts. I did not move the TH350 or NP205 as truck drove great at highway speeds and I didn't want to mess with the driveshafts. I used the dakota digital to pulse the ECM. I recently added electric fans from a windstar that I got from the auto recycler for around $40.00...I had a mechanical fan up until then. No issues just sounds better without the mechanical fan noise. And warms up quicker. Truck runs and drive great.

Truck looks sweet!! I am going to try to pull a Windstar fan set up tomorrow I hope... Was considering doing the Old Air Products fan kit they make, but can't swallow a $365 fan kit with a $50 shipping fee.

[pilotXC]

Originally Posted by derotoreut

I'm in the process of doing a 5.3L LM7 swap on my 1970 K10 right now. I'm using Pacific Fabrications front cross member. You are correct that the engine will not fit unless you change this cross member on the 4WD's. Also, my engine is sitting back really, really close to the firewall. I also did not want to move my NP205 forward and mess with drive shaft lengths (same as Suburban99). That's why I elected to go with the 5.3, 4L60E/NP205 combo. Everything fit right in. I'm using the Advanced Adapters PN 50-5311, which adapts the 4L60E to the 10-spline NP205. I relocated my fuel tank to the rear by using a Ricks Tank. I'm going with Dakota Digital gauges and getting away from the stock gauges.

Pacific Fabs 4WD cross member
Attachment 1960397


Attachment 1960398


Attachment 1960399

Your truck and shop are enviable!! Hope the swap is going smoothly!

[derotoreut]

Originally Posted by pilotXC

Your truck and shop are enviable!! Hope the swap is going smoothly!

Thanks for the kind words. I spent a bit of money and time over the past couple of years to update my shop. Unfortunately during this time my truck projects were put on hold. Hopefully now I can get back on track. Good luck with your build.

[WS7z]

So excited to see someone else doing a K20 with a 4l80 swap! Im about 2 years into mine and will be taking my time in between work and raising 5 kids. Look forward to updates and to see where you finally mount the engine. The 4l80 is something like 6 inches longer than the previous setup that you removed. Im curious how you will handle the drive lines as that is something I am not fully clear how to solve yet.

best wishes on the build.

[pilotXC]

Originally Posted by WS7z

So excited to see someone else doing a K20 with a 4l80 swap! Im about 2 years into mine and will be taking my time in between work and raising 5 kids. Look forward to updates and to see where you finally mount the engine. The 4l80 is something like 6 inches longer than the previous setup that you removed. Im curious how you will handle the drive lines as that is something I am not fully clear how to solve yet.

best wishes on the build.

I'll do my best to update regularly... I'm using an NP208 transfer case as well, which will add even more length to the whole thing. The engine and trans are now ready for the initial test fit, finished up getting them put together at the end of the day. Also got new inner fenders, from another truck not aftermarket, and got them cleaned up and painted today as well.

Anyone know if there are any other bolts holding the dealer aux tanks besides the 2 that go through the center of the thanks? I welded up nuts after the ones that were there broke off today and got the "bolts" out, but the tanks aren't budging still and I can't see or feel any other bolts holding them in.

Found a local guy that does a lot of parts collecting and got my inner fenders from him. He had a truck similar to mine in his shop and the bed was full of parts, I noticed a factory aux tank fill neck cover for the bed with the fill neck and picked that up. He also had NOS core support frame bushing kit, so I grabbed that as well. Great guy, his business is Classic Bow Ties and he does mail order a lot if anyone needs another resource for parts. classic.bowties@comcast.net or 503-866-1967. Also went to a U Pull It yard and grabbed a Windstar shroud and fan and as much of the wiring and relay I could. It's pretty awesome how well those fit up to a stock '72 4 core radiator. Will need a little modification and fab some brackets, but shouldn't be too hard to get it in there.

Wishful thinking, but hoping making room for manifolds on the passenger side of the frame rails is all I'll have to do to get the engine and trans to mount up. I got the engine mounts slide all the way forward as I assume I'll need them there if I have any hopes of not having to relocate the transmission cross member and the transfer case support bracket.

[pilotXC]

Originally Posted by suburban99

I have a 72K10 that I did a 6.0LS swap on as well. I used the dirty dingo cross member and mounts. I did not move the TH350 or NP205 as truck drove great at highway speeds and I didn't want to mess with the driveshafts. I used the dakota digital to pulse the ECM. I recently added electric fans from a windstar that I got from the auto recycler for around $40.00...I had a mechanical fan up until then. No issues just sounds better without the mechanical fan noise. And warms up quicker. Truck runs and drive great.

Did you happen to have any issues with the cross member? Did you use the clamshell engine mounts? I got my engine in today and with it slide all the way forward, I barely had a finger width clearance between the firewall and back of the engine. Something seems very off. I called DD and they said to send pictures, but I haven't got anything back in response yet to help. Just curious if you had any issues. Everything was put together exactly as they explain in the installation instructions... D on driver side with arrow pointing toward radiator, P on passenger with arrow pointing toward radiator.

I flipped sides and it seemed to be better but then also looked like the alternator might be too high to clear the hood?

I thought this stuff was supposed to just fit right in!!??!!?? Thanks for any help...

[prodjay10]

Did you place the frame stands in the v8 or i6 holes on the frame? Sounds like you may have them in the i6 position. Pictures help.
Posted via Mobile Device

[pilotXC]

Originally Posted by prodjay10

Did you place the frame stands in the v8 or i6 holes on the frame? Sounds like you may have them in the i6 position. Pictures help.
Posted via Mobile Device

There are not i6 or V8 options on the clamshell version, far as I know... There isn't even instructions on DD website for the sliders that come with the cross member for the 4wd.

[suburban99]

A couple of things....on my 72 there is next to no room from the firewall to the valve covers. I can slip a finger in but that's it. I used the dingo sliders and normal clam shell mounts. My turbo 350 is in stock position. The K series are different from the C series...They just don't have the room.

I see on one picture that you have an EGR style passenger exhaust manifold. I would find a 2006? or newer manifold that does not have the egr.

I had no issues with the alternator hitting.

My Saddle tanks have 2 bolts thru the middle (long)...and one on the outside that replaces the tie bar rod that stabilizes the wheel area.

I recommend the Windstar electric fans, there are cheap fit excellent and work good.

[derotoreut]

Same issue with my K10. There is next to no room for me either. I can barely slip my little finger between the passenger side head/valve cover and firewall. Again I'm using the Pacific Fab crossmember, but I positioned it so I didn't have to modify driveshafts. I also have very little room between the front driveshaft yoke and 4L60E pan. Maybe 1/4" if that!

Very little room between pass side valve cover and firewall.


Doug Thorley headers wouldn't work. Hit firewall.

[prodjay10]

Will coils fit?

[derotoreut]

They do fit, but tight.