LS Swap into M1028 LQ9 and 4l60e

TheOrigin

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I'm in the process of putting an LQ9 LS 6.0 and a 4l60e trans from the same truck into my 84 M1028 5/4 ton truck. I will update this thread with problems I encounter and what I did to resolve them.

I installed the engine and trans bolted together into the truck without removing the core support. It wasn't too bad to get it in but you will need to have the radiator out if you don't already you will need the room. Bolting a trans to an LS in a square body can be a bit of a pain so this is why I opted to install them still hooked together. It's a 2 person job don't try to do it solo.

To avoid issues I had. Remove the 6.0 oil cooler lines entirely from the engine. Also have the factory clamshell style mounts mounted to the LS Swap mounts you choose and everything attached to the engine. It is much easier to slide the engine and trans into place and line up the 3 frame mount bolts than to have the clamshells already mounted to the cross member. With the trans attached it is quite difficult to maneuver the motor mounts down onto the clamshells when they are bolted in place on the frame. I know some people who like to use the adjustable motor mounts for LS swaps on square bodies but I opted for non adjustable ones to prevent any issues of it ever moving around. The adjustable mounts are mostly recommend for applications where your mounting an LS engine to a transmission that came in your vehicle.

Removing the transmission dipstick will also give you some more clearance to get it in place but I left mine on and it wasn't a terrible burden. On the passenger side of the rear of the LS engine there is a bolt on the head with a long stud coming out of it. There was nothing attached to this on my motor but I did use it for the chain to put it in the truck. I ended up needing to cut the stud off that bolt head so it didn't smash a hole in my firewall. Use a normal bolt or cut the stud off ahead of time if using it, otherwise just remove it.

When the engine is out of the truck, it is best to remove the exhaust manifolds. It's very common for the bolt heads to be broken off from thousands of heat cycles. They will likely seal up fine and have no leaks but it's much easier to fix this issue when it's out of the truck and the engine will go in easier without the manifolds on it. They aren't hard to install later.

An NP241 from an 88-91 era blazer, crew cab or suburban will bolt right up to a 4l60e trans. This is what I'm currently looking for to put in my truck. Later model 241 cases are driver side drop and won't work
 

Skinny

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That is going to be a nice rig! Post up some pics.

Are you doing AC too? Be curious to see what setup you go with.

I would be easy on the 4L60 with that kinda power.

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TheOrigin

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I will eventually do AC but that's not a priority for a while. Will need to be a top mount setup because the regular location interferes with the LS swap motor mounts. If I end up having problems with the 60 trans I will upgrade at a later time but I'm gonna use the 60 for now. My motor was out of an Escalade SUT so it is definitely a 60. I don't think it will have any major issues being a 60. I have owned a few vehicles with 4l60 and 700r4 trans and seen plenty of people with big tires running 60's without any major issues simply due to it being a 60.

I only have a few pics rn and they are all way too big of size to upload. I will get some converted and posted tho.
 

Jeepadict

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Did you use an aftermarket cross member? What oil pan did you go with. Are you having to install a lift for proper clearance?

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Skinny

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I think you need a different pan or something like an ORD crossmember.

Good luck with the build.

I helped a friend out with a swap exactly like yours on a K10. Guy had his truck at a specialty shop for two years amd they finished nothing. Hacked a harness and laid it on the hood. I told my buddy who is working on it now to get the owner to buy an aftermarket harness.

I show up to plug it in and this company makes the 4wd harness with no 4Lo input wire. So basically as soon as this dude shifts into low its going into limp mode.

Jist curious did you get a rear VSS installed in the trans or put a switch for low range in? I'm sure at some point this truck will re-enter my life.

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TheOrigin

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The factory oil pan on the LQ9 and 4 fits fine. There is a lot of room on these trucks. It dropped right in with no clearance issues aside from the oil cooler lines as I mentioned. I don't see where the axle will interfere with it at all either. They don't have a lot of travel in stock form. I plan to do a 4" lift tho. The factory transmission cross member is very close to lining up I plan to modify it to line up either with some tabs or just drilling some new holes in the frame and moving it forward about an inch.

I will be getting an aftermarket harness. I don't see low range presenting issues if it does the factory ECM can be programmed to eliminate any of those issues. The GM ECM with the proper software can basically be programmed to do anything you want it to. Not sure what I will end up doing for the speedo output on the t case right now I will figure that out soon tho.

The trucks with LS engines have rear sump oil pans and won't interfere with cross members on these trucks or the 2wd versions. If I was using an LS from a Camaro, Corvette or GTO or the like, they use front sump oil pans and would require a different pan setup. I don't find any advantage to the LS engines from the cars in a 4wd truck application. The truck model 6.0 is of superior build quality o have seen countless trucks with these motors with 400k miles still running strong. Unless you just want an aluminum block the car versions are not any better and are 2x the price as well or more. The LQ9 is rated at 390hp and the LQ4 is 360hp. Only difference in the 2 is compression.
 
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Skinny

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Yes and no. Either the 60 or 80 at minimum need a transmission output speed. Input isnt necessary but helps with monitoring slippage and converter lockup.

Now for output you can out a electronic sender in place of the tcase cable which feeds vehicle speed to the ECM. The issue with that is when you shift into low range. The ECM doesnt know there is a gear reduction so it wont work right.

On the LS trucks the computer gets a signal to tell it that the tcase is now in low range and can compensate for the ratios.

Two ways around this. Install a rear reluctor in the trans housing so the ECM gets vehicle speed from the output of the trans. Yes the ECM wont see low range speed correctly but the trans will shift right all the time. Or signal the ECM that its in low range so it can do the math correctly.

Prolem is the 208 doesn't have a low range switch so I'm guessing you'd have to fab up a contact on the lever or linkage. You also need a 4wd computer/harness as the 2wd lacks the input wire.

So yes the LS ECM can be tuned and changed. You can change the parameters for ratios in low range, tire size, axle ratio etc. (I have an HP Tuner I use for this) but it still needs a rear trans VSS or a low range input.

On the 4L60 I believe there is a 40 tooth split tone wheel that you can bolt around the output shaft. On my 4L80, it requires complete teardown to put a tone wheel on the rear drum. There is a VSS modification for the 205 tailshaft but it is a few hundred bucks and you still have to figure out the low range switch.

Also if using the factory speedometer and cable, you need a place to thread that into. Dont forget that if you end up using a tcase VSS sender.

See clear as mud

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Jeepadict

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@Skinny does the NP241 from the 88-91 Blazers and Suburbans have the 4-low switch a guy would need for the ECM signal? I know the drop is on the correct side.

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Skinny

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Off the top of my head I don't think it does. Only the tcases that come in the LS trucks does. I believe there is a 4wd computer that works with the front axle actuator, tcase actuator, and 4wd switch on the dash. That computer signals the engine ECM when it is in low range.

I think the easiest and maybe the cheapest is use the speedo cable off the tcase to dribe the speedometer. Then install a rear reluctor in the trans.

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Skinny

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I think the easy way is to use this kit:


Dont feel bad, the truck my buddy took on to fix was in the same boat. A specialty shop didnt know what to do. The company that sold him a harness didnt include a low range switch wire nor did they specify how to get the trans output speed. Strange considering that is what they specialize in.

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TheOrigin

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I think the easy way is to use this kit:


Dont feel bad, the truck my buddy took on to fix was in the same boat. A specialty shop didnt know what to do. The company that sold him a harness didnt include a low range switch wire nor did they specify how to get the trans output speed. Strange considering that is what they specialize in.

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Thanks for the info. I will get this ordered up. It will be easy to install now since I don't have the t case yet either. Shopping for fuel related stuff rn. Going to put in a suburban tank with in tank fuel pump. I will add all this info to the thread later on too. The older NP241 I'm looking for only has a mechanical spedometer output.
 

Jeepadict

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Thanks for the info. I will get this ordered up. It will be easy to install now since I don't have the t case yet either. Shopping for fuel related stuff rn. Going to put in a suburban tank with in tank fuel pump. I will add all this info to the thread later on too. The older NP241 I'm looking for only has a mechanical spedometer output.
IIRC Dakota Digital has a nice analog to digital speed sensor sending unit. Would be super common for them since all their stuff is digital meant for an analog application.

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Skinny

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Yes but the problem is that there is no location inside of a four-wheel drive transmission to read the output shaft speed. So even if you put a converter box on the cable drive it still is in the wrong location.

If I remember correctly, I used the LS fuel pump inside of my tank on the factory sending bracket. I can't quite remember what it was but there was some small hang up like a clamp didn't fit so it needed a hose clamp to attach it or maybe the fuel line wasn't long enough. Or maybe the connector was wrong. There was some small thing but it's pretty straightforward.

Definitely post up your progress. I'm curious to see what the Suburban tank looks like. I am going to do the same thing and keep one saddle tank on the diesel truck that I have. I just haven't had a chance to get back there, I think there's some real location of cross members involved.

I would also say if you have the time and budget now is a great point in the project to put some real gauges in the dash. A lot of the aftermarket stuff can interface with the ls computer with no problem. So you don't have to add additional sending units for the gauge set on top of what's already there for the fuel injection.

I have these on the diesel truck and they are awesome. It is nice having gauges that not only tell you accurate information but also don't wander off requiring a tap on the glass to get it to correct.

Mine are made bu NVU but I have seen the Dakota Digital and they are nice as well. The fitment on them are better as they attached to the backside of the black bezel instead on their own bracket which require a lot of adjusting so they fit correctly in the hole on the bezel.

Of course what I just mentioned ads about a grand so it certainly is not cheap. But I wish I would have just bit the bullet when I did the 8.1 big block swap on my square Suburban.

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Jeepadict

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@Skinny Dakotas analog to digital sending unit comes off the transfer case tailshaft in place of where the speedo cable would be, takes the spinny cable mechanical output and converts it to a usable signal the LS and digital speedos can use.

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Skinny

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Yes but the ECM still needs to know when it is in low range since a 2.7 or 1.9:1 ratio change occurs from the trans output to the tcase tailshaft. It cant guess, when the ratios dont match it goes into limp mode or throw a DTC.

What you are saying is true but it is only half of the problem when doing it that way.

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