Below is a step-by-step general description of how to remove the cab on an LB7/Allison Duramax. Many models are Similar however there will be differences. Sorry about the lack of a couple pictures and the quality of others, If needed I can get more/better pictures. Hope it helps you out. The only time you will need to do this is for headgaskets or swapping a frame. Anything less than that and you do it in the truck, anything deeper than that and you pull the motor. I also added a link to the time lapse video. This job is very easy, special tools needed are just a lift. Fan clutch tools will help but are not necessary. Everything else is standard and really doesn’t take much. Good luck.


1. When getting out of truck move seat so that seat belt can be buckled through it as you will need it that way later on.

2. Raise hood into service position by removing one bolt from hinge where it connects to the hood using a 13mm then raiding hood and reinstalling hinges into other hole to keep hood vertical.

3. Disconnect batteries using a 5/16” or 8mm. Remove both positive and negative cables as both will stay with chassis when cab is separated.

4. Remove air intake hose. Box can stay with the cab. Don’t forget to unplug MAF.


5. Remove both fender liners using body clip tools and possibly some sockets on later models

6. Remove both driver’s side and passenger side CAC tubes.


7. Drain radiator by removing drain (if equipped). Use a funnel or 90* elbow to channel the fluid into a pail. If no drain plug remove lower radiator hose.



8. With coolant drained remove upper radiator hose from radiator, remove lower radiator hose from radiator, remove the larger hose that goes into the coolant overflow bottle and remove both heater lines. It’s safest to remove them from the engine as the fittings on the firewall side can get brittle.



9. Now Remove the grill from the truck by removing the row of body clip fasteners that connect to the top of it (Yellow in picture, red do not need to be removed), remove the bolt (if equipped) with a 10mm and then remove the grille by starting at the ends and pulling. If it is an older truck you will need a large Phillips screwdriver to turn the quarter turn fasteners to release the grille.



10. At this point you can also remove the bumper. It will give you more room to work. Using a 15mm remove the 4 bolts that are behind it that mount it to the frame. Remove one bolt on each side from the side braces and don’t forget to unplug your fog lights. Then it should just slide off.



11. Now remove the transmission cooler lines from the front cooler using a pan to catch the fluid that may drip. Then remove the transmission cooler lines from the radiator.


12. Next remove the upper fan shroud. To do this you need a 10mm to remove the bolts across the top of it and body clip tools to remove the 4 body clips that hold the two halves together. The TCM will be removed during this process so make sure to unplug it and set it aside.




13. Now you can get out your fan clutch tools and remove the fan with the clutch from the hub. If you do not have access to these tools you can separate the lower fan shroud so that it will stay with the frame instead of the cab.


14. Remove the serpentine belt from the engine at this time.

 

15. Unplug the two wires going into the A/C compressor then using a 15mm remove the 4 bolts holding it on. Then swing it over and lay it onto the passenger side battery.


16. Next you will want to remove the master cylinder from the hydrobooster. DO NOT remove the lines from the master cylinder, just use a 15mm and 13mm to remove the nuts that fasten it to the hydrobooster. This will ensure you do not have to bleed the brakes when finished.


17. Next you will want to remove the lines going to the hydrobooster. Wrench sizes are 16 and 18mm IIRC could be a little off though. Also remove the rubber line held on with constant tension clamp. Cap these lines to avoid puddles everywhere.


18. Next make sure you buckled your seatbelt through the steering wheel. This will prevent it from turning and braking the clock spring. Then using a 15mm remove the bolt that connects the ISS to the steering box shaft. Slide the two apart.

19. Next we will do the electrical. Starting with the passenger side. Unplug the wires from the coolant level sensor on the bottom of the coolant overflow tank, then unplug the wires going to the A/C dryer. That will complete the passenger side.

20. The Drivers side takes some more. Start by removing the firewall to engine ground using a 10mm. Next remove the smaller gauge ground wire that goes to the frame just under drivers side headlight.



21. Now remove the fender brace using a 13mm to remove the 4 bolts. Then remove the fusebox cover by pulling it over the tabs that lock it in place. Use this same procedure to remove the ECM cover after unclipping the TCM wires. Then release the snap clip that holds the ECM in place as the ECM will stay with the frame. While in that area also unclip the power steering hose from lower radiator shroud.



22. With the fusebox cover removed, pull up a chair. You’ve got some wires to unhook. Start by removing both wires on each side of the large fuse using a 7mm and 13mm. Then move onto removing the wire near it using a 10mm.


23. Next free the fuse box by releasing the tabs that hold it in place. Using a 7mm remove the Red square plug and the larger Black square plug. Also remove the white plug with large single red wire.




24. Next remove just about every wire connection underneath the fuse box, next to the fuse box and in front of the fuse box. Also remove the plugs if they are anchored down. Don’t forget to unplug the brake fluid sensor as well.




25. There will be another plug on the firewall you will need to remove from the stud and separate as well.


26. Next undo both large clips that hold the wiring harness going to the engine as well as the harness going to the ECM/TCM. Then wrestle the wires out of the fuse box and down under the fender so they can lay with the frame.

27. While down inside the fender you will be able to see where the wires that run to the rear and transmissions are fastened to the firewall. Remove them from here so they can lay with the frame. Double check all wiring. It should appear clear what is staying with the frame and what is not. If you have any aftermarket accessories you will need to address them as well. I cannot give guidance on them as every truck is different.


28. Now you will want to pull on the e-brake cable as hard as possible while inserting a pick into the hole provided in the e-brake pedal assembly. This will hold the tension off of the cable. Then separate it at the front joint. Once separated, depressed the clips and pull the cable out of the frame so it will go up with the cab side and the rest of the cable will stay down.

 

29. Next remove the shifting linkage by popping it off the selector arm, then remove the metal clip where it connects to the bracket and depress the taps to pull linkage out. Use a pliers to depress the tabs to release the clamp on the transfercase side.



30. Now it is time to remove the cab bolts. Using an 18mm remove all of the ones under the cab. Regular cabs also need to remove the support straps as well. Use an 18mm deep well and a 15mm wrench to remove the two bolts that hold the radiator support down.

31. At this point do a double check you didn’t miss anything, then position the truck so that th cab can be lifted by the lift. Position the lift arms underneath the pinch weld at the bottom of the rocker panels. Keep them as far out as possible though. If you position the arms too far in they can catch the mounts on the frame while lifting.

32. Once positioned, start the lift. Best to have a buddy during this process to lend a hand but you can get by if not. Keep a close eye on everything making sure it all goes up smoothly and fix any snags as you see them

33. Now your cab should be in the air and you can roll the frame forward to work on it or leave it where its at. Good luck.

 

Great write up