6-Speed Manual Transmission Swap
A Write Up by Lord Aries
I have always wanted a Manual Transmission in my Avalanche, well I finally got tired of wanting one and decided to do something about it! WARNING: A lot of reading awaits you below this point but, I think you’ll enjoy it… This project gets a 5 out of 5 Wrenches rating.
If you don’t understand how a Manual Transmission works and all the parts that go along with it, then you probably shouldn’t attempt this yourself until you have learned.
Plenty of guys out there have converted there 2wd Silverado’s to run a Tremec T-56 6-Speed transmission from a Camaro and this works great… IF you are 2wd and plan to never towing anything bigger then a Jet Ski… But, I wanted to keep my 4x4 and Towing ability if not augment those two things further so, that meant I needed a manual transmission from a Truck…
There are a few options for the GM Trucks in way of Manual Transmissions, here is a list of what was offered on the Silverado’s from 2003-2006:New Venture NV3500:
Light Duty – around 10,000lbs GVWR
5 Speed: 1 – 2 – 3 – 4 – OD
Used in 1500 Series Trucks w/4.8L V8 (and with a 5.3L but, very rare)New Venture NV4500:
Medium to Heavy Medium – around 16,000lbs GVWR
5 Speed: Low – 1 – 2 – 3 – OD
Used in 2500 and 3500 Trucks w/6.0L V8 (also used in 96’-2000 Diesels)ZF S6-650:
Heavy to Light Commercial Duty – around 26,000lbs GVWR
6 Speed: Low – 1 – 2 – 3 – 4 – OD
Used in 2500HD to 3500 Trucks w/8.1L Big Block and 6.6L Duramax DieselTransmission Gearing Auto vs. Manual Comparison Note:
For Manuals the Low gear is actually 1st gear but, since Low is only used for Towing and/or off-Road use the gear numbers are changed below for an easier comparison of the gear ratios.Type Model Low 1st 2nd 3rd 4th 5th
Auto 4L60e None 3.06:1 1.63:1 1:1 0.70:1 None
Auto 4L80e None 2.48:1 1.48:1 1:1 0.75:1 None
Man NV45 5.61:1 3.04:1 1.67:1 1:1 0.73:1 None
Man ZF S6 5.79:1 3.30:1 2.10:1 1.31:1 1:1 0.72:1Let the Madness begin!!!! Step 1:
Determine which Transmissions will fit the 5.3L.
ALL the motors in GM’s line up for the full size trucks have the same exact LS Series Bell Housing bolt pattern, even the Duramax!!! So, you can bolt up any of the Manuals to the 5.3L motor with out a problem. *LS Series Bell Housing mounting points seen here marked in RED.*LS Series Bell Housing mounting points seen here marked in RED.Step 2:
Determine which Transmission best Suites my Avalanche and the Cost.
I made some phone calls to a bunch of shops around the US that remanufacture these transmissions to find out which one would hold up in my truck and get the best cost.
The NV3500 was out of the question, it’s not meant for the kind of power my truck makes or the GVWR of the Avalanche. The NV4500 was the logical choice since it is rated for 450hp up to 16,000lbs GVWR. It is tough and since it was used on the 6.0L V8 it would be an easy bolt up swap just like the 4L80e Automatic is from the 2500 Trucks… But, this is me we are talking about!!!! I don’t want the logical easy choice; I want the complicated difficult choice!!! I want the ZF S6-650 6-Speed Monster Transmission!!!
The ZF S6-650 is rated for 650hp up to 26,000lbs GVWR! It’s big, it’s heavy, its made to take a ton of abuse and its just plain badazz! There are guys using stock ZF6’s for Sled Pulling in their Duramax Silverado’s making over 800hp and 1,400lbs of torque towing upwards of 20,000lbs! I think it can handle my ballsy little Turbo Charged 5.3L… To give you an idea of the sheer mass of the ZF6, the 4L80e and NV4500 weight in about the same at a hefty 185lbs w/out fluid. The ZF6 weights in at a staggering 240lbs w/out fluid!!! The overall case size is larger too and the gear sets are massive… *Seen here are the ZF S6-650 on the left and the old 4L80e on right.*Seen here is the ZF6 next to a cordless drill for size comparrison.Cost:
A remanufactured NV4500 can be purchased for about $1,450 Shipped, a remanufactured ZF6 goes for around $3,200 Shipped!!! So, it looked like I would be doing the NV4500 just due to the cost… But, I got very lucky at the last minute and found a used ZF6 in working condition for only $1,650 Shipped!!! The ZF6’s are very hard to come by used because they just don’t break. The only real way is to find one is out of a wrecked truck and buy it before a Transmission shop does. So, I went for it and snatched that bad boy up and it even came with a 90 day parts warranty.
For most all of the parts on this project you will need GM Factory Parts. I had a ton of help from a great guy named Pat at my local GM Dealer Parts Store, he even gave me wholesale pricing on all my parts since I work for AAA!!!
That said the entire swap can be done for just about $3,800 if you shop your parts wisely and do everything (that you can) yourself! And in case you were wondering, I sold my old Stage-3 Built 4L80e Automatic set up for $2,800. So, I only spent about $600 total out of pocket on this project and that was mostly on the new Drive Shafts. And I made up for some of that cost with sales of other old take off stock parts from my AV…Step 3:
Installing the Drive Line…Body Lift:
Unless you want to cut out the center tunnel/floor of your truck you MUST HAVE a 3 inch body lift to fit the ZF6! According to the Chevy Dealer, the 2500-3500 trucks actually have a factory 2 inch Body Lift on them to accommodate the NV4500, ZF6 and Allison 6-speed Automatic (as well as to clear the 6.6L Duramax in the engine bay)… Trust me when I say this is a must have because the ZF6 BARELY fit under the body of my truck… Not sure if you would really need the Body Lift with the NV4500 since it is smaller then the ZF6….Flywheel and Clutch:
The ZF6 will bolt up to the 5.3L motor thanks to the LS Series Bell Housing design but, you need a Flywheel and Clutch for it. The 8.1L and Duramax have a different Crank output on the Motor so can’t just use a full set from one of them. And the Splines on the ZF6 Shaft are larger then the NV4500’s so, you can’t use the clutch from the 6.0L set up either…
Enter Ace Clutch located in Sanford, FL, these guys know their stuff and got me set up. Simple solution, use the Flywheel for the NV4500 from the 6.0L. Mate that to the Clutch and Pressure Plate for the ZF6 from the 8.1L/6.6L and you’ve got Fun times ahead. Yes, these parts all bolted together like they were meant to be… Oh and unlike the T-56 Camaro setup that uses a girly 10 inch clutch, this set up uses a manly 12 inch clutch. And to top all this off, I also opted for an Upgraded Heavy Duty 8.1L Towing Clutch/Pressure Plate combo for even more clamping force.*The Clutch assembly installed onto the 5.3LTransfer Case:
The AutoTrac (NP246) transfer case we have in the Avalanche does not have the correct input shaft size to mate up to the ZF6 (just like with the 4L80e Swap). BUT! The bolt pattern is the same for all of the transfer cases so; this left me with two options:
1) Change to the Transfer Case to the 2500-3500’s NP263 or NP261 (about $900-$1,300)
2) Change the input Shaft $260 self installed or $460 installed
I went with Option #2 and changed the input shaft to the matching 29 Spline shaft for the ZF6. I did this myself in the driveway with instructions I got online, it was strait forward and fun to take apart the Transfer Case and get to see what goes on inside it. After doing this the transfer case bolted right up to the ZF6!
Now you might be thinking that the t-case from a 2500 or 3500 truck (NP261 or NP263) would be a better option but, that wouldn’t be entirely true. The power handling of the NP261 and NP263 over the NP246 is not that much and I love the AutoTrac feature for driving in the Rain and driving in the rain is much trickier with a manual that has this much power in front of it. So, I chose to keep it and IF I ever manage to break the NP246, then I will switch to the NP263. *Seen here is the Input Gear Shaft, the old 27 Spline shaft is removed from the planetary gear set and replaced with the new 29 Spline shaft.Mounts:
The ZF6 is almost 2 inches longer then the 4L80e and 4 inches longer then the 4L60e so; I had to modify the Transmission Cross Member to work with the ZF6. This was easy and I finally got to use my welding skills! I also had to notch out a section of the Torsion Bar cross member as well to clear the Transfer Case.*Seen here is the 4 Inch Extension support mount I made for the Transmission from 1/8 thick steel plate welded at all the seam points.Drive Shafts:
Obviously you will need to make some changes here; you can shorten your factory rear and have a new front made, this is about $350 total… I went for a custom upgraded front and rear using all Spicer Joints and Yokes for more power handling making my cost about $650 total for both.Starter:
I had to swap out to the starter from a 2500HD 6.0L to get proper engagement with the flywheel.Step 4:
Installing the Other Parts…
Clutch Pedal/Master Cylinder: I ordered the factory Clutch Pedal for a 3500 Silverado and after drilling out the pre-marked holes I mounted that it place. YES! Even though the Avalanche was NEVER offered with a manual transmission there are mounting points pre-marked for the clutch pedal! You will have to move the Throttle Body control (two small bolts and have to trim the Brake pedal down to a manageable size but, hey that’s easy when the other stuff is all ready done for you! Since the Master Cylinder was brand new it even came pre-bled and ready for install!
There is a Clutch Safety switch that you can hook up that does two things:
1) Truck won’t start with the Clutch engaged.
2) Releases the Cruise Control if you push the Clutch in.
I have had cars with Manuals that did not have these two safety features and never had a problem so, opted to not hook them up. I really didn’t want to go hacking into the wring to do it but, the Cruise Control is not working at all so it looks like I don’t have a choice and will have to hook it up at some point.*Seen here is the new clutch pedal and cut down brake pedal.Shifter:
Well, if you haven’t figured it out yet you have to cut a hole in the floor for the shifter to come up through. This is pretty self explanatory, measure 13 times and cut twice. HAHA I made the hole just big enough to fit the Shift Tower but, big enough to allow for side to side movement when the drive line twists under heavy acceleration/deceleration. I did this to keep road noise to a minimum; the hole that GM makes is huge and way oversized. The GM Shifter Boot is over $100.00 so; I made my own Boot using a Hurst Rubber Under Boot for sound control, a universal Leather Boot and some Diamond Plate… I think it came out pretty nice for only $32.59.
My used ZF6 was missing the Gear Selector Lever (the part that sticks out the top of the transmission) because it was lost during shipping, GM was back ordered and I couldn’t wait for them. So, I picked up one from a Ford F-350 since they used the ZF6 as well. The Ford shifter is a little different in shape and length but, works out better then the GM one because you don’t have cut the factory knob off to mount a nicer one and the Ford shifter is positioned better (closer to the drive) then the GM one.*Seen here is the entire Shifter assembly I put together.Step 4:
That leaves us with tuning the trucks computer for the Manual transmission, this can be done by Allan at Nelson Performance or if you have access to something like HP Tuners you can do it yourself. I borrowed HP Tuners from BigBlackAv and did it myself. Not hard at all, you just delete all the parameters for the Automatic transmission and turn off any corresponding error codes.
The only other thing to do is you put the old Automatic’s Gear Selector Sensor (under the truck) into Park or Neutral and Zip tie it up out of the way, this allows you to start the truck with out needing to hook up the Clutch Safety switch AND lets the Transfer Case know its ok to engage Low Range if need be.If Frankenstein drove a truck…
Big… Powerful… Loud… Fast… And just plain old Mean… Yep, this would be what Frankenstein would drive…
You would think the ZF6 would be clunky shifting, and hard to drive fast and smoothly considering its heavy duty nature… But, you (and I) would be entirely wrong! This is a German Engineered modern day transmission that is built to be driven and ooohhhhh can it be driven…
have totally fallen in love with my Avalanche all over again! The power difference of the Manual vs. the Automatic is impressive, the gear ratios of the ZF6 are perfection in never being out of the power curve and the clutch feels strong as an Ox. The shift gates are little larger then you would be used to in a car but, you get used to them very quickly. Before you know it you are rowing through gears and barking tires faster then you think…