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6-Speed ZF S6-650 transmission Swap

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Old 10-28-2007, 07:45 PM   #1
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Default 6-Speed ZF S6-650 transmission Swap

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!

I know plenty of guys out here have converted there 2wd Silverado’s to run a Tremec T-56 6-Speed transmission 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 Diesel

Transmission 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 0.72:1

Let the Madness begin!!!!

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.
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*LS Series Bell Housing mounting points seen here marked in RED.
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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… 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.
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*Seen here is the ZF6 next to a cordless drill for size comparrison.
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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 5.3L
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Transfer 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.

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.
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Drive Shafts: 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.

Installing the Other Parts…
*Seen here is the new clutch pedal and cut down brake pedal.
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Shifter: 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 parts are 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.

*Seen here is the entire Shifter assembly I put together.
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[size=12pt]If Frankenstein drove a truck…[/size]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…

I 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…

My big b!tch...
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Old 10-28-2007, 07:53 PM   #2
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that thing is a beast
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Old 10-28-2007, 08:12 PM   #3
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Cool install.

But to back up my T56 install, i've towed my boat to the lake several times and one trip being 100 miles round trip on the interstate averaging 80 mph. Also towed a tractor etc.

Just because Dodge wouldn't give the SRT-10 a towing rating doesn't mean it can't tow well.

I find that 5.13 gears do well towing with 32" tires and pull 2200 rpm at 80 mph and 16-17 mpg with my T56.
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Old 10-28-2007, 09:47 PM   #4
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Seems to me that my T-case is already pretty tight up against the torsion bar support. Didn't think you could bump it back another 4 inches.
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Old 10-29-2007, 12:15 PM   #5
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TurboGibbs, yea i would think with the right gearing and driving habits the T-56 could tow... But, I don't want to be the one that says that. LoL

DrX, I did have to notch out a small area of the Torsion bar support to fit everything. Didn't seem to weaken it at all but, i did weld two little gussets in place for saftey's sake...
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Old 10-29-2007, 04:16 PM   #6
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man that trans is huge ! . . . . . nice write-up/install. I think that a TB column cover will hide the shift boot.

You need to get your coustom name changed to Frankenstein's truck !
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Old 10-29-2007, 04:24 PM   #7
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You have one bad-*** looking truck! All I have to say is WOW!!

A+ for innovation on the tranny swap too. Very impressive.
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Old 10-29-2007, 04:43 PM   #8
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wow, baddddasssssss!!! I envy you , I want to go manual someday, whats next on the list? Solid Front Axle Swap
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Old 10-29-2007, 05:29 PM   #9
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Looks great.
Nice write up Great info to know. someday maybe i'll go with a stick if my leg feels better.
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Old 10-29-2007, 06:11 PM   #10
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thanks guys!
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