Skip to content
6/18/24 - We are working on website, production, and some in-shop project work. If item(s) you need show "sold-out" on site, please contact us for availability, those parts may be in stock. Thank you.
6/18/24 - We are working on website, production, and some in-shop project work. If item(s) you need show "sold-out" on site, please contact us for availability, those parts may be in stock. Thank you.

6L90 Transmission Bolt Up 4x4 Conversion Kit

Sold out

This is our updated high-performance adapter setup for converting the 2 wheel drive 6L90 to 4x4 without cutting anything. Our beautiful adapter tube is milled from a solid piece of billet Aluminum and is both extremely strong and not overly heavy. This adapter tube pairs with the hardened Chromoly stub shaft that changes the output from your 2WD 6L90 to match the input pattern found on many popular 241, 261, or Magna transfer cases. 

(Aluminum design replaces blue-coated welded previous iteration in photos.)

To accomplish this, simply remove the 2WD extension housing, bolt up our adapter housing and our machined chromoly stub shaft, and your compatible 241, 261, or Magna transfer case will bolt right up. 

This adapter kit serves multiple functions. Firstly, it eliminates the need to trim your 2WD output shaft. It shifts your transfer case back several inches, resulting in a shallower drive angle (reducing driveshaft feedback). Lastly, our spline adapter changes the output pattern from 36 splines (6L90) to a 29-spline design which fits many common NP/NV and Magna GM transfer cases. 

**As a quick note, this adapter does not impact the fuel tank. All GM 4x4 conversions using our parts can be completed without removing the fuel tank, both LWB and SWB vans. 


This kit is available 2 ways. You can either purchase just the adapters with the black mounting plate shown, or can also include the installation kit which includes the mount, gasket, gasket sealer and hardware to attach the t-case. 


We prefer the New Process 261 transfer case due to its quiet operation and durability. This noise reduction aspect is particularly relevant in a 4x4 van, where you're seated directly above the t-case.

The NP261 transfer case was used in many GM 1500/2500/3500 pickups from 1999-2006 and came with a 32-spline input (LD), and a 29-spline input (XHD). Our stub shaft is designed to work only with the 29-spline (XHD) input.

The XHD t-cases can be expensive, even used, and the LD case is perfectly sufficient for the vast majority of GM 4x4 conversion vans, so we now offer a direct replacement 29 spline input for the LD 261 transfer case. 

In short, if you are working with an NP261 transfer case that didn't come out of a Diesel or 8.1 pickup, you'll need the 29-spline 261 input in addition to this kit.

Non-van compatibility:

We have sold many of these kits to people converting non-van vehicles. This is a viable solution for custom applications and will operate just the same. Since the adapter tube pushes the transfer case further rearward than a typical 4x4 transmission, measure 10 inches back from the transmission body (pre-extension housing) and add your transfer case length to determine any interference. (Our adapter is just over 9" in length.)

The footer for the transmission tube is set up for a standard GM 4x4 transmission mount. You can visit our Multi-purpose GM trans mount kit which is a flexible adapter set for properly mounting your setup. (This is not required for Timberline van conversions.)

Fitment Designed for: 

Van Side - 2010-2023 Chevrolet Express 2500/3500/4500 series vans with 6L90 Transmission (4.8L, 6.0L, 6.6L, 6.6LGas). 

Will work with any 2WD 6L90 transmission, though please verify clearances for custom projects as noted above.

Tools Required:

Standard hand tools, RTV type silicone of your choice for sealant.


Transmission adapter tube assembly, Chromoly spline shaft, tensioning spring, steel trans mount adapter plate. Mount, hardware, RTV, Gasket, and hardware for full package. 

Tips / Skill Level:

1-10 (10 being most difficult) Level 1

This product may work with other model vehicles. 

Torque spec on M10 transmission case bolts and transfer case nuts is 37 Ft-lbs. 

Other Pertinent Part Numbers -  Anchor 2638 Transmission mount

Shipping, Fulfillment, Taxes, Quality, and Returns
  • Shipping: Our components are carefully wrapped & packaged and shipped via UPS, USPS, or FedEx, depending on what is available. If you require a particular carrier, please contact us ahead of your purchase.  Customers in Colorado may arrange for in-person pickup within 1-2 business days of purchase. 
  • Shipping/Fulfillment time for components: We typically ship within 1-2 business days of your order and we carefully monitor our inventory. In the event that we are unable to meet that timeframe, we will contact you and arrange either a full refund or a timeframe for fulfillment agreeable to the customer. 
  • Taxes: Colorado residents must pay a sales tax of 7.5%, no sales tax is collected on out-of-state shipments currently. 
  • Quality and Returns:  We are consistently complimented on the quality of our products and the ease of installation. Fabricated components are generally hand-built here in Colorado by seasoned professionals. Replacement or aftermarket parts are only offered in high-grade options.

    If you are in any way disappointed in the components, we will issue a full refund less the cost of shipping when the product is returned within 30 days of receipt. If you decide to return any components that didn't apply to your build or you changed your mind about, a shipping+15% restocking fee will be deducted from the refund.