The time has come, I have my RockBox and I'm going to be installing as soon as possible. My buddy is giving me his SBC 305 after I found that mine was in worse shape than I thought. I will keep this site updated as well as I can as long as I don't forget the camera or batteries I should be good. Wish me luck.

 

*The below text is taken out of the Advance Adapter Inc. literature that came with my unit.

 

The RockBox is designed as a low-geared reduction unit for Toyota Land Cruisers. This unit offers a 3.44:1 low reduction to your stock drivetrain. The RockBox, Part No. RB4210, fits the SM420 GM transmission. This kit is designed to fit the stock 10 spline transfer case, but we also offer this unit to fit a 16 spline transfer case (P/N RB4216).

 

To install the RockBox into the Land Cruiser with the SM420 4 speed transmission, the transfer case must be removed from the vehicle. A 1" body lift is recommended to avoid doing floorboard modification.

 

On the SM420 transmission you will be required to grind the ear down on the drivers side of the transmission. This is to clear the shift rod of the RockBox. This should be done before installing the adapter plate portion of the RockBox. The photo below shows the completed modification.

 

Refer to a Toyota service manual for the removal of your stock driveshafts and transfer case. This installation will require the stock driveshafts to be modified (shortening the rear and lengthening the front) to compensate for the RockBox installation.

 

The transfer case must be unbolted from the transmission and both surfaces must be cleaned. If the SM420 is currently installed into the vehicle you can install the RockBox with the Transmission remaining in the vehicle, or if the SM420 is a new installation the RockBox can also be easily installed to the SM420 on a workbench.

 

 

The RockBox must be assembled onto the transmission in two parts. We have pre-assembled as many components as possible to expedite your installation.

 

The first step is the adapter plate installation. This adapter plate adapts the RockBox to the rear of the SM420 4 speed transmission. As you begin the installation, be careful not to pull on the output shaft. If the output shaft is pulled outward from the transmission, the needle bearing that pocket into the input shaft could fall out.

 

The adapter plate indexes onto the stock rear output shaft bearing and is secured by eight socket head bolts. We have installed a new seal to isolate the transmission fluid from that of the RockBox. Do not use a stock gasket. Use a small amount of 518 Loctite gasket eliminator on the rear surface of the transmission. Make sure the Loctite is completely around the outside edge of the sealing surface so that when the adapter plate is installed it creates a bond to prevent any fluid leaks. Install (8) 3/8"-16 fasteners through the adapter plate and into the transmission. These bolts should be installed with a dab of Loctite 518 to seal the tip of the bolts, and there should also be a dab of loctite Thread Retainer on the threads of the bolts. Torque these bolts to 30 ft./lbs. Note: The adapter plate also has the shift rail seal pre-installed.

 

 

The RockBox drive gear and output shaft spacer will need to be installed. However, before putting the spacer onto the stock pain shaft you will need to remove the stock snap ring from the transmission output shaft.

 

The spacer sets the drive gear at the correct distance to mate to the cluster gear and also sets the end play on the transmission output shaft. Once the spacer is installed, the drive gear will need to be installed. Since the RockBox drive gear fits to the stock SM420 output shaft, you should check the output splines of the SM420 for excessive wear and replace the shaft if necessary. Use a small dab of oil on the ground diameter (seal surface) of the gear to allow an easy slip through the seal that is installed in the adapter plate. Once the drive gear is in place, make sure it is secured by installing the retaining washer and retaining bolt. The bolt needs to have thread lock on it then torqued to 85 ft.lbs.

 

 

The next step is to mate up the case portion of the RockBox. This is section has the shifter rod cluster gear and cluster pin, slider gear, and the new output shaft installed.

 

The case portion of the RockBox must be aligned to the adapter plate as you install the case. Alignment issues that must be considered are as follows: The thrust washer on the cluster gear, the tab on the washer must fit the pocket on the adapter plate) the shift rod must pilot on the adapter plate and the cluster pin must be piloted.

 

 

Use loctite 518 and apply one or two beads to the case flange to seal the case to the adapter plate. Taking all these alignment issues into consideration you'll need to assemble the case to the adapter plate. To simplify the alignment issues we have found that the thrust washer on the cluster can be placed onto the adapter plate and held into position with assembly grease. DO NOT FORCE THIS UNIT TOGETHER. It should slide together smoothly. The output shaft of the rockBox may have to be turned slightly to alighn the helical gears. The only other part that may give you a bit of fitting difficulty is the cluster o-ring going into the adapter plate.

 

 

As you assemble the case portion to the adapter plate and have the first part of the cluster pin piloted into the adapter plate, you can remove the bolt that holds the pin in place. This will allow you to finish sliding the case to the adapter plate smoothly and not disrupt the thrust washer on the pin. Once the case is together, tap in the two dowel pins until they are flush with the case surface. Install two bolts to hold the case to the adapter and then simply tap the cluster pin back into the case and reinstall the retaining bolt. (Note: The RockBox is shipping to you shifted into the low gear ration. This is to hold the low gear into place and allow for an easier assembly)

 

Once the case is successfully mated,start installing the case bolts and finish bolting the case halves together by torquing the bolts to 30 ft./lbs. Spin the output shaft to check that everything went together correctly. The shaft should spin with consistent pressure and not have any feeling of binding.

 

Once the RockBox is installed to the transmission we recommend installing the RockBox shifter bracket to the top of the SM420 4-speed transmission. Remove the front top two bolts of the transmission top cover and install the shifter bracket. We also recommend that you install the heim joint on the shift rail with the jam nut on the rock box.

 

 

Before installing the transfer case to the RockBox install the transmission and the RockBox back into your Land Cruiser and secure it to the stock bellhousing (if the transmission is out of the vehicle). Note: Due to the extra length of the transmission and RockBox, you may need to temporarily remove the rubber bellhousing mounts, letting the engine tilt back and allowing for an easier transmission installation. Be sure to have a jack under the engine for proper support. Test fit the stock transfer case into the Land Cruiser and check for floorboard clearance. The easiest way to do this is leave out the transfer case input/drive gear.

 

The transfer case is 5.75" inches further back than stock. The stock tubular crossmember may also be required to eather be removed or relocated further back to clear the new transfer case location.

 

Once these modifactions have been considered, install the stock transfer case to the RockBox using the gasket with gasket sealer. Install the transfer case drive gear and bolt the transfer case to the RockBox using the (3) 7/16"-14 x 5" bolts and the (2) 7/16"-14 x 1.5" bolts. Torqued to 30 ft./lbs. Install the output shaft washer and nylon lock nut to the output shaft locking the drive gear and PTO gear/spacer in place. Torque to 75 ft./lbs.

 

Since this assembly is fairly long we suggest the installation of our rear transfer case crossmember mount. This mount bolts to the rear of the transfer case and extends outward to the frame rails.

 

Install parking brake, speedometer, and new driveshafts acording to Toyota service manual. A longer parking brake cable and speedometer cable may be necessary. We offer an extension speedometer cable under P/N 716186-C.

 

Locate the shifter bracket for the RockBox on the transmission and cut an access hole in your floorboard for the installation of the shift handle. Bolt the shifter handle to the bracket and then connect the heim joint to the shifter handle clevis. Test shift the unit and adjust the linkage to achieve proper lever throw. Since the RockBox is a non-synchronized unit, the transfer case needs to be spun slightly to allow for the gears to mesh. Install the rubber boot to the floor.

 

The stock transfer case linkage will require modifications to compensate for the 5.75" of length added to the drivetrain assembly. We also offer a new modified transfer case linkage which changes the transfer case to a twin stick operation, P/N 715570.

 

Finish installing the driveshafts and reconnect anything else that may have been removed or disassembled. The RockBox is a self-contained unit that uses Torco MTF fluid or equivalent. The RockBox also has a brass elbow that requires a vent hose to be connected to it which will need to be run up into the engine compartment.