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Hydro Tap Toyota IFS Steering for More Power

Posted in How To: Transmission Drivetrain on July 25, 2017
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Toyota 4WD IFS power steering boxes used from 1986 to 1995 on trucks and 4Runners are a reliable, stout component. They are often used on solid-axle swaps done on later-model IFS Toyotas as well as finding their way onto Samurais and various other vehicles.

Three different power steering boxes are found on these Toyotas. An early-style 4WD box was used on 1986 to 1988 pickups and 1986 to 1989 4Runners. Later-style boxes were used on 1989 to 1995 pickups and 1990 to 1995 4Runners. Externally the early and late boxes vary in that the input section of the box is about an inch shorter on the early version. Internally they differ as well. There are also two later boxes with the year split about 1991 to 1992. Externally these seem very similar, but inside the power piston nut and sector shaft gearing is different. Also, the later boxes have a quicker internal gearing ratio, taking fewer turns of the steering wheel to fully exercise the range of the box. All year boxes mount the same way, and the hose tap locations are the same.

These steering boxes work well for adding hydro assist and can easily be tapped to provide the pressurized fluid for the hydraulic ram. Essentially we are using the pressurized fluid exerted on one side or the other on the piston, and routing it to one end or the other of the hydraulic-assist steering ram. One line will be pressurized when turning left and the other when turning right.

Here is what it takes to tear down, tap, and reassemble a Toyota IFS steering box. This particular steering box was from a 1994 4Runner. Steering boxes typically leak a good bit of fluid during disassembly. The Toyota service manual provides a far more detailed description of the rebuild than what we can show here. Should you happen to fully unscrew the power piston during the process, you will spill out the ball bearings inside. The Toyota manual provides instructions for their reassembly, and we have used them with success in the past.

With the pitman arm pulled off, the steering is centered in the middle of its range. Disassembly of the steering box starts with the removal of four bolts and the cross, or sector, shaft assembly. It may be necessary to tap the bottom splined end a bit to start the shaft moving out of the housing.
Some versions of these boxes have a centering valve that’s accessed from the top. We have found it best to remove the threaded plug with a well-fitting 10mm hex driver on an impact tool.
Here is the threaded plug and the parts that lie underneath that need to be removed.
Next, the worm gear valve body can be unbolted and separated from the gear housing while pulling the power piston assembly from the housing. If you don’t want to deal with the ball bearings in the power piston nut, then don’t unscrew it from the worm gear. In fact, you can turn the box fully left to retract the power piston up against the valve body.
The sector shaft oil seal at the lower end of the housing is removed, followed by a snap ring, a metal spacer, an O-ring, and a Teflon ring. At this point the sector shaft needle bearings that are pressed in the housing can be inspected.
Here is the bare gear housing after full disassembly. It’s good to familiarize yourself with its construction and note where the fluid paths are. Before drilling, we taped closed or blocked with rags some areas of the housing to keep metal shavings from entering the fluid ports or bearings.
One good location for the first hydro-assist port is on “TOYODA” on the upper portion of the box. The housing is thick here, but check before drilling to make sure this location does not interfere with your front body mount or anything else on your vehicle. Basically this port can be located most anywhere in this general area. It’s more evident once you have the housing stripped down.
Once the gear housing has been drilled to 7/16 inch on the side, 1/4-inch NPT threads are cut to accept a hydro-assist port fitting. Thread depth can be checked during tapping to ensure the installed fitting will not protrude too far inside the housing.
The second location to be tapped is on top of the steering box on the raised rib shown here. A passage lies under this rib and is where fluid is passed from the front of the box back to the main part of the housing. The goal is to drill the hole in steps, then tap to access the center of this passage without drilling past the passage. To get the threads cut deep enough it may be necessary to use a bottoming tap or cut down a standard tap, as we have done in the past. Again, it is good to be mindful of metal shavings and thoroughly clean the inside of the housing before reassembly.
We figured that while we had the steering box torn apart was a good time to do a reseal job to refresh the box. Here is the basic seal kit we used. We liberally lubed each seal with power steering fluid prior to installation.
When resealing the steering box, it is important to replace the smaller O-rings that are used at the gasket surfaces on some of the transfer ports.
New Teflon seals were provided for the worm assembly inside the control valve and on the power piston nut. Care should be exercised when installing new Teflon seals so as not to overstretch them. They should be lubed with power steering fluid and reassembled with care to prevent nicking or cutting them.
The power piston assembly is carefully reinserted back into the housing, being careful not to cut or otherwise damage the Teflon seal on the sharp bore edges.
The centering valve is reinstalled in reverse order once the valve body has been reinstalled.
New seals and components are installed at the lower output opening of the housing. They are lubed prior to insertion of the sector shaft.
Another O-ring fits on the sector shaft end cover.
As we mentioned, two versions of this later box were used. The top sector shaft here has three gear teeth while the one below has four. We currently have no evidence to favor one over the other. Just note there are some internal differences.
The final piece to go back in the housing is the sector shaft assembly once the power piston has been aligned to accept it.
Here you can see the two fittings we happen to use for our hydro-assist ports. Each is a steel fitting that is 1/4-inch NPT male on one end and No. 6 JIC male on the other.
Final adjustment of the sector shaft play is done after full assembly by turning the slotted head on the top of the box, then securing it in place with the jam nut. Adjustment should be made with the steering box centered in its travel, and you will usually want to recheck this after cycling the box on the vehicle a bit.

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