AISIN Hubs - Identification and Rebuilding Guide.

When we think of all the manufacturers who make locking freewheel hubs for 4x4s, some big names come to mind: Warn, Milemarker, and Superwinch. But one manufacturer's hubs are probably on more vehicles worldwide that these familar makes combined: AISIN. These hubs have appeared as original equipment on 4x4s from Toyota, Mitsubishi, Isuzu, Chevy, Dodge, Mazda, and Suzuki.

Aisin Seiki is a japanese manufacturing company that makes everything from auto parts to sewing machines to a temperature sensing "shower toilet seat". While I've never tried this latter product (and don't intend to!), their hubs are first-rate.

The hubs have a lot going for them. Their compact size -- about 2 1/4 inches deep -- means they stick out less than most aftermarket hubs, and therefore are less likely to get hit on rocks than deeper aftermarket hubs. The construction is solid: Forty-one of its forty-six parts are made of steel. Two parts (the cap and dial) are aluminum, and the other three are gaskets of various materials. The reputation of these hubs is stellar - I've seen a lot of hubs break on the trail, but never an AISIN.

These hubs do have their downsides. The part count is daunting, though 30 of the parts are simply washers, bolts, and nuts. The assembly, particularly the alignment of the tension spring, is challenging. Good luck figuring out how to put one together for the first time if you don't have a factory manual. And if you do manage to break one, new ones are usually hundreds of dollars apiece. The most common complaint, however, is the difficulty of removing the AISIN hubs from the wheel hubs. There are cone-shaped washers that, when installed, are compressed over the studs in the wheel hubs. This makes for a very solid mating of the parts, but these washers can be very difficuly to remove. Later in this article we'll show you a few tricks to make it easier.

AISIN hubs generally come on imported trucks, and their owners are accustomed to paying inflated prices for replacement parts. But there is some good news - used AISIN hubs are easily and inexpensively rebuildable to like-new condition. And many of the parts are interchangeable between hubs from differing vehicles. For example, you can use a junkyard hub from a Toyota for parts to repair a Suzuki.

I obtained four different flavors of AISIN hubs for this article. Clockwise from top-left in the picture are hubs from an IFS Toyota 4Runner, a solid axle Toyota pickup, a 1993 Isuzu Amigo, and one from a Suzuki Samurai, Of these four, the Isuzu was the odd duck - the hub body was much smaller overall (with a different bolt pattern) than the others, it doesn't use cone washers for mounting, and the dial is built in such a way to reduce the extent of the travel of the clutch. The factors combine to make this hub a very compact unit. Still, the clutch, pawl, springs, and other parts are compatible with the other hubs.

The Suzuki and 30-spline Toyota hubs are virtually identical except for the inner hub. The grips on the dial of the 30-spline Toyota hub stick out slightly beyond the cap, where on the others, it is flush. Functionally, the dials are interchangeable between the Suzuki and 26- and 30-spline Toyota hubs. The 26-spline (IFS) Toyota hub has a deeper backspacing between the mounting flange and the inner hub than the other hubs, in order to clear the spindle nuts. Because of this, the Suzuki or 30-spline Toyota hub body will not fit on an IFS toyota wheel hub, but the reverse should work; i.e. a 26-spline Toyota hub body should be usable on a Suzuki or 30-spline Toyota hub.

Theory of operation:

The part of the hub that actually engages the front driveshaft is called the inner hub. It is sized appropriately for the diameter and spline count of the axle being used, and is the major part that is different between hubs intended for different vehicles. When disengaged, the inner hub, attached to the axle, spins freely (or rather, stays put while the wheel spins around it) in the free wheeling hub ring, which is a piece of steel with a brass bearing surface, that centers the axle in the hub.

The outside of the inner hub has 22 splines. When the dial of the hub is set to the LOCK position, a steel clutch with 22 internal splines is pressed inward, engaging the splines of the inner hub. The clutch itself slides in the thick splines of the hub body, so that when engaged, the inner hub cannot rotate relative to the hub body. Torque from the axles is therefore transmitted through the inner hub, the clutch, and into the hub body. The body is securely bolted to the six studs on the wheel hub, finishing the torque transfer from the axle to the wheels.

When disengaged, the clutch is pulled outward from the inner hub. This allows the inner hub to rotate independently of the rest of the hub and wheel.

Procedures for a rebuild:

Removing the hub from the wheel
If your front wheels do not have sleeves covering the hubs, you don't even need to remove the wheel. I suggest ditching the sleeves anyways since they tend to trap water.

Make sure the dial is set to the "FREE" position. Remove the 6 cap bolts with a 10mm socket. Slide out the cap and clutch assembly. Note if there is excessive water, rust, or oil inside.

In some applications, you'll now need to remove a nut and washer at the end of the axle. In others, there may be a snap ring or other retention device.

With a 12mm socket, remove the 6 nuts holding on the hub body. Remove the 6 flat washers. The cone washers will be still holding the hub tightly. Its nice to know the hub will still hang on if a fastener falls off on the trail!

Maybe you'll be lucky and the cone washers will wiggle right out. More likely, they will need persuasion. The best way is to essentially vibrate them enough so they pop up far enough to grab with needle-nose pliers. This can be accomplished in several ways. One method is to find a socket with an inside diameter greater that the washers. Slip it over the end of the stud, and tap in gently with a hammer, being careful not to mar the hub body.

This is often the only encouragement the washers need. If gentle tapping doesn't work, spray a little pentrating oil on the washers, and hit the socket harder. A large brass punch can be held directly against the studs and whacked good with a hammer. Brass is soft enough to prevent damaging the studs or hub, but hard enough to transmit the shock loads we need. If that still doesn't work, put the nuts back on the studs, with just enough turns so they stay at the ends of the threads, then using the hammer and brass punch, beat on the hub body in various places. This can be so effective that the washers will literally fly off the studs. The nuts we slightly threaded on the end of the studs will prevent this.

With the hub off, its a fine time to to inspect and/or repack your wheel bearings. If you saw any signs of water inside the hub, you should plan on a repack. Water can get in via poorly-sealed gaskets on the hub. But it can also arrive through the spindle, For examples, on IFS Toyotas, sometimes water can get in between the outer CV joint and spindle. It then travels through the spindle and into the hub, where it rusts the hub and destroys the outer wheel bearings.

Wipe out any excess grease from the hub body assembly and hub cap assembly.

Disassembly of hub body
The hub body assembly consists of 6 parts: The hub body itself, the inner hub, the free wheeling hub ring, a washer between the hub ring and the hub body, and two lock rings. Remove the large inside lock ring near the base of the hub body, and slide out the inner hub, hub ring, and washer. Remove the smaller outside lock ring to separate these parts from each other.

Disassembly of cap
While gripping the dial with one hand, with the other hand press the clutch against the cap and turn counter-clockwise, in the manner you would open a child safety cap on a bottle of medicine. Note that there are two springs of similar diameter. This is normal, but the two springs are sometimes mistaken as one broken spring. Separate the springs from the pawl and clutch, carefully noting their alignment for future installation.

The springs are the parts that actually move the clutch in and out. When you turn the dial to the LOCK position, the compression spring is free to press the clutch in, as soon the the splines on the inner hub and clutch line up. Conversely, when the dial is set to "free", the tension spring pulls on the clutch, which moves as soon as any bindup is relieved.

To take apart the cap itself, remove the single lock ring beneath the cap. Now, carefully press the dial inward. Inside the dial betneath the indicator arrow is a tiny spring and ball that engages detents in the cap. Don't lose these. Carefully pry off the rubber o-ring around the dial.

Cleaning
We've now completely detail-stripped the hub. wipe off any excess grease and clean the parts individually. I like to use mineral spirits in a metal can to soak these parts. Harbor Freight Tools sells an inexpensive parts cleaning can (#35400) with a lid and a spring-loaded parts tray that is the perfect size for cleaning hubs, but a large coffee can will work. I like to let all the parts (except the o-ring) soak for at least a few hours. Using a toothbrush or parts cleaning brush, try to get all the gunk off of all the surfaces.

If you don't like dealing with solvents, a good cleaning with soap and water and engine degreaser can be effective. If you go this route, be sure to let everything dry thoroughly and then spray a light coat of WD-40 or gun oil on the parts to avoid any rusting.

If there is any rust in the parts, it is often just minor surface rust that can be removed with steel wool or wet/dry sandpaper. Minor pitting is OK, but if there is deep corrosion in the inner hub or clutch, you might want to consider getting another hub to use for parts.

A fresh coat of paint on the cap and dial can really make an old hub look brand new. Any color is fine, time to be creative. I've been painting my rebuilds black with a blue dial. Be sure to mask the inside of the cap and outside of the dial to prevent paint from getting on the seal surfaces. Several coats will last better than one. You can sand down the high points to make the pointers and words appear in bright aluminum against your background colors. I've never painted the usually-chrome hub bodies, but I can't think of a reason it wouldn't work.

Reassembly
Inspect your hub body. Sometimes the cap surface isn't flat because the hub has been beat against a rock. Flatten it out with a file to assure a good cap seal.

Assemble the hub body / inner hub assembly in the reverse of the method you used to disassemble. Apply a coating of grease on all contact surfaces - the bronze surface where the inner hub engages the free wheeling hub ring, both sides of the washer between the two parts, and the inner and outer splines of the inner hub. Here and elsewhere in the hub, don't use too much grease. We need to lubricate these surfaces to guard against friction and moisture, but we don't need to 'pack' the hub. I've opened up several hubs where there was so much grease it actually interfered with the operation of the hub.

Inspect the rubber o-ring seal. If it is cracked or otherwise damaged, replace it with a new one. Lightly coat the o-ring in grease, and slip it over the dial. Carefully insert the spring and ball inside the dial, and slide the dial into the cap. Make sure the pointer is between the FREE and LOCK positions. Turn the dial between these positions, making sure you here a click as it engages each position. When you're satisfied with the operation, install the lock ring. Set the dial to "FREE".

Using a cotton swab or similar tool, coat the diagonal ramps in the dial with grease. You don't need to be as stingy here - the pawl slides against this surface as the dial is turned, so good lubrication here will assume smooth function. Well-lubricated o-ring and ramps can really make the difference between a hub that simply works and one that is really smooth and easy to use.

Assembly of the clutch and tension spring
Lubricate the inner and outer splines of the clutch. Now comes the tricky part that always has me running for the factory manual. The tension spring holds the pawl to the clutch and is tricky to align properly. The end without the bend snakes into grooves in the clutch, until the end lines up with the gap in the clutch (see picture).
The end with the bend is also tricky. There are two tall and two short tabs in the pawl. The bend in the spring wraps just under one of the tall tabs, over a short tab, under the other tall tab, and over the other short tab, then down to the clutch. See the picture. It can be very tricky getting it all to line up correctly. When the spring is properly aligned on the pawl, double check to see that it hasn't slipped out of position on the clutch.

We're done with the hardest part. Slip the large compression spring over the pawl, and press-and-turn the clutch/pawl/spring assembly into the grooves of the dial in the FREE position. Rotate the clutch and pawl up the ramps of the dial so that they are tight against the cap.

Note that the pawl has tabs that cross the gap between some of the splines of the clutch. Align these tabs with the wide splines in the hub body, and slip on the cap assembly to the hub body. Temporarily install two opposite cap bolts. We want to test functioning.

With the dial still in the FREE position, verify you can, from the base of the hub, turn the inner hub relative to the hub body. Now, switch the hub to the LOCK position. If you can't turn it all the way, something is wrong - remove the cap and check the alignment of everything. If it works correctly, you'll hear a little click as the ball in the dial engages the detents in the cap. Depending on the relative position of the splines of the clutch relative to the inner hub, you may or may not hear a louder noise of these parts engaging.

Now, try to turn the inner hub relative to the hub body. If the splines happened to engage perfectly when you turned the dial, you will not be able to turn the inner hub. If they didn't engage right away, you'll be able to turn the hub a very small amount before the springs slam the clutch into postion. Either situation is ok, as long as the inner hub locks relative to the body. Turn the dial back to FREE. Verify that the inner hub is now free to turn.

Remove any remaining gasket material on the wheel hub and install a new gasket. Some RTV sealant will work in place of a gasket, but I always use the proper gasket if its available. Install the hub body, cone washers, flat washers, and nuts. Some anti-sieze compound on the studs and cone washers will make later disassembly much easier. Use a star-shaped order in tightening the bolts (like you would on a wheel) to ensure even seating. Torque the nuts to 23 ft lbs.

If your application requires it, install the nut and washer at the end of the axle, or whatever retention mechanism is on your axle.

Install the cap assembly and a new gasket as we did before. I like to jack up the wheel and test operation on the vehicle. If everything still checks out, torque the cap bolts to 7 ft-lbs.

Maintenance:

The hubs don't really require any regular maintenance. Water is the number one enemy of your hubs and your front wheel bearings, so after any excursion where you forded water deep enough to submerge the hubs, its a good idea to pop off the cap and see if water got inside. If so, repack the wheel bearings and clean and lubricate the parts of the hub.