Toyota Knuckle Stud Upgrade

 

   
 
 

Both the upper and lower knuckle studs on the Toyota axles are 12mm or roughly equivalent to a 1/2" stud.  I haven't had problems with the lower studs but the upper ones tended to work loose after a few runs.  I got in the habit of re-torquing them before every run.  

 A few weekends ago I was going through my routine and twisted one of the studs off in the parking lot.  I knew my day of trail riding was done but I decided to drive out to the trailhead and provide support for everyone else.    Everything was going good and I actually winched someone off the trail after another breakage.  On the way back from the trail things took a turn for the worse.  We were doing about 50mph and I clipped a small boulder that had rolled out into the road.  Immediately the steering felt funny, I glanced over at the drivers side tire for a while but couldn't discern if it was wobbling or not.  I noticed when I actuated the steering wheel, the drivers side wasn't responding.  I had already figured what happened, the blow from hitting the rock had sheared two more studs off.  we came to a stop and accessed the situation.  I ended up driving my tow rig back to the buggy and loaded it onto the trailer.

The best I can figure is the added stress of the full hydro steering and 37" tires is just too much for the existing studs. When you tighten the nut, the stud is designed to stretch which creates tension.  The additional forces the upper studs see must exceed their design limits because they are stretched even more but don't snap back.  So this leads to the continual cycle of tighten, stretch, tighten, stretch until the stud finally lets go. The only way to really cure this is to go to a bigger stud.  This will allow you to torque the nuts down with more force generating more clamping force.  To illustrate this I looked up the specs for a 1/2" Holo-Krome fine thread bolt Vs. a 5/8" bolt.  The suggested tightening torques nearly double and the resultant tension induced by the stretching of the bolt increases by nearly 10,000 lbs.  This upgrade should produce results slightly less than a 1/2" to 5/8" bolt upgrade.

The upgraded hardware can be found at your local GM dealer and are the same pieces of hardware used to mount most Dana 44 steering arms. Gm Part Numbers: 9/16-18 Stud #3965137, Tapered Washer #3965138 and Jam Nut #9442950.  I ended up picking up my parts from Parts Mike, I ordered two complete kits so I would have enough spares for one knuckle. You will also need to put a bigger taper in your steering arm to accommodate the larger cone washer.

In order to fixture the knuckle in the vise I made a plate that bolts to the knuckle via the lower studs.  This puts the top of the knuckle parallel with the top of the vice.  The holes were then re-drilled using a 33/64 drill bit then tapped using a 9/16-18 tap.

Old stud vs. new stud.  When you install the studs make sure the short end is in the knuckle. 

The numbers I used for the stud spacing based on measuring them with a set of calipers, this equates to roughly 30mm x 55mm. This is also the hole pattern I put in my knuckle fixture although two holes was enough to securely bolt the knuckle to the fixture.