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Moses Ludel

Button Head Screw Upgrade for Cast Steering Knuckle Spindle Bolts

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In my Jeep® CJ Rebuilder's Manual:  1946-71 (Bentley Publishers), I discuss and illustrate how to upgrade the spindle bolt arrangement on vintage Jeep® Spicer closed steering knuckle front axles.  I received this note from a friend who is restoring a 1971 Jeep CJ-5 Renegade V-6 model with the 27 front axle.  This exchange is useful for owners debating whether to upgrade the knuckle/spindle bolt design and how to approach the upgrade:

Eric's Question:  "Good afternoon, Moses.  Quick question.  I am doing a full nut and bolt restoration of a Renegade 1 to Jeep showroom condition.  It will not be rock crawled, and will see mostly fire and Forest Service roads plus one or two drives a week to work...Would you go through the process of spindle bolt reversal in my situation?  Thank you for your thoughts in advance.

My Reply:  "Eric...What year is the Renegade?  (1970-71?)  Is your question relating to a closed knuckle Dana 27 front axle and the use of button head Grade 8 hardware screwed outward from the inside of the knuckle—as I describe in the Jeep manual?

I’m guessing that you mean this stud modification for a closed knuckle front axle.  There is a benefit because the OEM bolts go into cast iron knuckle threads.  The tensile of iron castings is low when compared to fasteners/bolts with higher tensile.  The knuckle threads will pull out before graded bolts fail.

Installing “manifold” type (double thread end) studs and nuts is also no solution:  The studs will pull out the cast knuckle threads just like bolts do.  Button head studs, installed from the inside/out, will shoulder against the inside of the casting and cannot pull through it.

These knuckle threads are vulnerable to pulling out of the casting when 1) the bolts loosen, 2) tires are oversized with negative offset and wide wheel rims, and 3) “bouncing” on a rough trail or whoops overloads the spindles.  (You have none of this planned.)  Wide wheels and big tires definitely increase the odds of pulling these spindle/knuckle threads.

If you keep the stock arrangement, and if the knuckle threads still have integrity, make certain the OEM style bolts do not loosen.  Wire tying the bolts, a military protocol, is one solution.  Also, if you do have weak threads, go to Time Fastener at https://timesert.com and get a kit to properly repair the threads.  Don’t bother with Heli-Coils, they are way too weak and work poorly in this application.  If all the threads in the knuckle were Time-Serts, the risk of pulling threads would be dramatically reduced."

Continued from Eric:  "Thank you for the reply, Moses.  Yes, that is what I was referring to.  My Ren1 is a Mar 71 build (about 450 units before the Ren II's started rolling off the line).  Even though the knuckles are in perfect condition, given their age it would probably be in my best interest to do the modification since I am replacing everything with new in the axles (seals, bearings, races, bolts etc.)  I will re read your section in the rebuild manual on this subject again before I attempt it.  Thank you again for taking the time to answer this silly question...Looks to be a very easy and straight forward modification. No worries thanks to you. ;)...Thank you Moses.  McMaster-Carr is what I am going to use."

My Reply:  "Not a silly question, Eric…On a Rubicon Trail run in 1989, driving an FJ40 Land Cruiser project vehicle, a fellow four-wheeler and personal friend from Reno ripped an entire wheel assembly (backing plate/spindle/wheel/tire/brake hose, etc.) off his vintage Jeepster’s closed knuckle 27 front axle...The Jeep had a 350 V-8 and 33” tires.  Bouncing through a “V” of solid rocks, the outside tire tread making only partial contact, his aged front end let out an unforgettable snapping sound.  We spent the next 10 hours driving in the Land Cruiser to Auburn for recycled parts then back to restore the front axle on the trail...If/when you do this approach, be certain the button head screws are high-grade.  You will need to grind/surface (minimally) the knuckle casting where some of the button screws seat.  Otherwise, some screws will not be able to seat well...The casting was not created with machined flats at the inside ends of the thread bores.  You’ll figure this out once there."

My Footnote/Reply with Details:  "You can do it, Eric!  I use a die grinder with a 3/16” or ¼” cylindrical carbide bur to grind a minor amount of knuckle casting where the button screw seats.  On the Spicer 25 knuckles, there were only a few areas of the casting that needed to be flattened slightly or shaped enough to allow the button to seat better.  The idea is to have the square seat of the button head screw fit securely against the casting and not just catch an edge of the button.  Remove as little casting as possible to accomplish this.  If the button fits firmly, that’s plenty.

If you have a die grinder, a carbide bur tool works well.  I buy the less expensive Atrax brand burs at MSC.  You’re grinding on the cast iron knuckle, not the hard button head screw.  Iron casting is relatively soft.  A Dremel tool would work with the right attachment.  The Dremel is less expensive than a die grinder and bur.  The die grinder is much faster, and a bur will last longer.

Here is info on oxide alloy button head (hex socket) screws at Fastenal.  I have attached a PDF with grading details.  (I highlighted the ASTM F835 rating in this case, quite high.)  These screws are available in the length(s) you need, this is an example, see catalog pages for other sizes.  Pick the thread pitch/size and length you need, make sure it meets the ASTM F835 rating: 

https://www.fastenal.com/products/details/24104 

In 1970, I turned 21 and had a passion for the new Renegade V-6 CJ models!  Would have bought one if my income bracket had been higher at the time.  Settled for restoring a 1950 CJ-3A that I purchased the year before at San Diego…So pleased that you’re doing this restoration!  What work have you done?"

Grading Details (PDF) from Fastenal.  Use this grading guideline whether buying from Fastenal, McMaster-Carr or MSC:

ASTM Mechanical Properties Inch Fasteners.pdf

Eric updated that he has ordered these parts and tooling from McMaster-Carr.  Before ordering fasteners, verify the correct bolt/screw thread length needed for your knuckle/spindle and the individual screw locations.  I use toplock (crushed head) style Grade 8 nuts for this application.  The 3/8"-24 (SAE fine thread) screws that Eric ordered are a reminder why the OEM bolts pull the threads out of the knuckle.  Fine threads, though stronger in most applications,  are a recipe for failure in an iron casting:

Eric's CJ Knuckle Screw Order.jpg

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