2005 Joe Radwanski

Edited by Sparky

Acknowledgments

First, I would like to thank Vern (http://www.vernco.com/) for his excellent web page detailing the knuckle bolt upgrade, which is now available once again after this article was original written. I do not know if it is the original but it surely is the defacto standard. The credit for this particular variation belongs to Glenn Miller (jeepngem of earlycj5.com) and to Jim Johnson (jp2flata of earlycj5.com). Without their help my carcass would probably still be out in some remote corner of the desolate Sonoran Desert.*

Background

First, some manner of upgrade to knuckle spindle connection is highly recommended. In the original design the spindle connects to the knuckle with 3/8” bolts from the outside. The bolts go through holes in the spindle and thread into the knuckle. The threading into the knuckle is the problem. First the knuckle is cast iron and the threads have been cut into this cast iron lip. Cast iron threads are not as strong and durable as threads in steel. Actually they really suck. The lip were these threaded holes occur is not very thick, so the weak threads are also few. I would strongly suggest reading Vern’s web page on this subject as well as any others you can find so there is a complete understanding of all the minor complexities involved.

Stock Dana 25/27 Knuckle

Button Head Hex Bolt

This variation of upgrade is based on using a button head bolt. Other upgrades require the use of a particular wheel stud. These wheel studs are not readily available and the source I found wanted about $8.50 apiece for them. At six per side, times two sides, this gets kinda pricey. You may be asking why not a regular bolt? The upgrade requires eliminating the threaded hole and inserting the bolt from the backside. The hex head of a typical bolt would interfere with other moving parts inside the knuckle.

The button head bolts are more readily available and are reasonably priced. They could be purchased at any well stocked hardware store. The bolt I used I purchased from McMaster-Carr, www.mcmaster.com. They are a good source for many hard to find items. They stock the needed bolt. A box of 25 for about the same price as a single stud. Their part number is 91255A647 for the 3/8-24 NF x 1 1/4” hex socket, button head cap bolt. This is not a cheesy non-graded bolt. It exceeds Grade 5 and conforms to ASTM F835. Just right for this application.

Modifying the steering knuckle.

There is simply one thing we need to do to the knuckle for this upgrade. Spotface the backside of each hole. This will give the bolt head a good seat. The castings do vary, but they all have some manner of raised material or boss on the inner wall. Being a casting there are minor variations in the cast surface at each hole location. It is more important that the bolt head have a clean, smooth seat to bear against. This will help to distribute the stresses and therefore give us a stronger connection.

Clean spotfaces for good bearing surface.

It may be worth noting that the wheel stud method requires drilling out the threads, spotfacing and inserting the stud into the hole. Being inserted from the backside, the serrated portion of the stud will hold it in place and prevent it from turning while assembling the spindle. These serrations could slightly weaken the casting. When pressed in each serration produces a stress riser and also becomes a likely place for a crack to begin. This button head variation avoids these possible weaknesses. In fact, the threads can remain in the knuckle, we agree they are weak threads but they will help latter during assembly.

Spotfacing can be done a few different ways. If you have ever done any machining work and are comfortable with this you could do it yourself. Purchase a spotface and chuck it up in your drill press. If you exercise good machine shop practice a quality job will result. I looked into this method and found a spotface with a guide arbor for about $40. If you have no idea what I am talking about you could simply take the knuckles to a machine shop and pay them to do it. It is a simple task for a machinist. I happened to choose a different approach, I called a friend who owns a machine shop and told him I’ll buy lunch. Of course I showed up with knuckles in hand.

However you choose to accomplish this just remember to remove only enough material to give the bolt head a good seat. Milling a seat much larger than the bolt head diameter is removing unnecessary material and weakening the knuckle. They don’t even need to all be at the same thickness.

Here’s the button heads sitting in their spotfaced seats. Notice the brass bushing in the middle of the spindle. Those streaks are the marks your axle splines makes as your spindle leaves the Jeep!

Re-assembly

With the knuckles spotfaced you are ready to install the bolts. By leaving the internal threads in the casting we gain two advantages, a little extra strength and some help in preventing the bolt from turning. Remember when assembling the spindle onto the knuckle the bolt will appear as a stud. In other words, you can’t get a wrench on the bolt head when torquing the nut. Loctite will hold the bolt. While the knuckle is still disassembled (on the workbench), insert the bolts from the backside, use liberal amounts of red (high strength) Loctite under the head of the bolt. Slide the spindle over the bolts, run a nut onto each one and tighten it. This will ensure the bolt head is fully seated and under tension while the Loctite cures, overnight if possible.

The upgraded, reassembled front axle, the finished product.

Carefully re-assemble your steering knuckles and the axles. You know have an upgrade that is an improvement over the factory design.

Enjoy the confidence of an improved, stronger axle spindle. Happy jeep’in.

*Editor’s note, ’tis true, I saw the whole grisly event in person.