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Heim Joint Size Does Not Match the Mounting Stud


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Gonna pull my hair out over this one.  Trying to connect the 3/8-24 threaded brake booster input rod to the 1/2" stud (seen above aforementioned coupler in the photo) on my brake pedal rod.  The connector they sent is 3/8-24 threaded with 3/8" opening.  Can't find a connector with 3/8-24 threads with 1/2 inch opening anywhere.  Could go with 1/2-20 threaded connector with 1/2 inch opening but can't find anyone who makes reducing nut coupler for fine threads to get it connected to the 3/8 inch booster input rod.

 

Suggestions?

 

David

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David...I looked online for reducer couplings and heim joints.  In my search, couplers were straight-through thread size.  Heim joints each had the same thread size and stud bore size, an industry standard.

 

A couple of ideas...First, what's holding the stud pin to the pedal arm?  Is that a pressed-in 1/2-inch stud with a weld on the opposite side?  Or something similar to that arrangement?  If so, the stud could be drilled just enough to break the weld, then pressed out.  Cut the head off a long shoulder 3/8" Grade 8 bolt, leaving a proper length stud plus its threaded end. 

 

This bolt shoulder/shank would run through the pedal hole and could be welded on center at the opposite side to the pedal, localizing the heat to prevent loss of heat treatment in the bolt's shank.  TIG would be ideal for this kind of weld, it has a narrower heat affected zone (HAZ).  The 3/8" heim joint would slide over the stud and be held in place with a Grade 8 flat washer and top lock nut.  A 3/8" Grade 8 stud in this position would be strong with the heim aligned straight toward the booster.

 

Note: If there is concern about the gap between the bolt's shank and the bore of the pedal hole, an alloy steel sleeve or bushing, pressed into that gap, could solve the issue.  The sleeve would go into place with the bolt shank and be part of the weld at the back side of the pedal.  If TIG process, a slight weld could also be performed at the heim joint side of the stud, making sure the weld's crown is flat enough for proper fit of the heim joint.  This would be a tightly fitted stud, likely much stouter than the OEM pedal and stud.

 

Another solution would be the use of a 1/2-inch "female" heim that has a 1/2-inch stud bore size and a 1/2-inch thread size on the female threaded end.  The booster push rod stock of 3/8-inch 24-pitch could be centered in the female thread end of the heim joint and TIG welded in place.  TIG welding has great penetration without a wide heat affected zone (HAZ).  Confined to the end of the joint and done properly, the weld would not diminish the tensile of the threaded rod or the heim joint.  Since this rod pushes, it is not subject to pull or elongation stresses, and a proper weld would hold the rod on center.  The only downside with this is the confined space for this weld as illustrated in your photo.  Welding in this confined space would be tricky and require protecting the brake booster from heat.

 

Any welding around the stud or heim joint threaded end should be performed with TIG.  MIG (GMAW) and stick arc (SMAW) temperatures would be too high.  The only alternative would be brazing with a high tensile filler like Weld Mold 26-C (100,000 psi tensile strength!)  This would actually fill the thread area between the graded rod stock and heim threaded female end. This particular type of brazing can be done at a lower temperature of 1600 degrees F.  If done properly, the pushrod and heim would not "normalize" or anneal in the process and lose its tensile strength.  Here are details on Weld Mold 26-C brazing rod:  http://www.weldmold.com/weld-mold-26-c/.

 

If the reduction in stud size is worrisome, consider making a pedal "saddle" bracket to support a 3/8" Grade 8 bolt.  In this scenario, the pedal would be modified to have an extension saddle with an outer flange parallel to the pedal arm.  Again, you would remove the existing stud.  Instead of cutting the head from a 3/8-inch bolt, design this saddle or cage to support a through bolt.  The heim joint would be "bolted" in place and secured to keep the heim's center from rotating.  The bolt would be a pivot shaft rather than a stud if that works better.

 

From a strength standpoint, here are fastener specifications from Fastenal.  Our concern for a bolt or bolt shank in this position would be shear strength: http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf.  Note the details and comments on the shear strength of bolts.  1/2-inch diameter is clearly heftier than 3/8".  Assess the hardness and strength of the OEM pedal stud.  Make sure your approach takes these size differences into account.

 

Moses

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Moses,

 

I really appreciate your help with this.  I am hoping to be able to fix this without taking the brake pedal assembly apart.  In other words, I don't think cutting and pressing the stud out would be my first choice.  I thought about that but on the other side of the brake pedal rod it looks like this is pressed in place.  See the pic.  The brake pedal is the second from the top.  Sorry, it's the best pic I had of the other side.  The other problem with pressing it out, as far as I can see, is if I press the 1/2" stud out, it leaves me with a 1/2 inch hole and as you alluded to, I would end up trying to weld a 3/8" bolt into a 1/2" hole.

 

I even thought about trying to use a grinder to grind the stud down from 1/2" to 3/8" and hoping to get it as perfectly smooth and round as I could, but obviously that was just a thought that came from desperation.

 

The thing that argues in favor of trying that approach is if you look close enough at the pic, where the stud and the previous brake input rod eyelet were in contact, the stud has been worn down pretty good.  Using a spherical rod end is definitely an upgrade from stock in that regard; should prevent wear down the road (no pun intended).

 

I think what I am going to do is order a 1/2" spherical rod end and have that new end TIG welded to the end of the 3/8-24 rod.  The downside.....I lose the ability to fine tune or adjust the input rod effective length.  Will probably err on the side of having it just a little short as opposed to running the risk of having it too long.

 

David

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David...I appreciate your idea of being able to adjust the booster pushrod length. The trouble with "filling the thread hole" is that the heat involved with weld fill would take the tensile out of the heim joint end and likely ruin the spherical joint.  Also, a high enough tensile welding filler rod material would be difficult if not impossible to drill and tap—especially in a blind hole.

 

This brings up another idea:  taking a quality grade (at least Grade 5 preferably Grade 8) 3/8"-24 coupler and welding it carefully to the 1/2-inch heim joint's threaded end.  To reduce the stick out length of the joint's threaded end, the original threaded portion of the heim joint could be cut short with a band saw, keeping heat to a minimum.  The threaded coupler could be beveled at the weld end before fit-up and welding.  This would provide a deep enough weld fill for strength. 

 

Welding the coupler to the 1/2" stud size heim joint should be TIG process to minimize risk of heat damage.  Before welding, I would carefully insulate the heim spherical joint end from heat to prevent loss of tensile or damage to the joint's bushing—or loss of lubricant from the joint. 

 

Using the correct welding filler rod, the coupler weld to the heim joint would be strong.  You would end up having an adjustable threaded section at 3/8"-24 to accept the pushrod.  I'd use a jam nut to secure the adjusted pushrod at the coupler end.  Otherwise, the pushrod could rotate in the threads and change length.

 

If you do use the existing 1/2-inch pedal stud, I would tap the end of it to accept a graded top lock or nyloc aircraft nut.  The nut would allow tightening the heim joint's center against the pedal.  (You may want to add a graded flat washer if there is enough stud length.  The backside of the heim can be shimmed away from the pedal arm if necessary for centering the heim to the booster.)  Otherwise, if you use a cotter pin or clip like OEM, the high tensile heim joint center will rotate on the stud and continue to wear this stud out.

 

Moses

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spdljohn...Another idea if feasible:  Time-Sert makes thread repair kits for automotive and industrial applications.  I looked at the Time-Sert catalog online and am not certain whether there is an insert for 1/2"-20 outside thread size down to 3/8"-24 inside thread.  If Time-Sert has this size insert, you might be able to use a 1/2"-20 spherical (heim) joint with this "reducer" thread bushing insert.

 

See this video at the magazine:  http://www.4wdmechanix.com/HD-Video-How-to-Time-Sert-Repair-for-Damaged-Spark-Plug-Threads.html.  The company is nearby at Reno, and I've worked with them around spark plug thread repairs. 

 

Hold fast...I'll update on this possibility...I need to research further. 

 

Moses

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Moses,

 

I like your last suggestion.  I called Time-Sert.  They are closed for end of year inventory until January 5th.  I found this other company online that has what I need.

 

Looks like model # 240-0610 would fit the bill.   Ill let you know.  The only adapter I could find with fine threads external and internal was stainless steel.  Regular steel has course external and fine internal threads.  

 

http://www.use-enco.com/CGI/INSRIT?PMAKA=240-0610

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David...Great job, just saw your post after posting this reply, you nailed it!!!  (I returned to this post and edited it.) 

 

The 303 stainless steel should be adequate tensile strength.  Confirm the tensile strength from Enco...If tensile is sufficient for this application, for $4 and shipping, you're out of the woods...If the insert is available in a longer length than the 15/32" described, get it.  Or consider two inserts stacked and aligned properly to accept the pushrod threads.  This will distribute load over longer thread length and increase strength.  (Thread the two inserts onto a bolt for installation.  Keep Loctite off the internal threads of these inserts.  Once Loctite cures on the outer threads and joint threads, remove the bolt.)  Use 271 "red" thread locker on the insert(s) and be sure to install a jam nut on the pushrod to tie this all together and make a strong, secure piece.  The graded jam nut will be a buffer for the pushrod load, too.

 

For those interested, I came up with several companies that manufacture thread reducer bushings:

 

1) Time-Sert, specifically the "Big-Sert" line, offers solutions.  Here is the Big-Sert listing:  http://www.timesert.com/html/bigsert.html.

 

2) Keensert:  http://www.afscamloc.net/prod3.php and also within the products sold by http://www.repairengineering.com/keensert.html

 

Suggestion: Repair Engineering carries each of these brands.  In any discussion of these solutions, be sure to ask about tensile strength or equivalent Grade for these inserts.

 

3) EZ-LOK, one of the products carried by Repair Engineering (http://www.repairengineering.com/e-z-lok.html) and available directly from EZ-LOK at http://www.ezlok.com/InsertsMetal/index.html.  Here's more information about EZ-LOK: http://www.catalogds.com/db/service?domain=ezlok&command=locate&category=solid

 

4) Heli-Coil, I personally only use Heli-Coil on lower stress parts like stripped aluminum cases and such.  For a brake booster pushrod and alloy joint, I'd pass.  In load areas and softer material like aluminum, I've had poor results with Heli-Coil when compared to products like the Time-Sert.  Heli-Coil can be a terrific Sunday solution for a timing cover or valve cover stripped hole.  Here's a size chart:  http://www.noblefix.com/helicoil/HeliCoil-Size-Chart.html.

 

Be sure any product you use is tensile/grade appropriate for the application.  The advantage of a thread reducer bushing is obvious, there would be no heat involved with the installation.  Welding on alloy parts does involve diffuse heat, and any welding, like the coupler to joint described in my earlier reply, would require care and knowledge of how to insulate and prevent damage to the parts.

 

There are contact numbers at the website links above.  spdljohn provided the Enco link in his last reply...This "cold" solution without welding makes the best sense. 

 

Repair Engineering could be a resource.  Automotive machine shops and I really like Time-Sert; however, Time-Sert products involve specialty installation tools—perhaps too costly for a one-time job!  On that note, Repair Engineering may know  a shop capable of performing one-time specialty tasks.  Time-Sert, EZ-LOK and Keensert are each products that Repair Engineering carries.  Enco should obviously be added to this list!  Weigh costs...determine which approach is cost effective and safest.

 

Moses

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Great solution, David...I see that Enco offers only stainless in the 3/8"-24 to 1/2"-20 bushing.  They do have "Steel" in the 3/8"-24 to 1/2"-13 thread sizing.  Enco describes both as having nylon locking patches or pellets.  This will help prevent movement.  I would confirm from Enco whether the addition of Red Loctite 271 is helpful.  Also, ask about the tensile of the 303 stainless inserts.  I'm curious where this material, as manufactured, fits metallurgically. 

 

Note:  I'm pleased to see that Enco is an industrial and machine shop supplier, that the products are U.S. Made, too! 

 

Double inserts should do the trick for load bearing.  Since the rod gets pushed with the pedal application, you can see how a jam nut on the pushrod will help bear some of the load.  This reduces load on the insert threads.  The shoulder of the jam nut will clamp the pushrod to the end of the joint.

 

 Looking forward to some photos of your fit up.  Two inserts will provide nearly the same length as the new joint's thread depth!

 

Moses

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You will find the rest of the details on this brake pedal and heim/spherical joint project at:  http://forums.4wdmechanix.com/topic/494-nut-bolt-jeep-cj-7-rebuild/.  David and I discussed various solutions.  Read the posts and replies from January 1, 2015 to our January 5, 2015 conclusion.

 

David and his weldor finished the project up nicely, setting a good example for others...

 

Moses

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