Racer Build Series – NMRA Mustang Build – Control Arm Bolt Replacement

Rob Farley - Mustang Lifting Tires01   Rob Farley - Nov Proj 4

As part of our ongoing coverage of Rob Farley’s NMRA Mustang Build we are onto the next project which is rear axle lower control arm bolt replacement. FYI: in our last article we described his installation of a shifter solenoid for safety and performance reasons. You can see that at http://fuelab.com/racer-build-series-nmra-mustang-build-shifter-solenoid-install/.

Rob tells us that Fox Body Mustang lower control arm mounting bolts are a weak point when adding power – stock bolts will eventually wear out. As well, the bolt holes in the control arm mount brackets on the body and the axle wear and enlarge. A telltale sign of excessive wear is a “clunking” noise from the rear of the car. The worn parts can allow the rear axle to move around, causing the vehicle to drift or wander when driving, and under hard acceleration can make the vehicle to pull to the left or right. This creates real handling and safety issues. Many people have misdiagnosed the condition as improper alignment, and found a wheel alignment didn’t help the problem at all.

Rob says that using stock 7/16” size replacement bolts won’t completely solve the problem as the bolt holes in the axle and body mounting brackets may have become enlarged from wear, and there will still be free play. The solution is to “recondition” the bolt holes by drilling with a ½” bit, and then use ½” bolts in place of the 7/16”. This ensures tolerances will be much tighter to eliminate free play.

Please note that worn upper control arm mounting points can also create the symptoms described above. Rob has previously addressed the upper control arms, and the description of that procedure is not included in this article.

Rob will take us through the procedure for replacement of the lower control arm bolts as part of preparing his ’86 Mustang GT for NMRA competition:

The stock bolts are a 7/16″ diameter. I will be installing 1/2″ bolts. These bolts can be purchased at Home Depot or Lowes. Make sure they are hardened bolts – which are made for strength and are corrosion resistant.

Rob Farley - Nov Proj 5

Raise the rear of the vehicle and place a jack stand on each side, being sure the jack stand is located where it will not interfere with the lower control arm as it is lowered. Place the jack under the center section of the rear axle. To facilitate removal of the control arm bolts you may need to raise or lower the axle to release side load pressure on the bolts. Remove the bolts and lower control arm. (please note an overview of removing the rear control arms on a ’79-’04 Mustang can be seen on this unrelated video https://www.youtube.com/watch?v=o58Vf8HP1Z8). With the lower control arms removed, I use a 1/2″ drill to open up the current bolt holes in the body and axle mount points. My control arms have sleeves which I am able to slide out. I then secure them in a vise and use a ½” drill bit to enlarge the inner diameter to accommodate the ½” bolts. Of note, I use CRC Oil to ease the drilling process and prevent the drill bit from becoming worn out. Once all the holes and sleeves are drilled I test fit everything, and then apply caliper anti seize to lubricate the bolts and the sleeves.

Rob Farley - Nov Proj 2

Time to assemble: Put the forward section of the control arm in place first, slide one washer on the bolt, and then slide the bolt through. Once the bolt is through, slide a washer and a lock washer on, and then thread on a nut. Do not tighten yet. With the forward bolt loose and the axle on the jack, you should have enough movement to slide the control arm in place on the axle. Put a washer on the bolt and then slide it through. Now place a washer on the threaded end, then a lock washer, and secure it with a nut. Torque the bolts to factory specs and the job is done.

Rob Farley - Nov Proj 4


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