Suspension Fasteners Are Not Reusable?

[SubLGT]

I was surprised to see in my Subaru service manual that if you remove and reinstall the front lower control arm, none of the fasteners (3 large bolts and two locknuts) are to be reused. I can see why you don't want to reuse the locknuts (because they lose locking tension), but why can't the large bolts be reused? They get tightened to 70 ft-lb or 110 ft-lb, depending on the bolt.

Do the instructions to replace the fasteners come from the Subaru legal department (CYA), or is there an engineering rationale behind it?

 

[Gotch]

Locknuts usually gall the threads of the bolt as they are removed. The damaged threads are not as strong as original and so they should be replaced.

 

[SubLGT]

Two of the bolts do not use locknuts, and are still required to be replaced.

 

[UNC017]

Older cars used "castle" nuts with cotter pins to prevent loosening. But most newer stuff uses "interfereence thread" nuts (deliberately made slightly triangular or oval so that the threads "bite" into the threads on the stud or bolt). If you can get one of those loose without it galling, and with PB Blaster or SeaFoam you usually can, they still won't "bite" quite as hard when you torque them the next time, so they're considered out of spec and not reusable.

Also, the bolts may actually be torque-to-yield like head bolts often are.

 

[The Critic]

They might be torque to yield, or they may have threadlocker on them that requires re-application. Any info on the various Subie forums?

 

[another Todd]

I doubt suspension bolts are torque to yield. I suspect the bolts are used like a hinge pin, and 70 to 100 ft lbs isn't that much so there isn't that much stress on them. I would reuse them and not think twice. Now if they looked bent or badly worn, then that's cause for replacement. If it's a locknut issue just use some locktite.

 

[Doog]

Use red loctite on the old ones if they are not visibly damaged. They won't come off.

 

[Johnny248]

You would be surprised how many fasteners are not supposed to be reused according to the service manuals. That being said, many and many of them are reused every single day without any problems. Torque-to-yield head bolts and things like that should always be replaced though.

 

[Astro14]

Originally Posted By: The Critic
They might be torque to yield, or they may have threadlocker on them that requires re-application. Any info on the various Subie forums?


This.

Fastener replacement is quite a common requirement.

 

[cptbarkey]

what year is the subaru? if it's over say 15 years, and in a cold climate, i would probably replace the bolts.

 

[Thermo1223]

They are likely TTY bolts and should be replaced, is the extra $20 that hard to come by?

The procedure was put in place to minimize risk & injury due to fastener failure. Why spit in the face of it? There could be stress fractures in the metal that you can't see with the naked eye.

 

[SLCraig]

Strange.. Never replaced any suspension bolts of fasteners on any other cars I've worked on. Never on a Scoobie though.

 

[meep]

i did all 4 corners on one years ago. the hardware was nice and substantial. I reused....

 

[mechtech2]

Many suspension fasteners can be reused, even though it is recommended not to.
Why?
They have to cover their derriers.

I judge on an individual basis - experience and common sense.

 

[SubLGT]

Here are some photos I pulled from someone else's thread on a Subaru forum, showing the fasteners in question:

The 1st photo shows one control arm pivot point, and the locknut on the mounting stud. Manual says replace the locknut.

In the 2nd photo you can see the second pivot point of the control arm, and the threaded end of the horizontal bolt with its locknut, which gets tightened to 70 ft lb. The manual says replace them.

In the 3rd photo (same as #1, but from another angle), the 2 loose bolts here go into the body structure and are tightened to 110 ft lb. The manual says replace them.

 

[SubLGT]

Originally Posted By: Thermo1223
They are likely TTY bolts and should be replaced, is the extra $20 that hard to come by?................


I wish they were only 20 bucks. Based on past experience, fasteners get marked up 1000% or more at dealer parts departments.

 

[The Critic]

Originally Posted By: SubLGT
Originally Posted By: Thermo1223
They are likely TTY bolts and should be replaced, is the extra $20 that hard to come by?................


I wish they were only 20 bucks. Based on past experience, fasteners get marked up 1000% or more at dealer parts departments.


Regardless, it will still be less expensive than your insurance deductible should the unforeseeable happen.

 

[PandaBear]

How much is the fasteners from aftermarket?

I'd use new aftermarket over used OEM/original. Aftermarket should be reasonable priced.

 

[asand1]

The dealership I worked at VW/Audi, Subaru,GM did NOT replace fasteners in ANY vehicle. It is just a matter of liability.

 

[SubLGT]

Interestingly, the stud (with nut) shown in picture #1 seems to me to be the most stressed fastener on the control arm, yet Subaru says not to replace it unless it is damaged.