Anybody out there changed out the transfer case to driveshaft bolts? The shop manual calls for replacing these bolts (6) when the coupling is disassembled.

They can only be found on a Ford parts website and go for nearly $17 @. Why does the shop manual call for replacing these bolts after removal?

 

Many assembled components use thread lock coated fastners which is only good for one time. You could probably use some Loctite thread lock, the blue colored stuff on the old fastners.

If a assembly failed a operational test and was torn down, only the main parts are reused, fastners, seals and bearings are all scrapped although some bearings are sent out cleaned, checked, etc., returned to be used again.

 

So there is no issue with the strength of the bolts themselves?

I understand all about the practice of disposing of fasteners... but in many cases that is not a strength issue. If its just an anaerobic thread locker then I got it.

For example the manual also calls for replacing the u-joint cap straps & bolts. On my Suburban (400,000+ miles) I've replaced the u-joints several times over the years. It does not call for such replacement and I haven't without problem.

 

The tensil strenght won't change unless they get red hot. Unless fastners are removed/reinstalled many times like in machine change overs and threads wear out, they'll last a lifetime.

U-joint straps/bolts might have thread lock on them also. I've never replaced them on other vehicles either! I worked at where Ford built its driveshafts before it got moved and sold now but can't remember exactly because there were numerous applications or styles with slip yokes, flange mount, etc. The machines that balance the driveshafts have two heads or chucks that have to be changed back/forth for the different style and lenght constantly.

BTW> The balancing machines were built and designed by GM!

 

Bill,

Do the torque specs on those bolts give a ft/lb value plus an angle to turn after that torque setting is reached? If they do, they are torque to yield bolts and should be replaced. That type of tightening on bolts is becoming very common and can (and will) cause problems if reused.

 

These bolts are torqued to 27 ft-lbs with no angle beyond the torqued tightness specified. In other words they are not particularly stressed bolts.

So I find the Ford Shop manual words about disposal & replacement of these bolts curious when viewed in terms of the strength of the bolt itself. Ford sells them at $17/bolt with 6 required. NAPA Doesn't even carry them so I infer they don't view this as needed for the job.

Many thanks.

 

On what or where is such a procedure used? I've heard of running of running a bolt till contact was made plus a partial turn if a torque wrench isn't available but that's not very accurate. Trying to use a torque wrench can be difficult at times but figuring a addition turn angle would be impossible at times.

 

I'd re-use them. Not that it's up for a vote.

 

I have seen that procedure called out in a few places on cars & trucks. I have seen it called for in somewhat more places in the ship & submarine world. It is used to generate a specific, and very high, clamping force.

The issue is how to generate the clamping force needed for an application. It depends on the force required and the strength & elasticity of the bolt being used. Steel is like a rubber band but its elastic length change is so much smaller you can't see it.

The reuse issue is partly a function of whether it has exceeded its elastic range or not in use. If it went into the plastic deformation range then the bolt is seriously weakened for reuse.

In the end I just don't see 27 ft-lbs indicating any issue with exceeding the design application force and stretching the bolt. Just doesn't add up.

 

Almost all internal engine bolts on cars made in the last few years are these type of fasteners. You can use something like a Snap-on Tech Angle torque wrench or a std torque wrench with an angle plate attachment. Most often the plate is not required because the angle is simple (45 degrees or 90 degrees). They apply a very consistant clamping force on the bolts.

They are startiing to become more comman on other critical bolts that are on the driveline.