Moly lube

[78Chev]

In the instructions for installing DSG's stud girdle kit it says to torque the nuts to 80 ft-lbs if moly lube is used to lubricate the nuts and washers or to 120 ft-lbs if engine oil is used instead. Why does moly lube affect the torque value so much? If moly lube is preferred for the studs/nuts would it also be preferred for the cap bolts? If so what would the torque value for them be?

[john8662]

The moly lube is "slick" and allows for the fastener to be tightened easier than with another lubricant. This is because it takes more force to get the same amount of torque on a bolt/nut when working with oil than with moly.

I did notice those differences when installing my stud girdle kit too. Use the molly grease on the threads that will contact the nut and inside the nut. Oh, and you'll need a 12 point Deep 14mm socket for the job, I didn't have one when I did it the first time on the ol 6.5TD, 99% of my sockets are 6 point.

You don't really want to use the molly on the threads of the bolts for the rest of the main caps. Although I'm sure there is a way to calculate the difference in torque needed, and that will be up to the good Dr.

But use the molly only on the ends of the threads that will contact the nuts for the girdle, and use engine oil on the other end of the stud. Just make sure it threads in easily and bottoms out w/o tightening it, but just hand tight (with an allen wrench).

Then use the engine oil you're already going to use in the engine for the rest of the bolts and use the factory torque specs.

[78Chev]

Thanks John. I just got a deep 12 pt 18mm

[CleviteKid]

The thing to know about threaded fasteners is that torque is just a means to an end. That end is tension in the bolt, which will hold the joint together.

Torque has to do two things: stretch the bolt, producing the desired tension, and overcome friction between the bolt, nut, washer (if any) and parts being fastened. If you use a really good lubricant, like the moly lube, less of the torque goes into overcoming friction, and more goes into stretching the bolt. So if you use good lube and the SAME torque, you could over-stretch the bolt, and perhaps even break it.

The girdle manufacturer has evidently done some tests to give you torque guidance for two different lubricants, but that does not establish any universal formula for lube substitution. Stick with each manufacturers recommendations as far as lube, or lack thereof, and torque.

For example, the instructions in most owners manuals for lug nuts is to install and torque them DRY, no lube at all. If you do use lube, you could exceed the recommended stud tension, warp disc brake rotors, and even break studs. Be careful.

Dr. Lee :cool: