A Technical "Torque" question

[joegottberg]

Hi,

I'm preparing myself for a slave cylinder replacement this weekend or maybe next.

I was wondering about Torque Values. I know the value, but, my question is lubricated or dry threads? I used to use 75% of the torque value for lubricated over dry threads.

The only mention I found in the BMW maintenance manual refers to a DIN standard (which basically says "Gudden-Tight).

Any ideas?

Thanks

Joe

[cccpastorjack]

I always very carefully clean all threads TOTALLY and then lube them with a very light "film" of BelRay light lubricant spray. Just wipe on a thin film and then torque it to normal specs. no problems with that approach. If you want to borrow the lubricant, you can pick it up when you drop by later. I'll leave it with the tools. No loctite!

[joegottberg]

Jack,

I have heard it "both ways", that is:

1) Always lubricate threads, especially SS
2) Never lubricate threads.

When I used to Engineer things, I would calculate torque values for threaded fasteners based on DRY threads. If we used thin oil (or Loctite) we would consider the threads lubricated and drop the applied torque by 25%.

This would result in the same stretch in the threads (and bolt) and therefore the same clamping force.

I don't want to strip (or break) anything and if you've torqued the swing arm to 200Nm lubricated and haven't broken anything, I'm safe.

I know NOT to loctite the swing arm threads.

Maybe it’s just an academic question.

Thanks,

Joe

[murray]

Use some WD-40 keep it simple. The slave cylinder requires minimal torque.

Note: Use new washers on the banjo bolts and increase the torque by 5 %.

[joegottberg]

Use some WD-40 keep it simple. The slave cylinder requires minimal torque.

Note: Use new washers on the banjo bolts and increase the torque by 5 %.

Thanks Pete,

I was mroe worried about the swing arm bolts (147 lb*ft) if I'm off by 25%, I'm approaching yield stress. :eek:

Jack has torqued the bolts lubed to the right value and hasn't broke it, so I'm OK.

Thanks,

Joe

[dshealey]

the torque values for nearly every fastener on autos and motorcycles are specified dry. The few that are specified to be lubricated are usually stated so in the service manuals. Head bolts for one that I know of on most cars. The head bolts in the LT engine also specify oil on the head bolts and washers. Probably the only place on the LT that does specify lubrication for the fasteners.

[joegottberg]

the torque values for nearly every fastener on autos and motorcycles are specified dry. The few that are specified to be lubricated are usually stated so in the service manuals. Head bolts for one that I know of on most cars. The head bolts in the LT engine also specify oil on the head bolts and washers. Probably the only place on the LT that does specify lubrication for the fasteners.

Thanks Dave,

That was my suspicion. I like the threads lubricated just to prevent galling, but, I always adjusted the torque down to compensate.

I suspect I should do the same thing here.

25% reduction was the rule of thumb (when thumb used to rule). I'll probably use the torque wrench and the "Gudden-Tight" feel to judge.

Jack has torqued them to the 200 Nm and had no problems, so, I think I'm OK approaching that value.

Thanks Again,

Joe

[Sunshine]

Torque specs are dry unless specified to be lubricated.