I have a pretty straight forward question. For those who have replaced their differential who has gone in and checked the preload on their diff?

If so did you find that you had to change the shimming of the races at all. SKF calls for a minimum load of 1.1kN (247lbf), which is a pretty decent amount of force. Under any sort of load (cruising, engine breaking, accelerating) the force created by the ring gear being driven is probably enough to meet or at least come close to this requirement, however it wouldn't address any change in location due to thermal expansion of the case or when the transmission is in neutral.

All the research I have done in the ford community says that this is something you MUST do. So why is it that we dont seem to call it a requirement? Or is it just that we all do it anyway and it is considered common knowledge?

 

For LSD cars only?

I'd like to think that our Getrag boxes are bullet-proof as is.

Maybe I'm just not understanding what needs shimming and what it will do.

 

My OBX ATB diff was identical in case length to stock so the bearings should have same preload. After you press on your bearings to the Torsen ATB diff compare your measurements to your stock measurement.



Jeremy

 

Good call J, should have thought of that, hopefully it's the same. I actually went back and looked at your OBX install thread, but the implications of that picture had escaped me until just now. Thanks for laying it out so clearly.

Nabeshin, there are two bearing that locate your differential, LSD or otherwise. Since the differential experiences forces in two direction (up and sideways in J's picture) you use a taper roller bearing to locate it in place. That type of bearing can accommodate forces in both those directions (though to what degree depends on the taper) which is why it is used on our diff.

However if the force on the bearing isn't high enough the surfaces of the bearing can slide against each other instead of roll. If that happens then all sorts of funky wear can occur. Thus to eliminate such a problem when you install your diff you actually put spacers (shims) under the races you diff sits in, enough that there is actually ever so slightly too little space for the diff. That way when the gear box is bolted back together there is enough force on the bearings at all times, in our case 247lbf it would seem.