I had always thought that the side of a seal that faces out, or faces the installer, is the flat side, the side that can be tapped on. Have I been wrong all these years, or are there just some exceptions? I'm installing the input shaft seal on a zf s542. I was about to install it as usual, with the flat side facing me, when I noticed the seal has two sealing lips of different diameters. Then I examined the pilot/input shaft around which it seals, and found that where the seal rides the shaft is beveled. So, the smallest diameter lip of the seal would/should ride on smallest part of the shaft, and that would be the beveled area. That seems to be a no brainer, right? But, to put the seal that way means installing the seal how I always thought was the wrong side facing the installer, the thin rimmed side, not the side with the nice wide, flat tapping surface toward me. As to not damage the seal, such an installation means inserting something round into the groove of the seal, like a socket, and tapping on that. Has anyone seen this before?

Attachment 283346

You can see the taper/bevel in the image above. Having a seal sit there, with one sealing lip on the wide section of the shaft, and the smaller sealing lip on the beveled section makes for a challenging installation of a repair sleeve. The top edge of the sleeve has to be between the two sealing lips. If the lip that rides on the beveled section of the shaft comes into contact with the top edge of the repair sleeve while spinning, well, it will shred the lip and leak. I plan to mark where the old seal rides, then install the sleeve a bit lower than that so that the narrow sealing lip never touches the repair sleeve. Huh! I guess that is correct?

Attachment 284512

 

Seal design/installation varies. I'm not familiar with your particular seal, as I haven't rebuilt an ZFs. You're better off buying a seal driver set. I have a cheap Pittsburgh Seal and Race Driver set from Harbor Freight, and I've used and abused it. For the $20-30 I spent on kit a few years back, it's saved me on destroying seals. Some autoparts stores may have them available in their loaner-tool program also.

 

The seals are made to keep ????? IN. So on your input shaft you would put seal with flat facing out from the fluid. Does that make sense?

 

Normally I would say yes. However, you have to remove the trans case to change the input shaft seal on the zf s542, and the seal is installed from inside the case. The flat side goes inside the trans. The 'groove' side of the seal is seen through the bell housing.