Hey Rusty, please.... think - then post! Orren has it right.
That seal that you say "would get blown out..." It is the very same seal as the inner ones on the wheel hubs: NSN 5330-00-891-7826.
I think it was in the late sixties when they did that upgrade with the sleeve bearings, to replace those (weak) #392 tapered bearings. But the seal itself remained unchanged, even for the M35A3.
Due to its design it already acts as a big relief valve in itself, so there is no need for any extra relief valve.
The only thing that will happen if you pump too much grease in - either at the original spot or via an additional zerk on the cap - is that all excess will come out in between the seat and the bracket. And actually that helps to flush the whole assembly and carry any accumulated moisture and debris back out. It also ensures that the felt packing stays oily and the shaft doesn't corrode so fast.
Well I did think before posting. I blew out that seal when I first did the conversion. Without the "relief" the seal blew out like a cork in a bottle of seltzer when I was pumping in the grease.
So why in the world would you say to me "think before posting" ? You got something to say to me ? Or you just like dogging me ? I have a picture I can post if you don't believe me, which I'm sure I will have to dig out as you don't seem to believe anything I say anymore.
Just another thing for you to consider Gerhard. Why in the world would the military say to install the zerk in the bottom of the trunnion and then "LOOSEN" the cap before pumping in grease ? If as you say no damage would happen to that seal then WHY go to all that bother ?
As it was I had to remove all my wheels and trunnion assembly to replace that stupid seal !
I guess I had a defective seal according to you.
I forgot to add my seal was a hard "plastic" type seal. Not some felt seal.