Broken Rear Motor Mount Bolts

About a year and half ago I put new rear motor mounts in and ever since that I have had the bolts braking. Just on the rear mounts. This happens about every 30-50000 miles. The front mounts are also new have had no problems with them. I have the polly mounts in the rear and purchased them via E-bay. If I remember, I'm sure I crossed them with the OEM #, but If I didn't and they where the wrong mounts is this possibly the problem? I am using a grade 8 metric bolt just as the ones that come out. It just snaps the top off of them. Not at the same time, one time it will be the drivers and the next it will be the passenger side. I have talked to a few shops and nobody has dealt with this issue before. Oh ya this never started happening till I changed the mounts. Anyone got any ideas.
Thanks Terrance

 

Yes the poly mounts have steel sleeves. What is the torque spec for these ? I have just tightened them tight with a ratchet.

 

I think I might have found my problem. I order new OEM rubber mounts and installed. In the process of taking out the poly mounts I noticed on the driver side that on the bottom side where the mount sits on the two tabs that keep it in place that it was not sitting on the tabs the right way and messed up the holes. With that in mind I think this was letting the mount move just enough to brake the bolt over a period of time. So again no one to blame except myself. Hope this fixes it. Time will tell. Again thanks for all the info.

 

Kitty kicker thats a nice looking W9 you have