I will never buy Prothane products again!
I wanted to replace the rubber engine and trans mounts in my '73 BB Manual Trans. I'm installing polyurethane mounts because I want the engine to be more firmly mounted because the headers on the passenger side are very close to the frame. Soooo, I called Summit and asked about polyurethane mounts. The sales guy was very helpful and said that basically Prothane and Energy Suspension are the same so just go by price. I bought the Prothane because it was about $10 cheaper for the 3 mounts. After unbolting the stock engine mounts, they literally fell out. That's when the fun began. The new mounts were made too close where they mount to the frame (see pics below). So I spread both sets of the tabs apart about 3/32". The passenger side went in ok. The driver's side mounting holes didn't match up with the holes on the side of the block. So I had to substantially modify the holes in the motor mount to get it to bolt to the block. Then on to the trans mount. Everything went in ok, until the following day I noticed some loose nuts and washers on the floor beneath the transmission. One of the Prothane provided studs that go from the mount to the crossmember broke. As soon as I tried to loosen the other nut, that stud broke too! I was able to remove the broken studs with an EZ-Out. I'm going to reinstall the mount and use new Grade 8 bolts!

John


I had to spread the ears on both motor mounts about 3/32".



Both of the cheap studs supplied by Prothane broke the day after I installed them.

Using an EZ-Out to remove crappy broken stud.

 

FWIW-When I replaced the mounts on my 78 L-82 355 rebuild/upgrade in 2014, I reused the OEM GM bolts everywhere on the engine and tranny mounts. I always try to reuse the OEM bolts and nuts when possible when I replace/anything on the motor/tranny, if possible and safe......

 

ARPs & LocTite Blue.
Nuff said.

 

Moral of the story. Dont cheap out on your baby!

 

I know that socket head cap screws are stronger than grade 8 screws. So I thought that the socket set screws supplied by Prothane would be quality parts too. Lucky for me that they broke before getting the car on the road.
John

 

Seems something Not fitting correct, Not bad bolts ... fwiw, GR 5 is more than plenty at motor mounts ... GR 8 if it floats your boat. JMO

-add-
used ES brand with No fitment issue. Dunno, perhaps wrong part number mount was installed or mount was junk when produced; not bolts.