915 Trans Mount Question

[petercory]

The PET Catalog calls for a total of 4 Concave Transmission Mount Washers (I presume that to mean 1 under the head of the mounting bolt and 1 between the top of the mount and the body mount , per side), The Bentley manual only shows 1 concave washer under the head of each mounting bolt (a total of 2 washers). Which is correct?

[jason2guy]

you want two washers per side. if i remember correctly there was a service bulletin about this which stated if there was a complaint of mechanical noise from the drivetrain to flip the washers around. i think both ways are ok. i installed mine so the washer in effect hugs the rubber portion of the mount. i think the opposite of my install, was the fix for noise

[petercory]

Thanks, that's the way that I thought that it should be.

[john walker's workshop]

80s carreras used a different style of washer on top against the body. It has a hump in it. All the earlier cars only used one under the bolt head.

[81SC]

Originally Posted by jason2guy

. if i remember correctly there was a service bulletin about this which stated if there was a complaint of mechanical noise from the drivetrain to flip the washers around.

Here ya go.

[KTL]

The hump/bump washer JW describes was started with the G50 trans is used between the body and the trans mount. The lower washer under the bolt head is the typical smooth washer used in previous years.

Bumped washer is 911.375.305.00, smooth washer is 901.305.311.00

I have a rather large stack of those smooth washers if you need a couple. I collected them over the years from people switching to solid mounts (bad idea) or WEVO mounts (they have their own washers included with the mount) and figured they'd come in handy some day.

I always say, NEVER throw anything away from these cars. Not unless it's complete mangled garbage. Let me know and i'll drop them in an envelope for you.

[petercory]

Thanks for all the feedback, I've got 3 or 4 extra smooth washers, I was confused by the Bentley diagram vs the info in the PET catalog. Should I install the top washer with the cupped side facing the mount and reverse it if I experience vibration?