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If you read through my build thread, you will see where I originally filled a set of mounts with Shore A 75 urethane which turned out to be way too hard. It worked great, but transmitted a whole lot of vibration at idle - not unlike solid mounts. It took awhile to figure out what was going on as I worked through other possibilities - injectors, timing, fuel, damper and so on. I finally replaced the filled mounts with stock mounts as a test and the idle vibration went away completely. Knowing that it was the filled mounts, I did another set of mounts with very soft Shore A 30 urethane, and the vibration levels were virtually indistinguishable from unfilled ones.
The specific symptoms were bad vibration at idle to about 1000 rpm and then a secondary vibration at 1700-2000 rpm. At other times, it was very smooth. The secondary vibration turned out to be from the filled transmission mount. That wasn't nearly as critical, so I just replaced it with an unfilled mount. Ended up selling the filled mount to a forum member that wanted a stiffer transmission mount for performance reasons. He reported the same vibration, but was happy with the performance gains.
A quick side note - in the week or so that I had the unfilled mounts in the car, the mounts collapsed 1/4 inch.
I've been running filled mounts for 34000 miles now with no measurable collapse.
Vstech and Thayer, mods on this forum, have both driven the car so they can independently verify whether there is any adverse vibration levels.
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Current Stable
- 380SL (diesel)
- Corvette C5
- Manx
- Baja Bug
- F350 Powerstroke
- Auburn Boattail Speedster replica
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