Join Date: Mar 2011
Location: Mid Hudson Valley, NY (USA)
Re: Solution for the vibration on 2015 Sienna at 1250RPM
You need to be aware of the possibility of carbon monoxide leakage with this type of modification.
The purpose of the spring bolt is to keep a constant compression on a tapered/doughnut shaped gasket placed between two flanges. The spring bolt allows some system flexing as the engine rocks on it's motor mounts, and limits the total motion and vibration transmission to the exhaust system. But as it rocks, it wears down the gasket and the spring bolt tensioner takes up the slack and maintains compression and the seal. By placing washers / lock washers between the flanges, you've limited how much those flanges can come together as the gasket wears. Eventually that gasket will wear away an edge, and exhaust leakage will begin.
If you decide to do this, you must get under there and inspect it regularly with the engine running for signs of increased noise or puffs of air escaping.
Current: '15 Sienna Limited Premium (FWD), '14 Subaru Outback, '13 Honda CRV AWD.
Past: '08 Sienna LE (FWD), '02 Subaru Outback, '02 Honda Odyssey EX