Toyota reduced engine and transmission noise/vibration (NVH) via Dampers, Barriers and Absorbers....

However, NVH areas remain and respond well to treatment.

The cacophony of the fuel injectors is a primary example...sounds like ticking lifters.

The other is noisy (yet normal) serpentine belt accessories/pulley noise.

Fan noise follows, with undamped transmission and engine oil pans (steel not Aluminum) as a source.

This post deals with the M10-1.25 tapped through holes in the bottom of the front transmission housing where the torque converter resides.

These tapped holes reside on bottom of the front transmission housing.

On 1999 LS400, two of them are used for exhaust damping brackets while second two are unused and left open.

On early LS400, all 4 bolt holes were used to clamp this bracket.


1990-1994 LS400 Exhaust system

Close up of 1993-1994 LS400 parts diagram illustrates 4 bolt exhaust damping bracket depicting 4 bolt attachement... 1990-1994 (1995-1997?) has two affixing bolts and two extra damping grommets...


Bottom line, for whatever the cause, Toyota left the extra holes open, and so I cut two 10-1.25 washer head bolts to 8-10 mm length (to avoid hitting torque converter) to plug holes and block noise from escaping converter cavity.


Exhaust Damping brace attaches to bottom of front transmission housing.

Used M10-1.25 X 8 mm washer head bolts to fill tapped through-holes. Using a stethescope it is quieter in the vicinity.