Changed motor mounts- thumping noise on downshifts??

[ChrisIsAtool]

Just replaced both motor mounts with the 034 street density mounts. I did one side at a time to make sure I wouldn't misalign anything. I tightened the top nut on the motor mount as tight as I could and all the sub frame bolts are tight. I also aligned the motor mount itself as best as I could. Whats weird is the car now drives very well even when driving aggressively. However if I downshift and the revs aren't perfectly matched the car will make a loud thump from the engine bay. very strange to me since I double checked everything and it also drives well except for that. Also the thumping is very prominent coming around a corner and putting the car into 2nd gear without matching the revs, even if it only goes up to 1500 rpm.

[Rodgman15]

I'm not entirely sure, but I think you're supposed to leave them remotely loose to let everything settle into place, run it for a bit, then tighten it all down. Maybe that makes the difference? Hopefully someone with first hand experience will chime in soon.

[Davdraco1]

I did motor and tram mounts at the same time. Since you have stiffer mounts, your putting stress on all the other mounts. A loud thump is usually the rear diff mounts making noise. I would check all your other mounts since there is more stress on them with the stiffer engine mounts. Also, the trans mounts are easy as hell to swap out. The rear diff mount is too

[nynoah]

well keep on looking for more bad driveline parts. It could even be the rear dif

[Seerlah]

As others said, most likely other unupdated mounts. Most get clunks from the rear diff mounts.

But would also check all your upgraded mounts again. Make sure they are torqued still (sonethin could have came loose), and things like the studs for the motor mounts still intact. Even check things like cracks in your mount brackets. Still leaning towards rear diff associated mounts though, purely because it is the most common when having clunk issues. I even had this, and cured it with the stern power ring and stern rear diff carrier mount bushings.

Leaving the bottom motor mount nuts loose is for trying to deter as much vibration as possible. You basically let the car idle with the bottom nuts looose, let the engine find it's own groove, then torque the nuts down and break in the mounts.

[Davdraco1]

Just FYI, my car with street density motor and tram mounts had a vibration until 2000-2200 rpm then it smoothed out and went away. I got 200 miles on them before I blew the motor, so maybe it would have went away after they were broken in. Just figured I'd share if you experience any of that.

[Seerlah]

It's about tolerance and what to expect. I run 034 sd mounts all around with the 034 snub and bracket. I personally like this setup a lot, while another may think it to be rather harsh.

[Davdraco1]

I loved how it drove for those 200 miles. I also bought read diff carrier mounts too but never but them in. Next was going to be the diff mount from apikol or ECS