Replacing the rear springs with new BDS units. When removing the old ones, I see there was a rubber pad or whatever it's called on the upper spring perch. Nothing on the bottom. Is there supposed to be something on the bottom? 
Rear spring pads / isolators / cushions
- Thread starter dodj
- Start date
There are isolators top and bottom in stock form. The upper are rubber-like. The lowers are plastic and have tabs that engage the 3 holes in the axle spring perch. Some say the lowers aren’t necessary. In support of that idea, the front springs don’t have them. I replaced my rear lower isolators recently with Delphi parts from Rock Auto.
Uppers seem to be consistently there throughout the TJ run. The lowers disappeared at least as late as 2003. I have never actually seen a set of rear lowers on the dozen or so TJs I have spent time on.
The lower isolators are good only for creating rust on the lower spring perch. No other value.
Fwiw, mine has been with and without rear isolaters multiple times at various stages. I could never tell a difference in noise. Same with the front. No more rubber up there and nothing changed.
I doubt they do (lowers, I mean). But I haven’t done the experiment with and without. I replaced my uppers and lowers when I had my axle out because my ‘97 had them and the original lowers fell apart on removal and the uppers came with the lowers. Intuitively, I suspect the uppers may make at least a little difference in NVH but maybe not enough to be noticeable in a TJ.
Upper vs lower doesn't matter. The NVH is passing through a big spring. I suspect the real purpose of the isolaters is to reduce squeaks from the metal on metal contact. Even then, I rarely hear squeaks from the springs despite having lots of metal on metal contact at the springs.
That is what I did. I got Dana 44 from old TJ and it came with insulator, and I removed it. Had to scrape rust under it
NVH?
Nasty vehicle harmonics?.........
Noise vibration harshness. It's a catch all acronym to describe things relating to bushing isolation, shock tuning, tire pressure, things that transfer from the road into the cabin.
Well the spring replacement is done and went for a test drive...all good....no pesky NVH.....