So I’ve been trying to chase down a rough idle for months and months. But it now seems the engine idles decently, yet I can still feel a slight vibration in my seat. Only in D at idle. In park I don’t feel it, and while driving I don’t feel it. Even under heavy acceleration.
I had thought engine mounts, but I just replaced them and no help.
I’m now wondering if the poly spring mount and the poly trans bushing I installed are doing it? Has anybody else noticed any difference upon installing these? I did it so it would last longer, and my high rpm shifts are definitely firmer. But I may switch back to OEM if the vibration is a side effect ;(
Just getting any feedback, as it’s a big job. Would vibration come through my seat and not the engine?
What about supporting slightly with floor jack to see if there’s a difference?
I can’t speak from experience, I have the OEM mount, but it would make sense.
What I can say is that when I first installed it it was not aligned properly and I had some faint vibrations in my seat.
One of the first things I did when I got my car was change all the fluids and filters.I was amazed at the “extra engineering” that went into the trans. mount, and the extra work involved to do a simple filter change. I blew the dust off my welder, and modified the trans mount so I could use a GM full size car rubber mount. These also came in a “Poly” version, and as the underside of the car was coated in Jag. rustproofing, (oil) that is what I used.
I spent some time after that, trying to track down a vibration that was annoying, although it happened when driving along at around 45mph. I also spent a lot of time fixing the “rustproofing” leaks from the engine. Not having any luck finding the cause of my vibration, I thought I would replace the trans. mount with a conventional rubber unit. A simple job now. The vibration disappeared.
Your seat is pretty close to the location of the trans. mount, so I think you could be on the right track.
II realize no car shakes like a Harley. In 1992 Harley had a recall for motor mounts on the 1991 Dyna Glide. Seems in one year the rubber motor mounts hardened slightly moving what was once a transient vibration just off idle to idle. It was surprisingly substantial.
I was working the service desk at a Harley dealership at the time and had the opportunity to talk with a couple of Harley engineers. One guy started talking polymers and was way over my head in seconds.
Amazing how something as slight as composition, compression, fatigue or hardening with age can affect things.
Indeed, albeit the holes an the bracket are big and there is also some sideways movement.
When I went back to see what was wrong I discovered that the trans was not free to bounce up and down.
Loosened everything and made sure the trans was loose.
Can’t recall which way it was misaligned, but before I could feel the engine at my seat.
So I took a look and found that the little rectangle plate that the main post (with the big nut) feeds thru was slightly angled, putting friction on post. I removed the big nut, loosened the two nuts so the rectangle plate was now level, put the big nut back on, and then tightened the two nuts. Now I can actually bounce the trans up/down by hand.
Vibration is still there but I’d say has been reduced 50%!
I ordered rubber parts, I may replace one day, but for now the vibration is manageable.
I think that with the rubber bushing you will have an other 30% improvement.
I still have some, very very faint, noise coming through.
I guess if I wanted none I should have gone with the original foam bushing, but I rather not to have to replace it every couple of years.
yeah, obviously the foam bushing was a final solution to their contraption not working perfectly. Or maybe it was an excuse to change the ATF every couple years?
Finally got around to swapping poly bushing and seat to rubber. You are spot on! I would say 30% reduction. Like you said, its very very faint at idle, but i can live with that.
Wasn’t that bad removing mount the second time around, very straightforward, but still a feat of over engineering to deal with!
