vibrations at speed with poly trans mount
Teching In
Joined: Apr 2010
Posts: 46
Likes: 0
From: Southeast MO
I just installed the Prothane mount as well, any word on much much the shimming cuts down on the P angle and vibrations? I'd rather do this instead of forking out the 100 bucks for the GM mount.
well Ive heard you had to shim the xmember 3/8" Being that I only had 1/4" steel bar sitting around i only shimmed it 1/4". It seemed to make it better at some speeds and from 65-75 it seemed to have gotten worse...I am trying to get a measurement from the stocker so I know exactly how much i either need to cut off the mount or shim the xmember. Do you still have your stocker sitting around?
Well i figured id update this thread a little....i had a buddy of mine with a stock trans mount measure it with a digital caliper and it was 1.55" I then measured my prothane with a digital caliper and it is 1.80" a difference of 0.25". Instead of shimming the xmember because that didnt seem to work, i will be trimming down the prothane mount that 1/4". I will also be changing the front u joint on the driveshaft because that seems to have a tiny bit of play now....possibly from the mount and the bad pinion angle? I will post up with my results for anyone who has a similar issue thats driving them nuts.
I would like to get the ball rolling on this, does anyone have any insight into what the best way of trimming down the mount would be? I was thinking maybe a dremel for the poly, and a grinder for the middle of the mount. Any ideas?
My brand new stock mount was the exact same height as my prothane. The ES one was taller by a bit. You can bet the stock one squashes once the weight of the transmission on it though so thats probably more what is throwing your angles of rather than the actual height. My old beat mount was about 3/8 inch shorter than the brand new stock one I had.
Staging Lane
Joined: Jul 2006
Posts: 55
Likes: 0
From: Texas
I just had some tranny work done on mine and found that my gm tranny mount was busted, so I opted to get the poly one. Big mistake. I noticed on the 2 hour drive home @80-90 MPH I got this very noticeable vibration, but wans't sure what it was. I talked to a friend and he said it is very well known in both the LS and LT world that vibration WILL occur with the poly mount. Funny, I hadn't heard that til he mentioned it, I mean I am not new to LSs...lol. Well I am going back to the stock GM one.
My brand new stock mount was the exact same height as my prothane. The ES one was taller by a bit. You can bet the stock one squashes once the weight of the transmission on it though so thats probably more what is throwing your angles of rather than the actual height. My old beat mount was about 3/8 inch shorter than the brand new stock one I had.
I just had some tranny work done on mine and found that my gm tranny mount was busted, so I opted to get the poly one. Big mistake. I noticed on the 2 hour drive home @80-90 MPH I got this very noticeable vibration, but wans't sure what it was. I talked to a friend and he said it is very well known in both the LS and LT world that vibration WILL occur with the poly mount. Funny, I hadn't heard that til he mentioned it, I mean I am not new to LSs...lol. Well I am going back to the stock GM one.
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Verdad Gallardo I also now have a tiny bit of play in the front U joint or possibly the tail shaft of my tranny...hopefully its the U joint. I bought a new one and im going to trim the mount and change the joint at the same time hopefully that will fix the problems
IMO, ditch the Prothane trans mount and get a ES mount, and just grind down the preload bumps and install it with the preload plate, or just leave the preload plate off; problem solved! 
I've had no vibration issues (8yrs) with the ES trans mounts I modified that way.
I've had no vibration issues (8yrs) with the ES trans mounts I modified that way.
well, i finally got around to installing my energy suspension trans mount today, i trimmed it down to the 1.55 inch height like my stocker was...and i wish i could say my problem was solved. The car still vibrates like crazy at 75+ i could feel it through the shifter, the steering wheel, and i could see the passenger seat shaking along with my sun visors. I am going to try and change the U-Joint because it has a tiny little bit of play in it....im hoping that fixes my problem. Any other suggestions?
Did you ever check your drivetrain angles??? I just did a tranny build, clutch, tick master, a pro series torque arm, and a prothane mount. I did all my adjustments to the torque arm on jack stands and needless to say i screwed up and anything over 65mph had a weird 2 seconds smooth and 2 seconds choppy... Put it up on 6 inch blocks on all four tires and rechecked the angles and my rearend was 1 1/2 degrees off. so i have my engine/tranny at 3 1/2 degrees and moved my rearend from 5 to 3 1/2 degrees and i have had absolutely no vibrations at all since. So check your angles on the engine/tranny, your rear end, and your drive shaft and shim or grind your mount accordingly...
Everyone gives up on the poly trans mounts too quickly. I ran a Prothane on my old 97, and a Prothane on my current 01. Both of them had annoying vibes immediately, but the mount softens up within a couple weeks and ALL VIBES GO AWAY. It's much nicer with a poly mount because the shifter doesn't move nearly as much and shifts feel much more solid. It takes the poly's a couple weeks of driving to soften up and show its true value! 
Don't give up.
Don't give up. Last edited by HoLLo; Aug 11, 2010 at 05:37 PM.
I measured my stock trans mount (off the car) when I changed to the prothane mount. They were the same thickness. I also double checked my pinion angle before and after changing the prothane mount to be sure my PA didn't change. There was no change in PA what so ever, it was spot on my original measurement. I have run this mount on the factory trans x-member and now currently on a BMR TA relocation x-member. I have never had any hint of a vibration. I'm also running a custom driveshaft that I know is balanced perfectly behind the M6. The problem that some are having is driveline vibration due to driveline angle, well worn u-joints or driveshaft balance issues that existed prior to the swap and just went unnoticed due to the forgiving nature of the rubber stock mount. Look into the driveline issues to fix the vibration problem.
Last edited by Mguncowboy; Aug 11, 2010 at 09:01 PM. Reason: F'd up the first time
Did you ever check your drivetrain angles??? I just did a tranny build, clutch, tick master, a pro series torque arm, and a prothane mount. I did all my adjustments to the torque arm on jack stands and needless to say i screwed up and anything over 65mph had a weird 2 seconds smooth and 2 seconds choppy... Put it up on 6 inch blocks on all four tires and rechecked the angles and my rearend was 1 1/2 degrees off. so i have my engine/tranny at 3 1/2 degrees and moved my rearend from 5 to 3 1/2 degrees and i have had absolutely no vibrations at all since. So check your angles on the engine/tranny, your rear end, and your drive shaft and shim or grind your mount accordingly...
Everyone gives up on the poly trans mounts too quickly. I ran a Prothane on my old 97, and a Prothane on my current 01. Both of them had annoying vibes immediately, but the mount softens up within a couple weeks and ALL VIBES GO AWAY. It's much nicer with a poly mount because the shifter doesn't move nearly as much and shifts feel much more solid. It takes the poly's a couple weeks of driving to soften up and show its true value! Don't give up.
Don't give up.I measured my stock trans mount (off the car) when I changed to the prothane mount. They were the same thickness. I also double checked my pinion angle before and after changing the prothane mount to be sure my PA didn't change. There was no change in PA what so ever, it was spot on my original measurement. I have run this mount on the factory trans x-member and now currently on a BMR TA relocation x-member. I have never had any hint of a vibration. I'm also running a custom driveshaft that I know is balanced perfectly behind the M6. The problem that some are having is driveline vibration due to driveline angle, well worn u-joints or driveshaft balance issues that existed prior to the swap and just went unnoticed due to the forgiving nature of the rubber stock mount. Look into the driveline issues to fix the vibration problem.
well, verdict is in. Chasing this problem now, Ive changed from a prothane trans mount to some kind of mount i got from summit for 10 bucks, back to a prothane then to a completely trimmed energy suspension mount, Ive changed my driveshaft, torque arm, and now im back to a stock mount again. The vibration is still there to the point where it shakes my visors and passenger seat at around 70mph. So right now my setup consists of a different driveshaft from my bro in laws car that didnt have any vibration, a stock trans mount, and UMI adjustable torque arm (it came preset to 0 but the vibes were still there). Ive been messing with the pinion angle a little, but i dont really think im doing it right, so that could be the cause of my problem, however when it was set to 0 it still vibrated and im at stock ride height.
Driveshafts mounted 180º the wrong way have been known to cause vibrations because of the balacing weights mounted to them. Maybe try rotating that new one you put on?..
Also you say your car was perfect before the mount, maybe try an alignment, its a possible coincidence..
Also you say your car was perfect before the mount, maybe try an alignment, its a possible coincidence..