Looking to revisit the poly/prothane trans mount vibration issue—yes, I've tried various fixes, none of which worked for me. What I haven't tried, however, is an adjustable torque arm. Soooo, if you've cured the the vibration problem with that method, please chime in.

JamesC

 

 

As you will note in the following link, some members experience horrible vibrations (to include me) while others never encounter it. My hope is to use a poly or prothane mount but perhaps eliminate vibration with an adjustable TA.

https://www.thirdgen.org/forums/tran...ml#post4649528

JamesC

 

Might sound strange, but all of my vibrations went away after removing the trans crossmember, and letting the trans self center, and reinstalling the crossmember without putting it into a bind.

 

You might try this:
https://www.thirdgen.org/forums/tran...ml#post6221848

 

he was the original poster on that thread

 

Oh sorry. I think I wanted to suggest this (frame to crossmember spacers):
Old thread, I know.
But that is exactly what I had to do because the extra thickness of that preload plate
caused something (I think the exhaust) to hit the underside of the body. I made 1/4"
thick spacers to go between the crossmember and frame.

Edit: after reading through this entire thread, if I do have any high speed vibrations, I
think my first step will be to replace my metal crossmember to frame spacers with 1/4"
thick reinforced conveyor belting. And make sure that the driveshaft angles are equal
and opposite.

 

Start with a magnetic angle finder at the trans., driveline, and pinion. U-joint and driveline iperating angles are the primary consideration. That's ten bucks, or free on most smartphones.

Something else you should do, and it is basically free, is an audio spectrum analyzer app. on your phone. Tire vibration vs. driveline vibration is easily determined, as one example. This isn't likely a huge help, since you have new tires, but you may find it interesting to see what freq. is observed with your 3.73 gear car vs, your buddies' 3.23, etc.

Ultimately NVH is not going to be at its' best unless isolation is effective. Rubber between crossmember and floorboards, and space the mount similarly. And you'll negate he "need" for a poly mount by getting the torque arm off the trans. and onto a rubber isolated attachment to the crossmember. I can't remember what all is done to your car, but IIRC, an Adj. Angle TA is a lot more than "the basics."

 

I have a Umi adjustable torque arm and trans mount which takes the TA mount of the tail shaft and onto the there cross member. I never noticed a vibration with that set up until I swap in a poly trans mount. The only thing left not stock in my car is the driveshaft, I believe the rubber mount dampened the vibration from the stock DS more and the poly mount is picking it up. I just bought a new aluminum 3" .125 shaft hoping it's balanced better than the stock DS and takes the vibration away

 

I have an alum drive shaft, but it does nothing to alleviate vibration when I use a poly or prothane trans mount. Rubber has cured my issue so far.

JamesC

 

What exactly is your hypothesis for the Adjustable torque arm? ....if your angles are good, I don't see it solving any issues.

Fwiw, I tried the ES mount and it transmitted a lot more vibration....not necessarily at any given speed though. Went back to rubber.

 

Seeing what the angles are with OE rubber vs poly/prothane might prove interesting.

JamesC

 

My thoughts turn to the possibility that the polyurethane mount isn't necessarily the cause of the issue. Isn't it possible that the vibes go away with the rubber mount because it simply isn't transmitting the vibes, while the poly mount just telegraphs the vibes? Maybe the vibe is still there with rubber, it just dampens it enough that it's not detectable?

I wonder if the problem might be coming from something else that's slightly out of spec, or a stack-up of tolerances that result in vibes. Maybe there's a slightly tweaked part somewhere in the drivetrain, a misbalanced or bent wheel, axle, brake rotor, flywheel/clutch/pressure plate, etc.

I know we trust that replacement parts will be straight, and properly balanced, that OE parts that don't exhibit obvious issues are OK, but a mildly bent part, or warped part, or a set of combined tolerances could go undetected and cause an issue in use.

I'm rambling on, and it probably doesn't help bring about a direct resolution, but it's something to consider.

 

I've heard people say that solid engine mounts aren't too bad but a solid trans mount is the pits. That tells me a lot of vibration comes up through the trans mount. I don't know if you have a problem to solve as much as just use parts that are proven to work.

 

Thats were things get tricky, I can rip a oem rubber trans mount in no time which is why I went poly

 

Threw in my new aluminum driveshaft today, cut down on the majority of the vibration I was having. Also noticed I knocked of the stick on wheel weights on my rear driver side tire which is probably where I'm still getting some vibration at high speed

 

Anyone that had problems with poly mounts how exactly did you install them? I'm guessing here but I figure most of you did run the car with everything loose so it could re settle in to place. Just did my mount last night with the preload plate I have an 88 iroc with 88k miles I think I've only put 2k miles in 5 or so years my miles are a bit more harsh but I'd assume my motor mounts are in relatively decent shape compared to many which as stated could exacerbate the problem. Side stepping the clutch does wonders on a stock mount though.

No problems with mine tested to 110 then it got funky but I typically don't drive near that speed but I was trying to find a potential problem so I think I'm okay could've been something else altogether but I didn't feel like finding out.