Stock vs. Poly Transmission Mount (A4)

**pajeff02** · 06-14-2011, 06:07 PM

I have read a couple of threads on here concerning the difference between the stock and polyurethane transmission mounts, but never realized it would be a day and night deal. While upgrading our trans to a Performabuilt Level II, I swapped out the stock mount for a Prothane piece. Prior to the install, I had not driven the car in a couple of months due to winter, but it just felt a lot harsher than I remembered. Even in "Park" I noticed a difference when I revved the engine. Idle was about the same, but anything from 2,000 r.p.m. on up felt awful harsh.

Tonight, I swapped back to the stock trans mount and went for a ride. There was an immediate difference in how the car felt. It was so much smoother and all the vibration and harshness was gone. Revving the engine in "Park" no longer produced the intense vibrations and things were noticeably quieter. I still have to change out my stock engine mounts when I do the K-member install, but at this juncture I think I may just continue to run the stock rubber trans mount.

In my reading on here, I saw mentioned that removing the metal plate would cut down on the harshness, however, this does not appear possible with the Prothane piece. I know a lot of you guys have swapped out mounts and am curious on your experiences, especially with a brand other than Prothane.

**aggie897** · 06-14-2011, 06:12 PM

I have the prothane mount and I feel a huge difference as well. I welcome the vibrations, but then again I don't have to use it as a daily driver. Not sure about removing the plate though...

**jiveass** · 06-14-2011, 06:14 PM

i had a little more vibration, but not enough to make me wanna get rid of it. The power felt like it was being put to the ground more efficiently than the stock mount. I guess it all depends on what you want to get out of your driving experience. Im sure eventually ill look for comfort above all other, but for now, ill stick with the poly mounts.

**666ws6** · 06-14-2011, 06:29 PM

To tell ya the truth, I couldn't notice any major changes when I changed mine. Then again, with headers and an open cutout... somethings don't matter too much.

**pajeff02** · 06-14-2011, 06:45 PM

On our car it is not just "a little more vibration" -- it is harsh. I have LT's, a cutout, tunnel mount torque arm and a Moser rear, so I am well accustomed to noises. This just does not seem right.

**Lunatikgixxer** · 06-14-2011, 06:50 PM

i agree with jiveass.. the shifting felt a lot more solid and smooth compared to stock. I honestly dont see a big difference in the vibrations but i also have a cam that vibrates the car enough, so i probably dont notice it.

**km346** · 06-14-2011, 08:40 PM

I hated the energy suspension trans mount in my car (m6), replaced it with a new rubber mount after the first couple of days. FWIW i don't think its necessary in the first place if you have a tunnel mounted torque arm. There isn't nearly as much load being applied to the mount with the torque arm out of the equation.

I plan on buying a torque arm relocation bracket and running a full length arm, I hope that isnt as harsh as the poly trans mount was.

**transamtom** · 06-15-2011, 01:41 AM

I had swapped one into my LT1 and I hated it.

I went through one rubber mount a year and that was still better than the vibrations from the poly.

**bpopham22** · 06-15-2011, 01:46 AM

Prothane motor and tranny mounts here.....I can feel more vibration and firmer shifting due to my tune,but its nothing too annoying.....my LT's and borla exhaust get most of my attention.

**Firebirdjones** · 06-15-2011, 06:03 AM

Originally Posted by pajeff02

On our car it is not just "a little more vibration" -- it is harsh. I have LT's, a cutout, tunnel mount torque arm and a Moser rear, so I am well accustomed to noises. This just does not seem right.

My honest opinion Jeff,,,if you have a tunnel mount torque arm, go back to the rubber trans mount, it's not needed.

I run the poly trans mounts, but I still use the stock torque arm. I found the aftermarket mounts would raise the tail of the transmission 1/4" from the stock mount. Not only did I have to remove the plate, but I ended up milling 1/8" off the mount as well to establish the correct trans angle and keep my driveline angles intact.

After this I had no more vibrations. Although they still do transmit more noise. That's a given when you mount anything more solid.

**pajeff02** · 06-15-2011, 08:21 AM

Originally Posted by Firebirdjones

My honest opinion Jeff,,,if you have a tunnel mount torque arm, go back to the rubber trans mount, it's not needed.

I run the poly trans mounts, but I still use the stock torque arm. I found the aftermarket mounts would raise the tail of the transmission 1/4" from the stock mount. Not only did I have to remove the plate, but I ended up milling 1/8" off the mount as well to establish the correct trans angle and keep my driveline angles intact.

After this I had no more vibrations. Although they still do transmit more noise. That's a given when you mount anything more solid.

Thanks, FBJ! I think that is what I am going to do for now, leave the stock mount in the car.

**JayTA98** · 06-16-2011, 09:56 AM

I also had the vibrations that you talk about jeff. I ended up returning the mount and used stock oem mount.

**pajeff02** · 06-16-2011, 09:59 AM

Sounds like a common issue then. Wonder if any of the poly mounts are better than Prothane as far as isolating vibrations and noise?

**Firebirdjones** · 06-16-2011, 07:05 PM

Originally Posted by pajeff02

Sounds like a common issue then. Wonder if any of the poly mounts are better than Prothane as far as isolating vibrations and noise?

I would think any poly style mount that is pretty solid will transmit the noise. As far as vibration I'm not sure. Different brands may be made different thicknesses. I don't recall what brand I bought, it was a few years ago. I just know it was too tall, so I milled it. All my vibrations went away.

With that said, I would tend to believe that as long as you keep the trans tailshaft height where it needs to be, vibrations shouldn't occur.

I believe what you are doing is the real solution though. A good tunnel mount system to rid it from the trans all together, and then run a stock rubber mount. Problem solved. It's the way I wish they would have been built to begin with.

**98Hardtop** · 06-19-2011, 02:12 PM

Originally Posted by JayTA98

I also had the vibrations that you talk about jeff. I ended up returning the mount and used stock oem mount.

I did the same thing. I put in a poly mount and noticed a big difference in vibration. The next day I had a stock one sent to my work and installed it.

**c5z28** · 06-19-2011, 02:26 PM

I went polyurethane one day and back to stock that same day

**Smittro** · 06-19-2011, 03:22 PM

The more you turn them into dragsters the more comfort you will give up.
The harder the mounts/bushings the more mechanical harmonics transfer to the cockpit..

IMHO if ya want a quieter interior, and a softer feel, stay stock..
Just my .02 take it for what it's worth..

**Firebirdjones** · 06-19-2011, 03:43 PM

Originally Posted by Smittro

The more you turn them into dragsters the more comfort you will give up.
The harder the mounts/bushings the more mechanical harmonics transfer to the cockpit..

IMHO if ya want a quieter interior, and a softer feel, stay stock..
Just my .02 take it for what it's worth..

That's very true. All these poly mount bushings used, as well as solid rear axle control arms, stout torque arms mounted with heim jounts, stiffer lowering springs etc.....will all contribute to the transfer of more noise in the cabin. There comes a point where you cross the line in comfort and cruising while trying to mix speed and performance. How far do you want to go and how much can you put up with?

It's why I prefer to use the stock control arms and then box them in with flat plate, while still maintaining the factory control arm rubber bushings. It's a little stiffer boxed in, but yet the rubber bushings still allow a comfortable ride. Not to mention it doesn't cost anything, and that simple mod cured all my wheel hop problems

I do the same mod on my panhard bars with round stock that fits inside the pan hard bar. One inch beads of weld every 6 inches to hold it in, and it's stiff as hell, while still using the stock rubber bushings on the ends.
I use a poly trans mount, milled down to maintain the correct tailshaft height, (very important) then keep the stock rubber insert for the torque arm. I get no vibrations setup this way. I still have the trans firmly mounted to hold the torque arm down, (no more torn mounts) but the small rubber insert on the end of the torque arm still allows for a very slight amount of movement both under power and cruising down the road when the rearend is moving up and down,,,to keep noises down in the cabin.

All this combined improves the car to a degree yet I don't sacrafice any ride quality or comfort.

**jsmith564`** · 07-10-2011, 03:35 PM

well my car already had a problem. but i had all stock mounts to begin with and there was some vibrations. swapped to poly mm and a little harsher. but when i swapped out to a poly tm and it was unbelievably harsh. but in my case something else is wrong with the car. i took the car and spun it up past 70mph and popped it in neutral and it was smooth. my car is in the shop right now so i'll know something this week.

**JayTA98** · 07-11-2011, 03:49 PM

Originally Posted by Firebirdjones

That's very true. All these poly mount bushings used, as well as solid rear axle control arms, stout torque arms mounted with heim jounts, stiffer lowering springs etc.....will all contribute to the transfer of more noise in the cabin. There comes a point where you cross the line in comfort and cruising while trying to mix speed and performance. How far do you want to go and how much can you put up with?

It's why I prefer to use the stock control arms and then box them in with flat plate, while still maintaining the factory control arm rubber bushings. It's a little stiffer boxed in, but yet the rubber bushings still allow a comfortable ride. Not to mention it doesn't cost anything, and that simple mod cured all my wheel hop problems

I do the same mod on my panhard bars with round stock that fits inside the pan hard bar. One inch beads of weld every 6 inches to hold it in, and it's stiff as hell, while still using the stock rubber bushings on the ends.
I use a poly trans mount, milled down to maintain the correct tailshaft height, (very important) then keep the stock rubber insert for the torque arm. I get no vibrations setup this way. I still have the trans firmly mounted to hold the torque arm down, (no more torn mounts) but the small rubber insert on the end of the torque arm still allows for a very slight amount of movement both under power and cruising down the road when the rearend is moving up and down,,,to keep noises down in the cabin.

All this combined improves the car to a degree yet I don't sacrafice any ride quality or comfort.

i wish i knew about this trick before buying all my stuff lol. nice idea jones.