Poly trans mount

[Paul G]

Still working out the details from the A518 overdrive trans install from a couple of years ago. Latest problem is tearing the tranny mounts apart. I am surprised that they wont last more than 1 year. The 360 in the car now is torquey but not a power house, but still likes to rip the tranny mounts apart. They last about a year and then tear.

The A518 is using the GM style mount fabricated to fit the stock cross member. I have gone through 3 of these.


I just installed this Poly tranny mount, It is the Summit house brand.


I am noticing a distinct vibration around 3000 RPM on deceleration mostly. Cruising at speed is smoother than before. Maybe from the tail of the trans being held in correct alignment due to the stiffer trans mount? The engine mounts are stock rubber, drivers side replaced a couple of years ago. Also using the torque strap on the drivers side to keep that mount from ripping apart again.

I am a little concerned now about using a poly trans mount. I have been reading that a Poly trans mount with rubber engine mounts can be dangerous, damage to the trans case due to different rates of flex? 

[flyinlow]

Paul,

I use the same rubber GM pick up truck mount for the trans mount on my A518. About 30K. miles and it still looks good. Must be some unusual stress.  Mine is a '73 so the rear mount is on a separate cross member than the T-bars. A little different. I might try to rig a GO Pro camera under the car to see what is going on during driving.   

Have all the mounts come from the same vendor? Maybe a bad batch.

Craig

[Paul G]

The rubber mounts came from Oreillys. 

[fy469rtse]

Paul rubbers not rubber anymore,
Schumacher has one that that has internal steel inserts that will allow it to stretch so much before internal plate stop it breaking ,
But I like the idea of running a go pro to see what's going on , I have over 650 HP and I drive it like , you don't want know , can't understand why you break the so often ,

[flyinlow]

Yea ,I saw he was running the poly mount. Just wondered what was chewing up the rubber ones.

3000 rpm in O/D...about 80-85 MPH?  The rear axle would rotate nose (front) down slightly increasing the angle the  u joints would be running at during the time you where experiencing engine braking. The rubber mounts might have been absorbing more of the vibration before.

Just a thought.

[Paul G]

Strangly, the vibes with the poly mount are at low speeds not in overdrive. Slowing down to a stop in town. Felt between 3000 rpm down to 1500. I should have been more clear on that. Cruising in od is actually smoother with the poly mount.

[Paul G]

I have had enough of that poly mount. The vibs were driving me nuts. At certain rpm the dash would vibrate. At certain speeds the entire car would vibrate. It felt like an engine plate was installed. Took off that poly trans mount and put the rubber one back on.

[mally69]

Had this happen recently. I went through tranny mounts a lot, till I found that my engine mounts were no good they allowed my engine to rock a little too much and stressed the tranny mount enough that they would break. I had old original mounts   How I found this out is my flex fan just started bumping my top of my radiator. Just a thought to look into.