Motor mounts again.....

[DaBlackPearl]

Ok, this link is great because Will has some really crucial info on how to mod the mount......

http://www.pontiacbonnevilleclub.com/fo ... =12&t=2482

In this link, Will says "your mounts broke because they're OLD. No mildly modded L67 like yours will habitually break mounts. Buy good quality (name-brand) mounts, and once they're replaced, you'll be fine."

Will, these are the 3rd set of mounts in the past 2 years. Like I said, the front mount breaks and then within 6,000 miles ALL the mounts have failed. The mechanic even warrantied the front mount once. Regardless of Mods I am tearing up the mounts.

Everything on the front end is new. New axles, new/rebuilt trans, new cradle bushings, new struts/mounts/springs, new rack/pinion, new ball joints, new brakes, new spindles/wheel bearings, and new control arm bushings. I had the whole front end redone for just under $6k last year. I drive hard, really hard. I have fun spinning the front tires and usually replace a set of "H" series $105ea tires on the car annually from burn outs. I don't mind beating it and fixing cuz it is more fun to drive and I averag about 3,500 miles a month on it.

So, what are named brand mounts and which brand should I use?
What is the strongest bolt I should use for the mod?

When the mounts break I can tell because tire spin is less and torque steer is less. With new mounts there is a massive difference in torque steer when taking off. I don't mind that they are broke, it doesn't seem to be hurting anything except my CV joint boot rubs on the cradle and will put a hole in the boot if I don't fix the mount.

My mechanic recommends that I drive normally. I get that, but if I can do this mod and use a better set of mounts I would rather try that first. He is unable to get any type of performance mount so we bought the most expensive mounts that NAPA sold for the car. I also talked to Pontiac/now GM dealer and they said there was no TSB on motor mounts for that car.

[willwren]

When your first mount failed, your other mounts were already weak. Another old mount failed shortly after, adding far more stress to the new mount, causing it to break early. I have far more mods than you, and the only mount I have problems with is the front trans, and I'm applying significantly more torque to that mount than your car is. I'm also the only Series 1 that has such repeatable and severe failures on that mount (I'm breaking the steel parts now, not the rubber). Other than that, my other 3 mounts have only been replaced ONCE in the lifetime of the car.

How many times has each mount broken, and where are you buying them?

[DaBlackPearl]

Thanks Will,

They buy the mounts from NAPA. They are the most expensive mounts but I am unsure of the brand or if they are O.E.M.

22,000 miles ago the trans failed. When they took down the trans all the mounts were old and needed to be replaced. They also said that when they dropped the cradle the cradle mounts were dry rotted and that when they tried to re-install the cradle that it had play with all the bolts tightened. So I had them replace 12 cradle bushings. The suspension was shot so I had them install new springs, struts, mounts, and all new ball joints. I had a complete rebuild of the front end. Afterwards the car handled fantastic, rode nicer, and had all of that torque steer back like when I first did the mods.

I have been driving for the last 6,000 miles with blown front mount and when I brought the car in for a blower resistor replacement they showed me how all the mounts are failing again. So I blew the originals and then 22,000 miles later the new mounts. This current set that needs to be installed will be the 3rd set.

Before I replace them this time, I want to make sure I buy the BEST mounts that I can, and that I mod the front trans mount so that it holds up. In my case it might not be the mods or the power of my motor that is causing the stress on the front mount as much as it is my constant 0-60 light to light. I also shift the gears down to 1st and manually bring them back up for more rpm's out of the engine when taking off and I never drive with Trac-Loc on. Actually, I rarely downshift. I shift to first from a stop at a light and then upshift manually would be a better description. I do downshift to second in tight corners. But that is my "joy ride" entertainment during the long hours I spend driving.

I appreciate the help. I have done everything this forum has instructed me to do and the car is a blast and can throw down with any stock v8 in the 0-60 range. I suffer in the top end but that is OK cuz I ain't supposed to be doing 30+ over the speed limit anyway.

[willwren]

In my case it might not be the mods or the power of my motor that is causing the stress on the front mount as much as it is my constant 0-60 light to light. I also shift the gears down to 1st and manually bring them back up for more rpm's out of the engine when taking off and I never drive with Trac-Loc on. Actually, I rarely downshift. I shift to first from a stop at a light and then upshift manually would be a better description. I do downshift to second in tight corners. But that is my "joy ride" entertainment during the long hours I spend driving.

This is your problem. You are destroying the mounts prematurely by your own driving habits. Reinforcing the front trans mount will then move stress to the rear trans mount, and you'll kill it early too. When you take flex out of one mount, that energy gets applied somewhere else.

In addition to the mounts, you're beating on your motor and trans as well, not to mention your gas budget. These cars were not designed to be used the way you do it, or at least as often as you do. While I do 'spirited sprints and chirps' from time to time, I save my abuse on the car for the track.



As you beef up one mount at a time to prevent a failure, and end up with better motor mounts, the vibration you pick up in the drivetrain as a side-effect will also slowly cause damage to the engine internals. Damping vibrations is a key element of vehicle design for this reason. Added stress to subframe bushings will also be a big factor down the road. Trust me, I'm in the middle of that battle myself, but I don't abuse my car on a daily basis. My failures tend to be more along the lines of instantaneous peak stress catastrophic failures (if you do some searching, you'll see the steel portion of mounts literally snapped in half, and more than once). My rear trans mount is bad again due to 8 failures of modified front trans mounts over the last 2-3 years (and I put less than 5k a year on that particular car). My torque-axis mount and dogbone seem to be holding up well, but when I break a mount, I fix it immediately before other mounts suffer.