Passengerside front motor mount - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-18-2005, 09:15 AM   #1
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Default Passengerside front motor mount

Our passenger side front motor mount is definately in need of replacement but need to know if there is a way to replace without moving a/c compressor. Looks like you can't get to the block bolts otherwise. Any suggestions appreciated.
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Old 03-27-2005, 02:13 AM   #2
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No replies but just did it. Manual says remove nuts, raise engine, and replace. Musta bin a car without A/C because the manifold is right over the top of the mount.

Bottom line, belt comes off and the a/c compressor is unbolted. Is a good thing I have a vast collection of extensions in 1/2" increments and universals because they were needed. Only way to get bolt off back of compressor is with a short 1/4" drive socket and 3" extension. Anything bigger would not fit between the a/c lines. All front a/c mount bolts insert from back.

Whoever designed the mount with studs on both ends should be severly chastised. Have to jack the engine up a good 2" at the mount to R&R which means taking the driver'* engine and passenger transmission mounts loose to get it up far enough.

Then getting the bolts started again was an hour long exercise in frustration. Am leaving the reinstallation of the belt for after is off the ramps tomorrow (nice thing about FWD is that you can drive on ramps even on a slick garage floor. I always put a pieece of carpet under the leading edge to reduce the risk of slip)

However mount was definately badly torn - on tthe backside so was not visible in the car but engine was rocking so was necessary. Driver'* side was replaced a few years ago.

Moral: if you have a shop replace the motor mount - get them to commit to a price before starting.
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Old 03-27-2005, 12:27 PM   #3
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I'm not liking that.... Thats the mount I need to replace... But I do have the assortment of extensions and swivels....lol... Oh yay

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Old 03-27-2005, 04:32 PM   #4
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I suppose it might have been easier if I removed the second fan and radiator first but didn't want to go to that extreeme. Maybe if there were a way to support the a/c and manifold better, reinstallation would have been easier but reminded me a lot of time spent on my back trying to get a Saginaw (heavier than a Muncie) to align with the pilot bearing. At least then you could see the transmission bolts.

That said the mount nuts were not too hard because I have midsized sockets (half way from short to deep), that was the right lengthl for the back/ top mount nut which is only seen after removal.

Be that as it may, the Bonneville seems to be one of the few FWD GM cars that does not have a dogbone and that lack puts more stress on the mounts. Any idea why ?
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Old 03-27-2005, 06:34 PM   #5
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I guess the higher-mounted dogbones really help with the front-back rocking of the motor. :(
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Old 03-28-2005, 02:16 PM   #6
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The engien does torque and move to a certain degree, But I'll bet the dog bone helps keep the motor from torquing too much... I'm pretty sure that the 92 and later bonnies got the dogbone tho.. and the torque axis mount...

Padgett, without the dog bone mount on the 87-91 bonnies was the engine torquing enough to actually compress the mounts beyond thei designed limits? Yeah I know it sounds stupid...

I also noticed that with the newer set up, such as my 95 with a torque axis and doge bone mount the engine doesn't seem to rock too much, and the front end doesn't seem to be so proned to jumping up as you mash the throttle, the 91 moves...lol... Ok I'm out in left field here...

Padgett, whats the reason.... I'm drooling here..

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Old 03-28-2005, 03:14 PM   #7
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The issue is that in the 90 design, all of the mounts are on a flat plane that is entirely below the engine. Most chassis related torque is through the driveshafts which are close to but still above that plane. This creates a rotational moment through the mounts.

By adding a dogbone, you change the plane to a triangular section that is *much* more rigid.

One of the problems of the planar structure is that it is possible to "wind it up" until the tire breaks traction which releieves the force until it winds up again. When you hear a tire going eep, eep, eep, eep without an accomanying bang, bang, bang of axle tramp, that is what is happening.

For maximum traction, even forces that remain steady are better than sudden changes.
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Old 03-28-2005, 03:18 PM   #8
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Ahhh great explanation...

So thats why the 92 and up bonnies got the Torque axis mount and the dogbone...

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