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Upstate Saturn 11-02-2014 06:55 PM

Replacing all four motor mounts over a few months - does it matter what order?
I will be replacing all four motor mounts on my '01 SL2 over the next few months. I plan to do them one at a time as I get free time. Does it matter what order I do them in?

The top mount is shot, and although it's been replaced a few times over the life of the car, I'm pretty sure the others never have been. Now that the old girl is having her 210k makeover it seems like a good idea to replace all the mounts.

Also, do you think it's reasonable to do this with a bottle jack as opposed to a floor jack? I know all the videos use a floor jack, but at this point all I have is a bottle jack and jack stands. I think the upper mount would be pretty straightforward, but I'm not sure if the lower transmission mount is doable without a floor jack. Richpin looks like he's using all his considerable skill to get everything to line up and the bolts started.

OldNuc 11-02-2014 07:06 PM

Re: Replacing all four motor mounts over a few months - does it matter what order?
Any jack work as long as you don't bend the pan or break something.

OEM top mount, trans mount, late 97 or newer torque axis struts and the polly inserts. Engine must have an even smooth idle. That means good even compression. Clean flow balanced injectors. The 3 rubber exhaust mounts should not be stretched when the car is at rest, just supporting the exhaust. These 3 suspension pieces will be what couples the exhaust vibration into the floor pan so the stretchiness and thickness of these is how you tune them to not appear solid at some inconvenient RPM. The Walker 35119 isolator is thicker than the original OEM. They are cheap so modifying them is not a big deal. They thin nicely on a belt sander but if too thin they break and you will be buying a new exhaust.

If you have an uneven idle you will never reduce the vibration to zero. Setting the torque axis struts to zero tension/compression at rest is critical.

The torque axis struts are of 3 different designs and the 3rd design, late 97 production, have replaceable inserts. These are the stamped and welded design. There are 2 pictures in my gallery. What you are attempting to accomplish is restrain the engine free motion as much as possible without going solid. The main axis of rotation is on a line between the top mount and transaxle mount. The torque axis struts are positioned to restrain the normal torque reaction and drive axle wind up. The poly inserts allow enough motion to not act as a solid link but do not transmit vibration well either. The idea is to keep large excursions of the engine/transmission and exhaust to a minimum. Small displacement of the power train transmits to large displacement in the exhaust. The rubber hangers will deftly transmit this exhaust motion into the floor pan which simulates the head on a large kettle drum, with you inside of it. You can get a buzz in the floor that does not transmit into the upper frame or seats but the large low frequency pan displacement is pushed up to a higher frequency. the characteristics of the rubber mounts determines where this buzz occurs. The trick is to get it somewhere you do not care. By minimizing the powertrain displacement you minimize the magnitude of the exhaust displacement you have to deal with. You can slightly change the static exhaust position to take all the stress off of the flex connector and have the mass of the exhaust evenly spread over the 3 mount points. The muffler hanger basically controls axial twist on the exhaust. I used the Walker 35119 isolators and just stuck them on. Ended up with the buzz from about 50 to 57mph and this is a speed range that is only passed through so I did not pursue any further elimination. the bed liner should kill this 50-57 mph buzz all by itself. The OEM isolators are a softer rubber and thinner and would possibly isolate the floor better but as they were 10+ years old and I am adverse to dragging the exhaust down the road I decided to replace them. The harder-thicker isolator appears as a solid at given frequencies.

Top Engine Mount 21012185
long studs 11518885 use these if replacing a frowny mount and there are NO threads showing above the nuts.
Top mount nuts (5) 21006320
Transaxle Mount 21012951

The metal part that is bolted to the timing cover is different thickness depending on the mount and is easy to measure.
Frowny Mount 1.275" ~1 9/32"
Solid Mount 1.475" ~1 15/32"
The good mount is ~3/16 thicker than the frowny mount.

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Transmission mount replacement

Upstate Saturn 11-03-2014 09:18 AM

Re: Replacing all four motor mounts over a few months - does it matter what order?
Thanks, OldNuc, great info from you as always! :)

OldNuc 11-03-2014 11:07 AM

Re: Replacing all four motor mounts over a few months - does it matter what order?
Replace them all at the same time and get the OEM 3rd design dogbones and install the polly inserts. [url][/url] Also replace the 3 exhaust hangers, Walker 35119. RA sells a decent copy for 1.92 each. NAPA may have them in the Walker box, does not make much difference as they can be tuned with a belt sander if needed.

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