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Old 11-02-2014, 07:06 PM   #2
OldNuc
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Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 66,693
 

1998 SC2
Default 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.

Saturn OEM Parts Source
GM Parts Giant- http://www.gmpartsgiant.com/
GM Parts Direct- http://www.gmpartsdirect.com/
Get Saturn Parts- http://www.trademotion.com/splash/in...?siteid=214643
GMparts4U.com- http://gmparts4u.com/
Your local dealers - http://www.partsvoice.com/

Transmission mount replacement
http://www.saturnfans.com/forums/sho...=1#post1825741
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