skyman Posted November 12, 2013 Report Share Posted November 12, 2013 Finally got the front and rear motor mounts replaced today. The one just below the radiator and the one below the firewall. The results were a more solid feel when putting car in gear and when tranny shifts from 1st to 2nd, no more wobble in the gas pedal or flexing feel in the drive train. Thats the good news. Now....before with the old mounts, when at a stop lite, I could not tell the engine was running unless I checked the tack. Now, I can feel the engine running thru the seat of my pants. Also before, I had this intermitant vibration type feeling that when at turnpike speeds that would change or disappear depnding on road surface engine load or if car was in a bend in the road. This started in around 65 and got worse as speed increased. Now, It's there all the time abouve 63/64 and gets worse the faster I go. At speeds between 55 and 60/61 it's like a drone sound and you can also feel it. Also at around 70 on a nice smooth asphalt highway when turning the wheel into a bend in the road or just putting a little preasure left OR right on the steering wheel, I can feel the vibration in the steering wheel...kinda like a shimmy. Below 55 or so, there is no issue. I know there has been this vibration issue with some of these Devilles and people have changed tires and balanced and rebalanced tires to no avail. Me included. Then some have found the issue solved by replacing the bad motor mounts. Wondering...I noticed, my mechanic did not use a torque wrench when tightening the mounts. Would this be an issue...if he over tightened them? Another thing on my mind about this sound and vibration might be the front axle cv joints or maybe just one of them. Originals at almost 111,000 mile now. I noticed when I left the garage, when coming to a stop sign, I heard a knock knock knock knock from the left front wheel/axle area but has not happened again. I've heard that when the cv joints start to go they can knock....maybe vibrate also?? anyone have any thoughts on this or maybe gone thru the same problems? Link to comment Share on other sites More sharing options...
JohnnyG Posted November 13, 2013 Report Share Posted November 13, 2013 The way you are describing this vibration/noise/harshness is not the same as the road force balance issue that you may have suspected in the past. The tire issue usually occurs between 68 - 72 mph then smooths out, and it feels like an out of balance tire, even though all the tires are balanced correctly. What you are describing here is more of a CV issue or a wheel bearing issue. If it's worse when you turn one direction or another, I'd lean toward wheel bearings, if there is little change except when turning sharply, I'd check out the CV joints first. Don't forget, it could also be rear wheel bearings, but you seem to feel it in the steering which sort of rules that out. As far as feeling the engine running in the seat of your pants is definitely not right. Since the car isn't moving when you feel this, someting is NOT right with the motor mount replacement job. Either something is hitting the floorboard, such as the exhaust, or too long a bolt may have been used and it is causing the engine vibrations to be transmitted to the body. I'd look for metal to metal contact, or more correctly engine metal to body contact. I'd also solve this issue first before trying to figure out the driveline noise. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
KevinW Posted November 13, 2013 Report Share Posted November 13, 2013 Were OEM parts used? Some aftermarket units may not offer the same degree of isolation. Installation is also a factor, mostly the method of tightening in the case of 'single-stud' mounts. When an impact wrench is used, there's a chance the mount can be damaged and/or provide suboptimal performance due to rotation of the stud. I suspect the use of impact wrenches may be linked to the premature failure of replacement left (front) mounts. ___________________________________________________ Link to comment Share on other sites More sharing options...
skyman Posted November 14, 2013 Author Report Share Posted November 14, 2013 Today I took it back and we rotated and rebalanced the tires. Also had front and rear rotors turned. There is an improvment but not perfect.I can says that any vibration I now feel mostly in the seat of my pants and on the floor.Substantial improvment in shimmy when turning in bend of turnpike at higher speeds. Tomorrow I'll be driving it back to FL more than likley 60-62 mph to keep vibrations at a minimum. When I get back I'll have my guy loosen and retorque the mounts to the proper specs "52 lbs" and take it from there. Next step will probably be to replace front axles and hub bearings and see how THAT works....and perhaps the two motors mounts on the two ends of the motor near the left and right wheels. Link to comment Share on other sites More sharing options...
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