G50: 92Q vibration Help

[pbedrosi]

My car has been vibrating since day one, but it had been parked for a while so I thought the cheap Dunlops had flat spots. Well, between storage and shipping the car, to a recent time spent having the trans replaced my car had been sitting for about a year total.

When I got the car back after the 94 trans installation the car vibrated like crazy, almost as if all the wheel weights fell off. I'm freaking now thinking its the trans swap, but I remind myself how long the car has been sitting.

Next day I install 16" tires and wheels from our Quest van (new) to rule out the trans. Well I got rid of 75% of the vibration, but the remainder is bugging me.

During startup the car shudders a bit then smooths out between 10-30pmh, but when I reach 35-40mph the car really sharts to vibrate. I think my actual speeds are higher considering 16" wheels and 65 series tires. First gear starts are a bit better but not by much.

As I speed up the frequency increases and vibration starts to disappear around 80-85 mph. I can still feel the vibration in the center console and the seat, but not as bad as at 40mph. While decelerating the car still vibrates, regardless if I'm in gear or in Neutral. Again, when the car slows to about 50 the vibration starts to get bad, peaks at 40 and smooths out below 30.

When I had my oil changed at the local infiniti dealer the tech could only find bad rear shocks and busted engine fan (clutch I think, the fan is in one piece).

WTF is it? it feels to me like driveshaft vibration. Should I index the driveshaft? Could a bad motor mount couse this?

[maxnix]

WTF is it? it feels to me like driveshaft vibration. Should I index the driveshaft? Could a bad motor mount couse this?

I think the question is did they mark the driveshaft?

Are you saying the transmission shudders at initial launch after reaching operating temperature?

Do you know the Quest wheels are balanced? Are they safe at speed on a Q45?

[DrewQ45]

Take a read....

zerothread?id=201042

[elwesso]

Take a read....

zerothread?id=201042

cash money.... Probably going to want to get a new driveshaft, i bet your install place took it apart at the wrong place

[pbedrosi]

Sounds like my exact problem, I'll have to read all the details to make sure I completely understand the issue. the guys that worked on my transmissions mainly work on domestic cars, so it's likely they dissassembled incorrectly. I'll look under the car this weekend to see identify the alignment marks, if needed I'll keep aligning blindly until I can at least feel some improvement.

Maxnix, the shudder/vibration is cold or hot. Quest Tires are alomost brand new and in balance. I'm sure they're safe up to 120mph or so. I don't drive over 80 with this car.

Modified by pbedrosi at 1:26 PM 12/1/2006
Modified by pbedrosi at 1:28 PM 12/1/2006

[elwesso]

theres no easy way to tell. Either plan on getting a used driveshaft (out of a 94-96 preferrably) or get a rebuilt one...

[pbedrosi]

DrewQ45.....do you still have the second 94 driveshaft?

[Q451990]

While you're at it, replace the transmission mount and exhaust hangers.... Easy to do while you're down there. The shudder at start-up (especially if you're pointed up-hill) is a classic symptom of a bad mount - at least in my experience.

Heath

[pbedrosi]

94 trans I bought seemed to have good mount but let me look it over again. One think I have noticed is the creek and groan coming underneath the car, just below the font seats. especially under breaking. I have to take the car back to make sure these guys have the crossmember tightened properly.

Tanks for all the input, I have a lot of items to check.

[maxnix]

Must have 3rd motor (transmission) mount ("crossmember") replaced periodicaly along with hanger brackets.

[Q45tech]

Everything rubber isolated in front and rear suspension, subframe, exhaust hangers. mounts motor and transmission needs replacing frquently about every 60-120k to maintain near new ride.

Something close to 40 FORTY ITEMS [rear subframe has 6 alone].........unfortunately many are only availale as a metal arm rubber bushing system so rehab cost about $5,000 periodically with outside labor.

Add in 4 shocks every 4-5 years at $750-$1000.

Hopefully you can see why the $3,000 per year prorated is necessary as a budget number to maintain. Larger than 15" oem tires add signficantly to this number.

[pbedrosi]

After a quick crawl under the car this weekend I found the trans crossmember hanging 1/2 from the under body. All 4 bolts were finger tight. I fixed about 90% of the vibration by tightening the bolts. Next I may replace the trans x-member mount and center driveshaft bearing to fix the remaining vibrations.

[maxnix]

Next I may replace the trans x-member mount and center driveshaft bearing to fix the remaining vibrations.

May I suggest you will ASAP?

Misalignment causes accelerated war of driveline bearings, even just .5".

"Who loosened them?" should be your next question right after you order the 3rd motor mount and exhaust hangers from Joe.

[pbedrosi]

That would be the guys who R&R'd my transmission.

Funny part is they left a small impact socket over the nut that holds the metal shield just behind the tailshaft. After all the miles and vibration it still hung on.

How do you test if the motor mounts are okay? is it visual for cracks or do you try to lift the motor and look for excessive movement?

[maxnix]

Mostly by age. You can bet they are compressed and have littlelife, if any. left.

The old way was with the STillen FSTB one could rev the engine in N and see if the plenum hit the bar. About 1" - 2" of torsional deflection.

[Haitian_King]

i have that problem in reverse.

10-25 MPH, that's whenmy car vibrates and shakes, after that, it's smoother than a baby's bottom.

[maxnix]

Quest Tires are alomost brand new and in balance. I'm sure they're safe up to 120mph or so. I don't drive over 80 with this car.

What are these? Speed ratings of tires have as mcuh to do with construction standards as the top speed you ever drive.

[maxnix]

i have that problem in reverse.

10-25 MPH, that's whenmy car vibrates and shakes, after that, it's smoother than a baby's bottom.

I doubt you are travelling that fast in Reverse.

Sonds like your motor mounts (all 3) are toast.

[Haitian_King]

Wow.

I meant that my problem is like his, only in the reverse order. What the deuce can I do about the motor mounts?

My car just hit 85K, can it really be that bad?