[ds968]

The mechanic has two different and highly customized tools ( and expensive to boot ..) , designed solely for the removal and replacement of the bearing , so that particular task was not that big of a deal, but yes, getting that center nut loose was traumatic , even for an observer like me.. Hand torquing attempts were a joke , even with a 250 lbs mechanic standing and jumping on a pipe leveraged torque wrench . Two wrenches snapped and broke off . Then a 400 lbs torque power gun was used and the nut did not even budge. Lucky he also had the mother of all power guns, a 800 lbs torque one typically used for 18-wheeler trucks, and finally the nut decided to give up the struggle . Then the other pain was removing the two parts of the old bearing which remained on the wheel hub and the center thingamajjiggy ( no idea what that piece is called ) , which even though were subjected to another specialized tool for the removal, would not budge either . So they had to be cut off . I swear it seems all of the parts on this car are fused together . Just like the oxygen sensor removal which took hours , this was also hours upon hours ..

I thought my former mechanic who complained with every single job , exaggerated a lot and was just a whiner not happy with putting in with a little biit more effort to get something done, but after witnessing with my own eyes three separate jobs which required anywhere from 5 X to 10 X the amount of time vs. what others assert it should take, or what the " book " suggests it should ( yes, perhaps all true when the car is one year old , or has 10 k miles on it , lol ) I think he's been vindicated ..

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[unknown4u]

The part of the bearing must be set under pressure with a puller. If you have done that use the welder.

The electrode makes the bearing hot at one point. You do this a couple of times and the part is of the flange.


Since I discovered this I never cut anymore.

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[ds968]

It was NOT the bearing !! Arrrrrghhhhhh !! And all my instincts told me it wasn't, but not being mechanically inclined in the least bit , I figured I should follow the collective conventional wisdom and give that a shot first , since it was at a relatively reasonable cost. Not sure what to do at this point, short of making an appointment with a shop which can absolutely guarantee the timing of the inspection and road testing , because if I first don't drive the car for at least an hour , and actually best if it's an hour and a half , the symptom simply does not manifest itself. And it helps if's really hot outside as well .. And even then the rocks tumbling inside a barrel or burlap bag noise lasts only for the first one or two seconds either taking off from a dead stop with moderate acceleration ( pedal half way down ) , or going uphill with moderate acceleration , where the sound is a bit more pronounced. Past the first two seconds everything is fine and dandy ; all quiet , smooth, no noise on acceleration or on deceleration , nothing !

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[MCL968]

Wow, I think that car is possessed, or possibly needs to be repossessed. I really thought the bearings were going to solve the problem.

 

Refresh my memory, did you try different tires and wheels? I have heard of strange symptoms coming from delaminating tires where the delamination was internal and thus not visible from the exterior.

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[ds968]

Yes, I first switched the rear wheels / tires from one side to the other, and then later on I also bought a new set of tires ( not because of this , it was just time to replace the others ) and still experiencing the same issue . See modified post above with additional info , since I think I edited it after you posted your note.. i

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[MCL968]

OK, after reading the symptoms for probably the 10th time, I realized that I had a car that did the EXACT same thing.

 

My old Volvo P1800 had the same symptoms, low rumble on takeoff, or hard acceleration at slow speed. It would go away as fast as it started, and it was more acute when the car had been driven for a while.

 

I just wish I could remember what the cause was...

 

Kidding, it was (duh da-da DAAAA!) the center bearing in the drive shaft! The P1800's had a two piece driveline, and the center bearing was mounted in rubber and clamped to the floorboard of the car. It had a spline, a U-joint, and a carrier bearing. When the rubber degraded, the bearing would wallow around and rumble against the floor of the car and vibrate right up through the seat.

 

I was told it was the driveshaft "finding its center" when under load because the rubber was not holding it firmly in place.

 

Given the nature of the driveline on 968's, I don't know if the same problem could even exist or would produce the same symptoms, but it sure sounds exactly like what I dealt with years ago.

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[ds968]

Yes, that's precisely how it acts .. now if we can only find out if the 968 drivetrain has a similar setbup ..

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[968workaholic]

Did your mechanic look at the axles when he had them off to do the bearings? More specifically the condition of the grease? The driveshaft is housed inside of the torque tube, supported by metal bearings. No rubber couplers/supports that can go bad

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[ds968]

Yes, he looked and inspected all of that carefully - he checked both the level and look & feel of the grease ( not sure what the latter tells anyone, maybe color and texture or smell could point to something . ) but everything appeared to be fine. And no metal flakes or other signs of impurities / debris in there .


Well good to know there are no rubber components couplers / support in the driveshaft because this whole " only when hot " syndrome seemed to me to point at some rubber part being a culprit in the scheme of things . My mechanic thought even if the transmission mount warms up enough it could allow the trannnie to sway enough to put greater pressure on the CV joints under that kind of load and just for a couple of seconds when taking off from a dead stop , or uphill, or even on a hard accelerating right turn,


My mechanic still insists there is no way the differential could be the cause of this symptom because he said it would most definitely make noise when turning in both directions not just one, and as for the clonking rocks on takeoff sound he also said it'd mostly likely be there at all times and especially when cold, not only when the area heats up a lot after hours of driving. Similarly a CV joint would give some indication if it was bad, when cold and even during normal driving, not just on takeoffs when hot , right ? Or wrong ?


So I changed what was probably a perfectly good wheel bearing , ugh.. But like I said , it was relatively inexpensive in this process of elimination m.o. . Lucky my former mechanic did not struggle with the job , his price per hour was exactly triple my current mechanic ( different overhead and investment to recover ) and did not have the highly specialized equipment for removal and install of the bearing, so I"m pretty sure it would have cost me $1,500 + to change that single rear wheel bearing..


But it is what it is, so now it's on to the continuing mystery .. watch it be something totally stupid and simple ...

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