Vibration at low speed

hkusp45 · Post by **hkusp45** » 28 Sep 2018, 14:57

I have a 2005 XC90 V8 with 111k.. Last winter I heard a loud pop sound by the front driver's side wheel while turning slow in a parking lot that had patches of ice. As time went on I began to notice a low vibration while accelerating mildly, at low speed. The vibration would be more pronounced if accelerating mildly uphill. Now when I define this vibration, it's more like a wobbling feeling. The vibration would be felt around 1500-2000 rpm and at a speed of less than 35mph. If the vibration starts and I don't accelerate any harder, the vibration becomes aggressive until I let off the accelerator and the vibration stops. Now while accelerating normally at any speed or highway speed, I don't feel this vibration. However, while traveling 40 mph or higher, I do feel a brief vibration when there is a bump in the road.

So I decided to replace the front CV axles, lower control arms, ball joints, upper suspension parts, and outer tie rods. Prior to these replacement parts, the vehicle had new subframe bushings installed, trans flush, haldex fluid replacement. The problem still existed after the parts were replaced.

I did check the main axle shaft but I didn't notice anything loose. However, while using a pry bar on the driver's side front axle that enters the transmission there was a lot of lateral play; more than a 1/4". So is this lateral play the vibration I'm feeling. So to my question to any pros out there, can stress from the cv axle cause damage to inner transmission gear bearing, or is this vibration from something else?

Thanks.

Post by **ggleavitt** » 28 Sep 2018, 16:13

Probably a dumb question given all that you're replaced but is the AWD working properly? And is there any chance you're interpreting front wheel spin or front wheel hop as the imbalance, given that it's acceleration dependent and the engine in your car is a V8?
The yellow antiskid triangle on the lower right of the instrument panel come on during the vibration? If you drive the car somewhere wet and press on the gas, do the front wheels slip to any degree compared to the rear? Last but not least, does anything change when you turn off DSTC? Switch is the end of the turn signal stalk or the center console button set, it's in the manual somewhere.

I'm wondering if you have a broken angle/bevel gear. Easy way to check is all 4 wheels on the ground, reach up under the car (cold exhaust) and see if you can turn the driveline. You'll probably have a few degrees of rotational movement before it hits some end-stops but if you can turn the driveline to any real degree under this scenario, that is a problem.

If you could please check and get back on this, might help diagnose more easily (omitting what it's not).

hkusp45 · Post by **hkusp45** » 28 Sep 2018, 22:41

The vibration occurs once you gain speed, approximately 15 mph. It's really weird when it happens because you have to accelerate softly to have the vibration occur, and this wobbling feeling gets worse if you keep the acceleration consistent. Once I let of the pedal, the vibration goes away. This vibration feeling does not feel like it is coming from the tires. Sometimes the vibration is very subtle when accelerating, but if I accelerate normally (not like a sunday driver) you don't feel this vibration. It seems like just the right amount of acceleration, or bump in the road will cause this vibration. I do not get any errors or warning lights when the vibration occurs. I also do not hear anything unusual and the vehicle operates without any loss of power. I will attempt to test the DSTC and the driveline tomorrow. Thanks.

Post by **ggleavitt** » 29 Sep 2018, 00:15

The scenario you describe suggests it's not angle/bevel outright but would be good to omit.

All the engine mounts good? And is the wobbly feeling accompanied by any wobbling of the steering wheel? Anything different about car being straight or in a curve, any effect of braking while vibration is ongoing?

Anything you can think of differentiating rotational wheel speed from engine speed as the scenario occurs?

hkusp45 · Post by **hkusp45** » 29 Sep 2018, 11:40

I checked the driveline and there was a minimal amount of backlash (a degree or two). I drove with the DSTC off, and I was able to replicate the vibration. When I use the word vibration, the feeling is more of a low pulse wobble effect. The vibration doesn't affect the steering wheel, and you don't really feel it coming through the steering wheel. There is no vibration when braking: a passenger in the front seat can feel the vibration. As I drive the vehicle, I can feel a brief subtle low vibration while driving over any bumps or voids in the roadway, but it immediately goes away. If I pay attention while traveling at a higher speed (45-80 mph) and I hit bump or void in the road, I could feel a brief subtle vibration. Today it took me multiple attempts from a stop to start the vibration, and it appears the vibration will happen when the vehicle is going on an incline while making a slight left turn, and especially if the road is rough. When I was able to make the vibration today, the speed was around 18-22 mph @ 1800rpm. When I was testing the vehicle yesterday, the vibration started while making a slight left turn and going on incline. As I kept the acceleration consistent, the vibration became very aggressive, where you can really feel it. I let off on the the gas to avoid any more damage. Also when the vibration starts, the vehicle momentum does not feel like it's being effected; like a lunging feeling. It appears that road condition, low speed, and using very light acceleration will start the vibration.

The engine mounts are original and they seem to be in ok condition based on their age.

hkusp45 · Post by **hkusp45** » 29 Sep 2018, 11:44

The only next thing I can do is get a long endoscope and attach it the axle areas to see where this vibration occurs. Hopefully, I didn't install a new defective cv axle. I will recheck the engine mounts again.

hkusp45 · Post by **hkusp45** » 06 Oct 2018, 18:03

I made video clips of the cv joints and axle while driving slow speeds, and I was unable to observe any issues that would cause the vibration. However, in the video, you can see the transmission housing and the engine shake. The bottom engine mounts appear in good condition. I could see replacing the upper engine mount and the one on the passenger side, but I can't see this being the culprit in the shake. It almost seems like the vibration is coming from inside the trans. To make the vibration occur, you need to be soft on the acceleration, and at a low speed. The vibration occurs while going straight, but making a slight left turn and especially going on an incline seems to make the vibration occur more.

hkusp45 · Post by **hkusp45** » 13 Oct 2018, 17:56

I have finalized the inspection. The vibration/shutter is caused by the torque converter. I plan on changing the trans fluid to see if I can temporary fix this issue. I had changed the fluid in late 2107 with Amsoil. However, after changing the fluid I began to notice shift flares, and now the shuttering. Can Amsoil be the culprit. I'll let you know..

Post by **Roger_850T** » 14 Oct 2018, 19:56

Do you know the spec of the Amsoil that you put in? If it meets the JWS-3309 spec, then I would not be too suspicious. On the other hand, if it's a Dexron equivalent, you should definitely change it.

Post by **Roger_850T** » 14 Oct 2018, 20:06

I use Mobil 3309 for mine. The best place I've found to buy it is Summit Racing. They have it in quarts, as well as a case of 6.
https://www.summitracing.com/parts/mob-123062/overview/
Amazon also has it, but Summit has a better price.

Roger