I ask this question once every year or so just in case someone new has logged onto the boards.

I have an 89 XJS that has a very loud rattle from the trunk area that happens only when turning right, either at slow speeds (i.e., coming out of a parking lot) or when driving a curvy road. The harder right I turn, the worse it is. The colder the outside temps are, the worse it is. The less warmed up the car is, the worse it is.

It is sometimes joined by what feels like slight grinding from the rear end. I've also described it as: Imagine you have a box full of lubricated ball bearings and you start mixing them with a spoon. They'll move around but you'll hear the action of them doing so. This is more apt to happen when you're on the accelerator in addition to turning right.

Two different shops are puzzled over this. One of them removed both rear wheels and inspected everything they could see without disassembling the backend of the car, but found nothing. They reported all bolts to be tight. The second shop is similarly stumped.

The rattle, which can get loud enough you can't talk over it, definitely seems to be coming from the right rear corner. The other noise is more centered, perhaps coming from the differential.

I've also got a new problem where if I try to back up onto a ramp or uneven ground, I get a rotational rattle -- only in reverse gear. But I'm more concerned about the mystery suspension noises.

Jess

 

Sounds like it could be an issue with the LSD. With the car in neutral and hand brake off jack up one rear wheel and try to turn it, you should not be able to turn it. Don't forget to chock the front wheels so the car can not roll.

 

I agree with Warrjon, but while you are under there, check to see if you have those daft cup-shaped shields over the driveshaft universal joints? If so, take them off and see if the noise is still there. Also carefully check the brake calipers particularly the handbrake ones, in case something is fouling the discs.
Greg

 

I have long suspected the LSD for the ball bearing noise (I've been in cars with low LSD fluid level and it's a similar sound), but this car had all-new brake pads installed earlier this year and it didn't make a difference. I would think they would have noticed an impingement then. I will say, however, that we didn't touch the E-brake at the time and the E-brake on this car basically doesn't function. The car will roll too easily when the brake is set.

Jess

 

I don't see how a brake job would prove or disprove a bad LSD. The load required to bring the LSD into action is a lot more than would come about from work needed changing out brake parts.
The turning of the vehicle is what drives the diff clutch locking and harder turn or more right foot means more locking force, this is exactly what you describe.

 

I may have not used enough words to make the last post clear; I was agreeing that it could be the LSD while ruling out the possibility of the brakes being involved in any way.

Incidentally, the rotational grinding noise when in reverse gear is getting worse. Instead of having to back the car up a grade, I now get a little bit of grinding just having reverse gear engaged at all.

I also neglected to note that when turning right and hitting a bump, there is a significant clunking noise/feel from the center-rear of the car, not outboard at a wheel where I would expect a suspension failure to occur. I'm starting to believe the entire rear diff may not be properly located.

Jess

 

I think you need to drop the rear end and go over the whole thing.

 

Are you saying you get the noise while in reverse gear but not moving?

 

Yep. The rear end needs to be higher than the front end (i.e., backing uphill) for it to be very noticeable right now. But I have heard it a couple of times when the car was level.

Jess

 

If the car is stationary, either you have a gearbox that is shot and it is transmitting noise via the diff (this is quite common on some cars) so it sounds as if it is being generated from the rear, or have you made 200% sure that the exhaust is not fouling something as it wends its way though the axle cage? As if the car is not moving, I cannot really see how the diff can make a noise, unless the input shaft is so loose it rattles somehow when the propshaft is loaded with torque.
Greg

 

It makes sense that it's the gearbox. Sometimes at a traffic light, the car doesn't go when I let off the brake. Almost like it's stuck in neutral. If I give it some gas, it will suddenly catch and take off.

I'm planning to convert this car to manual at some point in the next year or two. Looks like that may happen sooner rather than later.

Jess