grinding noise on 91 xjs v12

[dave01]

when pulling away sharp,there is a grinding noise coming from diff area.under light/normal acceleration this does not happen.this was worse before fitting new dampers if boot had any load in it. 4 new dampers on rear so car is quite stiff, also there is a noise from transmission in first gear.

 

[Michael J.]

Dave;

1. Put the car on jackstands and remove the rear wheels. On each rear bearing housing there is a 1/2" diameter plug that you pry out. Check for grease in the bearing housing. If low, pump some grease in with a grease gun. Rotate the axle flange a few turns and add some more. You may have dry bearings.

2. Both rear axles have mud covers over the u-joints at each end of the axle. These have 7/8" approx. removable plugs that should let you get access to the U-Joints to grease them. Pump a few strokes of grease in each U-joint. Look at the covers for signs of rubbing on the exhaust. The covers can rub against the pipe, especially during hard accelleration causing a noise similar to what you describe as the car "squats".

You can adjust the position of the covers laterally along the axle shaft with the hose clamp at the small end of the cover.

I have had rubbing of the cover against the inside of the rear bearing housings and also against the exhaust. If the problem started right after unrelated work in which the exhaust had been disconnected recently, start with that.

3. Check the oil level in the diff.

It may be wise to check each of these items one at a time, go test drive to see if the problem eliminated. If you do all three at the same time, you may solve the problem, at least temporarily, but won't know which it was.

Good luck

 

[jessebogan]

Check your transmission mount very carefully. The rubber "spool" in the center of the mount disintegrates, and allows movement. This can produce noise caused by the driveshaft flange hitting the trans tunnel. It does not always sound as if it comes from the tunnel area. This is a common failure area, and can be tough to figure out if you are not aware of the source of the noise.

 

[John S Farrington]

You have gotten the gammut of reasons for XJS rear noises. Reference the half shaft U Joint dust covers that were mentioned; if they get loose they can make all kinds of noises. Since I routinely get the U joints greased, I find that the covers are a detriment since you cannot observe if the zerk is allowing the grease to flow into the joint. I prefer to cut them off of the half shaft so that I am certain the the grease has gone to the right place. A side benefit is that they cannot be the source of noise.

 

[dave01]

ive had a look at all that,greased all points and checked for any rubbing items all seems ok noise is still there seems to be coming from left hand rear.

 

[Michael J.]

Jack the left rear tire off the ground. Grab the bottom of the tire and wiggle it laterally to see how much play are in the left rear bearings. If there seems to be a lot of play, compare the amount of play with the right side. There will be some play when cold to allow for heat expansion of the bearings in use.

How many miles are on the car?

Do you notice the noise more in a straight line, or is it also present in a curve?

Are you sure that there are no chaffing marks on the L/H exhaust pipe where it goes over the axle?

What you are describing really sounds like the inboard U-Joint cover rubbing against the exhaust. Your description of it being worse before the dampers were changed and when the boot was full, both of which would allow the rear to squat lower, sounds like a chaffing problem.

Look at the distance between the exhaust and the axle on both sides. They should be the same. If the left side is closer, loosten the three bolt flange and move the pipe some before tightening the flange again to even up the gap.

Also, there is a rubber donut hangar and a steel mandrel welded to the pipe that fits in it right above the U in the pipe. It is hard to see, but if you reach up you will be able to feel it. Have the car on ramps at the rear or jack stands. Do not crawn under the car with it on a jack! The rubber can be worn or the mandrel out of the center hole altogether, allowing the pipe to sag enough to allow the chaffing.