Jaguar XJ40 Vibration at Speed, Prop Shaft
On the XJ40 a vibration that comes in at one band of speed is usually the prop shaft: the rubber Jurid coupling at the diff, the centre bearing, or the shaft itself out of balance. Tyres can feel the same, so I'd rule them out first by swapping wheels, then put the car on stands in gear and watch which part of the shaft shakes.
How bad is it · Garage, carefully
Drivable, but get it looked at
The vibration itself won't stop the car. Loose shaft bolts or a cracking coupling only get worse, so check them before a long trip.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
The prop shaft itself: a broken-down front section or an unbalanced assembly
The forward shaft is two tubes bonded together with rubber, and when that rubber breaks down the inner tube moves. The shaft and its Jurid coupling were balanced at the factory as one unit, so a tired assembly can keep shaking after every separate part has been changed.
A motorboat-like harmonic felt in the chest, for example between 25 and 35 mph, that survives a new centre bearing; on a lift the front section of the shaft visibly shakes in that range.
Car safely on stands, engine running in gear, and watch the shaft from the side. If the front section shakes, the bonded tube is the suspect.
Have the forward shaft remanufactured as a solid one-piece shaft and balanced, or fit a new complete shaft with the Jurid already attached and balanced together.
A tired centre bearing, or the two shaft halves out of line
The two-piece shaft runs through a rubber-mounted centre bearing, and these cars are sensitive to its exact position. The rear slip yoke must also line up with the front shaft; refitting it out of index brings a vibration even with good parts.
The vibration started after the shaft, gearbox or diff was out, or it changes with load in the car. A centre bearing can look fine and still be the cause.
Mark every flange before anything is unbolted. Check the bearing's left-to-right setting on its bracket and the indexing of the slip yoke to the front shaft. Don't add spacers under the bearing to chase it — that can make it worse.
Realign the slip yoke and fit a new centre bearing together. The dealer sells the bearing only pressed onto a complete shaft, and 1990–91 cars used several different shafts, so match the bearing bore to your shaft; on some cars an off-the-shelf rubber isolator from another make fits.
A tyre or wheel, not the driveline
An out-of-round tyre, a loose belt inside it, a bent rim or a wheel balanced on the wrong mount gives the same speed-band shake. XJ40 suspension hides imbalance until around 50 mph.
The vibration moves when the wheels are swapped front to rear, or it shows up only under light braking from motorway speed.
Swap the wheels front to rear and see if it follows. Have them balanced on the correct flange for Jaguar wheels — turning the wheel 180 degrees on the balancer should give the same reading.
Rotate or replace the faulty tyre, or straighten or replace a bent wheel.
A cracked or loose Jurid coupling at the diff
The rubber Jurid disc joins the shaft to the diff. Its bolts work loose, its holes slot and the rubber cracks — and it can be worn out while looking fine.
A shimmy around 30 mph, or a vibration that comes at the same rpm in different gears — for example about 2,800 rpm.
Torque the Jurid bolts first. Look for cracks and slotted holes. A coupling should come out and go back flat, with no one-sided compression.
Fit a new Jurid with the thick pads compressed under drive torque. The shaft doesn't have to come out: unbolt the centre bearing bracket, mark every position and renew the centre bearing rubber at the same time.
Worn universal joints or loose shaft bolts
The U-joints are the only lubricated part of the driveline, and the bolts between the gearbox and the first joint can work loose.
Vibration off the throttle that isn't from the tyres; a judder that starts after the diff or shaft has been disturbed.
Check all four shaft U-joints for play and the flange bolts for tightness — the front flange bolts are the hardest to reach.
Worth trying: tighten the bolts, then replace worn joints. They can be changed without a new shaft if every position is marked.
Perished rear subframe bushes passing driveline shake into the body
The large front bushes of the rear subframe isolate the diff from the body. Once they harden or break up, normal driveline vibration comes straight through.
A drone or slight shake from the rear at steady speed, together with diff noise at similar speeds.
Lever the front subframe mounts and look for hard, cracked or stone-filled rubber.
Worth trying: replace the front subframe bushes.
Tired engine or gearbox mounts
Soft or collapsed rubber on the engine or gearbox mounts lets the driveline angle shift.
Vibration felt at idle in Drive and at low speed, much less in Park or Neutral.
Look at the rear engine and gearbox mount rubber and the engine cradle mounts.
Worth trying: replace the worn mounts.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Swap the wheels front to rear
If the vibration moves, it's a tyre or wheel. Then have them balanced on the correct flange.
freeNote speed against rpm
Drive at the vibration speed in different gears. Same rpm — driveline or engine; same road speed — wheels or shaft.
freeSlip it into neutral briefly
Keep the engine running. If the shake stays at road speed, it isn't the engine.
freeTorque the Jurid bolts
And look at the coupling for cracks and slotted holes.
freeWatch the shaft on stands in gear
See which part shakes: the front section, the centre bearing or the rear coupling.
freeCheck the U-joints and centre bearing
Play in the joints, perished bearing rubber, and the bearing's position on its bracket.
cheap partsInspect the subframe and engine mounts
Hard or broken rubber lets normal shake into the body.
bushesRebuild or replace the shaft
A remanufactured solid front shaft, or a new one balanced together with its Jurid.
a shaftWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ40 Rear Suspension ProblemsIf it knocks, sits low or whines from the diff rather than shaking.
- Jaguar XJ40 Front Suspension Knock, Worn BushesIf the shake comes through the steering wheel with a knock over bumps.
- Jaguar XJ40 Transmission Problems, Limp ModeIf the gearbox slips, flares or shifts harshly as well.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.