Jaguar XJ40 Steering Wheel Shake
On the XJ40 a shake in the steering wheel is usually a front tyre or a warped front disc. If it comes at one speed, I'd look at the tyres first; if it comes when you brake, measure the discs and free the caliper pins. Bearing play and a rack moving in its mounts come next.
How bad is it · Garage, carefully
Drivable, but get it looked at
A shake under braking means the front brakes or wheels aren't right. A tyre losing air can go flat, so check pressures before driving far.
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.
Warped or out-of-true front discs
A front disc with run-out or uneven thickness pushes the pads in and out every turn. The steering wheel twists left and right under braking even when the pedal hardly pulses.
A wobble in the wheel as you brake from about 40 mph or more, or the whole car shaking under hard braking; spun by hand, the disc has a tight spot.
Discs needn't look warped — measure them. Dial gauge on the face with the wheel off, micrometer round the rim. On the 28 mm front disc (1990 on) the limits are 0.004 in total run-out, 0.0005 in thickness variation and 26 mm minimum thickness; 3.6 cars have a thinner 22 mm disc.
New front discs and pads; even discs close to the limit can cause it. Free the caliper slides at the same time.
A tyre losing air, out of round or out of balance
A soft tyre, a broken belt or sidewall, a flat spot or a lost balance weight shakes the front end in a narrow band of speed. It comes through the steering wheel when the bad tyre is on the front.
A shimmy in one narrow band, for example 48 to 52 mph, both accelerating and slowing; or a judder on the very first brake application. Swap the wheels front to rear and it moves to the seat.
Pressures first — no lower than 28 psi. Look for a bulge, a flat spot or a missing weight on the inside of the rim. Spin each front wheel against a fixed pointer: more than 3/16 in of radial or side-to-side run-out means a new tyre.
Replace the faulty tyre, then have the tyre, wheel, valve and cap balanced as one assembly — a road-force balance finds what a plain balance misses.
A sticking caliper or seized guide pins
If a guide pin or piston sticks, one pad drags or snatches. The disc overheats and warps, and the wheel wobbles under braking.
The wobble started after the car had stood for weeks, it comes near the end of a stop at low speed, or one front disc keeps wearing and warping on the same side.
Pull the pads and check the caliper slides freely on both guide pins. After a drive feel the hubs: a hot one is dragging. Compare the inner and outer pad wear.
Worth trying: take the pins out with a 7 mm Allen key, clean them and refit with copper grease; free or rebuild a rusty piston. Open the bleed screw when pushing the piston back so dirty fluid doesn't go back towards the ABS valves.
Loose or wrongly set wheel bearings
Front bearings on these cars are adjustable, and the rear hub's end play is set by spacers. Too much play lets the wheel and disc wobble, so the shake comes back even after new discs.
Vibration felt through the steering both on and off power, the same when coasting in neutral; it started after bearing work, or it comes on with the car heavily loaded.
Front on stands: rock each wheel at top and bottom and spin it by hand for play and roughness. If a rear hub was rebuilt, check its end play — it is set by choosing the spacer on the bench, per manual section 64.15.14.
Worth trying: repack and readjust the front bearings and retorque the wheel nuts; on a rebuilt rear hub, fit the correct spacer for the measured end play.
The steering rack moving in its mounts
The rack sits in rubber mounts, and once they soften the whole rack shuffles side to side, so the front wheels shimmy and the car wanders.
A shimmy with a vague, wandering feel around the centre; tyres, balance and joints all check out.
Car on ramps, a helper rocks the steering wheel while you watch the rack body. More than about 1/16 in of movement in the mounts is too much.
Worth trying: renew the rack mount bushes — the rack has to come apart to do it — or pack the gap between the rack and its mounts with a hard-setting polymer, which is quick and cheap.
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.
Check the tyre pressures and walls
No lower than 28 psi. Look for a bulge, a flat spot or a missing weight.
freeSwap the wheels front to rear
If the shake moves from the wheel to the seat, it's that tyre or wheel.
freeSpin each front wheel against a pointer
More than 3/16 in of run-out either way and the tyre is finished.
freeRock the front wheels for play
Top and bottom, on stands. Spin them by hand and listen for roughness.
freeFree the caliper guide pins
Clean and grease them; look at the pistons and compare inner and outer pad wear.
copper greaseMeasure the front discs
Run-out no more than 0.004 in; check the minimum thickness cast on the disc.
a dial gaugeWatch the rack on ramps
A helper rocks the wheel. The rack body shouldn't shift more than about 1/16 in.
freeFit discs and pads, then balance
Balance tyre and wheel together, preferably on a road-force machine.
discs, pads and a balanceWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ40 Vibration at Speed, Prop ShaftIf the shake is in the floor and seat, or comes with the throttle rather than the brakes.
- Jaguar XJ40 Front Suspension Knock, Worn BushesIf there's a knock over bumps as well.
- Jaguar XJ40 Power Steering Problems, Steering RackIf the rack leaks, groans or the steering feels heavy.
- Jaguar XJ40 ABS and Brake Accumulator ProblemsIf the pedal goes hard or the ABS warning comes on.
- 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.