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Jaguar XJ6 Front Suspension

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Jaguar XJ6: Front Suspension

Many people are intimidated by suspension work. On the Jaguar there is no real reason to be. The suspension is straight forward and easy to work on if you have a good manual and the proper tools.

Front Suspension Overview

The entire system consists of the upper wishbone, the lower wishbone, the body of the car and the stub axle. These four components make up a rectangle. The idea being that as the load on the wheel increases or decreases the wheel will essentially stay straight up and down as it moves up and down. This as opposed to how the older VW swing axles allowed the camber to vary from very negative under heavy load and very positive under light load. The ball joints allow the wheel to turn right or left as they are pushed by the tie rod which is in turn connected to the steering.

Front-end Geometry

The front end geometry of the Jaguar is very simple if you understand what they are trying to do. There are three terms that need to be explained first. These are castor, camber and toe in.

Castor

Castor is the fore and aft tilt of the axis about which the front steering is rotated. If the castor is positive (the axis is tilted forward at the top toward the direction the car is traveling) the car will be stable and tend to run in a straight line. If the castor is negative (the bottom of the axis is forward of the top of the axis) then the car will be unstable and want to run to one side or the other of the road. Thus the castor must always be positive for safety. The amount of positive castor determines, to an extent, the energy needed to turn the car.

If the castor is too much positive then the car will require more work to turn it away from the straight line and it will return to a straight line very quickly. This should be avoided. If the castor is not enough then the steering will feel light and "squirly." Race cars usually use less castor than street cars since they want a very light touch to the steering. The castor is adjustable using shims in front of and behind the upper ball joint. ALWAYS when removing the upper ball joint, take note of the number and position of the shims and put them back where you found them. You will have to take it to a front end shop later to have it checked, but always start where it was before the repair.

Camber

Camber is the outward tilt of the wheel as looked at from the front of the car. A positive camber means the top of the wheel tilts to the outside and the bottom of the wheel seems to point in. Slight positive camber is desired as the camber will decrease toward negative as the weight of the car is increased such as when going around a banked turn. Camber can affect the wear on the tires and the stability during cornering. The camber is adjusted using shims on the inside mounting end of the upper wishbone arms. Again whenever disturbing them, note where they were and replace them then get a fresh alignment.

Toe-in

The toe in is the tendency of the tires to look toward each other as crossed eyes. The front of the tire looks in. Since toe in decreases with speed it is desired to have a slight "static" toe in. At road speed the toe in may be neutral, if it is correctly adjusted, thus maximizing tread life. The toe in is adjusted by adjusting the length of the tie rod. This is one adjustment you can do at home with a ruler but I don't recommend it since it affects your tire wear. The cost of a professional alignment is about the cost of one tire but without it you will wear all four tires unnecessarily.

Front Disc Brakes

If you are experiencing a terrible shaking when you brake from high speed and you have been blaming it in the front suspension, try the brakes first. The brakes are easier to work on and cheaper to repair and when all is said and done, the front suspension is probably not the culprit. The most likely problem is warped front discs. Even if they are fairly new they can be warped and it does not take much to cause a real wild shake. The usual cause of warped discs is a rapid cooling after being overheated. This can happen on the way home from the dealer with a new car. All it takes is hard braking and a very cold day or a mud puddle to spray water on the disc while it is hot. Luckily it is a very cheap and easy fault to cure.

Removing the Front Brakes

The removal of the front discs is so simple that it will take less than 30 minutes per side even on your first attempt. There are two types of front disc brake calipers on the XJ6: 4 piston claipers and 3 piston calipers. The removal of the disc is different for the two different types.

The beginning of the procedure is the same for both types. After jacking up the car and stabilizing it on stands the front wheels are removed.

Four Piston Calipers

On the cars with the 4 piston calipers it will then be necessary to remove the calipers so that you can get the discs off. After removing the calipers they can be tied back and supported out of the way while still connected to the brake system. Do not allow the calipers to be supported by the brake line as this stress can break the line. There is no need to bleed the system if they are left connected. To remove them it will be necessary to depress the brake pads away from the disc. This can be done with a screwdriver as a pry bar. They only need to be pushed back enough to slide the caliper off the disc. When doing this the excess brake fluid is pushed up into the reservoir. It may be necessary to remove some of the fluid to prevent it running over. When the calipers are removed it is necessary to note the position of all shims between the steering arm and the caliper. Be sure there are none still sticking to the caliper that will fall off later and leave you wondering where they came from. They must be put back on just as you found them.

Three Piston Calipers

On cars with the three piston calipers the calipers do not need to be removed. It is only necessary to remove the brake pads. As in the previous paragraph it is only necessary to spread the pads slightly and then they can be removed.

Now you can check the runout with a dial gauge or by using a feeler gauge and a fixed point to measure to. The dial gauge is the easiest and most reliable. The runout should not exceed one tenth of a millimeter. If it does they need truing up.

If you are going to continue to remove the disc (the runout was excessive) on both types, remove the dust cover from the axle end, remove the cotter pin and remove the nut and thrust washer from the end of the axle. Do not, as some books will tell you, unbolt the hub from the disc. It isn't necessary and its a hell of a job if it is still on the axle because you have to feel around through a hole in the backing plate to get to the bolts. It is much easier to separate the two with the hub and disc on the bench where you can get to it. The disc and hub can now be slid off the end of the axle and out from under the caliper.

Put the whole thing on the bench and separate the hub from the disc. By doing the job on the bench instead of on the car you can get the bolts torqued down properly when you reassemble the two. On the car it is virtually impossible.

After the discs are removed take them to a shop and have them turned for pocket change. Remount the discs and your shaking front end will be cured. If it isn't, then you need to then check out the ball joints etc. You needed to resurface those discs anyway and it didn't cost much.

Fitting the Wheels

When you put the wheels back on, don't forget to use some anti-seize on the hub and on the lug bolts. Jaguar wheels being of different metal than the hubs are prone to seize and be difficult to remove. If you do have a stuck wheel the best solution is to put pressure on the bottom of the wheel by prying against the lower ball joint mounting in the front or a similar spot in the rear.

Ball Joints

I will not go into the exact procedure for working on the front suspension since I will assume that you have a proper manual. If you don't, get one. This book is not meant to replace a manual, only to educate you to the general ease with which you can maintain your own car. I will however tell you of one thing I did not find in the Haynes manual when I put in upper ball joints.

When I put the new one in I made the mistake of tightening the nut on the ball joint that fastens it to the stub axle upright of the wheel. The manual did not warn against that. Once it is tightened it is almost impossible to loosen unless the two horizontal bolts into the suspension arm have already been installed. And if they haven't it is next to impossible to compress the rubber stoppers enough to get them in. Catch 22! So, don't tighten the nut at first!

Instead, place the nut on the end of the tapered shaft just enough to hold the stub axle upright together, place the two horizontal bolts into the ball joint, then, and only then, tighten the ball joint to the stub axle upright.

Andrew Kalman offers the following suggestions when replacing the upper and lower ball joints:

  1. If you choose to do the job without removing the brake lines, calipers or rotors, make sure you have a nice, steady means of supporting this assembly without putting stress on the brake lines. I did it this way, and saved some time, but it's more aggravating than having the whole unit off. Careful -- this hub / rotor / brake assembly is heavy!
  2. Disconnect the anti-sway bar.
  3. You will need a small tie-rod separator, the kind that pushes with a screw against the object held by two "grabbers." I rented one at Grand Auto for a few bucks to do the upper one -- for the lower one I used a similar type, but with moveable jaws. It's pretty tight in there. I could hardly believe how much force was needed to pop the joints loose.
  4. I did not remove the metal lipped cup (C 30952) from the lower ball joint "body" -- in retrospect, using an XJ-40 lower ball joint would have been better. I used a Dremel tool to cut out the phenolic cup (one radial cut).
  5. The upper ball joint is much easier to deal with.
  6. You'll find a jack quite handy in repositioning the front suspension while disassembling and reassembling.
  7. After a few miles re-check the circlips that hold the rubber boots on -- one of mine "walked."

The lower ball joints are adjustable to get the desired clearance in the socket. The adjustment is done using shims. The newer XJ40 lower ball joints are said to be an exact replacement for the earlier XJ6 lower balljoints.

The upper ball joint is only replaceable, there is no adjustment when it gets worn.

Wishbone Mounting Bushes

Another area where wear occurs and can cause a loose front end is the inner bushes on the upper and lower wishbone mountings. The upper bushes are especially prone to wear. You can replace all of these yourself with a good manual and tools such as a spring compressor.

Steering Rack Bushings

The steering rack bushings are a source of alot of looseness in the steering of the XJ6. When they get old and worn the steering can get very loose.

Polyurethane Bushings

From Julio Loza I received the following advice on replacing the steering rack bushings.

The other suggestion I have is for changing the infamous steering rack bushings on the XJ6 with polyurethane ones. While doing this job, I found that there is a metal sleeve on the original bushings. It was not obvious at first that they were there since the metal sleeve looked like it could have been part of the steering rack. Only after I compared the size of the new bushings (which come with no metal sleeve) and the rack mount holes did I realize that these must be sleeves. Since they were tight in place and could not be removed, I took a saw to them. I cut two lines along the sleeves that release the pressure and allowed me to punch them out with a punch and hammer. Care must be taken when sawing so that you saw through the sleeve but not the steering rack itself.

Kirby Palm warns that cutting the sleeve out can be dangerous especially if it is still on the car. If you so much as nick the aluminum lug it can cause it to crack later. He suggests that cutting them should be a last resort. Kirby suggests first trying two 3/8 inch drive sockets, one the same OD as the bushing and one large enough that the bushing will fit inside it. Thread a 3/8 inch bolt through the two then draw it tight with a nut to pull the bushing out.

Grease Points

When maintaining the front end there are 9 grease points that need attention on a regular basis to prevent wear. The upper and lower ball joints all have a grease fitting unless the upper ball joints have been replaced. Some replacement upper balljoints are "lifetime" lubricated. I don't know whose lifetime, but they don't come with a grease nipple. There is a grease nipple on both the wheel hubs and on both the tie rod ends. The last grease nipple is on the steering rack.

 

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