I'm replacing the upper ball joints on my 2006 XJR. Unfortunately, that means I have to remove the air shock which ended up meaning I had to replace the rear lower control arm because the shock bolt was frozen to the bushing.

Now I'm at the point of torquing up the new parts. Is there any way of approximating normal position of the suspension when the car is stting on its wheels e.g., Is the front lower control arm parallel with the ground ? Since there is no resistance from the air shock I can't just jack until the car starts to lift.

thanks for any help.

 

[QUOTE=raschwar;

Now I'm at the point of torquing up the new parts. Is there any way of approximating normal position of the suspension when the car is stting on its wheels e.g., Is the front lower control arm parallel with the ground ? Since there is no resistance from the air shock I can't just jack until the car starts to lift.

thanks for any help.[/QUOTE]

Not really.

The car should level itself so long as the height sensors were not damaged and are positioned correctly.

When I replaced all rear bushings I jacked the rear up evenly so that both rear wheels were off the ground suspended level. This was so as not to warp the body.

Both rear shocks were extended. Battery disconnected before I started.

When I lowered the car the rear sat several inches too high.

I think I could have driven the car a few miles and it would have levelled properly.

However I used my JLR SDD software to do the leveling and height adjustment.

 

As said by Jackra, the air suspension will adjust to the correct height on reassembly if the height detectors haven't been disturbed.

As far as I know, the ball-type bushes on the lower wishbones can rotate, so are always relaxed, it is the Silentbloc-type bush that doesn't rotate that needs to be relaxed when the car is standing on its wheels. Hopefully somebody who has done the job will post advice here.

 

When I did all the rear bushings on my 2005 XJR they all had to be pressed out.

The lower shock bolts on both rear shocks had to be hammered out with not too much force.

I had a separate jack under the lower part of the shock to take the pressure off the shock bolt.

I did all of this at around 103,000 miles and believe the old ones were all original.

 

Thanks for the replies. On normally sprung cars it is specified that final tightening of suspension parts be done while the car is resting on its wheels. In the case of BMWs the manual even states that weights be added to simulate people in the car. The idea, of course, is to tighten the bushings so they are in their least stressed position when the the weight of the car is on them.

As an example, the Jag manual says: CAUTION: The final tightening of the front lower arm inner retaining nut and bolt must be carried out with the vehicle on its wheels. Failure to follow this instruction may result in damage to the component.

Without a lift I usually do this by jacking under the suspension until the car just lifts off the jackstand.

But the air shocks don't support the car like a spring would and lifting the suspension will not lift the car. So I'm looking for a reference point that will tell me how the suspension would sit if the car were on the ground. Sorry for any confusion.

 

I use ramps in that case.

 

I have the battery disconnected so I won't need an height sensor recalibration so presently there is no air in the shocks. I could put everything back together but I figure that if I can use a jack under the suspension while it's accessible with the wheel off the car I can move the suspension to the point where it would be if the it were on the ground. All I need is a reference like the horizontal relationship of the front lower control arm to the ground or the height difference from the the center of the wheel to the bottom of the side moulding at the wheel well. That'll get me close enough.

 

I don't have the info at hand, but there is a specification on setting the ride height that is the reference distance from the hub to the wheel arch. Raising the suspension assembly to roughly approximate the correct distance should be fine for torquing down the components. If I recall, there is a tool that fits on the wheel studs that is used to measure to the wheel arch, with an illustration and specs somewhere in the manual.

 

I have an 05 NA long wheel base, and I'm not presently in a position to confirm how similar/different our measurements would be.

However, when I replaced my front radius rod bushing and much later the rear control arms, I left my battery connected both times. I did not need any recalibration afterwards, nor did I experience any issues with that; but don't let my luck counter any authority that instructs you to do it your way.

What I did both times was to run the car and shift thru the gears after loosely installing the components and ensuring the struts aired up. At that point I snuck under the front and retightened the bolts, no jacking needed.
The rears were a little different, since I had jacked both sides evenly and at the end put jacks and stands under the control arms. Then I went to the front and jacked that end to balance the F/R weight distribution before tightening the rear bolts which would have been obstructed by the wheel.

Before doing the work, I did have reference numbers from garage floor to a taped up spot on the wheel well lip, but those were just written on the painters tape itself and I didn't save them after the job.


All that to say that if I were in your position, I wouldn't fret. I'd just start the car back up and drive it forward/backward just enough to wake the air suspension (that's all it took mine to go back to normal height after being deflated a few times). This should theoretically settle the suspension components at the right geometry as per your pre-calibrated suspension settings since your loose-ish bolts will allow the bushings to turn.
Then if you need clearance, use ramps/pieces of wood etc under the front tires (in conjuction with jacks and stands for stability) and then tighten the bolts
... or take measurements while the car is still running.


Good luck.

 

There are specifications however you need special software such as JLR SDD to set the ride height and it is a somewhat laborious process. I have performed the procedure.

If driving the car does not set the ride height appropriately 1st check that do height sensor has been damaged then consider a dealer/independent that has the appropriate capability.

 

Doing that would be a waste of time seriously. When you lower the car on its wheels you do the same thing.

 

If I understand the original question correctly, the air springs currently have no pressure and therefore if the vehicle is lowered onto its wheels it will be sitting too low and with incorrect suspension geometry.

In an effort to torque the new components at the proper geometry, the OP is trying to ascertain how to approximate that geometry before lowering the vehicle.

My take is that one would want to lift the lower control arm until the center of the hub is approximately at the distance from the upper wheel arch that is the reference for a calibrated ride height. I can't find my copy of the specs, but did locate an online reference to 386mm front and 373mm rear. This is measured from the center of the hub to the wheel arch with this tool:




Placing the hub at approximately this distance before torquing the suspension should result in the bushings being somewhat unloaded at normal ride height. Maybe not perfect, but hopefully better than just a guess.

 

With the car on the ground starting the engine may well raise the car to the level it was prior to starting work especially if the sensors have not been altered.

Measure the ride height as accurately as possible. If it very close you have the correct geometry and can torque down bolts correctly.

 

HJ808, you did indeed get the question correct. Others have mentioned the gauge also but I could not find anything on the actual measurements, thank you for that.

 

It is not just the geometry it is the load.

Without air in the strut you may get the correct geometry but not the correct load.

 

Exactly! Load even more so than geometry. The geometry is fixed by the components and their alignment. My question had nothing to do with that as alignment will be dealt with after assembly. Loading, on the other hand, affects where the wheels sit in relation to the rest of the car. When the suspension is not loaded it hangs low. Where it hangs depends upon the amount of "give" in the component rubber bushings attaching them to the car. The amount of twist on the bushing is determined by the position of the component when installed.

When the car is on the ground, and the shocks are charged, it weighs down on the suspension (load) and the component connections flex in relation to the body to a point where the weight of the car is balanced by the shock pressure. It is this position where the components should be tightened so that there is little or not twisting stress on the rubber bushings; hence the statement "tighten when wheels are on the ground". However, if one knew what that position would be the components could be set to that position BEFORE load was applied. ('when the car is on it's wheels this is how it will sit')Then when the car was placed on the ground and the shocks charged, the suspension would move to this predetermined position and, at this position, the rubber in the bushings would be in a relaxed position.

Essentially I'm saying this is how the suspension will sit when the shocks are charged and counteracting the load. Remember, I am not changing anything except the vertical position of the control arms when they are installed and all this does is affect how "wound-up" the bushing rubber is. I believe the component damage spoken about in the manual is the premature failure of the rubber if the load is not compensated for when positioning the control arms and the subsequent shearing stress imposed on it.

Sorry for the long post. All this because I don't have ramps! It's only my opinion but I believe the logic is sound. It's basically "where would they be if everything was done? Put 'em there before you do it and Bob's your uncle!"

Thoughts?



cheers

 

I think your logic is sound.

 

I don't have an XJ yet, but this is applied to every cars suspensions; "The final tighten of the bolts and nuts of lower arm should be carry with the car on its wheel.." have nothing to do with geometry or ride height or reference point, it's about stretch load on the arms and twisting on the bushes; As you see; If you tighten the bolt with the wheel hanging down, when you let down the car, the arm always carry a stretch load and the bush always being twisted, when you car hit a bum the wheel moved up so the arm stretch more and the bush is twisted further more, the result are they will worn or broke premature. As if you tighten the bolts with the car on its wheel, the arm and the bush always at their normal relax position, when you drive the wheels got bum up or drop down the pot hole, they only moved up and down a few degrees out of their relax normal position, that won't do any load stretching or twisting to the component.

 

I too, think that the logic is sound. We all know that we want to skin this cat, and why we should skin this cat. I think it's just a matter of how do we do it?

On the question of "this is how the suspension will sit when the shocks are charged and counteracting the load";

You say:
1. Give me the final measurements and I will jack the unloaded suspension and tighten the bushing there.
Makes sense

I say:
2. Since I don't know exactly what the heights and angles are on each of the 4 corners, and since the car sat at perfect height before I removed these components, how about I start the car, air the bags and then tighten the bushing after the control arm settles where it's supposed to be?
... or air the bags then take measurements if you will need to remove the wheel for access.
Again, key thing is to just place the bushing bolt and nut rather loosely in the hole to allow the bushing sleeve to still rotate.

If I were in your position again, I would still do my method because "if the ride height ain't broke, don't tinker with it", but I understand where you're coming from. Either way, I wish you the best of luck.