Hi Everyone
Today I replaced front right air strut and rear left air strut with arnott new air struts. My mechanic told me arnott front air strut is approx 2 inches taller than the old air strut I had in my x350 3.0 v6 which was the original jaguar strut.
How is that possible? I was told by the mechanic that other old two will also go bad since I replaced only two. I decided to replace only two because other two are fine at the moment
Ay idea why the height difference? Also since I have used new arnott Air struts is it not possible to calibrate to even height using the computer? Have I lost CATS with this replacement?
Appreciate any input.
P.S. it was a nightmare to get down arnott struts to Sri Lanka from all the way to states. I was hoping all my problems could go away with this replacement but guess I was wrong!
Thanks in advance

 

First I find it hard to believe Arnott struts are really taler. Send them a mail and ask. The calibration of the height is done by adjusting the relation between the value of the height sensor and the pressure (=height) in the air shock. Of course the Arnott shocks can be calibrated just like the OEM ones. I guess your garage doesn't know how to do it. And yes, the new Arnott shocks don't have CATS, it says so on their site. The rebuild ones keep the CATS function

Guus

 

Hi Sonic,

If I'm not mistaken, the actual ride height is determined by the air pressure in the air spring bladder, not the shock/damper structure itself. I'm wondering if your new Arnott shocks will settle down if you drive on them a bit, and I think Guus is correct that you should be able to re-level the suspension with JLR SDD, but if the car is driveable, I would suggest putting some mileage on the new shocks first (perhaps on some rough roads) to help them settle in before you do the recalibration. Obviously if the car does not feel safe to drive you may need to recalibrate first and then recalibrate again if the ride height of the new shocks changes as they break in.

Please keep us informed, and we'll also be interested to know what Arnott has to say in response to your inquiry.

Cheers,

Don

 

+1 on the SDD ride height calibration

Best guess is your mechanic did not have SDD or do the calibration.
My advise is to get a mongoose cable and SDD so you can do it yourself. It will come in handy in the long run as well

Cheers
34by151

 

I would never replace a shock on an X350 without doing the ride height calibration afterwards. It really is a must. In fact it's something that needs to be done periodically anyhow, as the front right loses it's calibration & you end up with uneven ride height at the front (on the later cars that only have one height sensor left front).

I did not realise that the Arnott own-design shocks do not have CATS. After reading the fine print on their site it does mention this, but they supply a dummy solenoid (prob. a resistor) to trick the air suspension module into thinking that a CATS shock is still fitted.

Since you have replaced right front & left rear only, that means the other two shocks still have CATS functioning, and being at diagonally opposite corners, i'd consider that very bad for the handling of the vehicle...(I won't say dangerous, but other people might).

You need to get hold of an IDS or SDD diagnostic system and calibrate the ride height, but first i'd think long & hard about replacing the other two shocks...

 

+1 on Cameron's comment.

 

Thanks for replies everyone. Car just came out of the workshop. He has done the calibration but he's still saying the side in which the arnott is installed is 1-2cm higher than the previous one which was installed. My question is during the calibration wouldn't it be possible to even out this difference ? Or is it too big for the calibration to do? If it's physically taller can it be made even after a proper calibration?
Also now I'm freaking out with all the handling comments. But am I the only person running with arnott + Jaguar OEM struts? So does everyone change all four? Or are the changed struts being in a diagonal position the issue?
Hoping someone can help me. Thanks

 

P.S mechanic told me he did the SDD calibration and he didn't get any fault message saying CATS is not inoperative on those new shocks.

 

Re the cats, just get 2 more adapters from Arnott

It sounds like he ran a diagnostic and not the ride height adjustments
I cant see any reason you cant level it out using SDD

It can be fiddly if the corners are way off due to diagonal weight shift.
Its critical to do it on flat level ground for this reason

Cheers
34by151

 

If he had done the calibration correctly then this would not be possible.

It should be possible, because i am quite sure that the Arnott shocks will be the same length as the OEM Jag ones. It's just that they are sitting higher because they require a different air volume/pressure, because they are not the same shock.

The issue is having different shocks at each corner.

The Arnotts are replacements, but they are not identical. Quite different in fact.

Apart from the valve rates being different, the CATS is also a potentially dangerous thing to throw in the mix. It's important to understand how the CATS work.

They have a soft mode (like when you are just cruising around) and a firm mode, which is activated under heavy braking, accelleration, or cornering.

By having a mix of CATS and a non-CATS shocks on the front axles, under heaving braking you would have one (very) firm shock, and one that is soft, I am pretty sure that's not what you would want in an emergency braking situation.

Two things.

1. The Arnott shocks have a resistor in them to trick the CATS system into thinking everything is OK. You do not have any "errors" but with your setup the system is definitely not working correctly.

2. The ride height calibration procedure with SDD is more/less outlined in this post ==>> https://www.jaguarforums.com/forum/x...ur-x350-75369/ instead of entering false values to lower the car, you just enter the real measurements. I doubt that your mechanic has done this, probably just read the codes, which there wouldn't be any. Does he actually have IDS/SDD?

I wouldn't do that. If you unplug the CATS shock & stick the resistor/adaptor in, the shock will be stuck in firm mode. It will probably just make things worse.

Exactly.

Sonic, you need to get two more Arnott shocks, and have the suspension calibrated correctly. I could not recommend anything else.

 

Cambo,

While I'm thinking about it, and for the record, I followed your excellent tutorial to calibrate the ride height on our '04, and just couldn't get two corners to arrive at the correct heights. I finally succeeded by using false "current height" settings to prompt SDD to overcompensate at those two corners, in the same fashion you used false measurements to prompt SDD to lower your overall ride height. By trial and error I managed to get all four corners within a mm or two of factory spec. Without your ride height tutorial I probably wouldn't have thought of "fooling" SDD.

Thanks!

Don

 

Another option is to use a set of corner scales.
If you dont have access to a set of scales and cant borrow/rent some use the bathroom scale hack
Once you have it level then adjust the ride heights adding or subtracting each wheel equally
The handling will also be a lot better but this wont matter near as much to those that don't want to go on the track

cheers
34by151

 

Hi 34by151,

I'm no expert on setting up race car suspensions, but my understanding of the use of corner scales is to set the static weight distribution of the vehicle as it will be raced, with the driver in his seat, the fuel at an optimum level, etc., in order to optimize handling for the specific track that will be raced (e.g. left-turning oval). I recall reading that in most race cars with an offset driver seat the ideal weight distribution cannot be achieved. How would the use of corner scales help set up the X350 air suspension if the goal, according to the Jaguar Workshop Manual, is to set the ride height of the front corners at 386 mm and the rear corners at 373 mm?

What would be the benefit of beginning with corner scales, and would you take into account imbalances caused by driver offset, the battery to the right in the boot/trunk, etc.? Any further explanation you can offer would be greatly appreciated!

Cheers,

Don

 

Glad it worked out for you Don.

I've always had problems getting the right front at the correct height (this is the corner without the height sensor) and have had to do a bit of fiddling with the numbers to get it correct. I'd just assumed that it was because I had lowered the car, but in the meantime we have come across several X350's with incorrect ride height at the right front. No doubt it's because of not having a sensor at that corner and the ASM having to "guess" the height based on air pressure compared to the left front.

 

As a matter of fact it was our front right corner was the farthest off, a full 2 cm if I recall. The rear right corner was also off and had to be corrected to a lesser degree, maybe 1 cm.

Cheers,

Don

 

Interesting. So the value of the front height sensor is not correct as input for both sides?

Guus

 

(1) So basically even with OEM struts and after a proper calibration is it not possible to level the front? The front right is always higher?

(2) when they removed the old strut from the car and kept the new one side by side with it, he said the new one was little bit taller. I wasn't there. I don't now why and what has happened there. But if that's the case isn't it possible to calibrate both to level?

 

If you follow the official procedure then it is likely that the right front will not be exact. I was able to get the fronts level but it was done by "cheating" the system. Jaguar define a wide tolerance of +/- 15mm in ride height, so your car may well be in tolerance, but it's definitely not "right"

Maybe it is. I don't know. But for sure you will are able to get the front level by cheating during the calibration. Did you even read the thread I linked showing how to do the suspension calibration?

But as I told you before, the ride height is the least of your concerns here...

Are you not at all concerned that you have different shocks at each corner of your car, and the potential consequences of this?

All the information you need is here in this thread, and in the one about how to do the calibration.

 

First up here are a few links on corner weighting, mostly so there is less to explain
http://grassrootsmotorsports.com/art...orner-weights/
http://robrobinette.com/corner_weight.htm

Remember they are not referring to cars like ours with an active suspension system. This is important as ours has the “height sensors” so the ASM can read where the wheels are and compensate.

To answer your question re battery location, driver offset (driver weight) ect, it does not matter on our cars. If you calibrate the system say without the driver the wheels will be setup in that calibrated position. If you add weight, say the driver or load up the boot the system will know this via the height sensors and add air put it back in the calibrated position

Regards doing the suspension calibration you have 2 issues to deal with
1. Leveling the car
2. Setting the ride height

If you go back to Cambo’s how to tutorial, it written from the position of lowering the car. So the assumption is made that it’s leveled.

Now if you go back a step and take the example that the car is not leveled. This is usually an imbalance from side to side and can be tricky to work out. This is trickier for cars with 3 height sensors rather than 4.

Doing this without scales is trial and error by adjusting the settings in SDD to compensate, recheck and repeat. However even without scales you can reduce the number of tries if you understand how corner weighting is done. What you need to get your head around is how the weight transfer changes the ride height of the other wheels.

IE lets say your rear wheels have identical heights (the height does not matter) and the front is not level, with the drivers wheel 10mm higher than the passengers wheel. Again it does not matter what the front and rear heights are. We are just trying to level the car side to side not front to back.

So with above you may think using SDD and lowering the driver’s wheel by 10mm will fix the issue, not so. What will happen is weight will come off the wheel diagonally opposite and some weight will be added to the rear and the passenger wheel and driver’s rear will get more weight.

Now without scales, assume you lower the driver’s wheel down by 10mm and leave the rest the same. You have now caused a weight transfer (causing the other 3 wheels to change height). This causes a change in the height sensors and the ASM to change the pressures to recompense.

Now let’s assume you use scales to try and level it out and remember we are just talking side to side and don’t care what the front/rear tilt is.

Using the same example what would we see on the scales? Well we would have the weight on each wheel, side to side % overall and for the front and back as well as the cross distribution.

What we would see is the drivers front has more weight that the passenger wheel. You will also see the rear wheels have different weight but are close. Why would this happen because the rear airbags will be a different pressure to compensate for the weight change. Now plug these numbers into a corner weight spreadsheet (see the second link above) or use the online calculator. The sheet gives more info but let’s plug the numbers into the online calc. You now have your actual and target weights. In other words how to compensate all 4 height settings ate the same time. This eliminates most of the ASM compensation. So how do you convert from weight to mm for SDD. Easy use a spreadsheet. For each wheel divide the measured weight by the target weight then multiply this by the value for the wheel in sdd

This won’t be perfect but it will be getting better and you can repeat to get it perfect.

At his point I’d like to go back to the online calculator and no scales.

Rather than plugging in weight in the calculator let input ride heights. Using the same example 386 and 396 for the front wheels and 373 for both on the back. What comes out is Front passenger=388.6, Front drivers=393.7, Rear passenger=370.4 and rear drivers 375.3. You can input these numbers directly into sdd.

So will the rear sill be level as it was before it was before?, Yes. What we have done is take out some of the compensation done by the ASM while also leveling the front (side to side).

Can you do this? Yes but it will take a lot more steps as we are not really looking that the weight transfer.

OK so lets now assume you have used the calculator, with or without scales, to get the car level (side to side). You will now have the overall height incorrect. As long as you add/subtract the same amount side to side you will raise or lower the car equally side to because the weight distribution is correct diagonally. In other words follow Cambo’s tutorial as the car is now leveled side to side and you just need to adjust the overall height and tilt

In other words we have built in the fudge factor Cambo is referring to first

So finally if you re read the second link how the adjustments are done is by changing the coil spring height. What we have done using sdd is adjust the airbag pressures changing the spring rates

Cheers
34by151

 

Not sure if anyone else is aware of this, but I was told by Chris (of Jag specialist Doncaster fame) that the air suspension works within a set of tolerancies. So while we may tell it to lower both corners by 25mm (or whatever) it may not actuallylower it by the amount specified due to the tolerance built into the system. I think he said it was 10-15mm. Pretty sure he allowed for that, as well as the high speed drop in his calculations when we were playing with the height on my car.

If this is true, then it makes sense why some suspension appears off on one side - its simply working within the thresholds of the air system.