My 350Z used to make a noise exactly like that. And sometimes it would go away too! It would drive me f-ing nuts! It took months, and I figured out it was the bolt that runs through the 'fork' of the strut (at the bottom) that had become loose and would rattle. The threading around the bolt deteriorated. It drove me nuts and nobody could figure out. Until I finally did...

Now it's a well known issue that some 350Zs shipped with struts that didn't have zinc coated bolts for the fork.

Here's what I'm referencing (these are XK struts). Replace the studs that go through those holes. If you replaced the strut, they may not have used new hardware.

 

It's still at the same shop. I am getting perilously close to revealing the name of the shop but I am giving them another chance to fix it. Today they told me they were 99% sure they had fixed it by securing the dust shield on the brake caliper.

So I drove over there (probably literally the 5th or 6th time since they've come up with a "fix"), and took the car for a test ride, and of course there was no change in the noise. I took the mechanic/technician on a drive on a bad road I found near the shop, and he agreed that it is a very bad noise.

I took videos from both inside and outside of the car:

Inside:
Outside:
When I returned to the shop, I spoke with one of the shop owners (the technician's boss). He has forty years of experience in working on Jaguars and other European cars. This is one of the preeminent import repair shops in the region, so I am hesitant to think they are idiots and that I will get better service elsewhere.

I suggested that since the noise goes away when the brakes are applied, it must be related to the brakes. Mind you the brakes have already been replaced (again) once since we switched to Jaguar-branded pads. I suggested that perhaps the brake caliper bolts or slider pins were damaged and/or loose. He said that it's not possible because he checked them himself and that there are no slider pins since it is a 2 piston design. Is this even true? The photos I see show one piston.

Furthermore, now the shop it investigating whether it could be a catalytic converter banging around. If they suggest replacing the catalytic converter, there is no way I'm going along with that and I will take it somewhere else.

Sounds kinda similar to this, doesn't it?
Also, here is a photo of caliper C2P15168 (front XKR brake caliper):

 

Actually that may not be the right part number for the brake caliper. There seems to be a lot of different ones (Alcon, Portfolio, n/a XK) and I'm having trouble figuring out which is which.

 

Regardless, there's more going on when the brakes are applied vs. just the pads getting squished. The rotational energy of the tire is getting absorbed by the suspension. Bottom goes back, top forward, front down, back up. In some form the brake action is eliminating the noise by loading the suspension.

Damn, a decent sized dead blow mallet against all the joints should find the noise. Do they have the car on an alignment rack where they can lift the front frame with the tires on the 'ground' to mimic the suspension or is on a four post lift with the wheels hanging down? If the latter then that's probably why they can't duplicate the problem. If memory serves they had to ship it for an alignment which means they may not have the means to troubleshoot the problem.

This is the type lift. It has the jack in the middle to load unload the suspension.

 

You are correct, they have a four post lift with the wheels hanging down and they do not have an alignment rack. I think the next shop/dealer I seek out will need to have one of those.

 

Then they are trying to trouble shoot a problem with the chassis in the wrong condition... They could do it if they had blocks under the tires to mimic the road. If they have 55 gallon drums they 'could' do the same but it's not nearly as safe as the alignment rack. Really surprised they didn't farm this work out with an explanation of what the complaint was. I assume your shop just told the alignment shop to verify it was aligned and not why it was really there.

With the alignment rack you can sit under the car and move the chassis up / down while watching the suspension articulate with in the limits of the shocks. It's pretty educational.

 

Well I just fired my mechanic. The car has been relocated to a shop I used to frequent before switching to this shop. I explained everything to the owner and he fully understands and sounds like he is using logic to approach the problem instead of wild guesses.

I'll keep you posted but it seems to me that he is highly suspecting the brakes.

 

It'll take a while as they go through all the basics to satisfy their curiosity and they also don't totally believe what you say until they see it themselves. I'm an industrial mechanic and it's how I think. Trust but verify. Been tripped up too many times by not verifying what's been done wasn't done properly. Eventually they'll have an AHA moment if you are lucky.

Do they have an alignment lift like shown above so they can exercise the suspension?

 

No they do not have an alignment lift, but I am confident they will find the issue without it and can provide me a recommendation to take it to a shop with a lift if they cannot find a solution themselves. I anticipate it won't take them long to make a recommendation based on past experiences here.

 

You haven't looked at the strut bolts just to eliminate that?

 

The mechanic (shop #2) just called me. He said they identified the source of the problem as excessive clearance (1mm) between the brake caliper and the pad on the inside pad. He said as a test and remedy, they welded some metal to back (or edge?) of the pad and the noise went away completely.

He suggested I just leave it like this and see how it does. I will pick up the car today to verify that the noise is indeed gone, and if so, I'll probably make this a weekend project at some point (replacing the brake caliper/pads and/or slider pins/bolts).

 

I guess I don't understand what they found. Why would you need to modify a brake pad to correct the problem. Something doesn't sound right here.

 

I think for a permanent "ideal" repair, the caliper would have to be replaced along with possibly the bracket and bolts. I don't know if there is a good way to check for exactly which component is damaged. I can hopefully do this myself, in the near future so that I can just redo the pads on the LF side without having to do the RF.

Now that I think about it, it does seem like there is some brake dragging but I have measured using a heat gun and both front wheels seemed like they were the same temperature after driving. If there was excessive dragging on the outside pad, then I would be concerned about rotor warping and uneven brake wear.

This is all assuming the noise is actually gone. At this point, I am still skeptical. But if it is true that the noise is gone, at least I know the noise is related to the brake components, specifically the caliper, caliper bracket, caliper slider pins, or caliper mounting bolts.

 

Something does not compute. So, was the pad under thickness? Was it the same on the other side? It's the nature of a disc brake for the calipers to breath and create a little gap when you let off the brakes so they don't rub all the time. It depends on the type of caliper as to where the gap is allowed. Floating calipers with the pucks on one side that have excessive gap are stuck but usually show up as running hot. Most pads have some gizmo that holds them to the caliper puck, usually a spring loaded arm for this issue. If the gap is more than the other side then do you have a sticking caliper or an ABS proportioning valve problem?

Welding the pad creates more questions than answers. The most obvious being why not fix the problem instead of the symptom? As a troubleshooting step was does it resolve? If the prop valve then it'll just pull back again once it get's a couple cycles. If the caliper will it now wear in a new 'rest' spot?

Interesting diagnosis.

 

I just got back from the shop. Your skepticism is warranted--the problem was not fixed. He showed me photos of what they did, basically where the pad is sort of keyed into the slots on the caliper, they added just a very minuscule dab of welding material to eliminate any clearance. This has had no impact at all on the sound. Since it doesn't change the pad thickness or its function, I'm not too concerned about this needing to be undone.





The mechanic went on a test ride with me and heard the noise and now understands what noise I was talking about (seems like the last mechanic had the same problem). He thinks that there is no way the noise could be related to brake pad play based on the heaviness of the sound (as opposed to light chattering/clicking). He put the car on the lift and he, another technician and I went over all the components of the front suspension, using a prybar to check for play. According to this shop, everything checked out OK (this is the same thing Shop #1 told me).

Both shops now suspect that the problem is indeed an internally damaged strut. This shop suggested that they remove the strut, and play around with it when it's off to see if there's any unusual noises. If so, then they will replace the strut. If not, at least they will have an opportunity to investigate other components while the strut is out, including the upper strut mount and the lower shock mount bolt/joint/bushing.

Again, these are two highly regarded shops, albeit without alignment racks, and they are both in agreement with their findings at this point.

I think I should go ahead and order those eBay Jaguar front struts, just in case they are needed. Apparently they are returnable. I will suggest that the shop use a new lower shock bolt. Does anyone have a part number for that?

 

One thing that has been bothering me--how come when they disconnected the sway bar end links (on both sides), and then tied them off and I went for a drive, both sides were clanking very badly on bumps? Could this mean that both front shocks are bad, and that the sway bar is helping eliminate any noises by helping transfer some of the force of a bump to both shocks?

 

Most likely the bars or tie rods were hitting something as the suspension articulated. Still, last thing first. How would a loose internal strut not make noise when you hit the brakes?

Review the X150 service manual, pages 158 on for a better understanding of how it all works. The strut just guides the spring and has nothing to do with forces on the suspension beyond compressing under vertical load, especially when you hit the brakes. The upper or lower A arm groups could have loose , worn bushings. The service manual shows how to load the suspension to check the ball joints.

 

P/N:C2P7192

Here's a great resource:

Online OEM Parts Catalog

 

The way it was described to me, braking puts additional forces on the suspension that could serve to dampen certain motions. You make some good points, though, and Googling this seems to show that most people look to the brake pads/clips themselves under similar conditions. My mechanic thinks the noise is much too loud, though, to be brake pads rattling.

After watching this video, I think I now understand why you say the suspension needs to be "unloaded" when they check some of these items. It seems like they should still be able to see any play by prying on items, though. I could understand if they were checking things just by doing a quick pull on the tire/wheel to check for looseness but they methodically went over every joint in the front suspension with a pry bar, comparing left and right along the way. Seems like I will have to go to the dealer if I want somebody to follow the Jaguar procedure since neither shop I've been to so far seems to see the need for this.


If this shop, however, does end up taking the shock assembly out, perhaps then the suspension will be unloaded and the cause will be more apparent. It doesn't seem like it's going to be very much labor for them to take the shock assembly out to do some more investigation.

One test I want to try tomorrow (I will go back to the shop in the AM) is to disconnect the active damping system and see if it makes any difference to the noise. This will make the struts go very stiff. If somehow it makes the noise go away, I would suspect that the shock itself has something to do with it, because if it was rattling brakes, this would probably increase the amount of rattling (not decrease it). But if it makes no change in the noise, I would probably not suspect the struts and would want to go a different route.

I am open to going to the dealer, but I'd like to see what this second repair shop plans to do to identify the issue. I don't think they were saying they're sure it's the shock, but I think it couldn't hurt to have some additional information by removing it and their labor rates are fairly inexpensive.

 

I picked the car up to wait for parts to arrive. I have ordered new struts in case they are needed and am special ordering lower strut bolts from the dealer which I will try myself before taking the car back to the shop. I literally just need to jack the front of the car up to take that bolt out, right? Do I even need to take off the wheel?