I had new front brake discs and pads fitted to my 2017 XFS 2-3 weeks ago and lost a lug nut in the process. When the brakes were done, the garage explained that it had been a difficult job and mentioned the sheared lug nut along with something about a seized alignment bolt. I'll be honest, I wasn't really sure what they were talking about at the time but the main concern was that I'd have an issue getting the wheel off next time.

Anyway, after some initial squeaking from the new brakes, the driver-side brake has continued to be squeaky. More concerning, though, is that there's an audible "knock" as the brakes engage. Not always, but when it happens it might then happen the next 10-20 times the brakes engage then it will stop for a bit. It doesn't happen when the car is stationary, only once I've gotten moving again and I apply the brakes, and it seems to only happen when I'm driving at slower speeds (30-40mph) and once I've started moving over say15-20mph. The brake pedal has to be pushed down more than a tiny bit for the knock to happen too, seemingly it happens as the brakes engage. The knock definitely comes from the area of the front driver-side wheel.

I was replacing the crappy chrome-capped lug nuts today so I had a quick look around for anything obviously loose when I'd taken the wheel off. The only thing I noticed was that there was a little bit of rotational wiggle each way if I grabbed the wheel studs, and when I wiggled them by hand there was an audible knock very much like what I've been hearing when I'm driving. I removed the front passenger-side wheel to compare and there was no wiggle there at all. Then I spotted the bolt in the photo below, which I'm fairly certain wasn't there behind the driver-side wheel.



I suspect this is the alignment bolt the garage were talking about, and that this is the source of the knocking.

Two questions for anyone more experienced than me:

1. Does it seem reasonable that the wiggle room on the driver-side wheel hub would cause this knocking as the brakes engage, and possibly the squeaking too? Seems logical to me, but one person I know has said it shouldn't make a big difference if the bolt isn't there and suggested the knocking is more likely an issue with the drop link.
2. Does anyone know what this bolt is called, or a part number? Presumably it should be straightforward to stick a new one in there to see if it resolves the issue?

 

That is a retainer and centraliser bolt, should not be absolutely necessary. However, the knocking and squeaking could indicate that the disc may not be fully engaged on the hub, that the caliper assembly is not tight, or that the pads are not seated correctly. I would take a close look at the entire job.

 

Bolt is M10 x 20mm

JLR part number is JDE29531

 

My guess ..... that missing bolt is the cause of your noise.

 

Seems logical to me but a couple of car folk have suggested otherwise. I've ordered a new bolt anyhow, will get that fitted and see if it solves the problem. If not I might just take it to the local Jag specialist to have a look.

Legend, got one ordered, cheers!

Nice one. Appreciate the input. The brakes look a bit fiddly to remove and I'm not sure I'd know what to look for so I'll try fitting a replacement bolt and if that doesn't resolve the issue I'll take it to my local Jag specialist.

I'll post an update here one way or another. Cheers!

 

If you look at the hole for the bolt it is chamfered, for a reason. It locates the rotor on the hub. It also keeps the rotor from rotating on the hub. That rotation, when the edge of the rotor hits the wheel stud, I think is the noise.

 

Yeah I realised that today when I took the wheel off to fit the new bolt. Unfortunately the garage snapped the head off of the previous bolt and the remains are still in the hole.



Now to work out how to get this ****er out without damaging anything else!

 

Use an EZ out. Start with a small pilot hole and you can probably do it in situ.

 

The "alignment bolt" is probably worth replacing if you can get the old stub out without too much trouble.
However, it being missing is definitely not the cause of your knock. Once the roadwheel is on and the lug nuts tightened up, the disc/rotor is held tightly against the hub by the lug nuts and cannot move, even with no alignment bolt present. The only purpose of the alignment bolt is to stop the disc becoming a bit loose when you remove the roadwheel, potentially allowing road grit to get between the hub and the disc.
Alignment of the roadwheel, disc and hub is made by close fitting of the central hole in the disc and the roadwheel and the raised part of the hub - the "alignment bolt" plays no part in this.

 

Makes sense.