Steering/ braking judder.

[MaxTheDog]

Hello All,
I took my MY2000 XK8 Coupe out for a little zip round today, as it was dry and let’s face it, any excuse is good enough.
Unfortunately all was not well, after around 20 or so minutes into the drive, a mix of country lanes and the M1, between 55 and 70mph there was quite a bit of steering wheel shake. It was also there at lower speeds when braking on slip roads approaching junctions etc. When I’d returned home, already thinking wheel balancing/ tracking tomorrow, as soon as I got out I could feel the heat off the OSF wheel. Bending down, the smell was not right to put it mildly and the heat could be felt on my face. The other three wheels were just normal ambient temperature. So I’m assuming I’ve got an OSF brake binding. All discs and pads were replaced last January prior to my ownership by a Jaguar specialist in Harrogate and I had both front reluctor rings replaced about a month ago. My questions are:
1. It about 35 miles to the Jaguar specialist- is it safe to drive there? If not would it be something either a local (2 miles away) mechanic could handle.
2. Reading other previous threads on steering/ brake judder, has left me really confused and concerned about the steering judder and road surfaces so any advice after clearing the binding brake would be greatly appreciated.
Apologies for the War & Peace but I thought as much background as possible would be preferable to just a handful of sentences.
Regards,
Michael.

[mike020150]

Since safety is paramount, I would be tempted to jack up the car to see if the suspect wheel spins using hand pressure. Then, whilst you are spinning the wheel, get someone else to press the brake pedal to confirm if the brake is working at all (it sounds like it should be but may be sticking occasionally). If pressing the brake doesn't have any effect or there is any free play when you rock the wheel on its bearing, just in case the wheel bearing is failing and risks a wheel leaving the car, arrange to have the car transported to a garage for repair work. In any event, a 2 mile journey sounds like a better idea than a 35 mile one. Mike.

[Astromorg]

As Mike says, 35 miles is not to be recommended. A couple of slow miles, maybe with a stop or two to check the temperature, should be manageable. Does the car try to pull to the offside as an indication of when it's actually seized on?

In addition to Mike's suggestions, I would add that a common cause of this type of brake (not Brembo) sticking on, is a seized or partially seized sliding pin - the caliper has to be free on its two pins to move enough to allow the pads to retract from the disc when the pedal is released and also to take up pad wear. One of the two pins has a rubber sleeve that if correctly lubricated can still slide but will also prevent vibration. Too often these pins are lubricated with a general purpose grease that eventually attacks the rubber sleeve causing it to swell and seize the caliper.

When brakes seize on and overheat excessively followed by a period with the car at a standstill - say in traffic or at journey's end - the uneven cooling of the exposed disc compared to the section of disc between the pads can cause the disc to deform enough to create a vibration through the pedal.

Standard XK8 brakes are well within the capabilities of a general garage workshop as they're fitted to a large range of other manufacturer's vehicles.

[MaxTheDog]

Thanks both Mike and Astromorg,
There’s no pulling that I’ve noticed, but arrangements have been made to transport it for repair.
It can be moved by hand pressure but not with the same ease as the NSF. I’ll await to see if the disc has suffered. I can’t detect any wheel bearing issue.
Regards,
M.

[Andy P]

Hi MaxTheDog.
I will just put in my two pennies worth (if I may) of what might be an issue and that is a sticky caliper piston.
They do corrode (they are steel) behind the rubber seal which prevents it returning fully.
The abnormal heat may have caused the brake disc to warp slightly but that does not always happen.
As Astromorg has said should be well within the capabilities of a general garage to sort out.
Good luck with it all anyway.
Here are a couple of photo's of the Jaguar (XJ/XK) brake calipers.
Take care.
Andy

Brake caliper piston on it's way out

Pair of brake calipers dismantled

[MaxTheDog]

Apologies for this very late update. Just for the record, the issue turned out to be the OSF caliper sticking on (You could feel the heat from standing beside the OSF wheel). I had both front calipers replaced, luckily there was no other damage and all has been well since.
Well, apart from blown head gasket (January, timing chains and tensioners done at the same time ) and upstream O2 bank 1 sensor (replaced tomorrow).
Regards,
Michael.

[mike020150]

After those hiccoughs, it's time to get out and enjoy driving the car in this nice warm weather! It'll be wet and cold again all too soon. Mike.

[MaxTheDog]

Absolutely!

[Andy P]

Hi Michael,
Glad you got it sorted and sorry to hear about your head gasket.
As Mike has said ,time to get out and enjoy your car now.
Take care.
Andy