Saturday my wife and I drove up to the Blue Ridge Parkway. For those of you from England or someplace, the BRP is a national park here in the US. It's rather unusual for a national park because it is really just a 469 mile long road through the mountains. The speed limit is 35 or 45 miles per hour. Commercial vehicles aren't allowed. It's just a very scenic, curvy, mountain drive.

Anyway... My wife and I were driving along and suddenly it sounded as if I had run over something and it was rattling around in the front left wheel well. Whatever it was bounced around for a few seconds, then the sound was gone. Everything seemed fine. Until I applied the brakes, that is. The first time I stepped on the brake pedal there was a very slight "clunk" sound from the wheel well. I almost thought it was my imagination. But then as we were pulling into one of the hundreds of scenic overlooks, I heard the "clunk" again. Then I could hear a very slight rubbing or grinding sound from the same wheel well. I thought this might be the end of our weekend drive.

I parked the car and examined the brake as well as I could through the spokes of the wheel. I turned the wheel to the side and felt around on the back side of the wheel to see if I could feel anything amiss. Everything seemed fine. I drove around a bit more, and applying the brakes would always cause the clunk, and then there would be the rubbing sound. The wheel wasn't pulling to the side as if the left brake was completely inop. I decided to just drive it home that way, but I was very careful driving it. Driving out of the mountains I used the transmission as much as possible to keep from using the brakes. When slowing down I would shift all the way up to "2" before applying the brakes. I left lots of room between me and the cars in front of me, just in case that left front brake was about to fail. We made it home safely.



I know you guys are probably going to hate me for this, but I just decided to see if anyone can figure out the problem based on the symptoms. I already know what's wrong, so this is just a troubleshooting game. The first person to answer correctly will get a free convertible top plug-and-play pressure reducing resistor assembly. I'm pretty sure I won't be giving one away.

So here are the symptoms:

What was wrong with my brakes? I think I'll let this play out until tomorrow evening to see if anyone figures it out.

 

Let's see ...

1) pad shim popped out

2) foreign material wedged between wheel and caliper

 

OK, I'll just tell you what it was. I can't find the part in the parts book and I need help. I hate going to the dealership without knowing the part number for what I need.

The picture below was taken from inside the wheel well looking out towards the brake caliper and vertical link. To help you figure out what you're looking at, the big red thing is the brake caliper. The green arrow is pointing at the wheel speed sensor cog thingy. The red arrow is point at the tie rod. The shiny thing right at the top of the picture is the brake rotor.



So now that we are oriented, look at the yellow arrow. There's supposed to be a bolt in that hole. It's one of two bolts that hold the brake caliper in place. The blue arrow is pointing at the second one, which fortunately is still there. The thing I heard rattling around in the wheel well was the upper bolt. After it came out, the caliper would make the thunk sound as it shifted when I applied the brakes. The rubbing noise was the caliper rubbing against the outer edge of the rotor.

I'm glad it was the upper bolt that came out. The lower bolt acted as a fulcrum and pulled the caliper towards the rotor when I applied the brakes. If it had been the lower bolt, then when I applied the brakes, the rotation of the rotor would have caused the caliper to rotate around the upper bolt, which could have really screwed things up.

Now that you know what happened, does anyone know the part number for that bolt? The parts book I have shows the caliper, rotor, pads, etc., but it doesn't show the bolts. Here's a picture. This is the lower one, but they are identical.

 

That's what I was thinking, which is why I wasn't too worried and kept driving. I also thought that maybe the pad had just fractured, throwing a chunk of it into the wheel well and leaving behind the metal studs that hold the brake pad material in place. (If you've ever gone a really really really long time between brake jobs you'll know what I'm talking about. I was young and foolish back then.)

 

Just run over to Home Depot/ Loews and match it! LOL

Take it to a dealer or auto parts store and match it up. Just might be in the auto parts store "HELP" section.

 

Well, it's a:

Bolt - caliper carrier to vertical link with a torque spec of 120-160NM.

Maybe Jim will come along and open up JEPC for you.

You want the factory bolt because it has threadlock preinstalled.

From the looks of it, you might need to remove the brake hose to get a socket on it.

edit: absolutely no on the substitute via Lowes, Home Depot, etc. In addition to the threadlock, the original will be at least the equivalent of a SAE grade 8 bolt. It is a critical safety component.. Try torquing a cheapo Grade 5 or less bolt to 160NM and you'll probably end up with a snapped bolt to deal with.

 

Agreed Plum. Was just being sarcastic. There is a number on the head of the bolt. Match the bolt with a bolt that has the same number. My search found no part number. I believe it to be a common bolt in the automotive sector.

 

Looks like part number is JZB100010

 

Ok then. The Rev pretty well knows what he is doing ... just didn't want the most prolific poster in the Girls on Jags or Not threads to depart us.

But for those following behind ... take heed.

 

im more concerned on how that bolt backed itself out. you've had those fronts apart quite abit, what do u suspect?

 

unsolicited opinion from a bystander:

a) re-used the bolt without loctite

b) got distracted in the middle of the job and never came back to that particular bolt for final tightening

 

I wish I had seen this yesterday, I could use one of them resistor thingies. So I submit the following pic as proof of my idiocy in forgetting to tighten the bolts on a caliper when I redid the front end.
A couple days after doing the suspension work, my wife told me about a weird clunking sound whenever she turned a corner. It was a little more difficult to diagnose since it only happened when she turned. Apparently, she stops pretty slowly when in traffic and never heard a clunk when stopping in a straight line; but she must hit the break every time she goes into a turn.
Fortunate for me too, it was the top bolt so no damage (other than to my credibility as a mechanic.) The Jag dealer didn't have any in stock and had to order me one. The number WhiteXKR gave you is correct - $2.65 +tax.

 

LOL! This forum is so awesome! Yes, I've had the bolts out before. I wasn't aware that I was supposed to reinstall with Lock-tite. I guess I need to remove the ones from the other side and reinstall them with lock-tite, too.

Ed, I see the date on the receipt is just two weeks ago! I thought for sure I was the only person this had ever happened to!

I know better than to use hardware store bolts for something like brake calipers. I've built a couple of airplanes, and it's a huge no-no to use non-aviation hardware on an airplane.

 

When I changed my brakes the bolts came with the new pads. You now have a different opinion on the purchase and use of a torque wrench.

 

Sam
This never happened to me, but a friends wife took her Jeep to the dealer and had a brake job done. Drove off the lot and when she applied the brakes caliber flew off and did $2000.00 worth of damage. They didn't even put the bolts back in or test drove the car.

 

Jesus jaguar co. That's just Hillbilly to have that bolt back out of there.

 

Almost certainly the case. Not that I'm excusing the poor workmanship, mind you.

An experienced mechanic....pro or DIYer....always pauses work after critical steps are complete, not in the middle of them. Not developing this simple discipline is simply being careless.

When I ran a shop I always told service advisors to WAIT for the right moment before interupting technicians. And I told techs to ignore any questions or distractions, from *anyone*, until the they are done with what they are doing. In fact this policy began when....you guessed it...caliper bolts were left loose on a customers car.

And this is one reason many technicians don't like customers (or anyone else) hovering over them while they work. Whatever the type of work may be I don't know *anyone* who does a better job with someone looking over their shoulder....but I know plenty who do a worse job.

I myself have made blunders when someone interupts my routine.

Cheers
DD

 

I had the brakes apart to paint them late last summer. I tightened them back down properly, but I didn't use the Loctite. It took almost a year for the bolt to back out. I called my local Jag dealer and they have the bolts in stock. I'm going to pick one up tomorrow to replace the one that was lost, and then I'll remove the other 7 and reinstall them with Loctite.

 

About the loctite thing.

In JTIS, at the top of the relevant page for the XK it mentions threadlocked fasteners. But does not specify which ones. Later in the page, it mentions re-installing the bolt, and the torque value, but does not specifically call out for threadlock on that fastener.

However, the presence of threadlock has been mentioned in rants on JF about that particular fastener by members undoing it for the first time.

very confusing, until 100-00 is consulted:

There is no direct mention of JZB100010, so it is still ambiguous. But, "probably" loctite couldn't hurt as long as the permanent locker stuff is not used. There is of course, the mention of threadlocker on the factory installs on threads here.

 

Ummmm...no.

An untouched factory installed caliper bracket bolt is unlikely to back out.

The bolts that have backed out have been after servicing when the person doing the service was not aware of the factory method.