XK / XKR ( X150 ) 2006 - 2014

Brake grab/pulse?

 
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Old 03-12-2019, 03:21 PM
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Default Brake grab/pulse?

Ok, so after driving MY 08 now for a couple hundred miles I know it's not my imagination. Can anyone comment on why it is that as I come to a slow rolling stop right before it stops dead there is a brake grab? It's not as noticeable if I make a quick complete stop. I read something about an anti lock brake issue in the first generaton while I was doing research on the 4.2's, could it be this or is this just normal?
Thanks,
Joe
 
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Old 03-12-2019, 07:37 PM
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Been searching the forum and the web and can't find the specific symptom. The car brakes great, just grabs hard right before it stops. No ABS or any other lights on, could it be wheel/speed sensors? Seems to happen after driving for a bit. Noticed the touch screen doesn't come on every once in awhile (a sign of weak battery), any chance battery related?
 
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Old 03-12-2019, 11:42 PM
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Yeah the screen turns off when the car senses battery is weak.
On the brakes, I wonder if its glazed pads or rotors. They are both pretty cheap to replace if you dont have much life left on them or they are old.
You said it happens after driving a bit- that would suggest moisture in the fluid. When did you last replace that?
 
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Old 03-13-2019, 05:42 AM
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Yes, seems to happen after the car has been driven for a while. Looking at the Carfax I do not see brake fluid being changed but the car only has 36000 miles on it. I will have to look into that. Thank you.
 
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Old 03-13-2019, 05:52 AM
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According to the Carfax it was dealer serviced up until the 30000 mile service. They listed antifreeze change but but I didn't see brake fluid.
 
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Old 03-13-2019, 08:28 AM
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Brake fluid should be changed every 2-3 year. Jaguar usually states 2. However, it does take some heat to make even old the brake fluid boil and that would reduce brake force not increase it.

What exactly do you mean by "grab". Creaky stop or a definitely harder stop than expected? Some pads creak more than others especially coming to light-pressure stops. Also when braking lightly, you should usually be able to feel the pad warm up and increase in friction a little but definitely there. The car slows more quickly without more pedal pressure. In a manual, you would ease off as you came to a halt and maybe even stop with just about no pressure on the pedal. With and auto, this is not possible as we are always braking against the engine's drive at idle. We naturally tend to easy off the brake as we come to a stop, aiming for a smoother stop. If you have a sticking caliper piston, for example, it will not retract as you ease of and could lead to that feeling of grabbing. Check if a wheel is hotter than the opposite one or has more brake dust on it (better is to jack up and rotate by hand after someone presses the brake pedal and release it).

I expect you know all this - just more description about the exact symptoms might trigger someone to suggest helpful things to check.
 
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Old 03-13-2019, 09:00 AM
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Thank you. What actually happens is as the car is slowing down almost to a stop with my foot just resting on the brake pedal it will grab real hard and cause an abrupt stop. Not crazy just enough to notice that it's not smooth. I would describe it as a quick jerking motion.
 
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Old 03-13-2019, 09:41 AM
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Hmm, if the pressure isn't changing (you are not pressing harder to stop) it could be a warped rotor, but I would think you would feel pulsing as the car slowed down if that was the case. So, back to the pressure not changing, there are only 2 things at play: pads and rotors. As the rotors wear, sometimes they form a lip on the outside edge. You can reach in there and feel the rotor (when cold!) to see if this is true. Maybe your pad is catching on this lip somewhere. ??

I'd get a brake fluid flush done (just because it is recommended) and ask them to check the pads and rotors.
 
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Old 03-13-2019, 10:55 AM
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I've done countless brake jobs on all kinds of vehicles, calipers rotors pads for all different symptoms but I've never felt anything like this, it doesn't feel like is caused by a mechanical problem, I know it sounds nuts but it feels like it's getting some electrical signal and reacting.
 
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Old 03-13-2019, 11:09 AM
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Like the emergency brake assist playing up?
 
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Old 03-13-2019, 11:26 AM
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Drive it in the dark and watch the lights carefully. The ABS pump takes quite a lot of current and you may notice the lights dim for a fraction of a second as it kicks in.
 
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Old 03-13-2019, 11:28 AM
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Maybe, I'm just not familiar enough with this car yet so I do appreciate the feedback. I will add that to the possibilities. I bought the car in Maryland a couple weeks ago where the Maserati dealer I bought it from had just sent it through Maryland State Inspection which I was told is one of the most comprehensive of all the state inspection. I am waiting for my PA tags so I can take it to local Indy for PA inspection. They are very competent, I will ask for the brake fluid change and their opinion.
 
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Old 03-13-2019, 12:03 PM
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Semi-glazed pads and/or rotors? That stickiness can occur if new pads were not broken-in correctly.
 
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Old 03-13-2019, 01:59 PM
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Originally Posted by Cee Jay View Post
Semi-glazed pads and/or rotors? That stickiness can occur if new pads were not broken-in correctly.
The possibility of this should still be on the table. To eliminate it, go out and re-bed the pads.
Get the fluids flushed. Maybe foreign particulate in the brake system itself? A flush is needed anyhow, so clear that possibility off the table as well.

I wonder if a caliper piston could be sticking? Not a common thing I know... but....

You might turn DSC off, just to be sure some g-sensor isnt playing tricks on the system.

Vince
 
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Old 03-13-2019, 03:09 PM
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I think you guys are right on! I just got out of the car after a one-hour Drive, 20 to 30 minutes no noticeable issue, after that I started to notice the "stickiness" when rolling to a stop.
 
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Old 03-14-2019, 12:52 AM
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I just read the sticky on here about the zf6 transmission. Is it possible the jerking that I described could be the harsh down shifting from second to First that is described as a potential symptom of the faulty valve body. Is that something that would come as the car warms up or would that be there right from the beginning. Would there be some type of Code that pops up?
 
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Old 03-14-2019, 02:09 AM
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Sorry to obsess about this but the fear of having an issue with the transmission at 36000 miles is daunting. This forum is a wealth of knowledge and forgive me for throwing things out there but just looking for someone who might have had the same issue.
so after searching causes for hard downshifting between 5 and 10 miles an hour and only comes when the car is warmed up I found two other possibilities, 1 is the MAF and when I look at the Carfax I see that it was replaced once already in 2011 at 22000 miles at the dealer. Could this have been an issue once already in this car? The second thing I came across is actually a low battery. I know that low battery causes all kinds of issues, and as I said in the earlier post, as weird as it sounds it doesn't feel mechanical it it feels like a response to a signal it's received. Either way I will be changing the battery and making an appointment with my Indy tomorrow ( who luckily are transmission specialist.) Car has a 1000 Mile 30- day powertrain warranty which is still in effect.
 
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Old 03-14-2019, 03:02 AM
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Originally Posted by Kongo1 View Post
Sorry to obsess about this but the fear of having an issue with the transmission at 36000 miles is daunting. This forum is a wealth of knowledge and forgive me for throwing things out there but just looking for someone who might have had the same issue.
so after searching causes for hard downshifting between 5 and 10 miles an hour and only comes when the car is warmed up I found two other possibilities, 1 is the MAF and when I look at the Carfax I see that it was replaced once already in 2011 at 22000 miles at the dealer. Could this have been an issue once already in this car? The second thing I came across is actually a low battery. I know that low battery causes all kinds of issues, and as I said in the earlier post, as weird as it sounds it doesn't feel mechanical it it feels like a response to a signal it's received. Either way I will be changing the battery and making an appointment with my Indy tomorrow ( who luckily are transmission specialist.) Car has a 1000 Mile 30- day powertrain warranty which is still in effect.
Guy, this is your mind playing tricks on you. If it cant tell the difference between a brake grab and a transmission downshift, its being paranoid.
That 30 day warranty is weighing heavy on your mind, its a powerful force.
Relax, there is nothing on this car that is ticking time bomb. That transmission is bulletproof.
But have your mechanic check it all out.

Also if you want to know what the lack of a downshift to 1st feels like, drive it in manual and come to a stop. Our cars dont downshift to 1 in this mode for obvious reasons.
 
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Old 03-14-2019, 03:35 AM
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Thanks, you're right I'm definitely paranoid and my mind is racing. I believe it is a jerking and when I read the ZF sticky about jerking I did wonder. The thread on the MAF sensor said that it's a hard shift from 3rd to 2nd as you come to a complete ​​​​ stop and that this won't be detectable when the car is Stone Cold, only after it has been heated up and driven for a while. Another thread said that they were getting this hard downshifting when coming to a stop, they replaced the battery and problem disappeared.
​​​​​ I'm bringing it in, I'll report back what the issue is in case it could help anyone else in the future. Thanks again!
 
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Old 03-14-2019, 01:15 PM
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Update: Indy is 90% sure it's the lock-up torque converter. It is not the first time he's seen it in these cars, especially since this car was only driven 1500 miles a year for the last 7 years. Suggest trans flush and drive the car, see if it dissipates and go from there.
 
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