As I've been having a hell of a time trying to diagnose squealing for nearly the past year, I've been paying very close attention to my brakes and how they perform. I've noticed something interesting...the ECU or something in the engine management system has an effect on full stop braking power. This may be old news to the more experienced folk, but it's still a mystery to me.

I've noticed that any time I do a hard reset on the battery, the brakes operate much more smoothly than usual, at least for the first day or two, until the computer settles back to normal. It's hard to explain, but the braking becomes effortless and just glides to a complete stop, with no groaning or jerking at the end. Its as if the engine is using its own power to assist in the smooth transition from braking to idle. Usually its very difficult for me to come to a smooth stop without a little jerk or groan, even before I started having squealing issues.

This also happened when I put in a new MAF sensor a few weeks ago. For the first few miles, I noticed the rpms would gently feather down to idle when coming to a stop. Effortless, quiet, smooth braking power.

Mind you, the problem I speak of is only when coming to a complete stop. Initial braking power is excellent. I just recently put in new pads and rotors, which seem to have greatly reduced the squeal, but it's still very difficult, if not impossible, to come to a smooth stop. I'm hoping the new rotors just need some time to break in.

So what is it in the system that causes this effect? Why do my brakes temporarily work better after a hard reset or the MAF change?

 

I just thought of something...could it have something to do with the throttle plate position? If the throttle stays open a bit more than it should at that particular moment just before entering idle position, that might cause the problem, no? I assume a new MAF sensor or hard reset would have an effect on throttle position, at least temporarily.

If this is the problem, how would I go about testing or fixing it? Perhaps I should do another hard reset and perform the throttle position relearn procedure, although that's never really shown me any difference before.

 

Jaguar's Press Release at introduction;

"JAGUAR INTRODUCES ALL-NEW 2004 XJ RANGE FOR 2004

Assured stopping: Four-channel ABS with Emergency Brake Assist (EBA)

Across the range, the new XJ is equipped with a sophisticated four-channel anti-lock braking system (ABS) as well as Emergency Brake Assist (EBA). The new ABS system operates in a more refined manner than previous generation systems.

EBA helps the driver in an emergency when maximum power isn’t being applied. Often in emergency braking, the driver does not press the brake pedal hard enough and, if this occurs, EBA steps in to help. New travel and pressure sensors on the booster and brake master cylinder sense emergency braking by assessing the urgency with which the driver hits the brake pedal. Maximum available braking power is then instantly applied.

The new XJ also features an impressive array of electronic driver aids, including four-channel anti-lock braking (ABS) with Emergency Brake Assist (EBA), the former a latest generation system that operates in a more refined manner than previously. (this is NOT the Electronic Parking Brake)

EBA helps the driver in an emergency when maximum power isn’t being applied, assessing the urgency with which the driver hits the brake pedal and instantly applying maximum available braking power if it is needed."

If you vehicle is equipped with adaptive speed control, you also have IBA, (Intelligent Brake Assist) which uses the radar from speed control to sense distance of objects in front of the vehicle, even is the speed control system is not being used.

The rate in which you transition from gas to brake, decal rate, sensor input and it's initial application will all affect this. Also, keep in mind the specified brake fluid for these vehicles is not just DOT4, but DOT4 LV that must meet ISO 4925 Class 6. The viscosity of this fluid is much different, and braking performance relies on it.

 

I do not have adaptive cruise control. Thanks for the info, but I'm not sure how it relates to my question. Are you saying that my ABS may be malfunctioning?

 

My very first question is, if you have changed fluid, (and it is specified every 2 years) and have you used Super DOT4 LV that must meet ISO 4925 Class 6. If you have, did you use standard DOT4 or Super DOT4 Class 4, rather than low-viscosity Class 6. It cannot be found in your local parts store. The viscosity of this fluid is much different, and braking performance relies on it. All X350's have EBA.

 

Yes, I did that a few weeks ago during my crusade against the squeal. Also rebuilt my front calipers at the same time, per your suggestion on the other thread.

I used Pentosin Super Dot 4.

 

I think if you look on the can it is Class 4. Same as all standard DOT4. You really want Class 6. Other automakers using this same system, like VW, BMW, etc... their owners also complain of strange performance issues when using not using the specified low-viscosity. Both ATE SL.6 and Pentosin LV are rated well, and meet the spec. I use the Pentosin LV myself, and bought a 5 liter jug.


http://www.ate-na.com/www/ate_us_en/...bf_sl6_us.html

 

How would the type of brake fluid be affected by hard resets and MAF sensor changes though?

 

There is a lot of things going on after a reset, and I cannot say this with assuredness, because I haven't tried it, but I would suspect until the relearn process happens, it may be in a default passive mode, until relearn. ECM plays a role. Next time you change fluid, I would highly recommend using Class 6. In fact, that is the specified fluid for this braking system.

 

Could it be a small air leak? (Affecting the brake servo.)

Easy to check fuel trims to rule it in/out.

 

I've checked the fuel trims. Seems well within limits both at idle and at 2500 rpm. I've also gone over all the vacuum hoses, brake vacuum hose, and double-checked the torque on the intake manifold bolts. No leaks that I can find.

I've also done the sinking-pedal test to see if the booster is working properly. I even did the dollar bill over the exhaust test to see if I had a burnt valve! Everything checks out.

Would back pressure from a partially clogged catalytic converter cause anything like this? Just grasping at straws.

 

When you first started the thread about your brake squeal, I tried a couple of times to point you to the pads, even recommending original Jaguar parts. It appeared that you didn't want to hear those advising you about the importance. I then took the time to explain how noise is made in that area, and certainly recommended a complete approach, including proper service of the caliper, which should be part of every brake job, and the most ignored, and now we get to the fluid itself. I understand what you are doing, is grasping for straws, and may not understand the importance of the ABS system itself, or the features Jaguar has utilized in the operation.

I'm not sure what you are trying to fix, is actually broken, but I will say that not using the specified pads and fluid, does affect the overall performance.

 

Resetting the car, MAF, and all those other engine related changes are NOT affecting your braking. As you pointed out, if the engine is idling faster, it may feel like it is braking differently, but that is not a change in the braking, but rather a change in the power the engine is keeping on the wheels as you stop.

If you have doubts, try shifting to neutral and then compare the braking before and after a reset.

 

ESP and ABS is part of the Dynamic Stability Control. They do affect the booster and overall braking.

http://www.car-engineer.com/esp-elec...ility-program/

 

It will of course idle faster if there's an air leak.

 

Everything that you suggested on the other thread, I tried. I even rebuilt the calipers and changed the pads per your suggestion. The caliper rebuild and fluid flush did nothing, but changing the pads back to semi-metallic did, albeit not being OEM Jaguar pads. I flushed the fluid, but with Super Dot 4, as I thought that was what was called for. I was unaware that it should also be a Class 6, so I thank you for pointing that out.

Now, regarding your tone and approach...I'd like to believe this is a gentleman's forum. We're all here to help each other in any way we can. I apologize if you feel I ignored your advice, but if you go back and reread that thread, you'll see that is simply not the case. I am simply trying whatever I can do at that moment.

Now back to the topic at hand, I'm assuming my next step should indeed be to flush the fluid out and replace with a Super Dot 4 Class 6, correct?

Yes, that's exactly what I was trying to say! Thank you for explaining it in a way I couldn't.

 

" Effortless, quiet, smooth braking power."

Why would you replace your brake fluid with class 6 , it was designed to aid in the ABS operation .

You are not activating the ABS under normal braking conditions .

And BTW ,

When you ask for help or advise on this forum , it is given with their best intentions and capabilities - for free !! . Even when you were told by FIRESTONE to replace your pads in regards to squealing brakes , what did you do...............you replaced the front wheel bearings ?? , don't go blaming others for their attempts to help , even if they are RIGHT or WRONG .

 

I understand your frustration, and I didn't mean to sound crass. Sometimes what is typed doesn't always convey the spirit behind it.

You are asking me for complex diagnostics, without seeing the vehicle, or having done any type of diagnostics, or test drive to even confirm any type of issue. What I've been trying to tell you in this thread, is that there are complex systems going on with regards to the braking system itself. There is ABS, ESP and TCS, EBA and ECU involvement in the way this vehicle stops. Sensors in the master cylinder, the brake booster, various other sensors like speed, yaw, decel... If it thinks you haven't applied enough pressure, it will itself.

Before spending any more on other things, I would certainly get SDD out and start looking for snapshots or stored codes. If there are no codes, maybe take it by a Jaguar dealer and get someone to ride with you, and offer their advice. Without a test drive, I'm reluctant to advise you further on this.

 

What in the world is going on here? Who did I blame?? I never blamed Box for anything. And I replaced the wheel bearings first because they arrived first. I ordered them on the same day I ordered new pads. It was always my intention to replace the pads.

I don't know where all this hostility is coming from. I never accused anybody of anything, and I just in fact apologized to Box for any misunderstandings. I am not asking for complex diagnostics or for anybody to take responsibility. I am asking for a brainstorming session. I'm asking for any and all ideas. And that's where it stops.

Mods, please close this thread. Things have gotten way out of hand for some reason.

 

" Everything that you suggested on the other thread, I tried. I even rebuilt the calipers and changed the pads per your suggestion. The caliper rebuild and fluid flush did nothing,"