Last week I had my brake fluid replaced, think they say do it every 2 years. No significant difference, but I do have a question.

The other day I noticed how hard I have to hold the brake to keep her from moving foward. I decided to check something as if I was checking stall speed. I put foot on brake and gave her a little gas. It takes an enormous amount of effort on the brake pedal to keep her from moving forward. Truth is I did not check stall speed, I was more concerned with whether the brakes should be losing or not in this kind of tug of war. . .

I didn't want to stress anything too much, so I didn't floor it or anything. Let me ask:

Should the brakes be able to keep her from moving forward even with significant throttle? I would have thought so, but this concerned me so I better ask. I recognize that this is not very scientific, I can't say how much throttle was applied, got nowhere near flooring it, and like I said I wasn't watching for stall speed, but wow it took a lot of brake pressure to keep her from moving.

Brake pads are not too worn out, if this is not right where should I check first?

If my "test" was too non-scientific to be of value, is there another way to test brake pressure needed to make sure things are OK?

Can I activate anti lock while driving? Yes. I've always noticed that the brake pedal is much higher after such an exercise though. (we all discussed this once, don't think it is any different than other cars)

Thanks, I appreciate your help.

John

 

That sounds wrong, the brakes should be able to hold the engine back, however I have not tried it on the XK8.

 

Racediagnostic's, yes that's what I thought too. Improper choice of brake fluid could do this could it ?

 

Or not bled properly.

 

Thanks Chris

 

FWIW, I felt my new-to-me car was initially very "heavy" under breaking. Felt like I was driving a fully loaded truck outfitted with normal car brakes. A bit too much pedal travel, too. I ended up doing minor maintenance of the brake hydraulics: with the assistance of a helper, I went around the car and bled each caliper. I started the procedure by gently tapping the caliper with a hammer to dislodge any bubble, then did the usual routine: fit the transparent plastic tube on the bleeder, apply pedal pressure, open bleeder, check for bubbles, then close the bleeder. I did this a couple of times after the bubbles went away. Kept an eye for the reservoir level, too. The net result was a much better brake feel after this procedure. Together with the throttle cable adjustment, the car feels completely different, the way Jaguar intended I suppose.

If it was me, I would check the brake switch once again. Normally, you would have messages if it failed, but I am not sure those messages show up instantly when a fault is detected. A faulty brake switch might possibly fail to inform the transmission that the car is breaking, and possibly make the car feel like it wants to lurch forward. Brake switch failure are very common.

Also, I would check the brake booster. It is vacuum based, so I would check the vacuum line to it for any leak. I suppose the booster could be faulty, too, but it is less likely.

Best of luck, keep us posted.

 

The pedal should feel firmer after a fluid flush but, assuming no other faults have developed in the braking system, it shouldn't take any more effort to hold the vehicle.

I'd suspect air has got in during the bleeding. My preferred method is to use an 'Eezileed' kit which ensures the fresh fluid is delivered under pressure:



This is my XK but it works just the same on any vehicle. Makes it a single handed job with no need for any pedal pressing.

Graham

 

Graham, Fmertz,

I sure do appreciate your help. I'm headed back to the mechanic tomorrow morning. Normally I would like to do this myself but I paid for it and they aren't too far away.

Does anyone remember a post from another well respected forum members that mentioned "a quirk in our cars where the caliper needs to be tilted" or something like that to best bleed one of the calipers ? It was quite a while ago but I remember something like that. Wanted to see if that rang a bell.

Thanks again John

 

John,

This is possibly the thread you recall in X308 forum:

https://www.jaguarforums.com/forum/x...kes-xj8-55730/

See post #4 by Sean B.

Graham

 

Graham, you are amazing. Don't know how you found it, but wow - Thank you. I'm off to the mechanic now. Will let you all know how it goes.

John

 

Just got back from the mechanic. Looks like FMertz gets the gold star this time. They spent 45 minutes bleeding the brakes. Looks like that was the issue, brake is now high, firm, and give the driver more confidence. Thanks everyone for your comments.

Could I still overcome the brakes with the gas pedal if I wanted to? We will never know my friends :-) I'd have to give her some serious throttle (crazy idea) and I can't imagine the unnecesary stress that would add to everything. Before the bleed it was different, a "reasonable" amount of throttle overcame the breaks way too easily. I had to stand on the break to get close to "winning" that battle.

John