I was driving my xjs yesterday and the front end suddenly started vibrating like a bent wheel. I stopped, looked it over, and spotted nothing. I was only 1/2 mile from home, so I limped home. However at the first stop sign I discovered I had no brakes at all, went to the floor. After brake loss, vibration went away. Checking out today I find brake reservoir full, no fluid on floor, none on tires or around rear calipers. Tried pumping up brakes, which got partially full. But a leak appeared, spraying from the top of reservoir cap vent. Some way bypassing brakes, but overfilling reservoir. I have no idea what might be at fault here. Other threads done refer to this that I have found. Help! Any ideas?

 

Hi Coolbreaze

Possible Stuck Front Caliper (and or Brake Pad) which was causing the Brake Fluid to Boil (especially with old Brake Fluid) that may have collected moisture

That would certainly do it, as the same thing has happened to me

Did you notice any funny smells or notice one of the Wheels was getting Hot?

When was the last time you changed the Brake Fluid?

Did you recently change the Brake Pads for any reason?

Do the Brake Pads look evenly worn? Not only on the Same side of the Car but also compared to the other side of the Car

Do the Rotors look scored or worn?

Has there been any long lay off since you last drove the Car?

Did the ABS Light come on at any time?

Can you or could you hear the Brake Pump running and is it getting Warm or even Hot?

Other things it could be but if any of the above applies, this would certainly help to sleuth it out

 

I checked the calipers, not stuck, rotors not scarred,wear is even, new brakes 2 years ago on rear. Car hasn't been driven for a couple of months. I didnt check the pump as yet. Could be very wrong here, but doesnt the pump only supply fluid to rear? Fronts dont work either. Abs did come on. I still can't figure out how fluid eventually when pumping brakes, ends up overfilling the reservoir. I will check the pump for sound this weekend.

 

Hi Coolbreaze

Although the Front Brakes are Conventional, you need the Brake Pump Running to Re-pressurize and Replenish the System as a Whole

Where you may have noticed if/when you have Bled the Front Brakes, as soon as you turn the Ignition On the Brake Pump will start running to Re-pressurize and Replenish the System

The Brake Pump should also cut out within 30 Seconds or it may Start Overheating and in the event it doesn't do that (cut out) then switch off the Ignition and let the Pump rest for Two Minutes before you try again

In Terms of Air in the System the ABS is not very forgiving and so whenever you Bleed the Brakes ALL the Air must be out, or you'll run into problems

Where if you've ever let the Reservoir run out of Brake Fluid, then you will also need to Bleed the Low Pressure Side of the System or you could easily find yourself in a never ending loop of Rinse and Repeating, getting nowhere!

One other possibility, is a loose or possibly worn out Wheel Bearing, so Jack up that wheel and see if you can Rock it from side to side or pull it back and forth, as anything in that area that can generate Heat can Boil the Brake Fluid

And almost instantly leave you with your foot going down to the Floor and no Brakes at all, as even the Front Brakes need to have Fluid to work

So I would say your First Priority is to Check the Brake Pump, to make sure that it runs but also cuts out after 30 Seconds and also make sure that the Brake Pump does not Start to get Hot

As if it does then that Brake Pump is living on Borrowed Time before it Burns Out!

Where you won't be able to get another one anytime soon, as they are NLA