I have read up on the procedures for bleeding the brakes, but I am unclear on how to remove the old brake fluid from the reservoir. I want to completely renew the fluid. If I drain some and keep topping up with fresh fluid I will simply be diluting the old fluid but not replacing it. I am also concerned that pushing the old fluid through the system may not do some of the delicate parts any favours.
Any thought appreciated.

 

Hi Billy

You could try and empty the Reservoir by using a Syringe but with the best will in the World, I very much doubt if you would get it all out, as it tends to collect in all the 'nooks and crannies'

When I do mine, I put a tube on one of the bleed nipples and let it drain into a jar after pumping the pedal 20 times to depressurize the system.

But if the Brake Fluid looks really bad, then you could drain off the Reservoir and afterwards take the Reservoir off the Actuator, which is held on by a single screw underneath.

Though you have to be really careful, as when you 'think' the Reservoir is empty, there will still be a lot of Residual Fluid inside, to such an extent that it will start to pour out all over the place.

Whatever you do, Don't get any Brake Fluid on the Paint Work! or it will Strip the Paint in Seconds and ruin the Car.

Its certainly not a method that I would want to use because of that Risk.

A lot depends on just how bad you think your Brake Fluid is, so in that respect draining it off is much Safer.

Pack plenty of Rag round the Reservoir and in the Engine Compartment, with some Towels or Blankets covering the front wing and if any Brake Fluid gets on the Rag, always pull it out from under the Car.

I never wear gloves when Bleeding the brakes, as if I get Brake Fluid on my hands, I want to know about it.

Also keep a Bucket of Soapy Water handy, to keep washing your hands or deal will any accidental spills.

 

My thoughts on this would be:
If I was to disconnect the fluid intake hose at the pump and drain the reservoir from there, it would only partly gravity drain due to the pipe being approximately half way down the height of the reservoir. Whist this would be okay for purging air, it would not work for clearing the reservoir.
Therefore, below the reservoir is a flexible pipe leading to the fluid intake hose for the pump. If I was to undo this and somehow direct it into a container the reservoir would fully drain. However, the fluid in the fluid intake hose to the pump would also drain leaving air in the pipe. This being the case after reconnecting the hose below the reservoir it would be necessary to purge the air out of the pipe at the pump (this is set out in the procedures involving the motor/pump unit, fluid intake hose, or actuation unit).
Perhaps as an alternative method, a pressure bleeding system could be applied to the reservoir and drained/purged of air at the pump side.
With new fluid in the reservoir and all the contaminated fluid removed I could follow the normal bleeding procedures without fear of contaminated fluid being pushed through the system.
I have read sound advice regarding pushing fluid back from the callipers when changing the pads and to undo bleed screws and clamp the flexi pipes before doing so, but would have thought pushing old fluid through the system from the reservoir equally hazardous. Furthermore, I often see a brake fluid change being done whereby the reservoir is half emptied and topped up with new fluid and classed as a fluid change, which it is not.
I guess if regular changes have been done it is fine to do a drain through the complex XJS braking system, the problem is in many cases the fluid changes have been neglected and I suspect this in my recently acquired car.

 

Hi Billy

It all depends how far you want to go but before you start pulling off hoses, the System must be depressurized or you could have Brake Fluid squirting out all over the place and you do Not Want That!

Always have a big piece of rag in one hand ready to cover what you are doing (just in case something goes wrong)

There are No Second Chances with Brake Fluid, if it gets on the Paint its 'Game Over' so do keep that in mind.

That's also true of the Engine Bay, so pack plenty of rag round everything to catch any spills.

While there are a number of ways to empty the Reservoir and which way you do that is entirely up to you.

There will be more residual Brake Fluid left there in the Reservoir than you might think, so if you thought it was empty enough to pull the bottom pipe off, you could be surprised at how much still comes pouring out.

In any event the System will need to be purged of Air when you have put in new fluid and are ready to bleed the brakes, which includes purging the Low Pressure Side of the System up near the Pump.

Only you have any idea how bad your brake fluid is, so it is going to have to be your call which way you decide to go about that.

 

What year is your car?

 

Billy-wink,

If you read the manual, you'll realise there is more than one chamber in the reservoir. There are feeds to both the pump and the actuation unit and return pipes. So you can't drain the reservoir just off the pump intake hose.

If you have sediment in the reservoir, you'll only get it clean by removing the reservoir. If you only have old fluid though, you could remove most with a syringe, then top with clean and keep bleeding and filling.

If you don't remove the reservoir or completely drain it, you won't need to bleed the low pressure side. The fluid on that side will be cleansed anyway through thorough bleeding of the rear brakes.

Remember to use the Teves method, not the Jaguar procedure, to bleed the wheel circuits.

Good luck.

Paul

 

1989 (April)