Brake accumulator discharge off car

As I continue to work my way through my car’s maddening brake system, I’ve determined that I believe my brake accumulator ball is bad. Luckily for me, I have an extra accumulator assembly from a spare. Unfortunately, I have no idea if it was discharged before the assembly was removed. As I’m still trying to wrap my head around exactly how the system functions, can someone tell me if there is a way to discharge it off the car so that I can remove the accumulator? If its not discharged, what will happen if I try to unscrew it from the assembly body? If I can confirm the spare is good and swap that into my car, I could potentially save myself a good chunk of money.

Hi Brett. The sphere is charged with nitrogen to some astronomical figure, easy check is if you cannot insert a blunt probe into the sphere then it is charged, if there is very little resistance throw it away. When you say you have a spare assembly, are you talking about a complete master cylinder set up?
If it is there is no problem unscrewing the sphere, apart from the torque required to remove it. Clamp the assembly in a vice and fang away on it.

Thanks for the quick response Robin. Yes, I have a spare of the complete set up just like the one in the attached picture. I had planned to perform the probe test, but want to make sure I can separate it from the assembly without the almost 600 psi internal charge shooting it like a rocket across the room and taking my hand with it.

Pulled the sphere off the assembly today without issue. Now I’m wondering what the point of depressurizing the system is. Is it just to prevent the fluid from spraying out when you disconnect the lines? Anyway, my spare is bad too. Looks like the internal diaphragm is ruptured since my screwdriver basically fell straight through without force. Now to buy a new replacement and get this brake system one step closer to factory spec.

Brett, don’t get confused by the term de-pressurise. This has nothing to do with the sphere per se it is the hydraulics in the braking system that is under pressure from the pump. Just make sure before you start that you have pumped the brake pedal sufficient times with the engine off until the pedal goes hard indicating that there is no further assistance. Once you have reached this stage you should be good to go. Just be aware that the early spheres are a different thread to the later ones. I’m not sure when the change occurred.

There are some posts n the XJ40 archives which refer to that subject. Here are a couple of examples -

Thanks guys. That does confirm for me that the threads were indeed changed starting in 1990. I’ll have to take that into account in my search since most websites list the same part number for all years.

Hi All,
I also had to replace my accumulator, did it myself took about 30 min.
You need to depressurise to allow the oil to leave the accumulator - although with a dead accumulator its still full of oil even after de-pressurizing. I have a 1988 model and ordered it from Australia - less than half price of Jagbits - shame as i would rather have bought here. The one i bought is identical and much easier to get off than i thought it would be. The later ones dont fit as the 1988/9 models have a larger diameter connector with a nipple built in. The replacement was made in 2016 so not too old. Pedal is soft and no more "low pressure’ warnings. Hoping that cures the banging of the hose that feeds the valve block from the engine pump
There was such much oil and in parts black liquid i suspect the diaphragm is shot.
The working pressure is stated as 210 Bar - with a test pressure of 315 bar. Its made by Exotech with BK 283138 stamped into it
Need to buy some fluid to top up - luckily still above min level.

Ian, where did you buy it from? I need one too for my '89.

HI Zigmund
I bought from a guy in Australia - on ebay

Guy ships to USA no problem. Took about 10 days. Unit was made in 2016 from memory so not old stock. works a treat and is exact same fitment.

did you buy one? You went rather quiet?