XJ40 removing the old hydraulic system

Hi, I am converting the old brake master cylinder hydraulic system to the newer vacuum master cylinder there are 4 connecting hydraulic pipes two of them go to the braking system and two go to the sphere and the green tank. My question is if I leave the pump in at the front of the engine do I have to join the two pipes together or can they be blanked of individually? The brake pedal is hard I have connected the vacuum line so waiting to test the system. By the way I have converted the rear suspension to coil overs and blanked of the pipe that goes to the rear this is ok. It seems that the pump at the front of the engine is connected to the air con ? Please anyone can help. Thanks.

Since you refer to a “green tank”, I am assuming this is the early XJ40 system where the hydraulic pump ran the self-leveling and the brake system, right? Hydraulic servo in between the pedal box and conventional master cylinder, right?

Kevin, this is outside my area of experience as my 1994 model does not use the same hydraulic system as your 1987 (no HSMO a/k/a green blood). I do not believe the hydraulic pump would be connected to the A/C system. Perhaps this info from the ebook on the former Jag-lovers site will be of help:


Your description is correct it’s the early system. My only concern is the front pump and the two pipes do I link them together this way I don’t have to remove the hydraulic pump correct?

I did my 89 and removed the pump, easy to remove and no wear on the engine.

Hi, did you notice the large pipes going to the Air con system? I will take some pics today and show you the pipes as I think they are air con pipes if not I will remove the whole system. Did you have to blank off where you took off the pump at the front of the engine?

There is no connection to the AC system. On the early car, if you don’t need the hydraulic pressure for the brake servo or the self-leveling, you can remove the pump. The blanking plate is long discontinued but it not difficult to make.

Yes you are correct my mistake. I have managed to remove all of the old system and have made a blanking plate for the engine pump. The only thing now is the low pressure and low oil alarm to fix I think I can short out these at the wires correct? Thanks for your replies they really help.

I think the low pressure light comes on with continuity on the switch as is opened to turn the light off.
Really straining my brain but I THINK the low hydraulic fluid is the same.