88 Jag XJ6 power brake problem

The power boost has failed on my 88 XJ 6- self levelling suspension still works fine, and the fluid in the pump is ok- Any one know of some simple tests to determine the problem area? Thanks in advance.

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Most likely, if the fluid levels are fine but you are getting no boost -- the accumulator is gone. A simple test is to start the car and bring it all up to operating levels. Turn off the engine then pump the brakes. The pedal should not get hard for at least 15-20 pumps If it does, you will have to replace the black ball located on the right side of the car tucked up above the suspension. You can only see it from underneath.

Webserve

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On the '88 XJ40, the accumulator IS the booster!! Unlike vacuum/air boosters with a separate servo, the XJ40 uses a liquid booster system. The pump on the front of the engine creates the pressure when the engine is started. It builds pressure in the system to between 1200 and 1500 PSI, When you step on the brakes, this pressures is released to assist in the braking process. The accumulator is simply a Nitrogen filled ball with a rubber diaphragm. Over the years of use, the HSMO (mineral oil) permeates the diaphragm and releases the Nitrogen and thus the pressure.

If you are getting no power assist when the engine is off than this is most likely your problem. The system is designed so that in the event of engine failure whilst driving you will still have power assist with the engine off to aid in braking. I am surprised, however that you have no warnings as to low pressure on the dash. (note: actually, he did, but has a lot of extraneous warnings)

Webserve.

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I think if you ask Phil Prince at Motorcars Unlimited, he will say the same thing regarding the accumulator. It is an Extremely common problem with the '87, '88 and '89 XJ40 with the Girling braking system. Also go to

and search the archives for "accumulator" You are best off searching the Moderns group since your symptoms were discussed for months, 4-5 years ago.

Get an after-market unit. They generally run $250-$300 depending. You want the JLM11659 NOT the JLM1904. The JLM1904 is for the 1990-1994 Teves system and won't work on your 3.6 litre. I bought mine from these guys

back in 2001. I bought the JLM11659R because it was less AND it is rechargable. It also carries a slightly higher pressure so the pump cycles less. Current price is $192USD plus around $10USD shipping. I would think you can get the same deal or close here in the States. Another easy test, although not AS easy, is to pump the brakes til they get hard and then simply remove the accumulator. You will lose very little "Green Blood" Take a pencil and with the ERASER end of the pencil, slide it into the opening. If it goes much past the threaded collar and into the ball itself, you need a new accumulator. With 1200 PSI on the other side of the neoprene diaphram, the eraser should hit rubber nearly immediately after entering the chamber itself.

In terms of the problem being with the booster -- it is possible -- but I doubt it. I have yet to hear of a booster being a problem with these cars, but I am sure someone - some where has had the problem. The accumulator, however IS a common problem.

In terms of doing re-solder work. I have often wondered, after spending time on these cars, how the Brits keep aircraft in the air!! Usually, if you are having a bulb failure warning, it is the module that needs a re-solder. Anti-lock is usually the tall relay by the petrol inlet in the boot. Pads low usually means the wire has broken on one of the 4 sensor wires. The clock re-setting to 12 is re-solder. Usually anything involving a circuit board can be corrected with a re-solder.