94 XJS V12 no power brakes , weak brakes
 

All, the brake pedal feels like there is no brake boosting going on. Furthermore, the brakes don't seem to grab well. These are two different symptoms as I owned a truck that lost its brake booster but could still stop pretty well.

I assume the culprit for the brake booster is the accumulator under the hood on the passenger side. Would this be correct?

If that goes, should I still expect to have good unboosted brakes?

If there a special procedure for removing it?

Thanks

I'm not at all familiar with the face-lift XJS or its ABS/ boost system.
Assuming it is a fairly standard hydraboost system I would check to see if you have pressure coming from the power steering pump.
The accumulator generally acts as a reservoir so you have boost in the even of a failure in the boosting system or if the car shuts down, the same way a vacuum boosted system uses a one-way valve to allow manifold vacuum in, but not out in case the engine shuts down at speed.

So if your accumulator was busted you would not have reserve boost, the brakes will be unassisted as soon as the car was shut off.
Whether Jaguar has some strange setup where this works differently than usual, i dont know. this is an ABS system from the 80s, which means its not at all standardized.

You can't really compare your truck "grabbing well" to the XJS. While you may need new pads or your calipers may be frozen up, its also likely your truck would have been easier to stop regardless, because calipers require much more force than drums, and odds are you truck had rear drums. Not to mention your truck probably had single piston sliding calipers instead of dual and quad pistons like the XJS does.

Sorry I don't recall diagnostics for hydraboost very much, obviously check your line, PAS fluid level, and make sure there isn't air in the system.

anyone else please feel free to correct me one anything, I really don't know the specifics of the XJS abs system or later boosting system

The booster on this is a Teeves pressure pumped system and not a standard vacuum boosted system. The black ball on the passenger side is an accumulator so that the pump does not run all the time. You should hear it run for a minute or so but should not run with every press of the peddle. However, it can affect the boost, it is not that dramatic. If braking effort is high, then I suggest that possibly one or more pistons are stuck in the calipers due to worn seals and water/rust on piston/caliper limiting disc clamping pressure increasing brake force. I know, cod after rebuilding my calipers, the brakes worked so much better :-) .

Thanks guys, the brakes will grab if you push hard enough. I replaced the accumulator with a junk yard one which did not help , but that means nothing as the junk yard one could have been bad too.

Check engine light also went on with an FF67 code. Plenty of work to do.

I would say remove a caliper to check out what the pistons and seals look like on the face, but that is a much bigger pain in the ass than usual because of the way the front calipers tie into the steering system.

All, thanks. I think that the first thing to address is the booster, once addressed, if i still ahve weak braking then I'll get into the calipers.