I recently bought a 1988 XJ40, 3.6L here in California.
It was a non-runner, but has not taken much to get it purring.
The biggest concern remaining is the feel of the brake pedal. Sometimes, especially at the start of a drive, the feel and response is fine, other times the pedal goes down too far and braking is minimal, a quick release and repress of the pedal always restores braking. I have bled the system twice, very little air comes out.
I have spoken with the seller and he states that the brakes were fine, but the master cylinder was leaking and this was replaced at a local tire shop. The bled them twice, perhaps even tried a second m/c, but never got them 100%. He learned to be ready to pump the brakes at times and never got them sorted. I have details for the tire shop and will call them this week.
This car is equipped with the hydraulic booster system, driven by a pump mounted on the engine. The self leveling rear suspension has been removed. The mineral oil level was low when I purchased and I have topped it off (took 1 litre of fluid).
I seem to recall that on one bleeding attempt, we had the engine running and the pedal feel was sometimes hard, sometimes soft and when the bleeder was opened after a soft pedal, there was typically no fluid coming out of the bleeder.
I am thinking that the master cylinder should have been bled on the bench and there is air in it, or it is faulty?
The plan this week is to call the tire center, then install speed bleeders, crack the unions at the master cylinder to bleed it, then bleed each corner again.
Any other thoughts or suggestions?
Presumably any faults with the hydraulic servo system would mean that the pedal feel was inconsistent, hard or soft, but there would always be braking action and fluid moving, which does not seem the case on soft pedal presses here?
John …
I think you’re correct in you deductions when you say :
“Presumably any faults with the hydraulic servo system would mean that the pedal feel was inconsistent, hard or soft, but there would always be braking action and fluid moving, which does not seem the case on soft pedal presses here?”
Remember all the hydro system or a vacuum system does is reduce the effort required to push down the brake pedal. I’ve replaced my master brake cylinder twice and even converted my brake system to a vacuum booster assist and always bleed my brakes at the calipers with no problems.
The fact that your pedal gets soft and travels too far leads me straight back to the master cylinder.
Thanks for the reply and the support. I hope we are both right on this one.
Do you think this could be just air in the master cylinder, or is it a faulty unit?
I see discussions on bleeding it in the car by cracking the unions on the m/c where the pipes exit and allowing air out there, so I will start with that. Maybe I need to remove it and bleed it on the bench though - I need to research that in more detail.
What about the ABS unit, on other (newer) cars there seems to be instructions to bleed them in all manner of complex ways, but for this car, it is never mentioned?
I think one more attempt at this, bleed the m/c in the car, bleed at each corner, along with cleaning the ABS sensors and pad wear sensors (intermittent pad low and ABS failure messages too), removal of pads and lubricating of slide pins, before I try removing the m/c and bench bleeding/confirming it is consistent when isolated from the system or not and needs replaced.
Never a dull moment 
John …
It can’t hurt to gravity bleed the master cylinder and then do the normal bleeding starting with the wheel furtherest from the m/c and working your way in. It still sounds to me like a bad master cylinder. If you have air in the brake lines it is going to act the same way every time you press the brake pedal. Not so much with a faulty master cylinder.
Brake pad low light … the way this system works is the the sensor on the brake pads (a small piece of metal) provides a closed circuit and keeps the light off. When the pad wears down to a certain level the rotor will rub on that piece of metal until it wears out and opens the circuit which then turns on the warning light. I’m not sure why you would be getting an intermittent light but that is the first place you should look.
ABS Failure light … Cleaning the ABS sensors is a good idea, very easy to do and as a last resort you can even check each sensors resistance at the control module in the trunk with a multimeter. But after cleaning the sensors if you are still getting that Antilock light pull out the ABS over voltage relay. It’s located in the trunk behind the carpeting just forward of the fuel filler pipe.
Take some test wires and apply 12v from the battery to pin 86 and pin 31b (the pin numbers are on the cover of the relay). You should hear the relay click or you can check for continuity between pins 30 and 30a. If you don’t hear the click or the continuity check shows an open circuit you’ve found the problem. Even if it checks good I would still take the cover off (you may have to cut away the sealant) and reflow the solder on the printed circuit board. while it’s apart make sure you check the fuse which may be an actual glass fuse or a piece of wire. if the fuse is good I bet resoldering the PCB will solve your problem.
John. Just thought I would mention that to bleed the rear brakes in your car the Jag manual calls for you to have the engine running to give a little more power when you depress the pedal to clear out any air in the system.
Thanks guys, Looks like I will be calling the tire guy, confirm his install technique, try bleeding the m/c alone (Cardone suggests plugs for the bench bleed, so maybe I can rig something with bleed screws or old, flattened pipes) followed by each corner. If not, I will take it out, mount it in a vise and see how it feels there. Pleasantly surprised to see remanufactured versions for around $60.
The pad low is very intermittent, and all pads look great, so thinking it is a bad wire/connection somewhere, wish the message suggested a corner!
The ABS message is even rarer, and hoping it will clear after sorting the pedal feel, but may as well clean sensors while each wheel is off. I had the relay out for a quick clean of the terminals on it and others, but appreciate the detailed instructions on the internals. Re-soldering does seem a common answer to its problems. Is there another relay on the car I can swap in to see if that cures it?
H S, thanks for the suggestion, and for not suggesting the electric pump will do it at position II, but I have already tried that. Will likely use that again for the next attempt.
I will get ot this in a week or two and update after that.
Hi John. There is a very good chance the intermittent pad wear warning light is due to a poor connection at the plug where the sensor lead connects to the car. It is a two pin plug and when it is disturbed for changing the pads ( you mention the pads look almost new ) sometimes the pins fail to make good contact when it is reconnected even though it is pushed all the way home. I cured the problem on my car by putting a single strand of very thin copper wire into the sockets so the pins were nice and snug when pushed home.
You say you have bled the system twice and ’ very little ’ air comes out. There should be no air whatsoever in the system for it to work properly and for the pedal to maintain a consistent feel.
Also, if the car has stood for a while you should change all of the fluid in the system. If the fluid is old and has absorbed moisture from the air it will turn to steam in the brakelines as it boils causing the pedal to go right down as you describe.
If the symptoms re-appear a short while after you have changed the fluid and after you were certain there was no air coming from any of the nipples after bleeding it in the way the manual describes, then logic says the master cylinder piston seals are not doing their job and it will have to be bench stripped. However, before stripping it off the car, it’s worth checking the system for any air one last time, just in case some has found it’s way in. if you do find any air bubbles check all the pipe connections to the M/C thouroughly. The air must be getting drawn into the system somewhere, and as the mc has recently been ’ repaired’ I’d definitely be checking everything that the tire shop did or didn’t do.
Well, it took a while, life got in the way, but I finally got a chance to get back to work on the car.
Following a chat with the garage that had performed the original master cylinder replacement and the owner, it was clear that they had a good idea of how to do the job well enough, and the brakes had been okay before they started, just fluid was leaking. They had ordered another replacement, but the last owner never got around to taking it back in. Based on that knowledge, and seeing a reconditioned m/c for under $50, I ordered a replacement.
Fitted that today. Bled it on the floor of the garage first, in a vise, blocked off one port to match the arrangement on my car, and fitted two speed bleeders to the other two ports. Bled quite a bit of fluid through those, until air free, before moving it to the car. I do see mention of easier bleeding using a big syringe, but did not have one to hand.
Fitting in the car was eased by having an assistant depress the brake pedal, pushing the rod out of the booster unit making it easier to fit into the m/c. Bolted it loosely to the booster, then removed speed bleeders one at a time and fitted brake pipes in, then tightened the bolts to the booster (this allowed a little movement in the unit when connecting the brake lines).
All felt good (I had actually also bolted it tight to the booster with the speed bleeders still in place and confirmed the pedal was firm, and therefore the m/c was not leaking internally) and I actually took a trip round the block to confirm the pedal remained firm and consistent and braking was efficient.
Back into the garage, wheels off, swap in the new speed bleeders, bleed each corner, then I took out each abs sensor and cleaned the gunk off them, then took each caliper apart and cleaned and lubricated the moving parts.
A longer test drive confirmed typical braking, if not the best stopping power, along with consistent pedal feel, they worked first time everytime, so I am crediting the master cylinder change with correcting the inconsistent pedal feel.
Unfortunately the anti-lock failure message came on, went off and came back, so more research needed there, outer coating of some wires was missing/cracked.
We also leatherique’d the seats, lubed the sunroof channels and fitted the antenna grommet, so more small steps have been made.
Need steering rack boots, then attention to the a/c before it gets too hot here.
John …
“Unfortunately the anti-lock failure message came on, went off and came back, so more research needed there”.
Did you the pull the ABS over voltage relay and test it according to my instructions … hmm.
LOL, it’s on my todo list. The test drive was at the end of a long tiring day and the pain in my limbs brought down the curtain on any other investigations.
I was just enjoying the fact that I had cured one problem with the m/c, but had found another with the steering rack boots. I was also happy to see only one error, no mention of low pad that had appeared before too, so jiggling cables had presumably helped there.
Small steps, but we will get there.
John …
Owning an older Jaguar isn’t a battle, it’s a war. And each victory gives you the courage to continue to march forward.
Fingers crossed, all is sorted on the brakes.
I did re-flow the solder in the relay, and bled the brakes again, fitted speed bleeders, etc. Also had to replace a rear hub, where the wheel studs were spinning. Fitted new steering gaiters as well.
Planning to drive her this week and see what else might need attention - A/C definitely needs fettling.
At least there are NO error messages on the dash once moving!