OB,

Well done on getting that union undone! Oooh, those threads look nasty! Not surprised it was tight!

Tks for your thoughts, but I'm no more of an expert on the 1995.25 system than most people here! However, it is a simpler system than the earlier system.

Also, don't underestimate the power of the servo. As I said, it runs a 6.5:1 ratio of assistance.

I also noticed that reservoir is way above the Max limit, so your hard pedal could be a vacuum lock when you press the pedal. You do need to have an air gap in the reservoir when the cap is on. However, you've got the fittings off now, so let's test that one out later.

I would do the following now:

- Leave the reservoir cap off, plug the rear port that you already had disconnected, put a container in front of the front port (or connect a short pipe)and gently press the pedal fully down. You should get a constant spurt of fluid coming out. If not, release pedal fully, wait, then gently press again, and again and again until you get a solid flow. I prefer not to flow the fluid back to the reservoir just in case there is any sediment in the m/c that contaminates the fluid. If you can do it with a clear pipe, so much the better as it's easier to see air bubbles.

- Once that is done, plug the front one, open the rear one and repeat the sequence.

- Once the rear is also flowing fully, undo both unions and repeat and check you have a nice constant flow of fluid from both ports under gentle pedal pressure.

- Plug both ports, pedal should then be rock hard.

- Start engine, pedal should be very little different.

- Only assuming all the above is satisfactory, reconnect the original pipes. Then bleed all the wheel circuits fully, as you will be probably have a tiny amount of air from the original unions to push all the way through the system to the wheels.

IF you can't get the m/c working properly with the ports open, I'd probably then take the m/c off and bleed it in the garage.

You ARE going to get there...eventually!

Paul

 

Hi NBCat

When I removed the small standard size Brake Pipe Union and lightly touched the Brake Pedal, (YES!) Fluid does come out regardless of Cap On or Off

If you Scroll back a few threads on this page: jaguarforums.com/forum/xjs-x27-32/cherry-blossom-restoration-1990-xjs-v12-122634/page152/

You will find a Video that Shows Brake Fluid being Pumped out with a very light touch on the Brake Pedal and used a Scrap piece of Brake Pipe to feed Brake Fluid back into the Reservoir, so that it would be Closed Circuit while I bled the Master Cylinder

As this was really the only way I could think of doing it

As for the bigger 12mm Union at the Front end of the Master Cylinder, I haven't had a Chance to do the same with that one yet but what I am thinking of doing would be the same thing with this one as well

So both of them would be feeding Brake Fluid back into the Reservoir (in a sort of Closed Circuit) in the hope of Bleeding any trapped Air out

Although before I do anything else (except for a few preparations) I am going to wait for Paul (ptjs) just in case he's come up with some other ideas

I'm not sure if we have ever had a problem like this on the Forum before, so hoping we can come up with a solution

 

You have to remember that the master cylinder is only part of the circuit. The ABS pump is between it and the brakes. If that got air in it by being drained by the calipers being off, you need to get it bled. Do the bleeding over and over, starting the car in between each time, as the manual I posted says to do.

 

Well done! Paul (ptjs)

Looks like you just Nailed the Cause of 'The Sinking Brake Pedal Problem' on my 1995 XJS 4.0L and although its too early to say for sure, it certainly seems like you have, as there appeared to be loads of Air trapped in the 'Brake Master Cylinder' just as we suspected

Owing to the Weather, progress has been Slow as I kept getting Rained off, where with so many Stops and Starts I was unable to set it up exactly like you wanted, although I did my best

But at least we know what's wrong with her now and it Thankfully doesn't look as though the Seals will need replacing in the Master Cylinder after all

There were virtually no Bubbles of Air trapped in the Rear Circuit that does the Rear Brakes, where the Fitting is on the end of the Master Cylinder but the Circuit that does the Front Brakes was a Totally Different Story!

Where as you will see in the Video, there was lots of Air in there that will need Bleeding out, although I'd rather wait for a Better Day so I can do it properly, as it may need doing multiple times, to get the Pedal feeling just as good as it should be

And also I haven't tried it with the Engine running yet, as that's the only way we'll know for sure

Thanks Again

Alex

 

Alex, Alex!
You Really need to get yourself some Real Big Pounders, Bashers and Hammers against the day this ever happens again! (that might be next week. )
What you have there is a mere Tapper! Not meant for such a serious task as you undertook.

As I've done a man's work in a woman's body all my adult life, I have found it necessary to acquire a selection of Equalizing Tools and Devices to be successful.
Below is a selection of hammers I just stepped out to lay hands on:

LnrB's Equalizers

On the Left, a standard Harbor Freight 24 ounce ball peen hammer (of which we have a selection from 8oz, to 36oz), which appears to me rather like what you used.

Next is an Original dead blow hammer (which we call The Short Handled Basher), a Lead Ingot (as you know lead does Not bounce) which belonged to husband's grandfather from the end of WW2. It works far better than Harbor Fright shot filled Non-Bounce hammers, It's only draw back is the head is so big.

Next on the right is my Go To pounder when I Really need something to move Now! It's about 5 pounds with narrow heads that fit almost anywhere.

Last is a Cross Peen which I got from my dad when I left home to embark upon my Misspent Youth.
It's only 3 pounds and needs a new handle but as he's dead now I will keep it forever.

If I need anything bigger than these, there is a 6 pound sledge behind the door, which spends most of its time when it's not beating on something, being a Door Stop.

 

A magnificent collection of watchmaker's tools, LnR

 

(1) Fitted New Front Calipers but owing to Pilot Error, let the Reservoir Run Dry! Please don't ever do that, as if the Brake Reservoir ever runs dry, then just like me you could be left with a Massive Problem to sort out!

(2) Having Fitted New Calipers, which was a 'Fun Job Not!' The Brakes didn't work and the Pedal went right to the Floor!

(3) Trying to figure out what went wrong was a Nightmare to sort out!

I Bled the Brakes and that didn't work and used 5L of Dot 4 in the process about £25 for 5L

And have so far used 10L getting absolutely nowhere if its all the same to you, I don't want to even add that up!

(4) Then I sort of thought I'd got them Working! with a good Hard Solid Pedal but when I Started the Engine, The Pedal went straight to the Floor

(5) Lots of very interesting and sometimes expensive suggestions, that included the possibility that the Seals in the Master Cylinder had gone dry and may need replacing! and I don't even want to try how complicated that might be or how much that would Cost

As I'd already been to Hell and Back putting on New Calipers including the problems of getting the Old ones off and that is not a journey that I really ever want to do again!

As compared to that removing and refurbing the IRS Cage, was for me an enjoyable 'Walk in the Park'

So all I could do was keep Bleeding the Brakes as well as the Brake Master Cylinder, while at the same time 'Multi Tasking' while praying for a Miracle to try and save me from the depths of despair

Where with Perfect Timing! my 'Partner in Grime' Paul (ptjs) came to the Rescue! with an Amazing Suggestion! and this was to remove the Brake Pipes from The Master Cylinder, then get the Master Cylinder Working First!

You can read all about this, earlier on in this Thread

So That's exactly what I tried to do, which basically was to purge the Master Cylinder of Air and that was nowhere near as easy as it sounds! unless of course you want to take the Master Cylinder out of the Car and 'Bleed it of Air on the Bench' which would have been the last resort for me

And so before I got to that, I tried everything that I could think of, to try and bleed out all that Air that was Trapped in the Master Cylinder where in the process of trying, I suddenly realized that this was not about to be any sort of a Walk in the Park either!




Master Cylinder to Brake Bleed Tube while Pumping the Brake Pedal (This should have worked but it didn't! so I'll Chalk that up as a Fail!)




Too Much Air in the Master Cylinder, so this was going to be a really long Night!

Then I tried even Longer Tubes hanging down from the end of the Bonnet/Hood but that didn't seem to Work either! as once I'd Pumped the Fluid up, it went back down again! Don't ask me why it did that, because I just don't know!

Maybe it was just expelling Air!




You can just about see the Brake Fluid in one of these long Bleed Tubes just above this Clothes Peg that I used to Mark the Level
But the Fluid wouldn't stay there as it kept on going down and so I had to Score that one as Yet Another Fail

At which point I had to Stop for a Cup of Tea or Two!

When inspiration suddenly hit me over the Head like one of Lnr's Hammers!

OMG! OMG! I was thinking!

This just might Actually Work!

So I took one of the 'Bleed Nipples' out of one of the Old Calipers that I had taken off some days ago while at the same time Hoping and Praying that the Thread would be the same, as where the Pipe to the Calipers had been removed by me, Following Paul's (ptjs) Brilliant idea

Of getting the Master Cylinder Working First (where Bleeding the Brakes could come later once that was out of the way)

Where to my Surprise and Delight, the Bleed Nipple Screwed Straight In!

So now I could Bleed the Master Cylinder as easy as Bleeding the Brakes!!!!

And so that is exactly what I did!




Steps Back in Amazement! at just how easy this was!

But what would happen when I started the Engine?

Would the Brake Pedal Drop to the Floor the Same as it had done before?

No it did Not!

That Brake Pedal Stayed Rock Solid! Engine Running or Not!

So basically all I've got to do, is reconnect the Brake Pipes to the Master Cylinder and then once having done so Bleed the Calipers in the Normal way

 

OB,

Well done! Great idea using spare bleed nipples!! I've always used blanking plugs, but that's much better!

Now you've just got to hope there's been no air pushed earlier to the abs module. Bleed as per Jal previous post.

Good luck!

Paul

 

Hi Paul (ptjs)

Cheers!

Although I have to tell you that this was one of the lowest points, that I have ever managed to feel while working on my Car, as even with long Bleed Tubes from the inner edge of the Bonnet/Hood down to the Master Cylinder, I just wasn't getting anywhere

And though I've never done it myself, I could well imagine how difficult rebuilding a Master Cylinder could be and even trying to find somewhere that has a New one for Sale, could be almost impossible from what I have been reading on this Forum

So I'm sure you can imagine my sense of Relief when the Bleed Nipple idea Worked, as once the Brake Fluid was Flowing though every time I gently pressed the Brake Pedal, I just kept Closing it down and down until I had to push hard on the Pedal

To try and insure that any Air could not be Sucked Back In, although I also tried it with a Self Bleed Brake Nipple, that I bought sometime ago (that never worked on my Car) and wouldn't Fit the Master Cylinder because the Thread to Screw it in was too long

Although if I'd had a Shorter one, then it may have just been Perfect for doing a Job like this

Something that I also didn't mention was that it was only the Front Brakes that had Air in, as I only Changed the Front Calipers which seem to be on a Circuit of their own

Being as you told me on the End of the Master Cylinder, while the Front Brakes were the ones Nearer to the Brake Booster itself, though in the interests of Research (Lol) had the Rear Brakes been the Problem, then you can also buy a Bigger Bleed Nipple, that looks like it would fit (though I don't know)

Once I Started the Engine, it was a full 5 Minutes before I touched the Brake Pedal, as I had almost convinced myself that the Pedal would go to the Floor as it had done before, so I guess you could say that I was already psyched up for more disappointment, that Thankfully never happened

If Air is Trapped in the ABS, would that just be Flushed out, when I reconnect the Pipes and Bleed the Front Brakes in the Normal way, or is there yet another unseen Mountain that has to be Climbed?

The only Good News being, that as Horrendous as this was (self inflicted and all from my own making) I now know how to do something I'd never done before and if you hadn't told me to disconnect those Pipes, I really don't know what I would have done

 

Hi OB,

It's kind of you to say so, but I can't really take any credit! After all, it's you that's done all the hard work! It's easy for me to try and be a keyboard mechanic! I'm just glad that you seem to have a working m/c free of air.

Will the rest of the system now bleed any residual air? We just have to hope so. The abs modules are usually supplied primed. So we have to hope that with careful wheel circuit bleeding, you will avoid trapping any further air there. Just bleed at the calipers carefully, allowing a few seconds between each press to allow the m/c to fully reprime with fluid. And although you only changed the front calipers, you opened both front and rear circuits so I would bleed all 4 wheels.

Good luck, I really hope you're on the home straight now!

Cheers

PAul

 

Hi Paul (ptjs)

Cheers! I never thought of that and you are right! as I did take the Pipe off the End of the Master Cylinder that does the Rear Brakes and so there could well be some Air Trapped in there somewhere

Impossible to do anymore to her today, as the Rain has really been hammering down and so as you say, 'let's hope the end is in sight'

Thanks again for your help and I don't mind admitting I couldn't have done it without you, I would have been lost!

Alex

 

Hi OB,

I've just been through a brake failure experience on my 2003 xjr due to a corroded rear brake pipe. Foot to the floor and a lot of fluid was dumped on the ground... a very scary experience. Replaced the pipe and had what sounds like a very similar experience to you, bled each corner of the car to death! A litre of fluid out of each caliper and still a spongy pedal. Looked on the X350 forum and found a similar post where the suggestion was to bleed the MC by loosening off the two brake pipes, slowly depressing the pedal then tightening up again and repeat.
When we took off all the plastic covers around the MC we found that there was a bleed nipple on the MC.. No mention of this in the manual. So we bled the MC using the bleed nipple (you could hear the air rushing out) and now we have a hard brake peddle. Hope you have a similar result.

 

Hi Paddy

No OEM Bleed Nipple on my Master Cylinder

It was just an idea I came up with 'Out of the Blue' so I am cautiously optimistic that all is ok now, except I've said that so many times that I'm taking nothing for granted, as while everything works on hard standing

The Weather has been so bad, that I haven't even managed to give her a run round the Garden just in case she gets bogged down in the Mud after all that Rain

P.S. I still haven't forgotten that Awesome Fix you gave me, about the 'Blue Relays' under the dash as having tried everything else that I could think of. I had run right out of ideas to get her to start

So that 'Blue Relay' Tip was nothing less than a life saver for me and if She won't Start for some reason is one of the first things I check

Much Thanks again for that

Alex

 

lex,
Your patience and tenacity are Epic!
Not Me!!


As I've mentioned previously, I would have done it way differently, but it's probably a Girl Thing.
I do hope you've got it this time.
(';')

 

I agree with LnrB as I have to force myself to be patient, yeah right. And if I'm dealing with an Idiot, it's just simply gone! The Lord has been trying to teach me Patience my whole life, and at 65. I Still Ain't Got None!!! Thanks For Trying God!

Jack

 

Hi Jack@Lnr

I don't really mind if things go wrong, as long as I know (or think I know) how to Fix them, as long as its not too horrendous, as very often thinking about it is often much worse than getting stuck in and then getting on with the job whatever it is

 

But as soon as I Start the Engine, the Pedal goes straight to the Floor with no effort at all, at which point I'm 99% Sure that it isn't the Master Cylinder but Air that has somehow got Trapped in the ABS

And while I've been all over YouTube looking for a Fix, I'm not the only one who's had this problem as I've found dozens of people, who were tearing their hair out and in a state of desperation of not knowing what to do

Where apparently you need to have the ABS reset with an OBD reader and not an 'el Cheapo' one either as some of the less expensive ones don't have this Reset Feature

It seems that Faults in the ABS can be caused by Air in the System, as well a Stuck Valves or even a Stuck Motor that won't Turn and so its really a sort of a Perm anyone from 10 (or maybe just three!)

Apparently this can Cost Megabucks for a 'Shop to Fix it' or to even diagnose the problem, where some guys (and gals) have ended up by being advised to go and buy a New ABS Pump, which can be so expensive that many have gone to the Scrap Yard in the hope of getting a working replaceement

There must be a much easier way, although this is really not the day for messing around with the Car, as the Weather here in the UK can go from burning Sunshine to Torrential Rain in Seconds, as its been doing all day

I'm fairly sure I can Fix it 'I mean how hard can it be' but as said this is not the type of day for experimentation

Though what would be really useful, would be if someone has a Circuit diagram of where the Brake Pipes lead to from the ABS

 

There's an Xjs technical guide at this link that show's a diagram of how the MC and ABS unit are connected together. Pages 11-13
http://jagrepair.com/images/AutoRepa...6%20update.pdf

 

Hi OB,

Sorry to hear that the problem is still there.

First of all the pipe connections on a Teves IV braking system, as per your photo:

- the 2 on the left at the top are the pipes connected to the master cylinder. I think the one higher up is from the secondary circuit and linked to the rear brakes. The lower one is from the primary circuit linked to the front brakes.

- the 3 lower pipes in a line are the output pipes to the brakes. As you look at that photo, the one on the right goes to the right front brake, the middle one goes to the left front brake and the one on the left drives both rear brakes.


As regards the continuing sinking pedal, there are only 2 things that are different when you have the engine running:

- you have vacuum assistance on the master cylinder at a 6.5:1 ratio
- you have the abs circuitry running

Now, my limited understanding of the system is that you can't get a sinking pedal on malfunctioning abs valves. Well, that's what I think!
But my quick perusal of the wiring diagrams also indicates that you don't need the engine running for the abs to be active, you just need the ignition on Pos 2.

So, the first thing I would do is take the servo out of the equation.

1. Don't touch the brake pedal. Make sure the ignition is off.
2. Because the check valve will be a one-way valve, you need to pull the valve out from the servo (NOT just pull the pipe off the check valve, as you'll still have vacuum in the servo) I THINK you should be able to wiggle it out (there will be a massive rush of air in as you release the vacuum.
3. Press the brake pedal. Based on what you've said, I think it will be firm. Release the brake pedal
4. Turn the ignition to Pos 2. I THINK the abs circuitry is now active. Press the brake pedal firmly. Is there any difference? If it sinks to the floor, stop at this point.

Despite my belief that it can't be this, it would seem the fault then lies in the valve block / low-pressure accumulator and we need to rethink the problem. However, if the pedal stays firm go to Point 5 just in case I'm wrong about the abs being enabled with the ignition on Pos 2.

5. Release the pedal.
6. Start the engine.
7. Press the brake pedal. I think it will be firm.

If the pedal is firm at point 7. It implies that the problem is air in the system somewhere after the m/c and it's only the massive assistance generated by the servo which is enabling you to feel it when the servo has been connected.

But if the pedal now sinks, again, it would seem the fault then lies in the valve block / low-pressure accumulator and we need to rethink the problem


But if the pedal is firm at point 7, then you need to reconnect the servo and go back to the bleeding sequence as detailed in the post by Jal. Start by buying another can of fluid!

Cheers

Paul

 

Hi Paddy

Thank You So Much!

That was Amazingly useful and is certainly going to be very useful to me

Alex