Hello all,

After lots of trials and tribulations (shoutout to Paul for his guidance!), I was able to rid my ABS booster pump of its airlock and bleed the brakes on my XJS with the Teves III system. Since I have not driven an XJS with working brakes, I was hoping for some information on how these brakes are supposed to operate. I.e. what is normal and what is not.

The good news is stopping distance is fantastic, and the brake pedal is quite sensitive. My doubts come in the following:

After repeated pressing of the brake pedal, the pedal gets quite hard, a vibration is felt, and a buzzing is heard. When this happen the brake assist is no longer active and significant pedal pressure is required I've made a video of its operation here: https://photos.app.goo.gl/YagGjL4GKCxSXSGB6
The pedal is pressed for the duration of this video, towards the end the noise of the pump changes and that is when the pedal feel changes. Is the noise of the pump expected? Is it expected for the assist to stop working if you are at a red light and holding the pedal down for over 30 seconds?

Cheers!

 

Hi John,

No thanks necessary, I've been happy to try and help!

You've got a few things happening there:

- The accumulator is discharging (as expected) and the pump is cutting in. The buzzing may sound a bit different to normal as you're discharging by holding the brake pedal whilst the pump is simultaneously trying to build pressure

- a very hard pedal is indicative of a faure in the rear circuit. So it depends if that is just a symptom of significant pressure loss from the accumulator or something else. So it depends how hard that pedal is becoming.

As regards whether 30 secs brake press equals a discharge sufficient to kick in the pump, I'm not sure. I'll test mine on Thursday for you. If its not right, the you have either:

- a faulty switch
- a failing accumulator
- residual air in rear circuits still

If its convenient do another rear circuit bleed following the Teves procedure precisely. If not I'll get back on Thurs, (unless any other member can test the 30 second press comparison before then)

Cheers

Paul

 

When you say "whether 30 secs brake press equals a discharge sufficient to kick in the pump", keep in mind that, in the video, the pedal is held down the entire time. The pump kicks on after ~5 seconds of pressing and holding the pedal. After ~30seconds, the tone of the pump changes with a corresponding change in the feel of the pedal (firms up and drops down). Maybe 10-20 seconds after holding down the pedal the brake light will illuminate.

I'm curious if the behavior here is normal and if the sound is indicative of a problem. Before renewing the system the pump hummed. Now it is louder and whiny.

I'll try to do a bleed of the rears again, will be up to the assistant though!

 

John,

If I've understood correctly, from the time that the pump first cuts out after fully building up pressure, you're saying that it then cuts in after just 5 seconds of first touching the brake pedal? If so, then I'd suggest there's a fault in one of the 3 areas I mentioned. I'll check mine but believe that a fully charged working accumulator should hold more reserve than a 5 second touch of the pedal before the pump cuts in again.

Start with another rear circuit bleed. As mentioned, use the Teves procedure, not the Jaguar procedure.

Cheers

Paul

 

Will do.

Also, just curious if you know the reason for the 15 second limit on bleeding the rears, and how strict I should be with that?

 

John,

I suspect it's for 2 reasons. As you know, when you touch the brake pedal, fluid is forced via accumulator pressure (not pedal pressure) to the rear circuits. So, with the bleed nipple open, you'll potentially discharge a lot of fluid in 15 seconds and the reservoir level could drop quickly. And you don't want it to drop so quick that you get air entering the rear chamber port. So it's no bad thing to keep the cycles short and keep the reservoir topped. The second reason might be that with that much fluid leaving the system, you could use all accumulated fluid pressure before the pump can re-pressurise it? So the rears would then have no fluid being pumped to them?

Paul

 

I suspect your second point is where I went wrong. I definitely tried adhering to the 15second limit, but with the limited access there were definitely times I struggled to get the wrench where it needed to be. I'm certain that it was open long enough to deplete the stored fluid.

I'll attempt a rebleed and report back.

 

Hi John

As Paul (ptjs) has advised you almost certainly need to re-bleed the Brakes

Not just the Rear ones as I believe that you were planning to do but also the Front ones as well, just so you can make doubly sure that no stone is un-turned

Except that before you do any of that, the most important thing of all is to Bleed the Low Pressure Side of the System, as if the Reservoir ever ran dry then you won't be able to Bleed the Brakes properly or if at all and as such you'll be wasting your time

This is nowhere near as scary as I may have made it sound when I first wrote that Post some years ago!

Basically just 3 Things you need to bear in mind while doing this

(1) Cover all the Paint Work with old Towels to guard against accidental Spills and keep a Bucket of Soapy Water Handy, just in case your assistant or yourself should accidentally spill any Brake Fluid during the process, while also keeping the Reservoir Topped up (as this will Strip the Paintwork in an instant)

(2) Don't break the Plastic Elbow when removing it from the Brake Pump or you might have a Problem in finding a replacement

(3) The Low Pressure Side is Gravity Fed from the Reservoir and even though there's no pressure as such the Brake Fluid can still Flow out fairly quickly and that being the case don't panic, just put your finger over the end while you settle your nerves and regroup!

Where Basically you let the Brake Fluid Flow into a Container until the Brake Fluid is Flowing 'Bubble Free' (takes just a few seconds) and then replace the Plastic Elbow into the Brake Pump (on the Fly) while the Brake Fluid is Still Flowing and then lock it in with its Spring Pin

Do this Low Pressure Side with the Ignition OFF

Link: How to Bleed the Low Pressure Side of the Teves MK1V Braking System How to Bleed The Low Pressure Side Of The Teves MK1V Braking System

One of the Biggest Problems when it comes to Bleeding the Brakes is having a 'Telepathic Connection' with your Assistant, who will hopefully always be on the Same Page as yourself throughout the process

Since that sometimes doesn't happen, I Accidentally found another way of Bleeding the Teves MK1V Brakes on an XJS which also works on just about any other Car and that is by Gravity Bleeding

(1) No Assistant Required

(2) Ignition OFF

(3) Don't Touch the Brake Pedal

(4) Keep the Reservoir Topped Up

(5) While it may take a lot longer, its also the most Stress Free Way I've found of doing this job

(6) At the end of the process before you turn the Ignition on in 15 Second Intervals as before (for the first time) as the Brake Pump Charges up Make sure the Reservoir isn't over filled or you Could have Brake Fluid Squirting out of the Top of the Filler Cap so Cover the Reservoir Cap with a piece of Towel or an upturned Plastic Container just in Case

Also most likely to happen when you Touch the Brake Pedal with the Ignition ON for the First Time, (usually only happens if the Reservoir has been over filled) but you have to cover all bases just in case!

Link: How to Gravity Bleed the Brakes on the Teves MK1V System

 

Hi John (Part 2)

Just to add to the above, the main advantage of Gravity Bleeding (in my own experience) is that while Brake Fluid is dripping out of the Bleed Tube that you put on the Caliper, Air cannot get in at the same time and so while it can take a lot longer

You can literally put your feet up and enjoy that Cup of Coffee (or most probably Tea in the UK) as long as you keep the Reservoir Topped up so it doesn't run dry, or you will have to start all over again

Though if you do this properly by always Bleeding the Caliper 'Furthest away from the Master Cylinder' you could also be Amazed at how quickly the ABS light goes out, compared to how it ever did before

Only when you're 100% that all the Air is out of the System and you have no Air Leaks anywhere else, should you consider whether the Noise and the Vibration in the Brake Pump could be caused by something else on the assumption that your Brake Bleeding adventure has yet so far failed to Solve this problem

As if not then it could possibly be:

(1) The Pressure Switch on the Brake Pump (which is that Gold 'Thingy')

(2) The Accumulator (Black Ball) may need replacing if the Rubber Diaphragm inside it has gone porous

But Don't go unscrewing the Black Ball Accumulator! on a whim without any further instructions, as even with the Engine Off the Pressure inside that Ball could be around 2 BAR 2000 PSI which is more than enough to kill you or cause you a serious injury 'You have been Warned!'

 

Thank you sir for the writeup! My assistant is currently booked for helping out with this task for the third time so I'll do it conventionally. I'd switch to your method but she is now as invested as I am to get this working! Though, I'll see when 5pm rolls around if that is still the case.

Couple of items/observations/paranoid thoughts I still have on the system:

0. What causes me to loose sleep is a hissing sound coming from the actuation unit when pressing the brake pedal. Can you or any other owner verify this is normal?
1. I have replaced the accumulator with a brand new one
2. The pressure switch could definitely be the issue if this bleeding fails. Luckily I have another bluetop switch from a 94 XJ6 to stick in there.
3. My ABS light does not come on at any point. Not during the ignition sequence, not ever. I suppose that means the bulb is out but was going to wait until the brakes were working before investigating further.

Tonight, I'll plan on bleeding the LP and the HP circuit following Paul's Teves procedure in the LEFT REAR - RIGHT REAR - RIGHT FRONT - LEFT FRONT order.

 

John,

A couple of thoughts:

There's absolutely no harm in trying OB's gravity procedure if you have an air bubble trapped in the caliper. The typical method of gravity bleeding is to wedge the brake pedal down and leave overnight with all the bleed nipples closed. Then in the morning, bleed each wheel circuit conventionally. The theory is that when the fluid is placed under consistent constant pressure overnight, any air will travel down the lines over a period of time and end up at the highest point in each caliper, thus making it much easier to then expel the air with traditional bleeding.

The problem is that any form of gravity bleeding can not theoretically work on the rear of a Teves ABS system as pedal pressure does not force any fluid (or air) to the rear brakes. The ONLY thing that forces fluid to the rear brakes is the accumulated pressure being allowed to enter the Actuation unit when movement of the pedal opens the valve. So any form of gravity bleeding can not expel air in the upper parts of the system, only air that may be in the caliper already.

As regards any problem with the pressure switch, as you know, it's the most difficult part of the system to test for most of us. The only real way to get a feel is to fully discharge the accumulator (turn ignition off, press brake pedal repeatedly up to 50 times until the pedal goes rock hard. Then turn on the ignition and count how long it takes the pump to run before cutting out. If it's really quick, you have a pressure switch problem. If it's very long, you have a problem with the pump, accumulator or switch - but which one?

If it takes 25-40 seconds, your going-in position is that all 3 are ok, specifically the pump. If the pump then cuts in every time you press the pedal, you start by assuming that therefore the problem lies in the pressure switch or faulty accumulator. But EVERYTHING must start with a system fully expelled of air, otherwise you get confusing results as everything gets discharged quicker from working harder to compress the air in the system rather than move the fluid.

Don't feel bad about doing repeated LP & HP Teves bleeding to remove the air. A number of us have been there!

Good luck

Paul

 

This system is a difficult nut to crack... I was only able to bleed the rear brakes today and, same as the last time, I did not see any air escape. However, the time for the brakes to go hard and the pump to change tones is now ~10 seconds longer so it does seem like there is an impact to it. I'll bleed the front tomorrow and hopefully that fixes it.

Side note, do you know what the O-ring setup on the HP hard line off of the pump housing is? I did not record this and would like to ensure I guessed right by putting an O-ring at the top. Wouldn't expect it to make any difference but figured it's worth the ask.

Cheers!

 

Well, bad news. I bled the rear and front circuits tonight following the Teves procedure. I am confident the system is purged of old brake fluid and air. Unfortunately, the pedal still drops to the floor after holding it for 15-30 seconds.

I'll try switching out the pressure switch to see if that fixes it.

However, I am worried the problem lies elsewhere and has something to do with the hissing from the actuator unit. While bleeding the front driver side caliper I saw several very small bubbles in the line. Perhaps the hissing is indicative of a poor seal on the actuator unit causing air to seep in and the pedal to not hold pressure. On a working system, if you leave it pressurized overnight, would you expect the system to have a full charge the next day?

EDIT: I'm more confident that my last thoughts are where the issue lies. Found a thread that describes a similar issue here: https://www.jaguarforums.com/forum/x...-insane-94827/
Bummed but I guess it is what it is. The question now is:

1. Replace Teves 3 with non-ABS system or later ABS system
2. Disassemble actuator unit and attempt to find and fix leak
3. Pay ridiculous amount of money for used unit

 

At the cost of my sanity, I'm leaning towards option 2.

That is, if this is a symptom of the problem. Can someone with a Teves III equipped XJS please let me know if their brake pedal hisses when depressed?

 

John,

I hate to say it, but although I've never seen a failed Actuation Unit, this may be what you are experiencing. If somehow the seal failed on the boost piston, I guess this could allow / encourage the pedal to move forward when pressed without the fluid itself being forced to the front brakes?

I'll be with my car on Saturday and will see what noises it makes and hopefully record it for your comparison.

Cheers

Paul

 

Thanks Paul. Yes, I am quite surprised. Searching the many car forums with this brake system shows no matches. Lucky me!

I'm on board with your reasoning. Since its such a PITA to remove this unit and re-bleed, I'm going to focus on the middle seal between master and boost piston, control valve, actuating piston, and main valve areas since those are all the areas in the path of fluid with brakes applied. Also, I really paid attention to the feeling of the pedal today and the best I can describe it is that it feels like the actuating piston travels further than it's allowed to. Like the boost piston loses so much pressure the brake pedal can overcome it when the pressure in the lines should prevent it.

If I'm successful with the repair, should anyone be in need of the o-rings to do it themselves, I'd be more than happy to send a kit of them out. I know my standard EPDM o-ring kit doesn't have the sizes needed, so I'll be buying them in packs of 1000 when I just need one.

Also, for anyone down the line with this issue, I did replace the pressure switch with no improvement. I am also using a new Bosch accumulator.

My times after ignition with no pressure in the system:
Ignition on: 00s
Brake Light off: 10s
Pump off : 31s

My times to the pedal drop:
Brake applied: 00s
Pump kicks on: 03s
Brake light on: 08s
Vibration in pedal: 10s (I will note that sometimes I get 30-40seconds before this point is reached. Seems to be a function of pedal force)

 

John,

I tried out the brakes in my car today and thought the following may be of interest:

- Ignition on (first time for a week) - Pump ran with usual noise for 3 seconds, then settled down to much quieter nose for 20 seconds then cut out.

- When brake pedal is pressed, there is a slight initial mechanical noise of linkage / piston movement then nothing. No further noises when pedal is held.

- If brake pedal is held, the pump does not cut in (I held pedal for 3 minutes)

- But if brake pedal is pressed / immediately released / pressed again etc, then the pump cuts in on every 4th press of the pedal and runs for 3 seconds.

That intrigues me, as it was something I hadn't realised about the system. It seems that the system depletes far more pressure on small repeat applications than when the pedal is held once with pressure being applied for a long time. Why is that?

Importantly, how does that relate to your problem? Well, the bit that confuses me is that if your pump, accumulator and pressure switch are functioning correctly(??), then why does your pump cut in after 3 seconds of a single press? There must be something in the manner in which stored pressure is being applied in your situation that means it is being depleted within the accumulator in a different manner to the normal operation in my car. The only things I can think of are:

- You still somehow have a lot of air in the Actuation system which is absorbing more accumulator pressure, hence the pump cutting in quickly and the pedal sinking
- The seals in the Actuation unit are failing so the pressure from the accumulator is being applied through all the fluid in the Actuation unit rather than just behind the boost piston and thereby again depleting the accumulator pressure quickly

I think I need to read the Teves documentation again!!

Paul

 

Much appreciated for trying it out and letting my know your timings as well. Definitely helps to have a baseline to shoot for.

The air in the actuation system is a possibility but I can't see how that might happen. I for sure believe it's the seals since the biggest clue is the hissing sound and rapid loss of pressure when the pedal is pressed. When the brake pedal is not pressed, it holds pressure for an acceptable amount of time, so it must be one in the path when pressure is delivered. Also the hissing noise was constant before I cleaned out the system and it had it's original brake fluid.

I'm going to remove the actuation system and do some testing on the bench to see if I can find the location of the hiss. My plan is to plug all the lines and create a vacuum on the HP input to the actuation unit. By pressing the pedal I should be able to find the source of the leak.

Thanks again.

 

Paul, concerning repeated applications using more system pressure:
In actuating an hydraulic or pneumatic system, there has to be a bit of (a) pressurisation occurring, i.e. work being done, ie energy being used; and (b) lost motion occurring, before the system does what it is there for. So in your system, I am guessing - analogously to a vac operated booster system with the engine not running - a certain amount of stored pressure is used up just to get the brakes on. Thereafter holding them on at a given clamping pressure on the disc should not use any more. Repeated ons and offs thus depletes the stored pressure and after a bit the system repressurises. This is if the system works like in theory!

 

Greg,

That makes perfect sense, tks!

John,
Tthe more I think about the hissing noise makes me think it must be be caused by pressurised fluid from the accumulator moving in the Actuation unit via failed seals. One way to try and prove that would be to turn off the ignition and fully discharge the accumulator pressure through repeated short presses of the pedal (up to 50), Then press the pedal and see if you can initiate the hissing sound. If it doesn't occur, it would seem to apply that it's pressurised fluid causing it, rather than just pedal application of pressure within the Actuation Unit. I'm not sure if that helps you to identify if it is a failed seal or which one? But it might help!

Cheers

Paul