Hi all,
Has anyone done this / seen any related documentation or pictures of the internals / know where the various seals etc can be sourced?

I've determined that my master cylinder/hydraulic actuator is leaking a tiny amount of system pressure into the rear brake circuit, without the pedal being pressed. I assume the control valve isn't closing properly
What I thought was old & sticking caliper pistons or maybe the in-line pressure reducer was actually the ABS causing the rear pads to drag.

I've also had various weird pedal sensations & issues in the past with bleeding. Basically, i'm fairly sure the entire brake system is gunked up with 'stuff'/sediment, probably from system neglect 10+ years ago, and want to give it a big service. I've seen previous threads on the valve block & replacing the electrical ribbon connectors, lots of information on the pump/accumulator, but can't find much info at all on refurbishing the hydraulics side of the system - seals, valves, microfilters, typical wear, accumulated deposits, failure modes etc etc.

If there isn't much info on this, If anyone has or knows of an actuator that has failed that they'd be willing to send me (UK), maybe I could disassemble, photograph internals for the benefit of the group, and try & find some sources for parts.

 

Hi Asdrewq

Having done some extensive research on this, I'm 99% Sure that the Valve Block is the same on the Range Rover P6 and so could still be in manufacture

But you'll have to go and look at one to be sure, before you go splashing the Cash

If you get a result be sure to let us all know, or you may be able to order one direct from Ate in Germany

Worst Case Scenario, refurbing one of these is a piece of cake and is nowhere near as difficult, as some may have you think, or you could get a working one from a Scrapyard and if you or anyone else has got the Vacuum Booster System, then I'm pretty sure that one from an XJ6 is exactly the same, as far as the Master Cylinder goes anyway

Good Luck

Alex

 

Hi Alex,

Yes I see from reading that the valve block/solenoids side of the system & repairs to it is a bit better understood. I've seen a few threads/pictures relating to that (some of them I think were yours!)
It's this bit circled in the below diagram that i'm more concerned about; specifically the disassembly & servicing of:
- Boost Piston
- Master Piston
- Positioning sleeve
- Control valve

My specific/latest issue I think is with the control valve, it's movement, & whatever lever mechanism is used to move it from the actuating piston
It's leaking the tiniest bit of pressure when it's supposed to be 'off', so is applying the fluid pressure from the accumulator to the rear brake circuit all the time.
But there's undoubtedly seals between the various pistons, orifices with filters etc where the fluid flows about this actuator, I think it all needs cleaning out as a minimum & will likely need replacing if I were to even strip it down.

 

If anyone's interested in how I diagnosed the control valve, my symptoms were as follows:

- car left overnight, 0 ABS pressure in the system, & the rear wheels would freewheel by hand with the car jacked up, no issues.
- turn on ignition and allow the system to build pressure in the accumulator, and over a period of approximately 3 minutes the rear brakes would begin to engage. It must be a tiny bypass of fluid & takes time to fill the fluid volume in the callipers & bring the pads close to the disk.
- rear brakes would then remain engaged/locked, even once ABS system pressure is depleted.
- Bridging pins 1 & 4 on the valve block with 12v to activate the rear brake circuit discharge valve would relieve the pressure, and immediately allow the rear to freewheel again.

Here's a pic of the control valve area I found online (in a non-english summary of Teves ABS, so badly translated), which is a bit more detailed than the Jaguar documentation I have found:

All those solid black bits in the diagram are I believe seals/o-rings, which probably all need replacing if you strip the unit down, and you can see there are lots of them.
Even more seals/o-rings in the traditional master cylinder area, if you disassemble the full unit:

 

The Master Cylinder Actuator hardly ever goes wrong, I've never even heard of one going wrong!

More likely you've just got an Air Leak and or else the system needs Flushing

Also you should NEVER let the Brake Pump run for more than 60 Seconds without a 2 Minute Rest in between On/Off Key Actuation's or you could burn the Brake Pump out and after that it may be 'Toast' and very expensive to replace if you can find one!

Good Luck

Alex

 

Very precise procedures to follow when bleeding the rear brakes. Not like a std car.
Front brakes are not a problem.
I am getting close to re-engaging with bleeding my completely refurbished brakes: new rotors, calipers, pads, hoses front and back. Rear brakes were not getting fluid. Took the booster out and flushed all the old fluid. Hoping for success when it goes back in the air next week.

 

Asdrewq,

Your assessment is interesting and may indeed point to the Actuation Unit. (As you probably know, it's not a "Master Cylinder". The "Master Cylinder is merely the small chamber at the front of the Actuation Unit that drives the front brakes.)

I can't disagree with your diagnosis, but as I've written before, I have never seen a failed Actuation Unit (although eventually everything will deteriorate. However, one thing you want to consider is whether it's not the Actuation Unit Control Valve that's at fault, but perhaps a misadjustment of the brake pedal which is causing a constant slight pressure on the Actuating Piston and thence pressure on the scissor unit which is enabling the Control valve to slightly open and allow fluid from the accumulator to enter the chamber and thus flow to the rear brakes? It;s definitely worth checking in this area before you start stripping the Actuation Unit.

Good luck

Paul

 

Hi Paul,

The pedal was my exact thought when I discovered this issue! I was initially pretty excited as I first thought I had a seized rear caliper (Which is a comparative nightmare to sort).
I have also had a few occurrences of the brake pedal sticking down a small amount in the past, meaning the brake lights were staying on. So all the symptoms were starting to make sense.
I thought it would just be a simple case of the pedal getting hung up on something- wiring, carpet, bad adjustment, maybe bent etc, alas not.

I now think the pedal was sticking for the exact same/related reason - there's gunk in the actuation unit/scissor mechanism etc that was preventing something from moving. This unfortunately aligns with another symptom i've had in the past - difficulty bleeding the front circuits the conventional way/pulling fluid through, & the pedal disappearing into the firewall when bleeding & not returning, & needing to activate the main valve to solve (I posted about this previously) - I think this is a symptom of the microfilters that sit between the reservoir & front brake pistons being blocked.

I've tried many combinations of pressing the pedal, pulling the pedal up, actuating the 2 rear solenoids & various combinations to try & use the hydraulic pressure to free something up, but nothing is working.
If I activate the rear discharge solenoid and press the pedal I get a nice surging fluid noise from the reservoir area as the fluid circulates back
If I activate the rear caliper isolation solenoid it completely blocks fluid flow to the rear - once the pressure is relieved, it doesn't return with power held to this solenoid. So I could in theory just leave this activated and drive the car with no issues, but also no rear brakes....
The one thing I haven't really tried yet is shock therapy on the pedal itself - vigorously pulling and pushing it. If I do this whilst also bleeding the rear, in theory any stuff I dislodge would just get flushed out of the boost chamber and immediately to the rear cllipers? Not sure if additional microfilters exist in this fluid path though that would just block up instead, maybe in the valve block? I'm a bit worried this might damage something permanently though - how robust exactly is that scissor mechanism & related parts? It all looks like it could be a bit fragile in the diagrams.

I just wish there existed some proper documentation of this unit. Stripping it down blind & with no source of service parts when it's 30+ years old is a road I'm not keen on.

 

Contacted a few suppliers in the UK who confirmed they don't sell seals and have no idea where to source.

Andy Harvey from JustXJS advised that he's seeing lots of these fail now with general gunk/sediment, & does do a complete strip & rebuild service for these units, but it's out of my budget.
He stated he had to have some seals custom made for the refurbs & wasn't willing to sell separately as his stock of these was running low.
So even if I can find an old unit to strip down and have measured, this doesn't fill me with confidence that any off-the-shelf seals will be able to be matched up in a catalogue.

 

Asdrewq,

There may be an inevitability of you stripping the Actuation Unit, but I would still explore every potential possibility that it might be something else enabling the fluid flow. I know Andy Harvey and I'll talk with him about his work and what he's been seeing recently, but I've still never heard of any owner in the club or Jaguar community who's had a failed Actuation Unit. - Gunked, Jammed, Failed Valve blocks? Yes. But the Actuation Unit itself? That's a new one for me.

How about disconnecting the pedal pressrod from the Actuation Unit and see if the scissor linkage is still allowing fluid flow to the rear of the Unit? That might help to determine if the pedal is stuck / pushing forward, or if the valve in the Unit is permanently very slightly open?

I'd also strip and clean the Valve Block separately as we've seen more potential issues in that side of the system

Good luck

Paul

 

Thanks Paul, I'd be very interested in what you can find out.
RE the pedal disconnect from the push rod - that's what I plan to do next. I've been putting it off because I didn't think you could physically do it from underneath the dashboard, & it required removing the complete pedal/booster assembly from the bulkhead in the engine side to access.
I absolutely hate working on my back up under a dashboard

In the interests of sharing related info, I've found the following in my internet trawl on this topic:

Chris Knowles who used to run KWE said he too had seen some issues with the actuation units on customers cars, mostly in the latter 5 years or so, had rebuilt a few & offered this cleaning as a service as part of their general overhaul of brakes/suspension (although didn't know any source for the seals). He had tried various solvents to attempt to clean this stuff in situ but nothing had worked.
I subsequently found the following pics on his site:

These are pics of the two 'master cylinder' pistons, circled in red in the below diagram.

It looks like they have little mesh filters on the suction side i.e fluid flows through these little filters when you are conventionally bleeding your front brakes. & they are blocked with general gunk/deposits.

One of my other symptoms was trouble conventionally bleeding my front brakes, where I
1) 'lost' the pedal when bleeding - pedal moved a single motion then lost all pressure/feeling of resistance after the first press during bleeding.
2) couldn't suck any fluid through at the front caliper using a vacuum bleeder, unless I energised the ABS fluid return solenoid for that caliper.
3) Had to energise the ABS 'main valve' to return pedal pressure, which I think was me effectively 'reverse bleeding', or at least forcing high pressure fluid through the tiny areas of filters that were still unblocked, back to the master cylinder chambers & returning a nice hard pedal. I think this only worked because I hadn't introduced any air into the system as I was just changing fluid. If there were air in those master cylinder chambers I think I would have been screwed.

I also found this pic of the same issue of gunk build up on the sliding piston mesh filter (apologies, I didn't note who originally posted it) - with what is possibly the 'central valve' still in place:


All this looks to be very similar to the issues/deposits that everyone sees in the valve block, pic again from KWE:

 

Asdrew
Although my car has mercifully not got ABS, I think this work that you are doing is extremely important for all owners of Teves 2 ABS-equipped cars. When you get it all sorted, which I am quite sure you will, may I suggest a proper writeup with as much detail, supply sources, photos and how-to notes, as possible, and it would make a very important sticky.
Together with what Orangeblossom has already posted on rebuilding the valve block electrics, this sort of resource would be a godsend to owners in the future.

By the way, I am sure if you talk direct to master cylinder rebuilders, of which there are loads in the UK, they are bound to have seals that will be the correct size.

 

Greg, I think you give me too much credit - I highly doubt my scattered investigation & information gathering would meet the standard of any sort of how-to guide. That said, I will post everything I find out in this thread & may look to compile it if it turns out to be fruitful.

Paul,
On the subject of pedal free play, i've had another look...
At rest, my pedal is sitting hard up against the metalwork of the car, as shown below. I can see the witness mark amongst that rusty patch, circled in red.
Is this normal? I can't see any possible way to adjust this, but it's just occurred to me that this could be my issue.
Should it be 'floating', or at least against a sort of at-rest rubber pad like you get in lots of cars?:



If anyone could grab a pic of the area from their own ABS car to compare it'd be appreciated.

 

Thought i'd try removing that black brake switch bracket that the pedal hits, and even grinding the pedal down a bit to see if this was somehow the issue/a way to find the point of total freeplay, but I don't think it is
For this to be the cause the only way I can think of it happening is if the entire pedal assembly somehow isn't bolted flush to the firewall, or the firewall in this area is bent.

I've been driving the car around today, getting it warm etc. Rear brakes still end up dragging whilst driving.
I have done some more investigation work to pin down the symptoms more precisely. This is the latest one from today that feels like it could be significant to determining exactly what the culprit is within the booster:

- deplete the system pressure completely, brakes aren't locked on.
- ignition on, pressurise system, rear brakes pressurise and lock up hard.
- press brake pedal one single time, the rear brakes immediately free up.

I've also found some pictures of some of the internals of a Teves master cylinder (Not XJS, but the one used by VW on various cars in late 80's/early 90's) & will post up later.

 

Asdrewq,

Did VW use a Teves Mk 2 Actuation Unit rather than just a Master Cylinder in their 80s / 90s models? I wasn't aware of that? But if they did, maybe that's a further source of spares for our cars?

As regards your continued symptoms, I'm intrigued (and still confused) by how the pressurisation of the accumulator can apparently leak into the Actuation Unit, but then get closed off by a single application of the pedal? What about if you touch the pedal once or twice whilst the accumulator is initially pressurising? Does that stop the initial lock of the rear brakes? Or if you avoid discharging the accumulated pressure before turning the ignition back on? Does that also avoid the initial lock? Also, if the rear brakes do lock up on their own, once you've released them with that single press, do they ever lock again on their own with the ignition still turned on?

Did you ever try my suggestion of just unbolting the whole unit and just slightly moving it out of contact with the pedal pushrod? That should be fairly easy to do. Does the lockup still happen if you then turn on the ignition? I think you have to eliminate whether it is inadvertent pedal contact that is always causing the issue.

Cheers

Paul

 

Hi Paul,

Yes, i'm not sure exactly which models/years it was used (Golf mk2/Corrado G60 apparently) in but here's a pic; it's the all-in-one format with the pump/accumulator together with the actuator. The manual is basically identical to the Jag one. Everything I can find reading indicates spares/servicing are just as much an issue.


I'm still confused as to my symptoms too .

In answer to your questions:
What about if you touch the pedal once or twice whilst the accumulator is initially pressurising? Does that stop the initial lock of the rear brakes? Not sure if I tested this exactly, but I don't think it made a difference
if you avoid discharging the accumulated pressure before turning the ignition back on? Does that also avoid the initial lock? sort of, in that I think the lock was 'worse' after discharging to 0% than just left charged. Both still drag though.
Also, if the rear brakes do lock up on their own, once you've released them with that single press, do they ever lock again on their own with the ignition still turned on? Yes if driven, but sometimes not repeatable if car just sitting in garage.
Did you ever try my suggestion of just unbolting the whole unit and just slightly moving it out of contact with the pedal pushrod? That should be fairly easy to do. Does the lockup still happen if you then turn on the ignition? I think you have to eliminate whether it is inadvertent pedal contact that is always causing the issueYes, I have the pedal box unbolted and drained now as I think i've exhausted diagnosis & am in process of removing it.

I've made this animated gif of the initial pedal application from the German Teves manual for VW;
I think it's basically something in this pic that's moving is sticking. Probably one of the parts that's subject to/able to be moved by the hydraulic pressure (hence my most recent symptom 'one pedal press' after charging from 0 to 100% de-locking the rear brakes):


There's also (I think) an element of temperature involved, in that as the ABS/the engine bay heats up, the rear start to stick more.
This isn't super scientific though. I tested this by manually activating the solenoid block, and rocking the car in neutral back/forward in order to get a 'feel' for the rolling resistance of the car with no brakes applied. Then further tested this by pulling into a layby with car warm, depressurising the rear brakes via manually actuating the solenoid block. & repeating.
Then repeating once they were dragging, repeating with the handbrake on 1 click etc, just to try to get a feel for it.
I ultimately got pretty in tune with the car by doing this & could tell immediately whether the brakes were dragging or not.

I also have an IR camera for my smartphone (HikMicro mini2) which i'd point underneath the car at the side of the road after coasting to a stop, to check the disk temperature & further try to judge how much dragging was happening:

I recommend getting one of these BTW. Not super cheap (I think this was about £200) but very useful for all sorts of things/diagnosis.

 

I've made progress...
I ended up completely swapping out my pedal/booster/valve block assembly with a 2nd hand one I picked up for approx £200.
Took a while to bleed the low pressure line back into the pump (Could hear it sucking fluid/trying to prime, then just sucking on air) but got there eventually, & after a thorough bleed through, including actuating the main valve to one-man 'pressure bleed' the front circuits like the rear & like I did in the past, everything is now working perfectly.
No more rear brake drag, no more pressure loss in the system when parked overnight, no more issue with fluid getting to the front brakes under gravity...

Prior to fitting the replacement one, I didn't really want to strip it down entirely & end up with a pile of bits, but I did disassemble the valve block to get an idea of the general condition of the internals, and it all looked good. There was a tiny amount of 'jelly' on one of the outlet/return filter, nothing major though, and all cleaned up nicely:





FYI, the 4 o-rings between the valve block and actuator are 10mmOD 2.5mm thick EPDM square profile. Despite looking a bit wonky I reused them and they are holding pressure fine. I think you could substitute standard o-rings here no problem as it's a simple static joint with machined surfaces:



So I will be dismantling my old actuator in slow time, taking some pics & trying to find out what was wrong with it. The pedal isn't being retained in the free play position for some reason, as in something is physically broken & it was sitting far too high in the car (& touching the metalwork of the car). You can see the difference in the static pedal angle in this pic, my old pedal on the right:



I've since realised I clearly wasn't the first person to remove it.
The battered reservoir tank from it being out of the car, and all the paint stripped from brake fluid should have been a clue of past issues... I also found this weird piece of mis-shapen plastic, on its side, in one of the reservoir inlets:


Stripped/wrinkly paint from old paint fluid spills:

Tidied up before I fitted the new actuator with a drillwire brush, Bilt Hamber Hydrate 80 rust converter, colour matched spray paint and lacquer:


Also if anyone's interested in the anatomy of the valve block, I made this.
The top row of solenoids block the fluid flow when activated, the bottom row of solenoids release the fluid from the calliper back to the reservoir when activated.
I think manually actuating all of these valves, along with the main valve to force pressurised fluid through these filters for the front brake circuits, should be a key part of regular bleeding/flushing fluid:

 

Asdrewq,

That's great work, really well done!

As you will have seen from dismantling the valve block (great work also on that!), the 2 key areas are scrupulous cleanliness on the solenoids and valves, particularly the seating of the valves, cleaning of the sediment from the filters, and the absolute integrity of the ribbon cable powering the solenoids.

Also really pleased that you got the low pressure side bled out. That can be a nuisance but without being bled properly, you'll never get the air out of the Actuation Unit and the back brakes bled. As you've realised, disconnecting teh feed pipe from the reservoir to the pump and letting fluid flow, then quickly reconnecting it is the key first step.

Also, (and this is just a random guess?) I wonder if that broken plastic bit in the inlet port to the reservoir was the key to the problem? If that;s the back port to the Actuation Unit, that plastic bit could have been slighly interfering with the inlet flow valve thus causing the Actuation Unit to constantly slightly pressurise and lock the rear brakes? Just a thought!

Anyway, well done and great pics! Glad you got it sorted.

Cheers

Paul

 

Hi Paul,

Thanks
That little bit of plastic is very confusing!. I've realised my old reservoir had a broken off nipple, but confusingly that piece of plastic doesn't appear to be the broken bit. Possibly someone's attempt at a bodge? not sure:
Here's what it should look like (pic pulled from web):


And here's what mine looked like, as you can see the thin bit from the port is broken off:



Not entirely sure if that port is a fluid return or supply, or a combination of the two. It would make sense if it is the return as when I was testing the fluid return solenoid on my old ABS (holding solenoid open & pressing brake pedal), I heard a distinct fluid squirting-type noise form the reservoir, which is much quieter on the replacement. Possibly fluid forcing its way past that plastic chunk.

I've been using the care regularly the past week and all does seems good, pedal could perhaps be a bit firmer when the system is pressurised so I might rebleed it (or it might be my imagination of what it used to be like, hard to tell) but my confidence in this ABS still remains low.

I have to confess I have also bought a 2nd hand vacuum booster/master cylinder/pedal, along with all the fittings, joiners and vac pipe etc to fit it from a pre 1988 XJS, just incase...
I realise i've effectively 'got lucky' with my fix so far, in 1)finding a reasonably priced ABS unit & 2) it not being broken.

I will persevere with the stripdown of my old Teves master cylinder & get some pictures though, with a view to seeing how to rebuild it/seeing what ports/filters might be blocked, as retrofitting to non-ABS is very much a worst case option if things break in future & are irreparable.