Hello All, Are there accumulator balls from other makes of cars that will fit the XJS,as jaguars price is horrendous. Are they a straight fit or a pain in the butt to fit ?
Rgds
Gerald
YES! Covered well "in-the-book-. Anyway- source Buick Regatta, Pontiac 6000, ect. SAME part. Also- maybe 2 possible sizes if you expand beyond the above, and the slightly bigger also probably a go, but I used the GM part advised above.
Are you talking about the vacuum booster for brakes? You can send yours in to Cardone for a rebuild at about $150-200.
Here:
Ho to check and replace Brake Accumulator in your Jaguar XJS.
Tested and works flawlessly (past 3 years). Slightly smaller - canât feel any difference apwrt from more frequent accumulator pump action.
Excellent article, Bangher ⌠and actually coherent (well, mostly) ⌠
I guess since you are our accumultor guru: did you see my post earlier about the connection for the accumulator and for the brake pipe (w. Bundy connector) being reversed in positions on top of the ABS assembly I purchased to replace the (OEM?) one on Superblue, my '94 4.0? This, despite the part #s on both parts being identical (and the vendor swearing on the Book that it is the correct one for a '94 4.0 XJS). Any idea how that can be? 
Hi Atty,
No.
Me no see. You fix with magic liquid. Or you give link, me see.
Me suspect you buy RHD part.
Could you not obtain a larger accumulator?
Any accumulator with membrane designed for brake fluid will work, the larger the better as it reduces pump cycling.
My calculations with a standard accumulator is that if 82 Bar gives 20 brake applications to hard pedal, an accumulator at 30 Bar (minimum spec) will be 8 brake applications.
Just an easy reference to test accumulator pressure.
Given the cost of these I could look into making an adapter for refilling the gas, but would need to make a brake fluid test rig, as I donât want to mix Brake fluid and LHM, as that could be disastrous for accumulators made for mineral oil.
Dieselman,
Been there few years ago, wondering if your conclusion will be the same.
Think about assebly, rechargable accumulators are very bulky and heavy, heavier the accumulator - greater the fatigue on accumulatorâs assembly. You can fit it remotely via extension pressure hose, but thatâs an automatic void of any insurance/claim on your vehicle. Another thing to consider - fitting, capacity and pressure rating, you will need to pick from something available on the market (try to find one and lemme know). Your lucky pick must collaborate precisely with pre-set trigger values of accumulatorâs pressure switch (min-on, max-off) - to get max operating capacity of brake pedal applications. Pressure accumulators are not linear which means that f.eg. 20 depresses on 80bar wonât give you 10 depresses at 40barâŚ
Pump cycling - hard to forecast what is better - pump will need to run longer continuously to fill up larger accumulator, then will switch on less frequently to top up - but will still work longer to perform this (your pressure switch defines this). Whatâs the difference⌠Accumulator pumps can get damaged while running too long, never heard about scenario where pump motor went bad due to frequent, short operation. Think about snowy conditions - with bigger capacity - you would probably overheat pump motor after few brake applications.
Bosch 0265202070 (in 2020 - was ÂŁ90 Sterling at Amazon with next day Prime delivery). Works flawlessly as per now. Rhe only risk is slightly lower capacity - which in theory would make your ABS work shorter period. In reality - it outperform 99% of aged accumulators currently installed in XJS platform globally.
Size- If Yugo, or French, Iâd carve hole in hood for cheap oversized. I chose stock size, âwellâ- at least âbetterâ bought, as advised-above.
Thatâs not how it works, the accumulator has no bearing on ABS operation, it just provides a reserve of pressurised fluid to stop the pump having to cycle and to provide a reserve of pressure in case of pump failure.
Pump cycling is what kills electric motors and should be avoided.
The calculation of how much reserve pressure is very simple, multiply the volume by the pressure to give a figure of Bar-Litres.
400cc x 82 Bar gives 0.4 * 82 = 32.8 Bar-litres.
A 450cc accumulator gives 0.45 * 82 = 36.9 Bar-litres, hence a larger accumulator gives a greater reserve of pressurised fluid.
The pump pressure switch is irrelevant to the volume of stored fluid, it simply switches the pump on/off at set pressures. No calibration is necessary. The effective accumulator volume decreases anyway as it ages and loses gas pressure.
By reducing the accumulator capacity you have reduced the reserve of pressurised fluid, so reduced the time before the pump needs to activate and the margin of safety until the pressure is depleted in the case of pump failure.
As long as the volume is fixed, the reserve of fluid under pressure is indeed linear, so a 400cc accumulator at 80 Bar holds twice the energy of a 400cc accumulator at 40Bar.
Itâs true that Boyles law means that as fluid is forced into the sphere and the gas volume is compressed, the pressure rises inversely square to of the gas volume, but thatâs not the issue here.
The issue is the original volume is less and the accumulator loses gas pressure over time, so has less reserve of energy.
Your statement that changing the sphere would automatically invalidate your insurance is going to need testing, but surely changing to a smaller sphere has a greater negative result, so will do the same.
I think an insurance company would find it difficult to prove that a greater reserve of pressure somehow caused brake failure and the claim they are being asked to cover.
Iâm not sure why you think you would need to go for a remote accumulator. The original one was larger than the one you have installed, so why would another of that size not fit and be suitable?
I donât mean go for a huge plumbing type rechargeable accumulator, just recharge the one you have.
All you really need to know is the volume of the original sphere and buy one that has a suitable fitting and a membrane made for glycol-ester solutions, the best would be an EPDM membrane.
Given that no-one changes their brake fluid on Jaguars, why they opted for using brake fluid instead of mineral oil is a mystery.
Old brake fluid causes system corrosion and blockages.
As Jp2 appears to have remembered, I do have some experience and knowledge regarding pressurised hydraulic systems, including testing and refilling accumulators, fitted to motor cars.
As your car is running on brake fluid I donât want to offer to test the static pressure, as the residual fluid in the sphere will contaminate my mineral oil rig, but I could make another rig for brake fluid only, if there was sufficient demand.
Filling is performed by forcing gas into the filling port on the top of the sphereâŚthe plug you used to remove the sphere, which I have advised to never use a power tool in that plug.
If the plug unscrews before the sphere, it will come out like a bullet.
Lets say the sphere has full static pressure and is locked on due to system pressure, so that plug has 180Bar of gas pressure behind it.
Once all system pressure is released the sphere should unscrew either by hand, or after a few clouts with a lump hammer.
If itâs on tight, use a strap, or band wrench round the circumference.
âŚprovides pressurised fluid when ABS kicks in, thatâs the idea of earliest generation systems. If you ever done a slide on the snow/with abs shagging your foot - thatâs when the extra pressure from accumulator is being depleted. Thatâs the reason why accumulator is there, usually - ABS is activated by ârapidâ events, mk3 pump wonât keep up with pressure build up in emergency situation (hence mk4 invented), especially with 12-pots XJS setup.
In terms of different accumulators/potential replacements - nothing bigger fits under the bonnet, unless relocated. I havenât found anything similar with same fitting/thread size - hence asking if youâre lucky?
Regardless of calculations and recalculations made, âwe can sayâ that the amount of pressure used with each brake depress is constant (under the same conditions). It doesnât matter if you have 100ml accumulator capacity or 10liter. The total pump work time will stay the same. With 100ml - shorter start up pressure build up, more frequent top-ups with shorter run time. With 10liter version - long start up pressure build up (with 10L - blown pump motor almost certain), less frequent top-ups, with longer run times (pressure switch activated pump at preset pressure and goes up to cut-of pressure point).
Pumpâs electric motor has its lifespan. Lifespan of electric motors goes down rapidly when overheated. I havenât seen any accu pump motor in need of recon or brush change - due to excessive use frequency. I have seen few blown due to extended run (bladder busted, pressure switch faulty, idiot driver).
Big-rechargable accumulators are big - because these are rechargable (rebuildable). The type we have in XJS is compact / non-rechargable. To ârechargeâ these - you need to⌠change the diapraghm/bladder. To change the bladder you need to cut it open on the lathe/unscrew where possible. To recharge it - you need to install charging port. Try to fit these within ÂŁ90 billâŚ
Mineral oil would work the best among âjag loversâ - majority of their cars are either rotting away when stationary or not being driven innthe winter season.
The problem with mineral oil (apart from different elastomer materials used) is that it wonât absorb moisture - creating tiny water drops in the system, think about winter surprise - where these drops are changed into âcheck valvesâ somewhere along the pipe.
I think youâve been working with plant/industrial equipment a lot, the hex/allen plug used by myself to remove the sphere is welded/brazed shut in civil cars since mid-80s, at least within European manufacturers (engineering safety design / later controlled by TS16949)
The bullet-trajectory is a myth - unless youâre trying to unscrew pressurised sphere (I agree - not so obvious for many DIY workshoppers), then the entirenshere can turn into cannon ball.
Just sayingâŚ
We have a number of âbombâ rebuilders (including for our Jaguars) in the States as does over the pond. Usual cost is about $150.00USD.
I personally rebuild the early screw-together RR / Bentley spheres at my shop which are of course serviceable without cutting or taping anything. Parts are still sane, at $50.00 each.
1 Like
I would be really surprised if the Teves III pump cannot displace more than the fluid requirement of the brakes in ABS operation mode, that would need testing with a flat accumulator fitted.
Irrespective, if the system pressure drops to the point the pump is required, the ABS cuts out, which returns the brakes to a âdead endâ system.
I am aware of how recirculating ABS valve blocks operate and currently have two cars with the same type. I have never known the ABS system deplete the reserve.
Motors do have a finite life, but start/stop operation is what overheats them and burns the commutator and brushes, so should be avoided.
You keep mentioning big rechargeable accumulators, why?
I havenât mentioned larger than standard accumulators.
I can guarantee that automotive accumulators do not have brazed in filling plugsâŚitâs how they are filledâŚand itâs how I refill them.
Unscrew the plug until the O ring displaces and squirt in some inert (usually nitrogen) gas.
Your description of how the Teves III system operates is incorrect, the accumulator is a store of pressurised fluid, used at all times, not just during ABS operation.
Due to the Teves III being an open return, recirculatory system, the reserve of pressure is used for every brake application, not just when ABS is in operation. If it wasnât, one couldnât deplete the pressure by repeatedly pressing the brake pedal.
Regarding using mineral oil instead of brake fluid.
Brake fluid is hygroscopic. Isnât the fact that people are not changing the fluid every two years (as specified), creating the problems we keep seeing on this forumâŚcorrosion and stuck valves.
Turning to the filling plug.
Take a pressurised sphere (82 Bar), being hydraulically locked on with 160Bar of hydraulic pressure.
That means the filling plug is subjected to 160 Bar of fluid pressure, with a residual 82 Bar of gas to give expansion force.
If only the fluid pressure existed it wouldnât be an issue, because once the volume increased the pressure would be lost, but the gas pressure expands into the new volume.
At the point the plug unscrewed it would still have ~160Bar of gas pressure behind itâŚthatâs 2320 psi / 1.6 Kn/sq-cm, accelerating that metal projectile.
A quick and dirty calc (say, 34 gram plug) gives an acceleration of 47m/s squared for the filling plug.
It may be the system pressure is fully depleted and so is the accumulator gas pressure, in which case the accumulator should unscrew easily, but it may be the accumulator and system are fully charged, in which case the filling plug will unscrew before the accumulator does.
If one unscrews the filling plug a good accumulator will be rendered scrap due to losing the gas.
My advice is donât unscrew accumulators, especially using power tools, by the filling plug.
1 Like
Surprise! 
Dieselman, I think weâre talking about the same principles, just some things are lost in translation.
I am aware how ATE mk3 works, I was referring to ABS-engaged scenario, where ABS solenoids are cycling repeatedly (snow, ice). Thatâs when your pressure is being purged excessively. Again, havenât seen accumulatorâs pump motor with worn brushes/commutator. I have seen overheated/blown ones due to constant operation. Even Jaguar is stating max run time in service manualâŚ
Iâve mentioned big rechargable accumulator spheres as I couldnât find any standard replacement - apart from Bosch mentioned earlier. As you seems to be deep into the pressure business - maybe you can find cheaper alternative???
Weâre also discussing standard disassembly issues on old/seized fittings, not scenario where someone is trying to get hurt. I will go by your advise next time and put my NIJ level 3 vest on
Youâve mentioned the way youâre filling them - are you sure weâre talking about the same type? If so - would you be able to explain how youâre recharging these? Removing the bolt with o-ring - with nitrogen squirt and then? Is there any valve in there? Just wondering i there is a trick on how to bolt it down quick enough⌠Itâs just my logic, Iâm not a proâŚ
For the sske of discussion, Iâve attached photo of recharged sphere (LandRoverP38)âŚ
Also photo of welded plug as per below:
Jeff, yupp, thatâs still higher than Bosch model mentioned earlier. There is plenty of âtechnologyâ utilised by The People - to recon these, itâs the recon cost that suggests going for new unit rather then fiddle.
I remeber Bentleyâs one, similar to Citroen, joy to work with, simple, easy, heavy, well machined. Everything can be stripped down and reassembled. This unfortunately was not adopted by ATEâŚ
The accumulators you show for LR P38 appear to use a central screwed in plug, which may be sealed using an O ring, but more likely liquid thread-loc.
Either remove the plug, or drill, tap and add a charging valve, then fill. A high pressure shrader valve would be more elegant than the added on filling valve shown.
I donât see any evidence of welding on the type with the hex drive, it appears to be a plug which almost certainly uses an O ring as the seal.
If one checks the pressure occasionally and doesnât allow it to fall below 30 Bar before refilling, the accumulator will last a very long time, probably outlasting the car in the case of only being used for brakes.
I am aware the pump has a 10% duty cycle, which in itself isnât going to be an issue.
I refill welded type Citroen spheres as a result of building a gassing rig to loosen the plug enough to lift the O ring off itâs seat, then fill with gas, then tighten the plug, all with the filling plug being in a pressurised gas, sealed environment.
For later âsaucer typeâ Citroen spheres, with a sealed in plug (welded/glued), most people drill the plug and add a filling valve, but I have been made aware of one company that claims they can extract the plug and refit it as they claim it is glued in.
As you can imagine filling spheres is a fairly hot topic in Citroen circles, as some of the cars have up to 10 of them fitted.
Citroen C6 suspension sphere regassing (youtube.com)
This chap is drilling the original plug out and fitting a plug with O ring, which more closely replicates the earlier type.
AutoMotoDaily Workshop Citroen C5 hydraulic suspension problem, spheres regeneration (Vordbrodt) ENG (youtube.com)
Look at the photo Iâve added earlier, had three of these somewhere, earlier and later model, earlier - the bead was around the nut, later one - spot weld from one side Canât be asked to go through my leftovers. (maybe later, during spring time).
In terms of adding a valve - itâs probably doable, but not cost efficient - hence this post. These are not made same way as the Bentley ones - you may not have much metal there to âadd a valveâ. Another thing - youâre adding almost a cost of new sphere - to end up with ageing/-leaking diaphragm/bladder. Whatâs the point?
I donât see any weld on your accumulator plug, which was my original concern.
Irrespective, if you keep the pressure up the diaphragm will last a very long time as it will flex less and what usually causes them to rupture is the diaphragm contacting the filling plug retainer inside the sphere, as a result of low pressure.
If you only have a single car and only one accumulator itâs probably not worth looking at recharging them.
I currently have 21 spheres in operation, so the cost balance weighs heavily towards regassing.
What size allen key fits that plug and how tall is the sphere from the base to the top of the spherical section?
My suspicion is that is a 400cc sphere. The one you have fitted looks to be about 250cc and is probably for a Mercedes SBC system, which doesnât use recirculating ABS.
If anyone has a scrap, preferably not ruptured, Jaguar sphere with the filling plug, I might look at making an adapter for it and could trial regassing a sphere.
TBH, weâve probably exhausted this topic. All the relevant information is in the Teves III thread.
I used this one from Amazon. Itâs been fine
That works with the facelift models, 6Johns?