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New ABS switch delivered yesterday

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On ‎4‎/‎4‎/‎2016 at 23:24, tmusc said:

I have found another one switch solution that may be possible. The switch is made by HYDAC and is the EDS8000. Some wiring may need to take place but the switch has the ability to perform all functions. I have ordered one and hopefully testing soon. This switch is quite sophisticated and is fully programmable and has the ability to show real time pressures.

this does look very interesting.

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In 1993 Lotus issues a service bulletin and changed the pressure switch to reduce the operating pressure on the system but nothing that I have specifies what the actual pressure change was.  The original switches were black and the new ones are grey.  All of the switches I've found in a Lotus have been grey, even on older cars so they had been updated.  Does anybody know what the pump activation and warning light pressures were on the original black switch vs the new one? I have just tested a number of original switches both black and grey and found the pump pressures of these grey switches are running from 1800-2300psi and the black switches are 2200-2700.  From my Lotus manuals the correct pressure should be 2200-2700 but which switch was that referring to?  I would just discount these numbers as a worn out switch operating below its normal pressures except that I tested 3 of each and they were very consistent, and the older black "higher pressure" switch matched the book numbers precisely.  I guess the good news in my case is that if the lower pressure is correct, I don't have to change the switch and if the high pressure is correct I have one that I can use. 

Does anybody have a grey switch that is pressure gage verified to be running at 2200-2700 psi?


Dave Cammack

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The 2200 psi "pump on" and 2700 psi "pump off" with 1800 psi warning values are from the Jan 1995 update of Service Notes Section JF so presumably they are for the later grey switch as the TSB states Service Notes Section JF.13 will be updated for the change of pressure switch.

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That's the same copy that I have, and I have always assumed the same thing, but finding the consistent results with these 6 switches got me wondering. I looked up the service manual for the 90 Olds Cuttlas which used the same system and came with a black switch and it lists those same pressures.  Of course GM could have updated the switch and service manual for those as well but unlike Lotus I have not been able to find a service bulletin for the Olds that replaced the switch.


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After some fairly fruitless digging around it may be that the Jan 1995 update of Service Notes Section JF has the original black switch settings as Section JF.25 lists the same values and, as far as I can tell, Section JF.25 has never been updated. This would then suggest that your test results of the grey switches closing at between 1800 to 2300 psi could indicate the correct pressures.

Did you test the low pressure warning setting of the switches?

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That's the same conclusion I have been coming to for the last  2 weeks but I've been doubting myself because everyone Seems to have accepted the 2200-2700 psi values as correct, including the people making these replacement switches. I had enough doubt that I borrowed a second pressure gage and verified my readings. Someone else reported today too that his '91 manual listed the same pressures as the '95. I wish someone had a printed spec on the grey switch but until then I'll assume these are good working switches. The low pressure warning is not as simple to check when the switch is working but I will test that this week and report back. 

Dave Cammack


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Grey Switch 1

pump on 1900-2350psi and warning at about 1600

Grey switch 2

pump on 1800-2300psi and warning 1500-1600 (the warning cam on about 1500 but didn't go off till 1600 so it was sticking a little

Grey switch 3

pump on 1800-2300 but the warning light was on full time below 1500 and on intermittently above 1500 indicting a bad warning switch. 

We tested with 2 Gauges and the second gage indicated about 100 psi below the above values for whatever that's worth. When all is said and done I guess I'll be sending my gauge in for calibration. 

So in the end it's still a really small sample. If you can get yours tested do so and report the results. I will say you should remove the switch periodically and drain that port and clean the switch. You don't get all that much fluid out but It seems to be a low point that doesn't get much fluid exchange and I drained out some ugly gunk on this car when I removed it the first time. That could be contributing to the switch failures. I'll have this car here for about another month so if anyone over here in the US wants to send me their grey switch to test, I'll test it, report the data and mail the switch back. 


Dave Cammack

St. Paul, MN 

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Both the black and grey switches appear to be quite repeatable within their respective ranges.   It's just that until now we haven't had spec values for the grey switch.   TSB-18, "Replacement of ABS hydraulic pressure switch", was full of information like the size of the socket to use and warranty charges, but gave no pressure specs for the new grey switch.   And the subsequent Service Notes thru the 1993-97 edition were never updated.   They continued to show the higher pressure specs for the original black switch despite TSB-18 talking about lowering the operating pressures.

Well, now we've measured a small sampling of switches, and while the quantity may not be statistically meaningful, the results are consistant.   1800-1900 psi on,  2300-2350 psi off, and 15-00-1600 psi warning light.   If you have a grey switch that has been delivering 'low' pressures compared to the Service Notes' specs, well perhaps it was supposed to.
It's also interesting to me that the new alternative switches, like the Bosch unit from Ralf, are running on the old, high pressures from before TSB-18.




Replacement of ABS hydraulic pressure switch.



To lower system pressure and reduce brake pedal stiction.   The new pressure switch, fitted into the pump/accumulator housing, has-been recalibrated in order to lower system pressure, and reduce seal friction in the booster/master cylinder assembly.   One effect of this change is to lessen any tendency of the brake pedal to 'stick' and not fully return to its up stop.



At the next opportunity on all ABS equipped ('91 M.Y. onwards) Esprit models prior to the following change point:



N 0236  (Domestic / Export '92 M.Y.)

- replace the ABS hydraulic pressure switch as detailed below.



Pressure Switch (inc. "O' ring,  B082J6137S,  1 off)

Socket Spanner,  39mm (1 ½“) long reach,  TOOOTl238F,  1 off

DOT 4 Brake Fluid - as required


Note that the original switch (A082J6I37S) has a black plastic body, and the new 'B' version a grey body.


The ABS pump/accumulator assembly is mounted at the driver's side front corner of the front luggage compartment beneath a protective-plastic cover.


The pressure switch is fitted into the housing beneath the accumulator.


Depressurize the accumulator by turning off the ignition and FIRMLY applying the brake pedal up to 44 times.   A noticeable change in pedal feel (to a hard pedal) will occur when the accumulator is completely discharged.


Before unscrewing the pressure switch from the pump/accumulator endplate, have the new switch ready and prepared for fitment to avoid the necessity to bleed the hydraulic system.   Lubricate the 'O' ring supplied with the new pressure switch using DOT 4 brake fluid and fit the ring onto the new switch.


On LHD cars, it may be necessary to release the relay bracket fixings for sufficient access to the pressure switch in the pump/ accumulator endplate.


Disconnect and unscrew the pressure switch from the endplate extension beneath the accumulator using a long reach 39mm ( 1 1/2") socket - available under TOOOTl238F.    Use a shop towel to absorb any escaping fluid.


Screw the new switch and 'O' ring into the endplate and torque tighten to 20 - 27 Nm (15 - 20 lb-ft).   Connect the harness plug to the switch.



0.5 hr/car.   Warranty claims marked S/B 1993/21 Class 2 should be submitted together with the displaced switch.


An updated Service Notes section JF.13 (ABS Hydraulic diagnosis) will be issued in due course.


End TSB-18




Edited by Esprit2
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I haven't checked to see what colour switch I have fitted as yet, but I certainly intend to in the very near future, and will post here. I imagine that my switch is the original from 1995, but I just cannot be sure, as I have only sketchy service history. Tim, if I can get the switch checked for pressures, I will. And as the HYDAC switch is programmable, it will be interesting to see how Tony fares with it.


I'm not sure if this has already been posted, but if not, and for the interest of all concerned, here are some relevant portions of the text to which Tim is referring, from the S4/V8 MY '93 onwards Lotus service notes:-


"The motor turns the three piston rotary pump and supplies brake fluid under pressure to the accumulator where it is stored and maintained at a pressure of between 15,200 kPa and 18,600 kPa (2,200 and 2,700psi). The accumulator stores pressurised fluid so that the pump does not need to run for three to five normal brake applications. A rubber diaphragm within the accumulator separates the fluid from nitrogen gas which is precharged to approximately 8275 kPa (1200 psi). A pressure switch fitted into the end cover of the pump/accumulator assembly closes below 15,200 kPa (2,200 psi) to energise the pump motor, and opens at 18,600 kPa (2,700 psi) to turn off the pump. A pressure relief valve is fitted to prevent dangerously high pressures being produced in the event of a control system failure. The valve is fitted in the booster/master cylinder assembly and opens at a pressure of approximately 23,500 kPa (3,400 psi) to bleed excessive pressure back into the fluid reservoir. The valve reseals at approximately 18,600 kPa (2,700 psi)."

Further down in Section JF, the notes say:-

"Note pressure when the motor shuts off or a high pressure limit is reached. Is this pressure more than 2,900 psi? If so, replace the pressure switch. Using the ‘Tech 1’, monitor the pump state while applying the brakes slowly until the pump begins to run. Note the low pressure point when the pump turns on. Does the motor turn on at 2,000 to 2,400 psi? If not, replace the pressure switch since it is turning on the motor at too low a point. DEPRESSURISE the accumulator before removing the switch."

And yet further down the notes:-

"Note the pressure at which ‘Tech 1’ indicates “OK” pressure. If this pressure is not within the 11,700 to 13,100 kPa (1700 to 1900 psi) range, replace the accumulator pressure switch. Note the pressure at which the pump turns off. If it is not within the 17,900 to 20,000 kPa (2600 to 2900 psi) range, replace the accumulator pressure switch. If the pump continues to run but maintains a constant pressure, perform step 9 of test D ‘Pump Run Time Too Long’. 5 . When the pump has stopped, press the brake pedal until the pump begins to run. If this pressure is not within the 14,150 to 15,850 kPa (2050 to 2300 psi) range, replace the accumulator."



Margate Exotics.

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13 hours ago, sailorbob said:

Good info Dave. I think it would be reasonable for those with after-market switches to assume:

Warning - 1500 psi

Pump on - 1800 psi

Pump off - 2300 psi

That's the same thing I was thinking. 



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  • 3 weeks later...

I got the switch, made the harness. I knew it was going to be a tight fit. In the end the switch was a little to long. I have ordered fittings to move the switch over. the electrics work though. now its just a matter of getting it installed. will update with photos when complete.

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  • 2 months later...



Hydac EDS 8000 switch

I've just fitted one of these, and it works perfectly.

Back in 2012 Darren (dodge1979) and I developed the two mechanical pressure switch fix for this problem - this works well and is the cheapest fix but it is difficult to find suitable switches with sufficient hysteresis and the set points are factory set. See thread “delco brakes get them working successfully and well”.

I then tried Ralf Burk’s single switch fix, and is easy to fit and works well but the pressures are also not adjustable. See thread “New ABS switch delivered yesterday”.

The Hydac switch is very neat and is very flexible, the pressures can be adjusted with a few button presses.

The attached images show what it looks like ...

Image 1 shows the switch as installed.

Image 2 shows the switch in action pressure, the actual pressure is displayed together with the status of set point 1 on the left (Green as the switch is open, i.e. not pumping) and set point 2 on the right (Red as the switch is closed, it opens if the pressure drops to 1600 psi).


1)      I fitted the switch to a short length of hose similar to the two switch fix.

2)      As the M14 fitting on original switch is rather odd the easiest way to attach to it is to use a copper washer and M14 bulkhead connector. This has long thread which needs to be reduced in length and then use an adaptor to convert this to a 1/4" BSP thread..

3)      Some simple wiring is required both to connect it to the original switch wiring and to supply 12 volts to power the switch.

The switch is an EDS 8446-2-0250-N00, I also bought the Hydac wiring connector. Total cost is rather expensive at about £450.

These Companies can supply the switch in the UK ….


I initially tried a EDS 8446-2-0250-000 which is cheaper and does work but needs two additional relays.

 I used the lower pressures as suggested above in this thread, these pressures do seem to give a better feel to the brakes.


Here is my Setup and User Guide,

Pressure switch settings and User guide

Pressure switch settings

Remove seal and replace with a copper washer

I used a copper washer  14mmx22mx1.5mm (the original seal must not be used as it will be dissolved by the brake fluid).

Units setup

Main menu, Extended function (EF)

Units (uni) = Psi (PSi)

Pump control (set point 1)

Switch point (SP1) = 2240 psi                                       10psi increments

Switch-back point (rP1) = 1800 psi           

Then in Extended function (EF) ….

Switch delay time (dS1) = 1.4 seconds                    0.01 sec increments

Select normally closed (ou1) = Hnc

Low pressure warning light (set point 2)

Switch point (SP2) = 1635 psi                                       min SP1 to rP1 =35psi    

Switch-back point (rP2) = 1600 psi


Then lock the switch settings (Pr6 = Loc) in Extended function (EF)


Power  feed

I took  the 12v feed to the switch using a piggy back fuse holder from the ABS 3 amp fuse (E5) with a 1 amp fuse, this also feeds the original switch and pump relay.  



Pump on pressures required are 2300/1800 psi, but ….

When the switch is energised (ignition turned on) the switch will close if the pressure is below the switch point to bring the pressure up to the switch point, this means that if the pressure is just below the switch point the switch activates for a very short time and if this is less than 1.4 seconds the ABS ECU flags an error code 62!

So by setting a switch delay of 1.4 seconds the switch will always activate for at least 1.4 seconds and therefore no code 62.

At the same time you need to reduce the switch point by about 60 psi which results in a set pressure of about 2300 psi and no code 62.

This means that if there is a fault that would normally cause a code 62 error no error would show, but I don’t think this would matter as all the error code are still active.

Pump runs for about 5.5 seconds (including 1.4 second delay).

User guide

Pressure is displayed in PSI

Left led is SP1

Right led is SP2


If SP1 is OK (open) led is green, when pressure is below the setting point  or actually pumping light is red. Will pump up to max pressure whenever current is switched on.


If SP2 is OK (closed) led is red.




Image 1.jpg

Image 2.jpg

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On 4/14/2016 at 08:30, ian29gte said:

If anyone is interested, I received an email from Ralf Burk today saying he has 4 switches in stock.

Well, bite the bullet...I sent an email to Ralf asking for one of his switches.

Mine is running the pump for only 4 or 5 seconds from completely depressurized and turning pump on with every press.  It's been flakey before, but seems to have completely given it up now.  Undriveable at this point, IMHO.


Hopefully Ralf has one or I'll be trying to copy the outstanding work Paul did above. 

Edited by Richard123
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Richard, I'd be looking seriously at that Hydac switch first. Although I think if I'd got to the same stage, it would likely be a vacuum pumped and servo system install.

Still, if Ralf has a switch, at least it's an easy fix for you.

Margate Exotics.

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11 minutes ago, ian29gte said:

Richard, I'd be looking seriously at that Hydac switch first. Although I think if I'd got to the same stage, it would likely be a vacuum pumped and servo system install.

Still, if Ralf has a switch, at least it's an easy fix for you.

The big advantage of the Hydac (as I see it) is the readout.  Balanced against that is the extra plumbing (hose), the powering on of it, the extra wiring, and the fact that it's an industrial switch.  Paul looks to have done a very tidy job of it, but it's certainly a job.

If I can slip in one of Ralf's switches I'd be right back on the road (it's my daily driver all summer).


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1 minute ago, Richard123 said:

The big advantage of the Hydac (as I see it) is the readout.  Balanced against that is the extra plumbing (hose), the powering on of it, the extra wiring, and the fact that it's an industrial switch.  Paul looks to have done a very tidy job of it, but it's certainly a job.

If I can slip in one of Ralf's switches I'd be right back on the road (it's my daily driver all summer).



Ah, OK, in that case you need the direct replacement.

I'm holding off for a while until I've cleared a whole raft of other maintenance and improvements this winter. Once the summer has finished I'll be getting going with them, and if I get time, money and enthusiasm to coincide long enough to make a decision on the brake system. It may be that PNM have the electric parking brake on sale by then, too.

Margate Exotics.

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  • 2 weeks later...

I decided to take the factory switch apart before ordering one of these Hydacs or phoning Ralf (email isn't happening).


Amazingly complicated little contraption.  Unbelievable design, lol.  A couple of points bear mentioning though (from my understanding of its operation, mind you.  No guarantee I am "seeing" this right).  

The small rubber plug on the electrical side hides an adjustment screw that pre-loads a spring clip that should affect all set pressures.  So turning that screw in should get higher pressures across the range. 

The two switches (pump and light) are just simple on/off contacts operated at slightly different levels by push rods.  The pump differential is caused by a diaphragm flipping from concave to convex.  On my switch the diaphragm has to flip before either switch actuates, which I think is a problem.  If I shim the light switch pushrod with a piece of paper, it actuates before the diaphragm flips which I think is right.  I suspect 22 years of service wore it the thickness of a piece of paper, lol.


I'm still messing about with it to understand it better, but if anybody wants pictures of one apart, now is the time.


I will likely put it back together and see if it works, but its certainly not designed to be rebuilt, lol.



Lotus Pressure Switch.jpg

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Interesting, thanks.

I still reckon the Hydac would be a better bet long term if you're sticking with the Delco. I'm still undecided, all the time mine appears to be working. I don't really want to spend any money on the Delco, only to find something on it fails!

Did you get another daily-driver then, Richard?

Margate Exotics.

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