QUESTION
Back in March 2015 I ordered and fitted your ABS switch set up to my Lotus Esprit.
However, just recently the low pressure switch seems to have failed.
The high pressure switch is still working perfectly turning off the ABS pump at 2700 psi (186 bar)
But after a period of storage during lockdown, the low pressure switch now turns on the ABS pump at at 2250 psi (155 bar)
No amount of adjusting the screw in either direction changes the set point which I'm lead to believe should be around 1800 psi (124 bar) according to the service manual.
I wondered if you've seen any of your low pressure switches fail in this particular way?
The pump now runs every press of the brake pedal so I need to replace the switch unless you can offer a repair service?
On the black high pressure switch, is there a way to adjust the upper and lower set points?
There only seems to be a single allen key adjustment and I can't find any technical documents for that particular switch?
M.W. - UK
ANSWER
From what your describe this particular fault has nothing to do with the low pressure switch.
The low pressure switch function is purely to monitor the system pressure and illuminate the ABS warning light on the dash.
If the pump operates on every brake pedal application then you need to change the accumulator.
For clarification purposes, the replacement switch supplied works in exactly the same way as the original switch design.
The high pressure switch that operates the hydraulic pump has a certain amount of hysteresis in its mechanism which is helpful.
The switch hysteresis in conjunction with the accumulator provides some "internal capacity" which assists by optimising the upper and lower pressure thresholds.
If this were not the case the hydraulic pump would run on every application of the brake pedal and not have time to cool down when driving in slow moving traffic.
From a safety point of view, I DO NOT recommend adjusting the switches without the correct equipment.
Copyright © 2022 Lotus Marques
Back in March 2015 I ordered and fitted your ABS switch set up to my Lotus Esprit.
However, just recently the low pressure switch seems to have failed.
The high pressure switch is still working perfectly turning off the ABS pump at 2700 psi (186 bar)
But after a period of storage during lockdown, the low pressure switch now turns on the ABS pump at at 2250 psi (155 bar)
No amount of adjusting the screw in either direction changes the set point which I'm lead to believe should be around 1800 psi (124 bar) according to the service manual.
I wondered if you've seen any of your low pressure switches fail in this particular way?
The pump now runs every press of the brake pedal so I need to replace the switch unless you can offer a repair service?
On the black high pressure switch, is there a way to adjust the upper and lower set points?
There only seems to be a single allen key adjustment and I can't find any technical documents for that particular switch?
M.W. - UK
ANSWER
From what your describe this particular fault has nothing to do with the low pressure switch.
The low pressure switch function is purely to monitor the system pressure and illuminate the ABS warning light on the dash.
If the pump operates on every brake pedal application then you need to change the accumulator.
For clarification purposes, the replacement switch supplied works in exactly the same way as the original switch design.
The high pressure switch that operates the hydraulic pump has a certain amount of hysteresis in its mechanism which is helpful.
The switch hysteresis in conjunction with the accumulator provides some "internal capacity" which assists by optimising the upper and lower pressure thresholds.
If this were not the case the hydraulic pump would run on every application of the brake pedal and not have time to cool down when driving in slow moving traffic.
From a safety point of view, I DO NOT recommend adjusting the switches without the correct equipment.
Copyright © 2022 Lotus Marques
