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Brake pedal makes whoosh sound

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Anyone had this :

on pressing thebrake pedal there is an audible whoosh sound coming on in the PROGRESS of pressing it. It then stops, holding the brake down is normal, but the pressure pump comes on and the feelable pressure of the pedal rises untill the pump stops.

The accumulator and swich have been replaced 2 years ago, and no tell tales go on.

Is it the actuator, that is the gaskets, worn ?

Olaf S400 project



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  • 5 months later...

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Put the car in the garage:-)

No actually ran out of time since I mooved. But talking to Steffen at R&B, he thinks its an air bubble sitting somewhere near the cylinder.

As soon as I get time I will have a go at re-flushing....

Otherwise :

as I am a little fed-up.....

will post!



Exactly what my car is doing after flushing, did you solve it ?

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Olaf S400 project



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Hi Olaf, yep I think it has air in the boost section of the master clyinder as well - spend 2 complete days trying to flush it to no avail.

I took all the ABS apart and manually cycled the ABS solenoid valves by shorting out some pins on the ABS computer harness and still no joy - it moves oil/fluid but no sign of any air coming out.

I did read a lot of these systems have to be bled on the bench and rotating/banging them in order to persuade the air to come out but not tried this yet - pain in the ass for sure.

I think I'm gonna throw it out and fit a dual master cylinder system in with no ABS and see how we go as the Delco system is just far too much hassle for it's worth.

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Erik / Olaf / Dave - I have sorted this...

3rd time of typing so I am gonna take it easy.

I have had a NIGHTMARE doing this job, seriously I have considered ditching the car becuase of it. Every step I have taken forward has been followed by 27 backwards, I'm totally emotionally drained from the past 6 days trying to sort it out and the stress I've had, plus 1 broken caliper !

I'll start at the beginning...

In the manual Lotus state to bleed the front brakes 1st and then the backs - I did this about 15 times (no shit, I've used gallons of fluid becuase it got contaminated and exposed) to no avail as the car still made the wooshing noise. I then spent 3 full days stripping the ABS down and installing a manual bleed switch onto the solenoid valves so they can be done individually. No joy.

The issue is when you push the brakes the accumulator / pressurised system depresurises to such an extent that the pump cuts in everytime, you also get a wooshing noise which is indicative of air rushing past or oil flowing over an air cavity - it is totally clear there is air still in the system, and it's my opinion its stuck in the boost chamber of the master cylinder.

It's also important to know the front reservoir compartment and the front brakes are totally isolated from the rear compartment and the rear/boost/power assist section of the brakes which leads onto the fix.

After exhausting many ideas on why the air is trapped, the only thing I could think of was to drain the front section of the master cylinder and then crack open one of the pipes leading to one of the front brake calipers. This allows the master cylinder to achieve it's full stroke and not be restricted by compressed oil.

The moment I done this and started to pump the brakes I saw more are coming from the small port in the rear reservoir chamber.

This is how I bled the system...

* After removing the oil and undoing the front brake line put a cloth under the loose connection to stop any leaks,

* Fill the rear chamber,

* turn the car on and let the pump run,

* Bleed the rear brakes as normal (rear right, rear left) - let the fluid run rapidly for quite a while but DO NOT let the reservoir run dry,

* Close the bleed screws and FILL the rear reservoir (important, see below)

* Get in the car (carefully if on the jacks) and hold the pedal 1/2 way down and switch the car on and off to cycle the solenoid valves (the reason why you fill the reservoir is to cover the solenoid valves with fluid, this stops more air getting into the reservoir),

* Cycle the valves 5-10 times,

* Switch the car off and depressuirse the accumulator by pumping the pedal 40 times (until the feel changes) - pump down hard, but lift up slowly - this will stop you sucking in any air bubbles that come out of the reservoir. It can help here to have a 2nd person watching the fluid.

* WAIT - either suck the oil out with a syringe or let the oil settle for at least an hour - use a torch to check the airiated state of the oil, tighten the front brake line again to stop any leaks.

* After waiting come back to the car and check on the state of the oil, if it is not clear and still has air in it suck it up and put new stuff in,

* Repeat all of the above until no air comes out no matter how small.

* If the noise persists then take the rear calipers off, unscrew the bleed nipple slightly and then wind the piston back, trapped air can get in there too !

* Bleed the rear calipers frequently (they dont take long)

The issue here is the accumulator generally sucks in airiated oil and compresses it making it almost invistable - again check with a torch, it's there ! I had to repeat this 5-6 times, possibly more and used a lot of oil but at long long last I've got rid of the hissing noise and the pedal is back to being 3 full on presses before the pump runs.

It's a TOTAL BALL ACHE but it can be done.

Jono's top Tips :

* DONT EVER DRAIN THE SYSTEM...this is what done it for me, I stupidly vacuumed it all out, flush only !

* Let the air settle - use a torch look at the oil, I garauntee it's saturated with tiny air bubbles - suck it out and replace it with cheap stuff before putting in the good stuff.

* Use cheap oil to do the flushing, the system takes 1.1 litres of oil to refill.

* Front chamber and brake calipers are completely isolated and indipendant of the rears and much less hassle to bleed, do them last

* Repeat bleed the rear calipers, take them off if necessary and wind the pistons back into the body (handbrake mechanism) to drive the air out of the chamber

* Persistance and Patience - it will tkae you the better part of 2 days, mainly waiting around for the air to settle.

Hope that helps, now going to my happy place - if I were a drug smoker I'd be having a meter long spliff :)

PS. Erik if by some means you can modify espritmon to open the ABS solenoid valves that would also help. I done mine the old fashioned way by shorting them to earth and they do help cycle the fluid.

Edited by Jonathan

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  • Gold FFM

Jonthan, thanks for all this info, I will discuss it at the Lotus garage when they start to fix my brakes.

Regarding your last remark, 'if by some means you can modify espritmon to open the ABS solenoid valves that would also help', I started a topic in the ECU/freescan section on Nov. 21 2009 to find out whether someone has information on the mode 4 protocol used by the ABS computer. With this information I should be able to add the capability to cycle the solenoids.

For the ECU, I found part of the information in the document 1988 GM P-4 Turbo PFI system, and figured out the rest by trying all sorts of bit-combinations. That is why it is possible to use Epritmon to control all the relays and solenoids that can cause a 26 error.

However, for the ABS computer I'm lacking a point at which I can start, so some minimal information about mode 4 is needed. The document that I used to read the ABS (A156AM.txt) only contains the specification of the mode 1 protocol of the ABS.

I just checked the topic again, 35 views, no replies, so apparantly the information is very scarce.

Anyway, if someone can provide the info, I will add the required code to Espritmon (which is freely available)


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Spek to Lotus ? Ask Bibs - I know they do have ECU guys there familiar with the older cars as I had a techy question answered that way.

Sure there is info there - might be worth adding not many Lotus Dealers have the Tech 1 anymore so cannot effectivly service the car.

I'm off to change the brake fluid AGAIN in my car to finally purge the air bubbles, joy of joys !

Edited by Jonathan

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If its never been shaken then these tiny bubbles in the new fluid should not be there. I wouldn't have thought you'd have shaken yours Jon, but have the containers been dropped recently? Gently pouring the fluid in the resevoir should not cause a significat ariation of the fluid, just the odd couple of bubbles and using a funnel angled so the fluid gently runs in should eliminate this altogeather.

With the cartons sitting on the shelves in the car places for so long I can't see how there could be any air in there?

Chunky Lover

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Its not that that airiates the fluid.

It's kinda difficult to explain unless I type a book on it but due to the nature of the system air can get into the complicated system very easily - it's a pressurised system not a vacuum powered one and the prob you have is when the system is disscharged any tiny air bubbles exand and get trapped inside the power assist chamber etc. It's totally and utterly alien to a vacuum system which aids the pedal, this acually pressurises the fluid.

When you switch on the system even does an air bleeding cycle - it's that bad. As the system is operated you sometimes get violent discharges of fluid (as I say under 2800psi of pressure) into the reservoir which gives the same effect as shaking your fluid as you say - if this gets sucked into the pressure pump it's a NIGHTMARE to get out.

The issue is the system was designed at the dawn of ABS, it's complex and problematic which is why cars made nowadays dont use this pressured system - it's just the nature of the beast (and why I am going to convert to a dual master cylinder sometime soon)

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Wotcha sorry for ? :baby:

I have seen people buy brake fluid and shake it like Tom Cruise in cocktail LOL so it's well worth nothing :question:

I always decant the fluid into smaller containers to add to the reservoir so i can get close in and not cause any bubbles - good advice.

The Delco ABS (Esprit 1993-1997) is just hyper sensitive to any sort of air contamination so it seems.

The pedal on my car was SHITE, I noticed 1 pin head sized dot of air out and things got better - also my rear caliper was losing about 1 drip of oil every 20 or so presses and this was enough to dull the pedal as well.

I've just been to shops and bought some more fluid to put through it again - I'll see if I can take a picture of the old stuff for comparison.

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