Calling All Brake Gurus

[Dasar7]

Hi everybody

Been tearing my hair out trying to figure out my brake problem over the last few months to no avail - therefore I'm hoping the brake experts on here can help.

Simply, on just about every drive my ABS light comes on and flashes. It sometimes starts flashing straight away, sometimes takes several km's before it starts flashing. Brakes work fine, ABS still works, it just flashes.

Also, my brake pedal will have an irregular pedal travel, in that it 'normally' travels a few inches when applying the brakes, but sometimes "tighten's up" and hardly travels at all.

I've had my mechanic bleed the brakes again (which the manual says to do with an irregular pedal) & there was a little bit of air that came out, but nothing significant.

Do I need to start checking sensors or is it possible it's something like the dreaded ABS pressure switch?

All help suggestions greatly appreciated.

Oh, by the way, car is a 94 S4, which has had the Brembo upgrade both front & back.

Thanks everybody.

David

[mr.oogieboogie]

sensor for abs i would say, have had the same problem on mine. the brakes on the s4 are a bit wooden as the abs is craps. i have the powerstop vented and grooved disc's as well as the green stuff pads (works ok for me)

all the best

[Dasar7]

Thanks Peter

I will go down this path anyway, but thought it might have been something more. (Scary when you get technical advice from the oogieboogie man!!!)

[Jonathan]

Irregular pedal is what I've always had on the GT3.

Had the fluid changed a few times now and nothing seems to cure it.

Also done other tests and they come out fine - suggestion is to have the unit serviced and cleaned up which is what I intend to do shortly (when my car gets back on the road, eventually).

In the back are 3 solenoid ports that do something I can't remember but they are important to the workings, if they are stuck or intermittent there will be a problem wih the power assist (this is the issue, the pedal feel is related to a 'boost' chamber pressure which not only pushes the piston forward but pushes the pedal back as well).

It's fairly complicated, if I work it out I'll try and do a write up on it.

[Dasar7]

Thanks Jonathon - a write up on this would be very interesting.

I don't mind the irregular pedal so much, but I'm concerned about the flashing ABS light. I'll report back if I find the source and fix.

Cheers

David

[DanR]

May need a new pressure bulb?

[Dasar7]

Excuse my ignorance Dan, but what's a pressure bulb?

[fflyingdog]

Sounds like your pressure switch,in fact i would put money on it........

Nick S4s

[Dasar7]

Nick (fflyingdog) I was afraid you'd say that. If it was the pressure switch, would I notice a loss of braking performance though?

Also, has anybody got any further with trying to source these switches from a different manufacturer or source?

Thanks again all.

David

[DanR]

David if you have a look at item 31 on page 249 of the manual that's what I was speculating may be the problem. It's the accumulator, a nitrogen charged (200 bar iirc) bulb that provides the power assistance.

[MGFCrasher]

Hi,

There ae a few threads on this now,it must be a bad time or the year for S4's.....anyway.

It will be one of three things (assuming all the fuses etc are ok). Pressure Switch(ouch) Accumulator(ouch) or wheel sensors(not so bad) On my old car the light would go out (once I had replaced the accumulator and switch that is ) and then come on again at anything over 10 mph which pointed to the wheel sensors.

Try cleaning the sensors on the wheels with wd40 first .(cleaning wouldnt help mine and one had been snapped off anyway..doh)

Secondly with the ignition off pump the brake about 40 times.Then switch the ignition on and listen for the ABS pump whirring at the front of the car(it will help if the bonnet is up and the abs cover removed to hear this).Mine only worked if you hit the switch with the wheel wrench.

If the switch has gone it will virtually feel like you have no brakes as there will be no pressure in the accumulator.

If the wheel sensors are gone you will just lose the ABS.

Pete at PNM has my old switch and is seeing if they can be re conned but as far as I know Lotus had one left...

Rich

[fflyingdog]

Wasn"t there something about maybe being able to rebuild these switches? I agree with Rich,i have had all sorts of problems with my abs system over the years,i even went as far as getting an abs accumulator from the states needless to say it wasn"t the accumulator(luckily i purchased it from Gm parts direct and was very cheap,working for an airline helps!) i went through 2 switches within a few months (grey molding is new one with reviewed start stop parameters)"We" (Lewf folk) must be able to sort this out and source one from a reliable source or do a group buy? its a poxy cheap switch ..and how much do people want for it yeah stupid stupid ridiculous money,if i had an old one i would try taking it apart and finding out exactly what fails internally it cannot be rocket science...................ah now thats better rant over ! By the way you can use the Lotus Obd11 wotsit thingy and it will always fail the abs computer so dont go that way,plus of course its always wrong.

Nick S4s

[MGFCrasher]

Hi Nick,

As I think I said Peter at PNM has my old grey switch so maybe he can come up with something. Perhaps if Superdave is in the workshp at some point he can raise it with Pete.

I got the black switch not grey from Lotus.It was still

[Jonathan]

Quick test #1

Switch the car on + engine, press the brakes.

After the 3rd push you should hear a wirrrrrrrr noise from the front (ABS pump)

Repeat a few times.

Switch off - now push that pedal like a bugger (at least 40 times) - now switch the car back on, the wirrrrrrrr should last about 30-60 seconds.

Thats a basic pressure switch and accumulator test.

If the pump runs every time after the pedal push then the acc is buggered.

If the pump runs outside of the time after de-presurising the system then the pressure switch is up the blink.

All the accumulator does is to eleviate the load on the pump, if it wasn't there the pump would be going 2 to the dozen every time you stuffed the middle pedal in.

If ANY of the 2 components are shafted you will get a decrese in braking performance.

Just as a guide mine seems to work fine under these tests BUT I dont have the ABS light which seems to me that there is a genuine fault with yours, usually when the sensors go the light is solid on the ABS warning so I think you might well have a pressure switch gown.

[fflyingdog]

The accumuilator also gives you a certain amount of pedal applications in the event the pump fails ,sort of a head of pressure to get you stopped if you have taken no notice of all your flashing/steady abs warning lights, think we need to make this abs trouble shooting procedure a "sticky" what do you think?

Cheers

Nick S4s

Good write up Jon forget how many times i have typed that lot out!

[Dasar7]

Thanks everybody. I will go through the ABS test again this weekend, but last time I checked this, a couple of weeks ago, ABS pump and test all seemed to work fine, plus pedal 'feel' is fine.

I will also start with cleaning the sensor's up (might as well) & go from there.

Jonathon, it is a very good write-up, thanks.

Will report back after the weekend.

Thanks all

David

[lemoncurd]

Having been another one with the brake issues, I would add my $0.02 and say unfortunately it sounds like it might be the pressure switch.

Good luck with the sensors, I hope that sorts it out for you though....

Edited January 17, 2008 by lemoncurd

[Dasar7]

Quick update.

Removed & cleaned all wheel sensors, & found Right Front sensor has been 'resting' on the speed sensor ring & slowly being cut away.

Am going to put in a couple of shims and see if this fixes the problem otherwise, might need a new wheel sensor.

Still, fingers crossed, this is my only problem.

[fflyingdog]

Quick update.

Removed & cleaned all wheel sensors, & found Right Front sensor has been 'resting' on the speed sensor ring & slowly being cut away.

Am going to put in a couple of shims and see if this fixes the problem otherwise, might need a new wheel sensor.

Still, fingers crossed, this is my only problem.

Let us know how you get on.

Nick S4s

[Kimbers]

Mine were wooden as well but that turned out to be because the calipers were seized and only the rears were working properly!

[MGFCrasher]

Thats a good point .Both my rear calipers were seized solid,but I freed them off when I changed the pads.One need several controlled hits with a large hammer before freeing off.Really wanted new ones but someone elses problem now.

I tried cleaning my front sensors but despite hours of spraying and soaking etc they still didnt work.(not sure what goes wrong with them) . Put new ones in and bingo ,light off!

Rich

[htiek]

My ABS light has been on since I got the car in December. I managed to haggle getting it fixed as part of the deal and she's booked in on the 31st to get it fixed.

After reading some earlier posts I was worried that it could be the pressure switch, but trying the tests I read about here the pump seems to be operating correctly.

Anyway, Sunday was really my first chance for a bit of a blast and although the pedal feels a bit wooden the brakes were effective enough. Well, after stopping to take some pics of the car (as you do!) next time I moved off, no ABS light. Aha, probably just a dodgy wheel sensor then..garage has got off lightly.

But here's the thing..having not driven an ABS Esprit before I found the brake pedal 'feel' a bit disconcerting. It feels like its pulsing under my foot even though the wheels are nowhere near locking up and something under the front bonnet is noisily banging away, a valve I guess. I think I preferred the 'old' pedal feel when the ABS wasn't working!

Does this sound familiar to anybody?

It was nice to have a dashboard clear of warning lights for a change, but, she's still going in to be checked though.

Cheers,

Keith

[fflyingdog]

Hi Keith

Glad you have fixed your snag,fyi my brake pedal feels exactly as you have described ,but as for the "banging" mine doesn"t so probaly best to get it looked at ,just a thought but the banging noise couldn"t be caused by the jack or something similar loose in the front ??

Cheers

Nick s4s

[MGFCrasher]

Hi ,

I have read a number of posts and the pulsing seems to be a characteristic of the system.

I too would look at the loose wheel brace thing for the banging(it tends to be used to knock the ABS switch into action by some owners and could have been left unclipped!)

Hope the problem is as simple as a sensor.I would get them to replace both anyway as they are prone to going wrong.

Rich

[mr.oogieboogie]

hello keith may sound a bit stupid but is the bonnet closed as i thought i had closed mine the other week drove off and under braking banging noise, bonnet not closed on one side. look for any thing loose.

david glad it was the sensor, if its being cut through, replace it.

all the best