Calling All Brake Gurus

[MartinL]

Hi guys, your help needed........recent purchase of S4 with Hi spec front brake conversion,disabled abs,Hawk fast road/track day pads, I am 14stone 6foot and fit but find it impossible to stop the car from any speeds, my 8stone wife describes the car as fu... dangerous, i have read through all this thread and done the tests i can............the pump is heard to work for 30 sec. after draining pressure fully (approx. 50 pumps of pedal) and cuts in after 2or 3 depressions when running but it still seems to have no assistance to the braking force, i have tried fitting softer front pads with little improvement. pedal travel is short before bite and has no "air in system" feel about it, i have asked about other owners only to be told ...S4 brakes are crap! I realise its an over complex system but my 40 year old Elan puts this to shame, something must be failing or I have high expectations.

many thanx. in anticipation of your help or informing me this is the best i can expect!!!

( NB. I can not lock the wheels on a wet road! all calipers and pads are free and clean)

[Jonathan]

The prob is it's an old system in age terms.

Once I found all the leaks in my SE's vacuum line to the servo the car pulls up perfectly well and so should your S4.

So all your calipers and pads are moving correctly and freely ? (check pads are free, you'll be amazed what can stop the caliper's clamping)

The accumulator and pump seem to be working. You can test for internal leak by holding the brake ON hard - you shouldn't hear a pump noise if the system has no internal leaks.

I wonder if you might have a blockage in one of the many solenoid ports inside the master clinder - does it pull to one side or the other ?

Seems like there is no pressure getting to the calipers themselves though.

If you can get it to a speacilist or dealer with a TECH1 they can monitor the pressure with that tool.

Other than that an MOT centre can stick it on a brake tester and see what force each wheel are pulling.

In my opinion, sounds master cylinder related.

If I get time tomorrow I might put up some blurb on a webpage about the mastercylinder itself.

Edited December 8, 2009 by Jonathan

[MartinL]

Hi Jonathan, thanks for that, Car pulls up in a straight line, all pads and calipers free, no leaks when holding pedal down, just no assistance!

martin

[Bibs]

The brakes are race quality, they are very good and you'll see Brembo's on many motorsport applications. Check the relay on the bulkhead, accumulator and give the pressure switch a gentle tap just in case. Taking the switch out and giving it a good clean as described in this topic will be a great help.

Lotus have a prototype switch being tested right now, watch this space!

[Jonathan]

Excellent news Bibs.

I do fear it's master cylinder related.

The delco mastercylinder isn't overly complicated but you're not getting pressure to the calipers.

Reasons why the pressure switch/accumulator isn't on my radar :

1. You're taking 20-30 secs to build up pressure after pumping the brakes 50 times, thats normal. If it was under pressure this wouldn't take anywhere near that time

2. After 2-3 pumps the motor works, that tells me the pressure is falling to a mark and the system is building it back up.

3. You'vew tried holding the brake down and switching the car off - that should prove the accumulator because the boost valve should be open and the accumulator (not the pump) should be keeping the boost section of the master cylinder on.

The other thing you can try is to sequence the relays on the master cylinder, there is a way to do this in the manual but you need a tech1 tool....although anyone who knows electrical/electronics I am sure can rig up a hot wire to flutter the relays. This is used to clear any air in the master cylinder. Have you tried flushing the fluid though with cheapy halfords stuff ?

I did that with mine and blew a lot of crud out of them when I 1st had the car.

If it were my car I would take the whole lot off, clean and check everything.

As I say I'll have a look on a webpage thing tonight and post up as I have a lot of drawings and info on the system I collected but not yet shared.

You definatly need to know what pressure the lines are at (again tech1 can do this) - I wonder if Espritmon (erik's freescan esque software on here) can do this I know he was looking at it.

Sounds like you have the later stages of a problem my car has which is an intermittent brake pedal response - some days it's perfect, others it's sloppy although it stops the car perfectly.

I'll try my best to publish this info asap.

[fmxa]

Bibs,

Any news on the new switch mate? I know a few of the local guys out here in dire need of this part!

[fesuvious]

bump

[bzguy]

Indeed, bump, my pressure switch is dead as well

"Lotus is working on a solution", for quite a while already

[fflyingdog]

Hans

Clear your PM box out ,i may have a solution for your switch

[bzguy]

PM Box cleanered out

Thx in advance Nick !

[ramjet]

Guys,

Back on Page 10

If anyone wants to know more I can follow up with Steve in Melbourne and let people know of cost etc.

Michael.

[Bibs]

Who is having problems with their car right now due to this, local to East Anglia perhaps?

[fflyingdog]

These guys may be able to help,if someone is willing to go through all the testing or maybe Lotus could help? I have one of their switches but have not had time to test it out.

http://www.pvl.co.uk/pressure_switches.htm

[bzguy]

I would be happy to test one out ; install, have Eric's program run on it & test with tech tool

What type of their catalogue do you have NIck ?

Let my car be the guinnee pig ; hopefully it works, sould be a BIG help for a lot amongst us !

Edited May 9, 2010 by bzguy

[CarlC]

Right that monster socket (1-1/2 Inch) has been ordered. I'm going to give Mark T-C procedure a go and do a pictorial write up with full credit to Mark for his sterling work!

[CarlC]

1 1/2 inch socket ...it is not! Its too big.

But I've got the pressure switch off with a set of adjustables. Being threaded into the aluminum body of accumulator its not rusted in and came out with relatively little resistance. Which is novel for working on our cars...

A little more cleaning required to night ready to give it a try this weekend and put Mark T-C's process to the test

Fingers Crossed.

[bzguy]

Good luck Carl, let us know on the outcome !

[CarlC]

Pressure switch cleaned and re-installed. Pictures taken of the whole job so a little guide to follow but anyway to check the results, I topped up athe fluid took her for a test drive.

Well the ABS light doesn't come on at all now under braking but the car is braking all over the place with heavy pull to the left. When pressing the brake pedal from 40mph you get some inital braking but then the pedal drops lower then you get a little more brake power but it doesnt feel like assisted braking. Low speed braking, pedal feels firm as I'd expect.

probably need to do a full bleed of the system.

[bzguy]

That's good news, hope to see the guide soon online

If you would have the chance : just connect the car to the Lotus Tech 1 tool, it has an automatic bleeding programme (ie to take out the bubbles in the circuit)

[CarlC]

Thanks Hans, I'd love to get my hands on a Tech1 to bleed the brakes that way...

Unfortunatley... I'll be having to use the more difficult Tech2 tool, of 'her in doors' doing some pedal pumping with me on the floor using a spanner.

Although, an EspritMon upgrade to do the job would go down a treat...

Edited May 22, 2010 by CarlC

[eriks4]

I still do not have the information to command the ABS computer to do a bleed procedure. However, if I could borrow a Tech 1 with the ABS cardridge, I could try to record the datastream and figure out the protocol. Then can add the bleed function to Espritmon.

[CarlC]

Hi Erik,

Your EspritMon software is great anyway and the fact that it provides full diagnostic on the ABS is brilliant. Just wanted to thank you for your great work on the software you've done. Adding the brake bleed procedure would just be the 'icing on the cake'! if we could ever provide the necessary info for you.

[Jonathan]

Tech1 procedure is easy

push the pedal down and swich the car on - you should feel the brake pedal rumble like it is in ABS mode. Repeat many times, that is the tech1 procedure.

I did a few pages on it in another thread. PS never ever fully bleed the system dry, took me 4 days to re bleed the system when I done it.

[nodemgr]

1.5" socket was too big? the 1.375" I bought was too small...

[CarlC]

Hi Jeff,

Yes, 1.5" is to big, it slips over the edges of the switch nut. The guide I'm writing is going to suggest not bothering spending (£10 / $18) on a one time huge socket and just use a set of adjustables as the switch comes out fairly easily once the whole unit is flipped over.