BRAKE SERVO : HAVE TO PUSH HARD THEN SUDDENLY WORKS

[tonycharente]

My S4 Elan's brake servo has become a bit "all or nothing". When I just brake gently nothing much happens - no apparent servo effect and the car therefore hardly brakes. When I push hard, the brakes suddenly brake quite hard - the brake servo seems to suddenly start working. The car then brakes really well. It's really hard to brake smoothly.

I've tried numerous searches without finding anyone with the same issue.

Any ideas, please?

Many thanks.

Tony

[Hawksfield]

Tony
is it Girling if. so it's seal or air valve problems.

[tedtaylor]

sounds like boosters hanging up. rebuild them.

[alan.barker]

Hi Tony,
Throw your Servo in the bin.
Fit +2 Discs on your yellow ragtop.
Alan

[tonycharente]

Sorry for not replying sooner - been very tied up of late.

I'm going to check out the "air valves" (assuming that to mean the one-way valves in the vacuum circuit ???)

I'm not up to rebuilding a brake servo, so it would be buying another one should I not find a cure.

I don't have a "yellow ragtop" - I have a red FHC... Changing to +2 discs and presumably calipers sounds like a lot more work and expense than just buying a new servo. Also having a servo makes it less of a shock changing from all my other cars, old and recent.

Thanks to all,
Tony

[alan.barker]

Sorry wrong Tony,
Know a different one in France with a yellow dhc.
Alan

[tonycharente]

Not to worry, Alan !!!

I'm a founder member of Club Lotus France. I just tried to find you on their website, but you don't seem to be a member ?

Cheers
Tony

[alan.barker]

H Tony,
Was in club Lotus France back in 2000 for a year. I know Serge Audiger and several others in the club. I live in Morbihan 56 near Lorient. My Sprint fhc was on the club Lotus Stand at Lorient Expo.
Amicalement
Alan

[tonycharente]

Hello Alan,
I was present at the very first Club Lotus France meeting in 1982 when we used to live in Paris. We returned to the UK in 1984, retiring to the Charente in 2002. I kept up my CLF membership throughout,

I know the founding president - Dino Rossetto - very well. He lives in Fréhel : so your neck of the woods but still a long way away. He has an absolutely amazing collection of old Lotus's - in various states of repair...
Let me know if you'd like me to put you in touch.

Cheers
Tony

[alan.barker]

hi Tony have sent you a pm with my email address
Alan

[tonycharente]

Hello again Alan,
No trace of your PM in my PM in-box.

My email address is tonyyvetteparfitt AT gmail.com

Cheers
Tony

[tonycharente]

UPDATE
Yesterday I looked into checking out the non-return valve in the vacuum pipework, but couldn't find one. Research showed this to be because it was a plastic device that plugs into the servo. Mine like many others these days is a replacement "Lockheed style" servo, not the original Girling. Further research showed this valve to (probably) be part number "BAU4856" and readily available for sale. So my next step will be to buy one of those and see if that cures my problem.

I'll keep you posted, but meanwhile I was amazed to note that the official Elan Workshop Manual says (of the Girling servos) : "After 40,000 miles (65,000 km.) or 3 years, whichever is reached first, the servo unit should be replaced together with the vacuum hose by new parts." Wow !!!

[alan.barker]

The Lockhead style need to be fitted at a special angle or they stick etc.
Alan

[tonycharente]

I think my servo is correctly mounted at the right angle - I used the supplied fitting kit and in any case initially it worked perfectly.

For the time being I've dropped the idea of buying a replacement non-return valve, as thinking about it I don't see that it could be causing my problem.

On the other hand going back to "Hawksfield" 's comment (Is it Girling if. so it's seal or air valve problems.), and having done more research, I now realise that the air valve has nothing to do with the non-return valve, so I shall be investigating the air valve as my next step.

[tonycharente]

UPDATE : NEW QUESTIONS, PLEASE.
Today I took the Elan for a spin and observed the following:-

Whilst going along I tried putting the car into neutral, switching off the ignition, and braking. Still the same "on or off" servo effect, but the servo did work, so there is a working non-return valve (I think ???). However it only worked once, after which there was no servo effect at all. Is this normal?

Going with the engine running and the foot off the accelerator, and braking hard enough for the servo to start working, there is a sudden, short lived, increase in the revs. I think this may be due to a temporary change in the mixture (richer or weaker ???). Is this normal?

Do either of the above findings provide a clue to the source of my problem, please? ("When I just brake gently nothing much happens - no apparent servo effect and the car therefore hardly brakes. When I push hard, the brakes suddenly brake quite hard - the brake servo seems to suddenly start working.")

Many thanks to all,
Tony