Help with brake servo

[marklowe]

I am in the process of putting my 1967 S4 back on the road, it?s been stored in a garage since 1999.
My last big obstacle is the brakes, the master cylinder, disks and hoses have been renewed, the callipers and servo were overhauled by Classicar in Cheshire.
The problem that I am having is that there seem to be a delay in the servo operating,
You press the pedal with little effect, when you press a little bit more the brakes suddenly grip well.
The car failed its MOT because of this, the tester was quite good and explained that when the brakes griped it was enough to lock the rolling road.

Any suggestions on what may be creating the problem?
As an alternative other threads have championed the removal of the servo, are the brakes be sufficient to pass the MOT if the servo is removed?

[1964 S1]

Hello, I can't answer the question about the MOT as we have no safety inspections here, but removing the servos may be your answer unless you choose to replace/rebuild them. (again?)
Your word delay is a bit unnerving.
The symptons sound like air in the line to me, and I'll bet it's getting in through the servos. I'd try bleeding the brake lines a few more times and then report back with the braking results...
When the servos quit working on my +2, I will probably remove them and not replace them. Forty plus years and Elans are still very light compared to any road car except that durn Elise, and four wheel disc brakes are still state of the art. I think my +2 will still stop fine and I don't think a smaller Elan will suffer from a servodectemy.
Good luck, Eric

[marklowe]

The MOT inspector suggested air in the system also, so on Sunday I re-bled the system and tried leaving the system under pressure overnight to force out any remaining air. I have a firm pedal, but it still feels like two stage braking.
I?ll have to have another go tomorrow.
Mark

[types26/36]

I cannot see how air in the system would cause the symptons you describe, if it had air in it then it would be a soft pedal which would become firm by pressing the pedal a few times.
The way you describe it, it sounds as though the pads are grabbing or snatching which to me would indicate a fault with the servo.
Why not make up a small pipe to bridge the inlet and out let servo pipes after disconnecting them, of course you would have to bleed again.
This would eliminate the servo and you could feel how much effort the brake pedal has, some people change the master cyl. to compensate for this but I do not think it is nessesary as I ran both an Elan and a Europa with the servo bridged while I overhauled the servo's.
In my opinion the brake effort is not excessive and there would be no reason why the car would not pass an MOT like this and as a foot note a servo does not improve the braking power, it only reduces the effort to apply that power.
What happens if you disconnect the vacuum line to the servo? does it still grab? by disconnecting the vacuum it would also show you how much effort is needed.

[richardcox_lotus]

IIRC, dependant upon the type of Servo you have, some of them (Lockheed, I "THINK"), have this kind of characteristic BY DESIGN. i.e. Single gentle prod on the pedal for normal braking, but 2 rapid prods on the pedal greatly increases the Servo boost thus making you do an emergency stop.

It may be worth discussing it on the phone with Classicar, & seeing what they think.

If it turns out I'm talking bo**ocks, (always a possibility) it's possible the Servo is sticking. Not unusual after a rebuild, but if it's the case, then I would expect the fault to be intermittant, not the consistant behaviour you are experiencing.

BTW, It seems recently that the number of posts on this forum relating to Servos is increasing exponentially !

[marklowe]

I?ve tried the brakes with the vacuum pipe disconnected and there?s no grabbing of the brakes, just that you obviously have to apply more pressure.
The Servo is a Gerling Mk2A if that makes any difference.

[types26/36]

I (Lockheed, I "THINK"), have this kind of characteristic BY DESIGN. i.e. Single gentle prod on the pedal for normal braking, but 2 rapid prods on the pedal greatly increases the Servo boost thus making you do an emergency stop.
If it turns out I'm talking bo**ocks, (always a possibility) i

Not saying you are talking bo**ocks, but got to say I've never heard of a system like that would'nt haveing to make two prods on a brake pedal loose valuable time in an emergency stop?

[richardcox_lotus]

Hi Brian
Yeah, it does sound a bit odd, but it must be true as I was told it by a man in a pub

I hasten to add by an elan-owning colleague & we were discussing Servos & a third- elan owning colleague had experienced the same behaviour.

That's why I thought it was common !

BTW is there a collective noun for Elan-owners ??

A Gaggle ? A Herd ? Or how about a Loon ?

(It's been a long day. I'll get my coat)

[hatman]

A 'breakdown'?

[worzel]

Hi

Try looking at the air valve at the top of the servo.

A common fault with these is the tendency for the brakes to stick on after releasing the pedal. Lockheed advised me that the small bore piston that operates this valve can also produce symptoms similar to those you describe.

The problem can be made worse because of where the servo mounts on the two seater- right where the bonnet drains so water hits the filter and seeps in.

If you wanted to verify air in the system remove the outlet pipe from the servo, substitute a bleed nipple and bleed it. The pedal should now have absolutely no movement (exhaust the servo first by pressing the pedal a few times with engine off).

John

[types26/36]

HiTry looking at the air valve at the top of the servo.
A common fault with these is the tendency for the brakes to stick on after releasing the pedal. Lockheed advised me that the small bore piston that operates this valve can also produce symptoms similar to those you describe.John

John, It was mentioned that it was a Girling mk2A which has the air valves on the side with a rocking lever arrangement.
http://www.head2head.free-online.co.uk/ ... _sheet.htm

[worzel]

What can I say- I must continue with the treatment!

John