Lotus Elan

Brake Servo vacuum air leak

PostPost by: Monster666 » Fri Mar 30, 2018 2:00 pm

Does anyone have a diagram of a brake servo. I have a S4 SE Elan, 1969. Having looked at the Matty site I think it may be a Lockheed servo as it looks the same as the one on their site.

The brake servo and pop up headlights are run from the same vacuum system. Following a visit to the garage last summer for the hand brake to be rebuilt and a few other jobs it returned and the lights wouldn't pop up. They said the manifold had an air leak. In my ignorance I believed them.

Anyway, shoulder op & being out of action for a while means I've just started now been able to work on the car. Having removed the vacuum pipe going to the servo and blanked the pipe, the lights pop up.

Listening to the servo I can hear an air leak around where the brake slave cylinder attaches. I'd like to see the servo components so I can work out how to fix it.

Thanks
Grahame
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PostPost by: billwill » Fri Mar 30, 2018 4:52 pm

Quick way to find this kind of info is to do a GOOGLE search for key words and then select images.

Browse the images and open any interesting looking pages that result.

https://www.google.co.uk/search?q=lockh ... kl-7X4a8VM:

Image
Bill Williams

36/6725 S3 Coupe OGU108E Yellow over Black.
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PostPost by: Monster666 » Fri Mar 30, 2018 5:04 pm

Thanks Bill

I was searching the text and not getting anywhere - I'll try images
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PostPost by: Monster666 » Fri Mar 30, 2018 5:21 pm

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PostPost by: tedtaylor » Fri Mar 30, 2018 5:36 pm

my bet is if the shop was working on the hand brake, that he most likely "bumped" and dislodged the air line to the vacuum light switch. that's why your lights don't go up/down AND the hissing sound. That's what happened to me. Good luck!
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PostPost by: alan.barker » Sat Mar 31, 2018 8:24 am

I would think they dislodged the "T" vacuum piece on the Chassis Crossmember
Alan
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PostPost by: Bigbaldybloke » Sun Apr 01, 2018 12:14 pm

I'm used to a Plus 2 so am surprised that the headlamps and brake servo vacuum systems are linked at all.
On mine the brakes have an inlet manifold tapping on the rear cylinder and the headlamps from the front cylinder so a fault on one does not affect the performance of the other. I'd check on yours to see if this is how it should be and if not I'd consider modifying it for safety. Both the brakes and the headlights at night are rather critical systems and to have a common point of failure does not seem like a good thing to me.
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PostPost by: Monster666 » Sun Apr 01, 2018 1:09 pm

Thanks for all the comments.

The lights and switches are fine as when I isolated the vacuum system, so the the brake servo was not in it, the lights popped up no problem. The T piece is new with a good seal.

It does seem a design fault that both the brake servo and pop up lights are on the same vacuum system but that is how it is on my model.

Having cast my mind back to last year - I took the car to the MOT station and it failed on the handbrake. I then took it to the recommended garage and they sorted the handbrake. I drove it back to the MOT station on a round about route of around 10miles and it drove lovely.

The MOT station put it on the ramp and immediately failed it on the brakes - the pedal had gone to the floor.

Back to the garage. The seals in the master cylinder had failed. Replaced and brakes fine but headlights not coming up.

So did the MOT 'person' stamp so hard on the brake pedal that he popped the seals in the master cylinder and put a hole in the brake servo diaphragm....as I'm wondering if that is what I can hear from the servo?
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PostPost by: alan.barker » Tue Apr 03, 2018 9:13 am

Both Brake Servo + Headlamp vacuum come from n?1 inlet on a S4 Elan.
You just need a non return in each line and the system will work 100% no problem.
Imho no modification required :wink:
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PostPost by: Monster666 » Tue Apr 03, 2018 11:45 am

After a few days phaffing around I got to the bottom of it.

There is only one one non-return valve in my vacuum system and that was starting to fail, so I replaced it. But this was not the root of the problem.

The main problem was that the seals in the air valve, activated by the air valve piston, were not sealing properly allowing continuous flow of air through the air valve into the vacuum system. The seals looked fine when I took it all apart. The air valve diaphragm had no holes or tears in it. I cleaned up all the faces that the rubber seals mated to and slightly stretched the spring in the air valve and hey ho, everything works.

Time for a drive....
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PostPost by: alan.barker » Tue Apr 03, 2018 11:52 am

Bravo.
One non return is where the vacuum hose is fitted on the Brake Servo.
The other non return is where the vacuum hose for the headlamps is fitted to the brass connecter at the inlet track on n?1 cylinder.
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