Lotus Elan

Vacuum pods

PostPost by: jimj » Wed Jun 17, 2015 11:55 am

I`m continuing to have a problem with the issue of droopy pods on a totally restored Sprint. I`ve replaced the one way valve with a Sue Miller one (the right way around). I`ve tried connecting each pod separately to see if one was faulty. I`ve even sealed each tube connection with silicone but I haven`t checked the switch, hoping it`s not that!
My question is this; how much (yeah, I know) suction should you feel with your finger over the end of the tube from the switch to the first, left hand, pod? I can feel a little, just sucking gently, with the engine ticking over. Is that normal?
Jim
P.S, I`ve splashed out ?3.75 inc. postage for an automotive stethoscope from ebay just now to see if I can hear a leak anywhere.
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PostPost by: nmauduit » Wed Jun 17, 2015 12:35 pm

it should be easy to clear the switch issue (or one way valve ...) by temporarily by-passing it : you'll see if you draw enough vacuum to pull the pods up then. You may also get an idea if your system leaks by opening it up after a variable delay after engine switch off (say 5", 1 min, 5 min etc...) and assess if the vacuum is comparable (it would of course be useful to insert a vacuum gauge, if available). One part not to forget in the tests is the chassis cross member, which acts as a vacuum tank... good luck !
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PostPost by: jimj » Wed Jun 17, 2015 2:10 pm

After the engine is switched off the pods go down pdq. even dip as I rev. the engine.
I had an idea, number 394, while walking the dog. I disconnected all the pipework from the non-return valve and put my finger over the end to feel the suction and it wasn`t great, should it be?
Jim
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PostPost by: m750rider » Wed Jun 17, 2015 2:30 pm

If your pods are going down immediately after shutting the engine off you have a bad leak somewhere.. Get a MitiVac pump and start testing throughout the system till you find it - it will be very clear.

It is very common for the headlamp switch to leak, You can disassemble it and repair it if that is the case.
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PostPost by: nmauduit » Thu Jun 18, 2015 12:45 pm

I assume you've routed the vac hoses like stock (e.g. not swapping in and out vac tubes on the switch), and already (double?) checked the one way valve or switch (can do it by blowing through it to get an idea, direction included) - if need be, you can by pass these components by putting a piece of tube instead to momentarily check the rest.

when blown into, my vac switch
pulled: connects top and bottom together (no leak to the outside either)
pushed: blocks the top tube (the one closest from the body that goes to the tank then one way valve via the T) and opens the bottom one to the outside (for venting the pods without loosing all the vacuum in the tank and creating a leak while the pods are up)

Leak hunting can be a challenging sport when it is small one - if "pdq" means a few seconds you're after a big one (again, assuming the circuit is standard), which should not pose major headache to identify... if the pods go up at some point during operation, the drawn vacuum should be enough to get them to work as the system with a (leak free) non return valve will gather the maximum vacuum drawn by your engine (which is not a race one with radical cam overlap I understand), so there should not be big mechanical issue to look into (bend rods with friction of inadequate range of motion, ...).
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PostPost by: jimj » Fri Jun 19, 2015 11:09 am

Right, I`ve found it, it was the switch. Following excellent advice I by-passed the switch and the pods came up and stay up, still up now after fiddling about removing the switch.
But.....there`s always a "but",there seems nothing wrong with it. I can blow through the tube furthest from the switch body, it`s clear at all tmes. the other ones is clear with the switch pulled but I can blow into it until blue in the face with it closed.
The trouble is that it`s when the switch is pulled open and the pods up that there`s a leak, presumably. Now, are you with me? with the switch pulled open, if I cover the one that does close, i.e. nearest the switch body, holding a thumb tight over it, I can blow through the other one and just, only just expel air. Is this enough of a leak?
Assuming it is, how do you dismantle the switch and re-attatch the 2 body parts to each other?
Jim
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PostPost by: jimj » Fri Jun 19, 2015 11:35 am

Supplementary info; I tried swapping the hoses around which makes no difference.
Jim
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PostPost by: collins_dan » Fri Jun 19, 2015 1:08 pm

There is a good post on here about opening up the switch to get a better seal.
lotus-twincam-f39/vacuum-switch-t13457.html
I recently added zip ties around my switch from front to back, so the assembly is really tight. I now have a really good seal and the lights on my S4 now stay down for 24 hours. Dan
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PostPost by: prezoom » Fri Jun 19, 2015 3:24 pm

Be sure to check the flatness of the switch where the tubes are attached. On mine it was anything but flat. I draw filed the surface and used sand paper stuck to a flat surface to make sure the rubber block was also flat. I also cut a small piece of rubber sheet to fit between the spring and the rubber block to increase the pressure. Assembled with some rubber grease. My pods will now stay fully up for four days before drooping.
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PostPost by: jimj » Mon Jun 22, 2015 9:46 am

I`m having no success prising apart the switch, even tapping a screwdriver with a hammer into the join. I`m loathe to be anything but gentle. In any case, testing the vacuum seal, sucking and blowing, it seems to me that the switch is working perfectly, yet it can`t be. Replacing the switch with a length of tube makes the pods stay up.
Any tips on prising it apart, gently?
Jim
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PostPost by: nmauduit » Mon Jun 22, 2015 5:14 pm

haven't opened up one lately, but from what I remember the parallelepiped body consists of 2 halves made of U bend flat steel (approx 2mm thick). They are kept together via 4 tongues going through matching 4 slotted openings in the opposite U (2 on each side of the 2 tubes), and locking is achieved by chisel hammering the tongues.

To release the 2 Us, one needs to bend back (of file etc.) the elongated tongues so that they fit again inside the slots. One may be careful not removing too much material as a way to lock them again after repair will be needed.

hope that helps short of a photo...
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PostPost by: collins_dan » Mon Jun 22, 2015 6:27 pm

Since the main body is such a tight fit, maybe try inserting some red rubber grease into the main body via the back tube. This is the one that needs to be sealed for the system to hold them down. The leakage is likely because the rubber is not making a good seal. Some red rubber grease might help. Worth a try anyway. Dan
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PostPost by: john.p.clegg » Mon Jun 22, 2015 6:49 pm

Jimj
Reading your post prompted me to have a go on one on the shelf ( rusty seized ),after 5 mins of prying ( thought it would take 3 hands hammer and chisel ) it came apart...insides rusty BUT the problem was evident ( should have taken a before piccy ) the flat bearing surface looked like a blind man with a bastard file had finished it....five minutes with some Al oxide paper and emery and I'l bet lots on it being air tight...

2015_0622lightswitch0002.JPG and


I'll put it back together with some girling rubber grease and put it back on the shelf...


If you want a borrow or want me to do yours just pm me

John :wink:
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PostPost by: jimj » Mon Jun 22, 2015 9:36 pm

John, let me know when you`ve tested it. I was out in the car tonight at the car thing at Brough and the Barrell at Bretton afterwards. Luckily it`s downhill from there so no brewer`s droop on the short drive home.
Jim
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PostPost by: john.p.clegg » Tue Jun 23, 2015 5:08 am

Jim

Sadly I've got Mazda electric pods,thought you'd try it....

John :wink:
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