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Author Topic: Low vacuum sensor (Update)  (Read 126 times)
roy4matra
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« on: October 07, 2021, 09:08:16 pm »

In the Bagheera Series II instrument panel there is a row of seven warning lights at the bottom just below the rev counter or tachometer to give it its correct name.  These from left to right are: Green for Side Lamps; Blue for Driving lamps (I think); another Blue for Head lamp high beam; Yellow for Low Fuel warning; Red for Low brake fluid; another Red for the Low vacuum warning; and finally another Red for the Ignition warning light.  Having that vacuum warning light was quite a sensible idea, because if the system has a leak then it not only means the head lamp pods would be slow to lift or maybe not lift at all, but the air leak would also weaken the engine mixture which can be really bad and lead to damage, as a very lean mixture burns much hotter as well as quite likely causing pre-ignition and detonation.

Knowing that the Bagheera used a rear chassis cross tube for the vacuum reservoir and that the end caps commonly leaked owing to corrosion, and the head lamp pods would not rise without the engine running owing to the lack of stored vacuum, that means many Bagheera should have had that warning light illuminated!  Yet I've never heard of that being the case, which suggested to me that either they didn't have a sensor, or it wasn't wired up or working.

However, I have seen a sensor in the front of a 1977 Bagheera, mounted near the centre of the car on the bulkhead, and it is round and deep, a little like the oil pressure switch on the engine, which is understandable since it is doing a similar job, except the pressures are negative in this case.  However, I am curious to know if they were ever wired up and worked.  Has anyone ever seen the vacuum warning light come on?

If anyone has a Bagheera with one of these fitted, could you check it out for me please.  The vacuum side should have a small tube linked by a tee-piece into the vacuum tube that connect the reservoir (or inlet manifold) to the white vacuum valve that operates the pods up or down.  It should have at least one wire or possibly two.  If it operates the warning light by simply earthing it, then there will be just one wire, but it could have two if it is fed power first and then the second wire returns the signal to the instrument panel.

Thanks for any help.

Update  I have now checked the original Matra Bagheera parts catalogue, and it appears the vacuum sensor was only a German market requirement, and therefore would only have been fitted to Bagheera built to German specifications.  It appears there may have been a relay or control unit as well as the sensor.  The special part numbers involved are: Relay or control 0030499500, Vacuum sensor 0030499900 and Mounting block for sensor 0030450000.  These are for all Series II cars, the early Series I up to chassis number 20242 in 1976 had a different part number for the Relay or control which was 0003757700.  So who still has a German specification Bagheera?

The photo is of the strip taken from an early Murena which had basically the same instrument panel as a late Bagheera. Low Vacuum warning is next to the Ignition warning light.

Roy
« Last Edit: October 10, 2021, 09:06:22 pm by roy4matra » Logged

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