Vacuum issue .

Mad4slalom

Mad4slalom

Well-known user
Hi all, out for a little blast last eve, had lights on 1st position, sidelights on , headlights down . I stopped to top up fuel, by the time I paid and came back to the car, I started up and started to drive out of the forecourt I noticed the headlamps came up unevenly, the wiper door sort of opened and closed and I could hear the astro ventilation flaps in the rear area opening and closing. I then drove off and they settled down and seem normal again now. I know the vacuum tank in the fender is supposed to hold enough vacuum for a couple of operations without motor running , I dont think mine has ever managed that so I think it had lost vacuum while i was refuelling and when I drove off immediately after re starting motor there was insufficient vacuum so the wiper door and lights tried to open as they fail open, by which time the motor had made more vaccum so everything closed again? Is my take on it a possibilty? Maybe a slight leak in head lamp switch ? as normal daytime driving i have no lights or sidelights on so issue of low vacuum doesnt show itself ? Any ideas or suggestions appreciated. TiA 👍
 
Chuffer

Chuffer

CCCUK Member
Mad4slalom said:
Hi all, out for a little blast last eve, had lights on 1st position, sidelights on , headlights down . I stopped to top up fuel, by the time I paid and came back to the car, I started up and started to drive out of the forecourt I noticed the headlamps came up unevenly, the wiper door sort of opened and closed and I could hear the astro ventilation flaps in the rear area opening and closing. I then drove off and they settled down and seem normal again now. I know the vacuum tank in the fender is supposed to hold enough vacuum for a couple of operations without motor running , I dont think mine has ever managed that so I think it had lost vacuum while i was refuelling and when I drove off immediately after re starting motor there was insufficient vacuum so the wiper door and lights tried to open as they fail open, by which time the motor had made more vaccum so everything closed again? Is my take on it a possibilty? Maybe a slight leak in head lamp switch ? as normal daytime driving i have no lights or sidelights on so issue of low vacuum doesnt show itself ? Any ideas or suggestions appreciated. TiA 👍
Click to expand...
Firstly check the non return valve in the vacuum line to the manifold . It may half failed allowing air to slowly seep back into the system . If that checks out OK then check for leaks with a vacuum test kit , they are not expensive . The technical definition of a vacuum is `f**ck all in a pipe ` , so if you have more than `f**ck all ` in the pipe you have no vacuum ! :LOL:
 
Chuffer

Chuffer

CCCUK Member
I don`t know how many inches of mercury the C3 draws in vacuum but another reason the vacuum system may loose it`s efficiency could be old and perished hoses that could collapse under normal atmospheric pressure of 14 psi .
 
Roscobbc

Roscobbc

Moderator
Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........
 
Mad4slalom

Mad4slalom

Well-known user
Roscobbc said:
Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........
Click to expand...
It has a street cam , no power brakes, I will take it out again and see if it is still playing up. When I first got the 72 , the headlights and wiper door would open once and then close on every start up. After a couple of years it suddenly stopped doing this and has been fine apart from the odd random event.
 
Chuffer

Chuffer

CCCUK Member
Roscobbc said:
Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........
Click to expand...
Interesting figures Ross , I did not expect it to be as high as 18 HG or more . Most of my experience and training in vacuum operated systems is on steam locos ( needless to say :LOL: ) because the braking systems are either fully vacuum operated at 24 ins HG on Great Western built locos or combined steam / vacuum at 21ins HG on other types . Being able to test and find faults in the complex systems was a crucial part of our training.
Those of us of a certain age will remember the erratic nature of vacuum operated wipers on Ford Prefects et al that nearly flew off the screen when you came off the gas !! :ROFLMAO:
 
You must log in or register to reply here.
Top