Vacuum hoses

[paul james]

I've got a 1.3 SR with sport carbs, the Oil Seperator on the back of the block has two pipes coming out of it. The larger one which throws out fumes and a bit of oil sometimes I have connected up to a catch tank. The thin pipe has the end blocked up with a screw. What does this thin vacuum pipe do exactly? and should I have it connected upto anything?


Also while mucking about with the car yesterday, I accidentally left my inspection lamp on the brake servo vacuum pipe (the one closest to the servo, coming from the inlet manifold), which then got a hole burnt into it. I can't seem to find any replacement hose for it - its 14mm inner diameter. Anyone know where I can get some? and does it have high air pressure going through it?

[craig green]

The servo pipe, just cut the holed section out & bridge it with some fuel pipe & jubilee clips either side. Its under vacuum not pressure.

As for the breather, I expect the other end has a vacuum feed to draw the fumes into the breather box. (not entirely sure, I'm a fuel injection man)

[paul james]

The servo pipe, just cut the holed section out & bridge it with some fuel pipe & jubilee clips either side. Its under vacuum not pressure.


This is what the haynes manual says to do, and what I want to do since I can't seem to remove the end connected to the servo anyway. But I can't seem to get hold of any hose thats the right size, 14mm would be right to go over the top of the exsisting pipe if I cut the burnt section out. Been everywhere locally, even a hose specialist, checked sites online, nowhere seems to do 14mm inner diameter pipe of any kind.

Currently I've just covered up the hole with blu-tac, probably not an ideal solution.

And excuse my stupidty on the subject, but what is the purpose of the vacuum pipe anyway?

[AlexW]

The smaller pipe coming from the box mounted to the block is connected to the back of the carb on standard carbs, Unsure of sport carbs tho.

[craig green]

Get some new petrol/injection hose as close to the servo vac pipe as possible, drop it into boiling water for a moment, then whip it out & push it over the pipe ends.

I've done my servo piping on my 16XE the same way.

[paul james]

Ordered some 13mm hose off ebay, when it arrives I'll try that hot water trick you suggest

[dhdev (Oli)]

And excuse my stupidty on the subject, but what is the purpose of the vacuum pipe anyway?
The servo pipe provides a source of vacuum to the servo (approx -0.8bars). The servo contains a diaphragm, in the in-active state it will have vacuum applied to both sides of it. On applying the brakes the back of the servo diaphragm (the side by the driver) will be vented to atmosphere. This provides a positive pressure gradient across the servo diaphragm, and since Force = Pressure x Area, a force (or boost) is added to the applied braking force :thumb:

[Adam]

It does a good job of it too.
I drove without the servo piped up and nearly hit the back of the car in front when i first pressed the brakes lol

[craig green]

My servo failed twice when I was at uni (failed 1 way valve) having to drive 70 miles home in the dark on twisty B roads isnt fun.

Thats how I know the issues between different Nova servos & MC's that arent compatible etc.

[dhdev (Oli)]

It's one of the things that I strongly disagree with on brake legislation. IMO the failed servo performance should be better on new cars. Boost levels seem to be getting larger and larger, so in the event of servo failure most people wouldn't stand a chance.

[Adam]

Yep, a lot of modern cars are heavily servo'd.
So anyone so use to that brake feel would be in for a big shock if they suddenly had no servo assistance at 70mph....