Vacuum hose

[JonnyT]

Hi Guys,

Just looking at lashing down the vacuum hose. I have the following questions if I might.

The build manual states that the hose must go upwards from the carb. How much does this need to be by?

It then goes through the one way valve and must go below the inlet to the servo before going into it. If this is right (which makes sense but possibly overly cautious with a non return valve) my servo hose is very very close to the headers which seems to me a bad thing.

If I go up as it comes out of the carb, can i dispose of it going below the servo inlet, or can it be lower by just a very small amount?

Thanks in advance,

Jon

[futureproof]

Unless I misunderstand or am missing something - a vacuum hose ? I have never heard of why it should go up ? A vacuum is a vacuum whichever way up you are.

I would recommend the non-return valve. I think I liberated one from an Audi or more expensive VW in the scrap yard. This will ensure that the brake pedal is "reliable" - otherwise you could find that if you brake quickly after accelerating you have a hard pedal (no vacuum to help).

:thumb:

[Nobby]

From memory the hose is supposed to go up from the manifold/carb vac port so that any fuel that might get into the hose runs back to the carb and not into the servo past the one way valve. At the servo end the same applies - any fuel that might get that far will pool in the vac hose and won't get into the servo where it might cause failure of the diaphgram or seals. A lot of mights I know!

The vac hose isn't far from the headers - Dax sold me an "SVA" heat shield that mounts below the servo and provides some heat protection for the servo and hose. No mention of this in the "Guesswork Manual" as usual!

[SJ]

Hi Jon,

It is important to loop the vacuum hose to prevent the possibility of vapour getting into the servo system. The technique is to build in an 'S' shaped curve into the hose so that it goes upwards from the manifold towards the bonnet (go as high as you can without it touching the bonnet), then come downwards towards the servo (avoiding the headers) and then turn back to join onto the servo to form out the bottom of the 'S'.

The one way valve is also required (remember to fit it the right way - there should be an arrow showing the flow). I have mine about 2-3 inches from the servo connection.

At my SVA the inspector required me to add additional heat shielding to the vacuum hose using a heat wrap. I did this and took the opportunity to tie wrap it alongside the line of the bonnet to stop it falling onto the head.

Regards

SJ

[futureproof]

Ah good point - throwing unspent fuel in the system could make it more interesting, so maybe up hill is the answer.

I am surprised you say that the manual is cr*p though. I found that it would work as a wheel chock in an emergency and if the car stops and its cold you can screw up the pages and stick them up your jumper or start a fire with it.

Actually there is a whole new thread here
"100 uses for the build manual"

[JonnyT]

Thanks guys,

Does it have to go as high as it can towards the bonnet? No practical reason for not wanting to do this but it looks cr** looped over the top of my nice shiny fuel hose. Yes for that comment I accept all the ridicule, but I'd rather not take it above if I can help it!!

What is the SVA heat shield? Is this a piece of bent metal that suddenly becomes worth 15 times the material price because it has two holes, one bend and is sold by Dax?? Could I have a pic of this?

Cheers

[futureproof]

TBH I never considered this for the SVA and I passed 1st time. My pipe is hidden under a big chrome air filter, heads back to the bulkhead where a neat copper pipe (10mm fuel pipe) is pinned to the bulk head. Then another piece of flexi pipe goes to the servo. I followed this "neat" approach under the whole engine bay so that there were not loads of rubber pipes and hoses all waggling around under the hood. I just pinned down every pipe I could with "p" fasteners.

My opinion was that my tester was looking at the overall build quality and making sure that nothing could be worn through with general use rather than nit-picking. But if you get one who has just fallen out with the missus and his thing is servo pipes.......??

I am lucky (some may say) in that I spend most of my working day looking at cars, but the question I always came back to was "would a manufacturer do this ?" If the answer was no then I did not do it either. You would not expect to buy even a Hyundai or skoda with pipes flopping around under the bonnet. My servo will expire from sitting on the exhaust long before a few engine fumes kill it.:boohoo:

I havent got any good pics but you can get the idea.

[dave]

Originally Posted by SJ

Hi Jon,

It is important to loop the vacuum hose to prevent the possibility of vapour getting into the servo system. The technique is to build in an 'S' shaped curve into the hose so that it goes upwards from the manifold towards the bonnet (go as high as you can without it touching the bonnet), then come downwards towards the servo (avoiding the headers) and then turn back to join onto the servo to form out the bottom of the 'S'.

The one way valve is also required (remember to fit it the right way - there should be an arrow showing the flow). I have mine about 2-3 inches from the servo connection.

At my SVA the inspector required me to add additional heat shielding to the vacuum hose using a heat wrap. I did this and took the opportunity to tie wrap it alongside the line of the bonnet to stop it falling onto the head.

Regards

SJ

The one way valve will see to keeping the vapour from getting into the servo.
If in doubt about any of this then open the bonnet on your tin tops and look where the pipe goes.

[Nobby]

Originally Posted by JonnyT

Thanks guys,

Does it have to go as high as it can towards the bonnet? No practical reason for not wanting to do this but it looks cr** looped over the top of my nice shiny fuel hose. Yes for that comment I accept all the ridicule, but I'd rather not take it above if I can help it!!

What is the SVA heat shield? Is this a piece of bent metal that suddenly becomes worth 15 times the material price because it has two holes, one bend and is sold by Dax?? Could I have a pic of this?

Cheers

Jonny, you got it in one. The 'Shield' is a bit of 2mm ally with some reflective heat proof material stuck on the underside. It is curved to fit under the servo and I made up 2 brackets to fix it to the inner wing and footwell. About 15 quid from memory. That's about 30 times its worth!!

pic attached.

[keane]

Just read this and had to add my tuppence worth, just received my stoneguards from Dax today, nice pieces but £165!!! to my door, complete p**s take, hopefully I shouldn't have to buy anything more from them!! regards. Dave