hydro vs vac

[driftin jo]

hmm... interesting...

so that tube just gets the feed from the IM then goes to the servo and that's it? nice and simple!

Yes its that simple, out of those this one would be my choice from an A8 diesel.

http://www.ebay.co.uk/itm/Audi-A8-D3...item2a0bf7e669

[S2central.net]

V6 AAH engine uses a small vac reservoir.

[A80Avant]

and that is always in line with the actual servo,right! ok

[S2central.net]

Well it's a vac reservoir for the changeover valve on the IM but the principle is the same. Not sure if capacity is enough for enthusiastic left foot brake fun on boost though. Bit it trial and error required here - I expect there must be lots of choice for vac bottles across various cars and trucks.

[V6quattro]

My avant ABY has a vac reservoir in the left wing if i'm correct????

[A80Avant]

yes, but that is the carbon canister. Should be the Right fender

[V6quattro]

Yes at the right it is the carbon canister. I removed it yesterday . But at the left wing there is a (vacuum) tube with a one way valve going in to the wing. I will take some pixs on Monday when i remove the inner wing.

[S2central.net]

Yes of course the S2 already has a vac reservoir at the front - well the aircon equipped cars do - its a reservoir for the recirc solenoid... seems nutty I know but yes Audi made that so the recirc function works whether you are in vacuum or boost !

And of course there is a rear vac reservoir for the rear diff control - it is also vacuum controlled.

It might be worth trying to re-use the front vac reservoir - it only has a single port AFAIK so you need to work a T-piece and 1-way valve into things the right way so you could hook it up to a brake servo.

[johne]

This is a pic of the vacuum reservoir from a '96 A4 used for the climate control recirc vacuum operated flap motor, part number 8D0 820 601, the non-return valve pushes in the black hole on the right and it's 190 x 140mm.

I'm in the "not sure if any extra reservoir is needed" camp but if it was me I'd move the diff lock vacuum reservoir under the bonnet temporarily and see how you get on before getting into electric vacuum pumps or engine driven ones.

John

[V6quattro]

Yes of course the S2 already has a vac reservoir at the front - well the aircon equipped cars do - its a reservoir for the recirc solenoid... seems nutty I know but yes Audi made that so the recirc function works whether you are in vacuum or boost !

And of course there is a rear vac reservoir for the rear diff control - it is also vacuum controlled.

It might be worth trying to re-use the front vac reservoir - it only has a single port AFAIK so you need to work a T-piece and 1-way valve into things the right way so you could hook it up to a brake servo.

Had a look on the vacuum reservoir in the left front wing today. Looks a little small but i will use it for my vacuum servo just in case. I have driven other turbo cars with only a one way valve and they ware fine.

But what are you mean with the rear vac reservoir? I havened noticed that. Or is it only on the coupe?

[S2central.net]

Location on B3 coupe is in behind the rear quarter trim - just forward of the rear wheel arch on LEFT side (UK PSG side). Cannot recall if B4 is same place though.

[A80Avant]

a separate vaccum reservoir does not need to be that big the way i think of it. It should be there to assist the servo 'just in case' OR for left foot braking, which may not be that common. If the car is mainly for tracking purposes, then sure, it would make sense to fit a proper big one.

[S2central.net]

Agreed completely on that... and its loads simpler than fitting a vac pump.

[A80Avant]

the servo is on, brakes work.... BUT i think the garage has cocked up a small detail, even though i told them...

apparently because the servo comes really close to the steering rack (LHD), they had to make a high pressure hose from the rack to the pump and ditch the original one with the metal loop at the end. Personally i think that would have worked if slightly bend out of the way,which was my original suggestion.

They didnt, made another hose, and the power steering now makes heavy noises and on ends of turning, you get a slight vibration as well.
The hose wasnt also tightly done at the rack and they hope that this was the problem with air being sucked in the system, however i believe that the OEM hose has specific construction(which is why costs 180GBP), to eliminate noise and vibration from the pump.

I had to leave the car with them to get the servo out again to reach the hose and tighten things up, but unfortunately i see myself buying the hose all over again and doing it the proper way... Damn....

Brakes work like butter by the way...

[Billman]

If the original costs 180 pounds then it is no special at all. If the price was 800 then maybe yes.

The plain usual air con low pressure pipe costs at audi 200 euros and 40 if you custom make the same.