Vacuum reservoir needed?

[clyde]

When installing an AHU or ALH in a Mk2 Jetta — the gas cars had a vacuum reservoir — is the original vacuum reservoir necessary? The TDi engines have vacuum pumps…

 

[turbodieseldyke]

Mk3 tdi's don't have them. Don't some people remove the vacuum ball from ALH's too?

 

[CanadianALH]

Mk3 tdi's don't have them. Don't some people remove the vacuum ball from ALH's too?

Yes. Guthrie is a big fan of deleting everything except the line from the n75 to pump and the line to the air box. Cleans things up and less places for a vacuum leak. And for a swap this is ideal.

 

[clyde]

Thanks! And who is Guthrie? Surely it ain't Arlo…

 

[Nuje]

Guthrie = @burpod, tuner extraordinaire.

 

[Shenandoah]

No vacuum ball on my Audi TT -> TDI (alh) for years. Haven’t had any issues.

Burpod tune on it…….

Eric

 

[burpod]

havent had a vac ball in years. your good without it no need for the little checkvalve to the n75 either. think about it

 

[PickleRick]

I kept the reservoir in my system because, in theory, you'll have one last time to push the brake pedal if the engine loses power.

It is harder to stand on the brakes to stop a 2 ton suv on 33s than it is a 1.5 ton car on stock tires.

 

[AndyBees]

I used the Vacuum Reserve Ball as well as the check-valve with the ALH install in my 84 Vanagon. I've never had a vacuum leak issue.

Obviously a different vehicle, but my 95 Blazer's brakes work much better with vacuum reserve ball.

 

[G60ING]

I ran the reservoir in my corrados, its good for hvac controls on the early sliding hvac systems that don't use booleen cables. never had an issue having a reservoir.

 

[r3gill]

Who is Guthrie?

 

[Nuje]

Who is Guthrie?

aka @burpod

 

[Lug_Nut]

When installing an AHU or ALH in a Mk2 Jetta .....

Enough about the A2 already. Where are images of the DeSoto?

... hvac controls on the early sliding hvac systems that don't use booleen cables.

I had always known of the rigid (not stranded) cable with push as well as pull capability called a "Bowden" cable.

 

[dieseldonato]

Haven't had a vac ball in my jetta for the past year at least. Don't see a need for it either.

 

[AndyBees]

Without a vacuum reservoir the things that use vacuum depend on the limited amount in the hoses and what the pump is immediately producing.
The vacuum gauge I have mounted at the dash on my TDI Vanagon shows an immediate drop in vacuum when hitting the brakes. The rebound is not instantly. Considering the ball is easily mounted and the engineers concluded the systems need the reservoir, I recommend keeping it in service.

 

[jimbote]

Without a vacuum reservoir the things that use vacuum depend on the limited amount in the hoses and what the pump is immediately producing.
The vacuum gauge I have mounted at the dash on my TDI Vanagon shows an immediate drop in vacuum when hitting the brakes. The rebound is not instantly. Considering the ball is easily mounted and the engineers concluded the systems need the reservoir, I recommend keeping it in service.

Agreed

 

[jimbote]

Mk3 tdi's don't have them. Don't some people remove the vacuum ball from ALH's too?

Mk3 used boost to control the turbo. With the mk4, engineers saw the need to have a vacuum reserve due to higher demand. Both my tdi swapped vehicles retain the ball.

 

[burpod]

I've also mounted a vac gauge and tried my best to deplete vac with braking such that it would affect n75, in a couple cars, and was unable to unable produce a scenario that would affect boost. If you have leaks I could imagine it would be of help tho

 

[burpod]

vw engineers also do lots of dumb things... like.. the plastic shroud to funnel air to the intercooler rubs holes in it (seen countless times). silly boost pipe o-rings for "quick connect" connections that constantly leak, thermo-tee o-rings constantly leak. on the BEW, insane overly-complicated intake manifold crap going on and with egr coolant pipes leaking/cracking

 

[ZippyNH]

Remember years ago a neighbor using basically a coffee can (when they were metal) as a vacuum reservoir. Just opened it up, poured out the coffee from a small home, soldered a connection in... installed it. Laughed like hell for a long time seeing the chock-full of nuts can under the hood, but it worked as long as I can remember...from the mid 80's till the 90's when the car went away

 

[PradoTDI]

It depends on your application, in my LandCruiser with a new dual diaphragm brake booster I can drain down the vacuum (using the stock Toyota vacuum reservoir for single diaphragm and no VW vacuum ball) in about 3 or 4 full pumps of the brake pedal. I can hear the exhaust note change due to the N75 being out of vacuum. I am planning on installing a second vacuum reservoir to help supplement the stock one.

 

[burpod]

It depends on your application, in my LandCruiser with a new dual diaphragm brake booster I can drain down the vacuum (using the stock Toyota vacuum reservoir for single diaphragm and no VW vacuum ball) in about 3 or 4 full pumps of the brake pedal. I can hear the exhaust note change due to the N75 being out of vacuum. I am planning on installing a second vacuum reservoir to help supplement the stock one.

for sure . but in an mk4 or mk3-vnt-converted... i tried my best to be slamming on brakes and then go for max fuel. was unable to get vac low enough to be an issue. i have not had vac balls in 10+ yrs and never had a single issue. ymmv

on a side note, what one might percieve as needed vac for boost might not always be what's needed, tune depending

 

[PradoTDI]

for sure . but in an mk4 or mk3-vnt-converted... i tried my best to be slamming on brakes and then go for max fuel. was unable to get vac low enough to be an issue. i have not had vac balls in 10+ yrs and never had a single issue. ymmv

on a side note, what one might percieve as needed vac for boost might not always be what's needed, tune depending

Valid point, I had lost track of the original point of the thread regarding a Mk2 swap.

I haven't forgotten about tuning, still battling a myriad of issues that prevent me from driving the thing regularly. Hopefully by the end of November that will all be taken care of.

 

[jimbote]

vw engineers also do lots of dumb things... like.. the plastic shroud to funnel air to the intercooler rubs holes in it (seen countless times). silly boost pipe o-rings for "quick connect" connections that constantly leak, thermo-tee o-rings constantly leak. on the BEW, insane overly-complicated intake manifold crap going on and with egr coolant pipes leaking/cracking

Most of these things you've pointed out are unforseen, long term, wear issues, not stupid engineering. Swirl flaps on a BEW might seem overcomplicated, but those cars actually do feel torquier, and are slightly less smokey, with them functional. Keep in mind, VW engineered these cars for extremes, some of which you may not be encountering. High altitude could be one of those, as vacuum is harder to achieve the higher you go.

 

[AndyBees]

Well, if I am wrong, please explain to set my head straight.

When the "go pedal" is pushed down it tells the ECU the driver is asking for more Fuel and more Boost.
So, what does the N75 do? To achieve the increased boost demand, does it apply more Vacuum on the VNT Actuator or does it Release Vacuum?

I say the N75 releases vacuum as the very stiff spring in the VNT Actuator is much "faster" than the 23 to 29 inches of Vacuum.

 

[jimbote]

Well, if I am wrong, please explain to set my head straight.

When the "go pedal" is pushed down it tells the ECU the driver is asking for more Fuel and more Boost.
So, what does the N75 do? To achieve the increased boost demand, does it apply more Vacuum on the VNT Actuator or does it Release Vacuum?

I say the N75 releases vacuum as the very stiff spring in the VNT Actuator is much "faster" than the 23 to 29 inches of Vacuum.

The vacuum is already applied, at least at idle, in anticipation of boost demand.

 

[dieseldonato]

Fail safe for the turbo is with spring pressure to open the vanes. Needs vac to close them. I deleted my vac ball too, and tried every way I could think to get hard brakes and lack of turbo response. Couldn't make the vac gauge go bellow 15" vac, which is still more then enough to nearly close the vanes fully and ample vac for braking needs.