TDI install retrospective: Vacuum System

Continuing the process of back-documenting what I did to put a TDI engine into an old (1972) air-cooled VW bus. Today's post is all about the vacuum system. It is super short, because there really wasn't much to it. Before I start, Hapy ThanksGiving and White Friday to my US readers.

Bus Needs
The TDI has a few things that require vacuum, and the bus has one: the brake booster. The original engine supplied vacuum from the manifold through a pipe that runs along the driver side to the brake booster underneath and behind the driver seat (under the bus). Fortunately, 30 years of engineering marvels later, the brake booster in the modern car is supported by a very similar vacuum. It is so similar, in fact, I just needed to plumb the brake booster outlet on the vacuum pump to that pipe and that need was solved. Power brakes? Check.

TDI Needs

from TDIClub

The TDI engine has it's own needs. The turbo needs a signal to dump boost. That actuator is vacuum powered. The EGR is vacuum signaled as well. Each of these have a different valve triggered by a signal from the computer (the N75 and N18 respectively). Since I pulled my EGR equipment, I simply blocked the signal line leaving the N18 and left everything else in tact. I mounted the control valves to the floor support that runs just to the inside of the spare tire well. The system needs the vacuum ball, the pump, of course, a bunch of T fittings and a source of clean air. I source the clean air from the main air intake. I will get to the air system later, but simply put, I took an old air-flow metering (MAF) housing and replaced the sensor with a simple vacuum nipple. This air flow metering housing was the same size as the rest of the fresh air intake, so it was just one of the components that were strung together after the air filter.

I spent a great deal of time drawing and diagramming before I did this. Ultimately, that was unnecessary; I was working from fear. So many systems work the other way: air pressure, water pressure.. the direction of the media is the same as the force, so when you look at a vacuum diagram, its all upside down. Air goes one way, the force of the air used to open and close things goes the opposite direction. Basic vacuum versus pressure, like the switch on your MityVac. It is the media (air) leaving that is the force, not it arriving.

With that perspective, I could made a plan. Ultimately, all I was doing was changing the lengths of the hoses, so this turned out to be pretty easy. I set the pieces out and started replacing lines with new vacuum hose. In many cases, I cut a different length than what was originally in-place because my placement required it. I retained all pieces of the system with the sole exception of the EGR (which I may re-introduce). The hose that would have gone to the EGR was simply terminated with a cap.

Prior related posts:
Preparation
Fuel System
Physical Mounting

Next related posts:
Air, Intercooler and Exhaust
Primary Electrical
Cooling
Secondary Electrical
ECU, dashpod and Sensors