How is the N75 solenoid linked to both brake assist and wastegate?

ocelot

Veteran Member
Joined
Oct 9, 2005
Location
Fairfax, VA
TDI
'96 Passat TDi
I strongly suspect a turbo failure in our '98 Beetle TDI. I asked on another forum where to start looking, and somebody mentioned some sort of N75 solenoid. He said the failures of these solenoids are very rare, but if there have been problems with the brake assist to start looking there.

The thing is, there have been problems with the brake assist. My question is, how is this thing linked with the brake assist in the first place, and what else does it control? Also, how do I find out if I have to replace it?
 
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compu_85

Gadget Guy
Joined
Sep 29, 2003
Location
La Conner, WA
TDI
... None :S
There is one vacuum pump on the side of the engine. It supplies vacuum to both the brake booster and the N75. If either developes a leak, it will affect the system.

-Jason
 

DeafBug

Gone but Never Forgotten: Requiescat In Pace
Joined
Sep 22, 2000
Location
Twin Cities in MN
TDI
2001 NB
If you suspect that one thing is causing problems in two areas, then I would guess that the check valve thing is probably bad or dirty. If you start at the vacuum pump and go toward the back, you will reach to a small part where the there is a large tubing going to the brake booster and a small vacuum line come out on the left side. That part is probably bad or dirty. Replace the whole thing as it is only about $50.
 

BORA115TDI

Well-known member
Joined
Sep 21, 2005
TDI
TDI115/2000/SILVER
very ocasionaly i have problems with brakes (3 in one year but really temporary) it fells like the pedal its harder to step and it doesnt brake as strong.

But the first time it happend i had no brakes at all i thought that i had pressed the wrong pedal...lol

And im also having problems with my turbo with boost fluctuations...
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
The N75 works on pressure, not vacuum. There should be no connection between the vacuum pump and the N75.
The red hose connects turbo pressure to the N75 valve.
The black hose connects atmosphere to the valve.
The valve determines which is connected to the waste gate chamber via the blue hose.
Red to wastegate: Wastegate valve opens to bleed off boost pressure.
Black to wastegate: Wastegate vents to atmosphere, Wastegate valve closes and boost builds again.
<edit> This is true of the 96-98.5 A3 and B4. The A4 and newer? As rdkern posts below they may be different.<end edit>
 
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rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
On a 98 NB? I thought it had the VNT/Vacuum situation with the N75. No?
 
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