E30 Brake Booster Check Valve

[marquis-marc]

Hi there!

I'm rebuilding my 1989 325is and was going through the brake booster vacuum lines and the pieces that go with them and stumbled across the Brake booster check valve.

The valve on my car looks like this:


When I looked on realoem the part number was: 34331158113 and required use of this vacuum cap (11611437560)

New Valve:


Question is- what's the purpose of that extra connection I've circled in red? I'm assuming the vacuum cap realoem lists as used in conjunction with the check valve is to cap this.
So why have it added there if it's just being capped?

Wanted to make sure I'm getting the right part before I pull the trigger.

Thanks!

[Northern]

This version of the check valve was always expensive to replace, maybe it was easier to source this style so they caved and updated the part number?

If I had this style booster vacuum, I'd update to the late single-port setup and either block the extra TB port, or source a 1990?+ throttle body.
I looked in RealOEM and can't find the setup I'm talking about, but at least as early 11/89 production manual cars should all be this way.

Pics in this thread:

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m20/305263-brake-booster-vacuum-lines-before-and-after-tb

[Northern]

https://www.fcpeuro.com/products/bmw-check-valve-support-vaico-34331156703

They're also 1/10th the price.