CJs 928

Just got done with my intake refresh, fuel lines and vacuum line replacement and noticed (after hours of reading on rennlist) that everyone has a brake booster check valve (blue and black thing that attached to the 3 way from the the booster) but me. I can't find it in the IPB and don't want to wait for one to be shipped either-can these be sourced (generically) from a local parts supplier (autozone etc)? If so, what did you buy?

Thanks!
I have an 87S4 Auto.

Tom in Austin

Mine cracked and Roger at 928srus came up with a replacement in just a few days. I also replaced the rubber seal on the booster while I was at it.

CJs 928

You are right; Roger is the best and could get it to me quickly. I was just wondering if they were generic since I was going to autozone/advance auto within the next hour to get some other stuff.

stolarzj

You can run without it, just hook it up later when you get it. Your cruise and HVAC may not work right without it, but that's all.

Mrmerlin

the blue valve is made to keep the reservoir at the maximum vacuum possible, this will happen at idle or hi engine speed coast down, if the throttle is opened quickly the vacuum pressure will drop ,
without the blue valve then reservoir vacuum pressure will also drop causing faulty operation of the various vacuum controlled systems
HCV , CC, HVAC system, it may also affect the brake booster with a lower vacuum

CJs 928

thank you for the replies.

dr bob

Answering your question directly: You can use a generic check valve from Autozone or wherever, picked for the tiny hose size used. Make sure you install it in the correct direction, with airflow available towards the booster only.


Many folks seem to want to remove this valve, since the factory valve also provides a bit of restiction to airflow. If you have a leak in one or more HVAC diaphragms, it might increase flow enough to recover system operation at engine idle. Of course all the vacuum actuators in the HVAC system will relax as the engine load increases and intake pressure rises, and the vacuum-operated flappy won't be right. So replacing the valve may cause you to get into the rest of the vacuum system to see why it was removed. They seldom fail, but may be acidentally damaged while doing something else, so there may be a quasi-legitimate reason for pulling one out and forgetting to replace it.

CJs 928

Thank you for the explanation Dr. Bob.

jpitman2

I think Dr Bob means air flow FROM the booster? Its the manifold that sucks, not the booster. Connect one side to the manifold pipe, and you should be able to blow in the other side, but not suck air.
jp 83 EuroS AT 52k

dr bob

OP was referring to the little check valve between the splitter and the booster line, so air flows through that check valve FROM the splitter side TO the booster side. The "booster side" really connects to the vacuum hose to the manifold, where it attaches to the dedicated brake booster check valve. Air flows from the splitter, through the check valve, to the manifold.

ROG100

If you find an alternative please let me know the details.
I sourced a Ford one and a Mercedes one and both would not work unless you used a smaller diameter vacuum line.
At $18.95 it is an expensive part and I am sure there is a cheaper alternative out there.
Roger