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Filter in Brake Booster Vacuum Line?
#766136 October 06th 2020 11:18 pm
Joined: Oct 2020
Posts: 4
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Joined: Oct 2020
Posts: 4
My daughter says her van stalls when coming to a stop after driving for a while at highway speeds. She says the van starts fine, runs good and is fine while she drives on the highway. if she doesn't stop, all is good. The problem appears when she needs to stop, the engine dies. I drove the van around the city, no issues but she says the problem is more apparent when the engine is hot after hours of highway driving (lots of hills/mountains on our highways here in British Columbia).

Sooo, I was wondering if the brake booster has a vacuum leak, I have not tested it yet, but when I looked at the service manual, it says the van should have a filter in the vacuum line going to the brake booster. Her van is on the third owner, and it appears the filter is not installed. The van is a 1989 Dodge B250 and has a 318 with Holley Fuel Injection.

Does the filter matter? Any hints on how to test the brake booster for a vacuum leak? Is that uncommon?

Thanks in advance,

1989 Dodge B250 Camper Van 318 Cubic Inches or 5.2 Litres
Re: Filter in Brake Booster Vacuum Line?
sierracierra #766863 October 25th 2020 9:57 pm
Joined: Mar 2007
Posts: 4,403
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Joined: Mar 2007
Posts: 4,403
Likes: 2
That filter may actually be a filter for keeping oil vapors out of the brake booster, or a one-way valve depending on what you've got. Some vans even have both.

Since the brake booster is full of vacuum, once the engine shuts off, atmospheric pressure pushes any fumes in the manifold into the booster, where the rubber parts can be attacked over time.

You could attach a hand operated vacuum pump to the booster to see if it holds vacuum.

As for substantial vacuum leaks in out of the obvious places, try the charcoal evaporative canisters and their hoses. Those hoses frequently turn mushy and split wide open. The master canister (with the vacuum actuator on top) has a rubber diaphragm inside which can rupture, causing a very substantial vacuum leak. When you attach a hand vacuum pump to that actuator, it should hold vacuum.

Among my favorite stealth failures on vintage vans is the fuel tank cap. It has a breather valve built in. Driving at highway speeds, you develop maximum vacuum from the fuel pump. If the breather valve in the cap fails, you will starve the carb for fuel, and can literally collapse a tank. All you need to do to eliminate that as a culprit is to try opening the cap when you've got a stall and listen for a "whoosh" of incoming air to replace the built up vacuum. It's possible to drive with the cap partially cracked open too, though that does have some potential safety issues.

-It's been such a LONG TIME... BlueShift>> 1981 Dodge Ram B250 Custom Sportsman Maxi Van

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