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millenniumtree 07-20-2008 06:39 PM

Homemade PVC Vacuum Reservoir (Now with Photos!)
Yesterday, I built a PVC vacuum reservoir to increase my engine-off braking ability.

I used about a 2ft length of 3" diameter PVC pipe, 2 pipe caps, and a threaded hose barb to connect the reservoir to the brake booster.

I drilled a 3/8" hole in the end of one of the pipe caps, threaded the brass hose barb in, then cleaned out the inside of the pipe and glued it up with PVC cement.

I then cut the vacuum hose coming off the brake booster (on the booster-side of the one-way check valve), inserted a T, and connected the reservoir with 1/4" vacuum hose and hose clamps.

I took it out for a test drive and went from 3-4 presses on the brake pedal to 6-8! So I've basically doubled my safety margin! Yippie!

Currently, the reservoir is held in place with liberal use of zip ties. I'll probably whip up something a bit more permanent in the coming days or weeks.

PVC melts so obviously don't put one of these next to the exhaust manifold or you'll find yourself suddenly without brakes!

cfg83 07-20-2008 08:15 PM

millenniumtree -

Eeeeeen-tay-rest-ink, :) . Can you post some pictures?



Tango Charlie 07-21-2008 08:48 AM

Very clever! I'm going to add this as a 'planned mod' to my Vibe.
I agree with cfg83; we need pictures!

Daox 07-21-2008 09:46 AM

Definitly need pictures. :) Sounds like a nice cheap mod.

millenniumtree 07-21-2008 10:31 AM

Very cheap. About 15 bucks. I tested it again this morning, and got 6 full presses on the brake, and one more that was effective but not as powerful as the first 6.

I see it as just an added margin of safety, because I practically never press the brake that many times. On a big hill where I didn't want to grav to 60mph though, it might pay off. :D

Oh, I'll have pictures this evening. I'll try to remember to take some when I get home. It's really pretty much exactly what you'd expect though. A PVC pipe, capped on both ends, zip-tied under the hood with a hose connecting it to the brake booster hose. :P

instarx 07-21-2008 05:04 PM

Hmmm, but does it have any effect on the FIRST brake press after the engine starts? In other words, does it take time to evacuate the resevoir to give you boost? So if you have to panic stop just a few seconds after starting off (for example you start through an intersection just as some nut decides to run the light), do you have brake boost?

bbjsw10 07-21-2008 06:01 PM

Very cool idea I was thinking the other day about this but couldn't figure out something cheap. Great Idea on pvc. I have some of that in garage.

bennelson 07-21-2008 06:09 PM

I was talking about EXACTLY this same thing yesterday!

The discussion started, talking about a PVC tube cannister for vacuum for an electric vehicle, and then moved on to talking about doing this for an ICE (internal combustion engine) vehicle for better braking on extended Engine-Off-Coasting.

Good Job! (I second the "post some pictures"!)

dcb 07-21-2008 06:15 PM

instarx, I seriously doubt it has any noticable effect. The return of brake boost feels pretty instantaneous when the engine restarts and this seems to have doubled the capacity, so it is 2 x Instantaneous.

millenniumtree 07-21-2008 11:44 PM

Yes, double the engine-off braking capacity, and no, there is no noticeable difference in braking effort or effect. I've took some decent stabs at the brake pedal for testing purposes, and there seems to be no difference in braking ability. It'll still lock up the tires quite readily.

Here come the pictures!!

Parts needed: 3" PVC Pipe, 2 pipe caps, 1 threaded hose barb (brass)

Connection to vacuum line To the left is the check valve that prevents vacuum escaping when the engine is turned off. Then the T connector (3/8", 1/4", 3/8"). Use properly sized hose clamps and make sure there are no leaks. I'm going to replace the T with a brass unit when I next get to the hardware store. The plastic bit from the auto parts store is just too flimsy.

This thing is pretty big. It's zip-tied in place for now but I'd like to add some beefier pipe strapping that's screwed into place. It holds well right now, but it could be better.

The hose barb connection on the reservoir. I just drilled a hole in the end of the cap and threaded the hose barb in. (It's a 3/8" ID pipe thread used for water lines) If you drill the hole JUST big enough for the threads to get started, the brass pipe thread should cut its own threads into the PVC and make an air-tight seal. I'm sure I don't have to tell you, but make sure the inside of the pipe is CLEAN. Anything left inside here could potentially get sucked into the engine, or plug up the valve, causing your brake vacuum to leak out when you shut the engine off.

The car. Bone-stock base-model 1.5L 16-valve.

Blatant self-promotion. (53mpg is the average of my last two tanks)

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