Power brakes delete
 

Has anyone done it?

I realize that PB is free power, but only having a few pumps during EOC is a PITA and a little scary when the pedal turns to stone when you need it.

I am looking at getting a 96 aspire. It has manual steering already, but it does have PB. Not sure if it has ABS. I suppose having ABS would mean I am stuck with PB as well.

I'm told you can increase the size of the vacuum tube for the brakes, giving more reserve power. But it's easiest just to momentarily restart the engine. Remember, modifying your brakes haphazardly could be fatal.

pete c
Power brakes delete

+1 :thumbup:

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Having previously owned and daily driven a couple of cars without power assisted brakes (from the factory), one with drums all round and one with discs at the front, I wouldn't go back.

For a classic that's only used on weekends, in light traffic, no power assist works OK.
For a daily that may have to cope with lunatic drivers in peak hour traffic, I wouldn't risk it anymore.

I would guess that a 2100 lb aspire with front discs would stop just fine. Actually retrofitting though is probably not worth the effort.

Going to a larger vac hose may provide faster recovery, but it really doesn't add much to the stored vac. I think a better alternative may be adding a second vacuum tank. An extra tank, the size of the booster should double the number of pumps you have.

Maybe a vac gauge would be a good idea as it gives you a little warning that you are about to run out.

Do what I did on my EV conversion. Used Volvo vacuum pump from a wrecker. A vacuum switch (http://www.evsource.com/tls_braking_system.php - third item down) that turns on the pump through a relay. My brakes work great with no ICE sucking anymore - as good as they were stock.
http://i1119.photobucket.com/albums/...rtYEw60_12.jpg

Thanks, mech. 35 bucks for the switch and the pump from a boneyard for a few bucks sounds like it might be worth it.

You can make a vacuum bottle out of PVC pipe for just a few bucks as well, then just "T" it in to the brake booster after the check valve.
I like the electric vacuum pump idea tho.
Making your car harder to stop seems like a bad idea, if for some reason someone else goes to use your car they could get hurt or killed and that doesn't save a whole lot of gas.

Power Brakes
 

I have opted for a larger booster (290V) + 1" master cylinder and it seems to work well.

Would you do a write-up on your mod... I'd love to see it. Is this really a fuel saver?

There really isn't a fuel savings to speak of here other than being able to EOC for longer stretches.

I might give the PVC pipe idea a try. Pretty sure I can do it with junk laying around the basement.

My setup doesn't have a vacuum reservoir. The pump cycles basically every time you stab the brakes. It works very well, but I am going to add a reservoir only to make it more stealthy in parking lots.

This is the first mod I would do if planning to EOC with an ICE car.

You can see how it's wired on the right bottom side of my schematic:
http://i1119.photobucket.com/albums/...ps5fcd61e8.png

Just put the car in gear, with the ignition off when you want to stop. It will make vacuum.

This works well.

I use a maintained ignition kill switch so that I can EOC and still use engine braking down long hills.
A welcome side effect of this is that it keeps the brake vacuum "topped up" for emergency use.

Never dawned on me to engine brake to produce vaccum, never too old for the light bulb to brighten. Thanks

I do understand spinning the engine up via the tranny quickly restores vacuum and I do it all the time. It is just that it would be nice to be able to coast long stretches which require occassional brake taps without having to worry about whether or not I have a pump left. As many here already know, you go from full power to nothing very quickly. There have been times when this has caught me a bit off guard. It has never resulted in an accident and I would like to keep it that way.

As if you're not a big enough hazard doing EOC you have to try this?!?!!?

My take on the EOCing is dangerous debate.....

EOCing does mean you have some loss of maneuverability with no PS. It also increases the chance of running out of brakes if you do not pay close attention to your vacuum supply (the point of this thread).

But, EOCing takes increased attention to what you are doing. This increased attention helps with the two leading causes of accidents, IMO. Not paying attention and falling asleep.

In my 30+ years of driving, I have found that dozing off from boredom is by far the biggest risk. I have driven tired and in my misspent youth, driven drunk. And from personal experience, I can say tired is far more dangerous that a little drunk. A lot drunk is a different story. So if EOCing means I stay more involved, it also means I stay more awake. So any slight risk that comes with possible loss of brakes/steering is more than offset by the fact that I am conscious.

The way I approach this is, if I've used 2 or 3 pumps (out of 5 usually in my car), I'll do a quick bump-start-key-off cycle to restore it. That way I'm not running close to the edge. I do it when things are nice and clear, so it's not a problem if/when an emergency does come up.

I don't have a vacuum boosted brakes on my suburban, but if I did here is what I would do.
First off I would give the brake booster its own vacuum canister isolated with a check valve. That canister would have an additional vacuum pump plumbed into it with a vac switch set to turn the vacuum pump on at around 14''Hg.
Then I would add a warning circuit, a red light or LED (always hot) that grounds through another vacuum switch set for say 10'' to 12'' of Hg.
That way you always have power brakes or a warning light if you don't.

What you say is good. I have been putting off adding a warning for a while. I had my vac pump relay crap out last week - but luckily in the welded closed position, so the pump just ran constantly

I have a low oil pressure light that [obviously] isn't being used anymore. I plan to hook that up to the existing vacuum switch so it turns on every time the pump turns on. Sure, it isn't a second sender, but at least I will be able to see the pump cycle during normal driving and notice when something abnormal happens...ie..the light not going out when it should.

I've had the power assist go out on my brakes once. I thought I was going to die.

Firstly, the brakes were designed for power assist, so without it the pedal seemed to be only making suggestions to the brakes. I'm certain I could have decent brakes without the power assist, but the pedal travel would probably have to be about a foot and a half to make it happen.

Secondly, the vehicle is a diesel 2-ton with an automatic transmission. There was no way to achieve ANY kind of vacuum by shifting, or restarting, or anything. The vacuum pump belt had broken, so that meant no power assist. Blimey.

Thirdly, it's bad workplace karma when you work for a Christian ministry and the vacuum pump belt goes, and suddenly you're exercising your vocabulary in a non-Christian manner. Oops.

If having more power assist for braking is important to you, why not grab a couple vacuum reservoirs at the junkyard and just plumb them in? You'll have a few more stops left in the system that way.

It's the unpredictability that is the problem, right? The extra vacuum reservoir volume seems the right way to go to me. Some indication of the vacuum remaining in that volume would also be useful.

Since the pressure difference is quite low (~10.3psi/70kPa) almost any container could be made to work maybe even a re-purposed carbonated drink bottle or bottles. The PVC pipe is likewise low cost, light and inexpensive.

A restriction in the feed to the additional reservoir volume might be necessary to prevent the engine operating with high inlet manifold pressure on start up for an extended period (maybe you'll get a spike in the idle speed or a hard start).

There'll have to be a one way valve between the inlet manifold and extra volume anyway. One source for an in line unit will be the brake booster vacuum check valve found on cars with a turbocharged gas engine.

A pressure gauge would provide a better indication of the vacuum reserve left than a simple switch and light. The GM MAP sensors (there are others which are similar) are really simple and widely available for very little cost used. Feed it 5V and provide a ground connection and the signal can be read off with either a cheap digital multimeter or a panel meter. They are almost linear wrt pressure vs voltage.

You might want to check what pressure the one way valve that traps the vacuum in the brake booster opens at for reference.

Suggestion, something stronger than a pop bottle.

Agreed - those are great at holding pressure, but useless for vacuum.

I would love to see you get a ticket for this so you could try using this defense in court. The judge would throw the book at you and tell you to your face that any sober person that would consciously hamper their brakes and steering is a threat to everyone on the road despite being conscious and sober.

I'm not unfavorable to delete the vacuum brake booster, because of weight and complexity. Altough it's not really heavy, it's one of the few small things that can be modded for weight-savings, and gives more freedom for intake manifold mods. An uncle of mine did it in a Suzuki Vitara, using a Chevette master-cylinder, and it worked well.

When I started engine off coasting, I drove over the top of a hill, shut the engine off, pumped the brakes until the reservoir was fully bled down, and proved that I could stop on a downhill grade without any vacuum boost. The brake pedal force was high enough to convince me to leave the vacuum boost system alone.

I would be skeptical to delete the vacuum boost only in a vehicle fitted with ABS brakes, but since I'm probably not going to get a vehicle fitted with them so soon I'm still convinced to delete the vacuum booster...