Power brakes delete

[mechman600]

Originally Posted by oil pan 4

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.

[elhigh]

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.

[Occasionally6]

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.

[wolydotmatrix]

Suggestion, something stronger than a pop bottle.

[PaleMelanesian]

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

[ConnClark]

Originally Posted by pete c

So any slight risk that comes with possible loss of brakes/steering is more than offset by the fact that I am conscious.

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.

[Pawtuckett]

Originally Posted by ConnClark

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.

[cRiPpLe_rOoStEr]

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.

[JRMichler]

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.

[cRiPpLe_rOoStEr]

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...