Cheap power brakes for electric car? - Fuel Economy, Hypermiling, EcoModding News and Forum

bennelson · 07-10-2008, 04:42 PM

Hey everyone,

As you may know, I am converting a car to electric.

One of the problems with an electric conversion, is that you lose the "waste by-products" of the gasoline engine, namely, heat in the winter and vacuum year-round.

I have seen that there are some electric vacuum pumps available through EV conversion places, but they are all very expensive.

What would really be needed to create vacuum for power brakes?

Could something like this work?
air suck pump

Doesn't say if it is AC or DC powered, but if it is DC, it would then just need some sort of simple control to turn it on and off at the right time.

Whoops, I just noticed, it isn't electric, but rather air powered. Does that mean I could hook up an air compressor tank to it and just have that aircompressor run while hooked up to house power, saving it in an air tank for later?

Would this work? Any other ideas?

MetroMPG · 07-10-2008, 04:54 PM

I would be looking into junkyard vacuum pumps from diesel cars. Maybe ask some of the TDI drivers here how their brakes work.

MazdaMatt · 07-10-2008, 05:19 PM

MUCH BETTER IDEA: Upgrade to a larger master cylinder and remove your brake booster. You will never lose boost, have better brake feel and lighten your car significantly by removing the part and not adding a vac pump.

MetroMPG · 07-10-2008, 05:57 PM

The FS has a discs/calipers upgrade from the 4-cyl car. Much easier to use than the 3-cyl setup without vacuum.

I've also heard that you can simply puncture the diaphragm in the booster reservoir (drill through it), and it significantly lessens the amount of pedal effort required. Not sure I totally buy that idea though - not enough to try it on the FS anyway (in case we ever want to add vac assist).

Ben: I can attest to the insanely hard brakes without assist in my '98 3-cyl.

MazdaMatt · 07-10-2008, 06:01 PM

drilling through you booster will kill your boost and increase your pedal effort as though you were eoc'ing and pumped the brakes till they were hard. If i were doing this, I would see absolutely no option besides replacing the MC with one that does not require boost. I will be doing that to my track-only car soon.

MazdaMatt · 07-10-2008, 06:06 PM

oh yeah, drilling a hole would also have the same result as a vaccuum leak... bad idea

dcb · 07-10-2008, 06:20 PM

a vacuum leak on an electric car?

MazdaMatt · 07-10-2008, 06:25 PM

a vacuum booster on an electric car? (see my point?)

Funny... new tech (EV) brings back old tech (properly sized MC with no booster!)

dcb · 07-10-2008, 06:58 PM

I'm all over the manual brakes suggestion. The booster on an ICE could probably be disabled without destroying it or causing a vacuum leak though. Just fish a bit of plastic wire through the check valve and block off the hose going to the engine perhaps.

edit: heck the check valve might be removable.

dcb · 07-10-2008, 08:39 PM

I did just did an experiment on a metro, when I pulled the hose from the booster there was a noticable noise of escaping air, so it seems likely that the check valve was external. I plugged the hose end removed from the booster (jammed in a round thingie of the right size) and took a test drive (no traffic, slow speeds).

Initially it felt pretty much like it does when the boost runs out. But I got a lot more confident with it as I used it. No problem locking up the tires, it just takes more pressure which legs have plenty of, especially in a panic

I am starting to think a big problem with running out of boost is the sharp transition to no boost braking. If you never have boost it seems pretty manageable. More leverage wouldn't hurt though, and of course your mileage may vary.

MetroMPG · 07-10-2008, 09:53 PM

FYI, the comments under this post describe the "puncturing the diaphragm" method. (Note: this only pertains to power brakes. Under no other circumstances should you puncture the diaphragm!)

EV Weblog: Larry's EV

Not endorsing the idea - just putting it out there.

MazdaMatt · 07-11-2008, 09:45 AM

The "typical" way to quickly disable your booster is to undo the hose from the booster and plug it. The booster just won't have a vaccuum source and you won't have a vac leak. The "Proper" way is to take out the whole booster and upgrade MC. Removing the booster will remove a few rubber parts that you have to squish before pressure gets to the lines. Just removing the vac line means you are still squishing this stuff.

The hard part to get used to is that braking is now proportional to pedal PRESSURE, rather than pedal TRAVEL.

Instead of upgrading MC, you should also be able to alter your pivot point. Since this is not a racing application, you don't really care if the pedal moves 3-4 inches. For my track car when i do this, i will want about 0.5inches of travel to full lock-up.

dremd · 07-11-2008, 05:02 PM

The pump you pictured is most likely AIR powered. (Venturi action)

The TDI has a cam driven Vacuum pump.

The Supra has an Electric Pump! It is however very small You could use 2~3 Should be able to buy them cheap; you can remove them and only loose your cruise + brakes under boost. (Who ever stops when they are boosting?)

MetroMPG · 07-11-2008, 10:36 PM

Ah, thanks, dremd - I didn't think about a mechanical pump.

And I hadn't considered turbo cars needing an auxiliary pump. Interesting.

steensn · 07-16-2008, 10:23 AM

You could always impliment and SCB system like we make for hybrids

I would suggest grabbing an electric vacuum pump from a diesel or even a lot of newer cars with cold start have them in it. Go to a GM dealership and get a part number for one of their vacuum pumps and see if there is a cheaper version somewhere.