brake booster + open throttles?

[touge_ae101]

well had an interesting problem yesterday at manfeild. during racing about a dozen times (intermittent, tried different braking techniques to resolve) the pedal went super hard and lost all feel. luckily i pulled it up each time in the middle of heavy traffic but i'd love to get it sorted.

gathering ideas from mates, it seems although the brake booster is just not working. now i don't know anything about brake boosters and how they work but how reliable are they? are they a common thing to break or can a couple years of extremely hard driving wear them out?

another thought was that i run open quads on my blacktop and is it possible to struggle to get a strong enough vacuum signal to properly power the brake booster? i've been told you can double up the vacuum signal by using another unused vacuum line (only one i use is for MAP in the Link) and adding another one way valve..

car is a standard ae101 with blacktop, wilwood front brakes and ae111 rear calipers.

any semi-educated thoughts/ideas/experiences??

[sergei]

If you go full throttle, there is a check valve that prevents the vacuum escaping back into manifold.

Healthy brake booster should have almost no leakage of vacuum if it is not operated. You could T into a vacuum gauge (between booster and check valve) and see how fast the pressure drops after you shutoff the engine. There is also much simpler test: shut off engine, wait a minute and press the brakes, if pedal is hard, then your booster is leaking (or the check valve).

On 20v there are 2 check valves, since the booster is fed from each side of the manifold.

[Lloyd]

Other option is put a vacuum canister in as a "vacuum reserve" so to speak. That is if your booster is still fine and you're running out of vacuum still. Check valve will make a big difference if you haven't got one fitted, or its faulty.

[RomanV]

Or if it's really problematic you could try fit an alternator from a diesel, as they have a vaccum pump attached for the brake booster sometimes.

Have never tried it though, just being an internet mechanic.

Definitely start by checking out the one way valve!

[KwS]

how do Mr2s get the vacuum feed for their booster, a long vac line or electric?

[levinguy]

a long vac line

[touge_ae101]

ok sweet thanks guys i'll have a play with it tomorrow and see if the booster is leaking. if not i think a resevoir might be the way to go.

[touge_ae101]

ok so tested it out. after 5mins of engine off the booster is still doing its job for a few pumps of the brake, so if it is a leak it must be fairly small.

seems weird thats it become a problem all of a sudden as i've done plenty of hard track and road driving before now. but i suppose i should be looking at a vacuum canister of some description to help make sure the booster doesn't run out.
has anyone seen/got pics of something like this? seems like it shouldn't be necessary, haven't seen/heard of it being a problem before.

[sergei]

Some euros (Saab) have vacuum booster vacuum pump (or vacuum booster booster pump ), that might help. The volume of the booster is fairly large, so if you are using that, you will probably need ~1L sealed container that will not collapse from vacuum...

Are you sure it is vacuum booster issue and not overheating pads (you press hard but it does not stop)?

[touge_ae101]

i would be suprised if i'm overheating my wilwood race compound pads... only a 6 lap race as well and getting the problem by 2-3 laps in. not going super fast so that is pretty unlikely. it still stops alright, just looses all feel and goes super hard.

sweet i'll weld up a stainless box to fit in the engine bay somewhere.

[sergei]

Oh Audi and VW use them as well: P/N HL000844000 or Hella HEL1910902




Speaking of pumps, the Prius should also have one...

[jaypines]

hmmmm... are those electric vacuum pumps running on full duty?

[sergei]

hmmmm... are those electric vacuum pumps running on full duty?

They could be pressure activated.

[rollaholic]

you can find em on volvos too

[Grrrrrrr!]

Just out of interest, how much vacuum do those pumps make?

[touge_ae101]

hmm been thinking about this some more and could it be possible for my left foot braking to cause this problem? i use a bit of brake of full throttle through a few corners just to steady the car and i find it helps the diff work when pulling through corners a bit better.

how does it work for a turbo car then? presumably when its on boost there is no vacuum?? what happens if you want to left foot brake etc?

[Dell'Orto]

Install a Pajero/other diesel motor alternator, problem solved

[matt dunn]

Install a Pajero/other diesel motor alternator, problem solved

PITA to do,

oil feeds and returns,
and Diesil alt's are not the most reliable.

You should still have decent vacuuum no mattter what,
so maybe it is just not plumbed in right?

Where does the feed come from and how big is it?
Are you running the BT manifold and ruuing it of the centre port on top??

Needs to be at least 10mm to each cylinder minimum if you run 4 throttles.

[QikStarlie]

should have heaps of vac. i ran my starlet booster off the 2 small lines on the outer throttles, teed together. lucky if they are 4mm. no tank. never had any issues.

maybe the booster/piping is only leaking intermittently. i'd replace whats there before trying anything else

[wordnz]

how does it work for a turbo car then? presumably when its on boost there is no vacuum?? what happens if you want to left foot brake etc?

There's still vacuum before the turbo.