Brake Booster tips...

[Matt Dyne]

With the recent testing of the Antilag system on the Legacy (great idea that...what a change to the car, but that's another story) the brake booster, which relies on vacuum has gone out the window(as I anticipated).

There has been a number of different suggestions bandied round amongst people I've spoken to and just thought I'd check with you guys before I did anything.

These are the options that I've considered (or been told about):

1) wind the antilag back a little to ensure some vacuum in the system. Tried this it's hopelessly inconsistent. some corners you'll approach thinking the pedal might be hard so you brake early and find that it's working fine and have to accelerate to the corner again others you'll be going in a little quick and no brakes !

2) A vacuum resevoir. This is apparently just an in line pressure tank between the booster and the manifold that stores vacuumn. Haven't seen this in action, although Rob Nunn has it. In my mind though, it still relies on some vacuum in the system which in my case there probably won't be.

3) Pedal box. Get differing ideas on this one. Seems pretty expensive and time consuming (getting the piston sizes right) but others say it's reasonably cheap

4) Spoke to the Possum Bourne guys who said you could cut the guts of the booster out and replace it with a solid rod to the master cylinder. I assume by the same logic, you could just piss the booster off and make a block that replaces it.

Any other ideas ?

Ta,
Matt

[eski]

a hose to the navis mouth! if they're going to steal oxygen, they may as well be usefull!!!!

[Matt Dyne]

Nice one Brett !!!

Any USEFUL ideas ?

[eski]

Is there any reason you couldn't get a small electric vacuum pump and hook it straight to the booster??? I don't know what sort of pressure is required but it would give you the same pedal feel every time. Or am I just being a twit.....

[Matt Dyne]

Ah yess...

Option 5 was to look at running a diesel alternator. Diesels, due to compression ratios, don't have much vacuum either so run a vacuum pump that sits on the back of the alternator. Not sure about this and apparently they are pretty bulky and might not fit in the standard Subaru spot.

This initially was the most interesting option because the standard boosted brakes are fabulous.

Matt

[Ballast]

Go with the easiest one! Option 4 sounds the best, even if your pedal feel is different at least it will be consistant unlike option 1 and 2. Option 3 is just harder than 4, unless you get some one that has already done it and copy it. Either that or 5 sounds like it is worth doing some research in to.

Interesting problem though, something I have never had the pleasure of having......

[Matt Dyne]

Can also apparently change pivot point on the pedal. By moving it up a little bit (ie pivot further up the pedal) the effort decreases but (using physics) the pedal travel would increase somewhat.

I have a spare booster, so tonight I'll punch the centre of it out and see what happens.

cheers,
Matt

[Daniel]

Matt - the new pedel box with twin masters would be the best, the "replace the booster with a rod" theory will work but will give you an awfully heavy pedel even if you move the pivot point. Forget about using the deisel alternator it would a) be cheaper to get a pedel box (my alternator was $760 trade, 3 years ago) b) a heap of work (see a ) Hope this helps


There must be second hand pedel boxes around for those things, surely?

[Matt Dyne]

Well an update for those that are bored...

I spent Sunday morning pulling apart the brake booster. Who would have thought just how complicated those things are. I pulled out about 1kg of crap from diaphragms to steel plates, a huge spring (which explains most of the effort when the booster is disconnected) blah blah blah.

I now need to weld it back together (it was held by pushed in sections of the rim) and get the new longer rod.

The pedal clevis pin slides into a u section that was bolted to the booster rod.

Here's a Q, what should I make my new solid rod out of ? I'm assuming there is a huge amount of force on this thing, so threaded rod (which is laterally weak) would be out of the question. I thought about getting the right thread (it's an M something) via a huge bolt (needs to be about 300mm long though) so I'm off to the metal centre today.

Any other ideas ? Don't have a lathe to spin something up.

Matt

[Daniel]

I'm guessing it'll be a M8 or M10 course thread - I think your right, find a HT bolt the right thread and lop it off. Alternativly, can you remove the whole booster asembly and mount the master onto the firewall directly? (save more weight ) and use the original rod?

[Chris]

Whilst on the topic of boosters, has anyone with a non turbo car experimented with a solenoid lockout in the booster hose?
Non boosted brakes on SS for extra feel, then when your leg is sore and your on transport, flick the switch and boosted brakes.

Comments anyone? :

[Spac]

Why not just set it up right without the booster? A dead booster in place adds substantially to the effort you have to put in, and still kills (some of) the feel. Correct piston sizes will mean you'll never want for a booster at all...

[Matt Dyne]

Have you tried driving without a booster ? I could hardly push the pedal, let alone heel and toeing.

My feeling is cut it out of the system all together.

[Swill]

(it's an M something)

Jeez that narrows it down a bit very tidy.......

Have you tried driving without a booster ? I could hardly push the pedal, let alone heel and toeing.

Yes and its called a balance bar/ pedal box and it sounds a whole lot eaiser and cheaper than all this crazy booster that doesnt boost, then when it doesnt boost , has no feel, if it has no feel my leg(acy) gets sore and if its it did boost id have no anti-lag action.... I think I got all that right anyway have fun, brakes are over rated, just ask rev till it pops Fro....

[fro]

Originally posted by YRALLY

anyway have fun, brakes are over rated, just ask rev till it pops Fro....

Hey, it didn't pop. Just bent slightly

And I don't know if I'm the one that knew about the brake so much. I think Guy definitely knew about them!

I just love this discussion:
The scene is a post engine transplant test run - 2am around a relatively quiet Canberra suburb. A 180B approaches corner still gaining speed
Guy (sniffing the evil burning brake pad smell): "Is that the brakes going off?"
Fro (still accelerating whilst pumping the brake): ""Hmmm, yup!"
180B spears across "inside of corner" and across residents front lawn, leaving two nice lines in the turf.
Fro: "Gone off I'd say."
Guy (removing fingers from fingermarks in seat): "Fro, it's not cool to roll in people's front yards."

It's amazing how poor standard brakes suddenly seem when you double the amount of grunt you've got...

Getting back to the original topic... Legacy, have you thought about using some hexagonal tube? You could thread the internal diameter, and have adjusto bolts in either end, and it would probably be stronger than a straight rod. Maybe even thread the clevis straight into it, depending on how it actually operates.

Or is there a space constraint that wouldn't allow you to do something like that?