bpu699

I know our brakes are vacuum assisted, at least on the 930.

Last time on the track when I was getting towed, I was shocked how little braking I had with the motor off...

The tow truck kept signaling to brake, yet I barely could. Took some force.

With motor running, I can easily haul the car down from 120 mph with my toes...

Do these cars really have that little braking without vacuum and with race pads???

Really made me wonder how people stop on the track when their motor blows...

Honestly, felt like the brakes on my non vacuum assist 914 were more powerful...

Anyone ever experience this on the track? Had a brake vacuum line go? Lots of folks check their brake lines and fluid often. Never hear much about vacuum lines...

dan212

yes - thats what happens with power brakes. No engine - No power assist on the brakes. To be expected.

I have been towed a few times and knew to press much harder. Its not that they don't work, you just weren't expecting the difference in pressure needed.

They do work. I actually disconnected the boost on my 996 GTB years ago because it was too much for my taste. I was quite happy with that feeling and could haul the car down at speed, but it kind of freaked out some mechanics when they got in to move the car in the shop and a light touch of brakes made no difference - I always warned them though.

mark kibort

yes, most are all vacuum assist and there is quite a bit of effort to brake the cars without the engine connected... doesnt have be running, as it makes all the vacuum under decel, even if itsnt running. the good news is , you have a vacuum booster, which stores vaccum to run the brakes. upon a catastrophic engine failure, when its not spinning anymore or all the valves are bent..... you can have a power assisted brake effect to make one emergency stop, as long as you dont modulate the pedal, it will slow and stop safely. pump the brake, and all bets are off. better be up to date on your squat workouts to slow safely, depending on the car!

bpu699

Thanks for the replies... didn't know there was a reservoir of vacuum reserve...

PPo

Careful... there *may* be a reserve. Some remove the reserve system to cut weight and/or complexity in their track/race car.

mark kibort

usually there is ... no booster reserve and you end up with no brakes going from WOT. it stores vacuum under any condition but WOT. depends on the the car, but most all sports car racers have the vacuum booster. and as long as it isnt leaking, you have power brakes initially when the engine dies or grenades.

bpu699

You never see posts about checking vacuum lines to the brake booster... Can't say I ever replaced one...

Now I have to figure out where it is on the 930 motor.

mark kibort

usually, if it is bad, your idle will go up, as it will be a false air leak to the intake. but if it is not bad, it just means the vacuum in the booster can fall over time faster, but no way it will be a problem in emergency situations. it would have to be a big leak to be a problem.. and like i said, you would notice it at idle.

Shark Attack

I feel you have a vacuum leak, t