I've checked around the wheels/connectors/master cylinder, but I still can not find any leaks. The resevor almost completely dries after 300~400 miles of driving. Any ideas?

I'm new to DSMs, but on the face of it, if the fluid is not ending up on the ground somewhere, it sounds like it's making through the vacuum booster and getting burned up with the fuel. Like I said, I'm not sure if this would apply to DSMs, just pulled my first one home 50 some hours ago. So, maybe some of the pros here can shed a better light on it. But in the mean time, check the vacuum line to your brake booster and see if there's any fluid in it.

I've never heard of a master cylinder leaking into the booster, then into the intake... not to say it can't happen though! Probably see some weeping where the two meet, if the master cyl was bad. You've checked all your lines - even at the junction on the firewall under the intake?

Do you have any pedal "feel" problems?

MB

Originally posted by bullettdsm
Do you have any pedal "feel" problems? MB

I noticed that I was leaking fluid due to the "feel" problem. When I fill up the resevor, the brakes works perfectly. I guess I will need to look into it a little more. I will check tomorrow.

This smells of master cylinder. Be sure to pull back the rug inside, and look under the insulation for leaks. You are just losing so much fluid, I can't believe you can't see a puddle forming, lol.

MB

I know you had said you checked around the wheels, but check the bleeder valves on the calipers for any fluid, make sure the bleed valves are tight.

Originally posted by justins71
I've never heard of a master cylinder leaking into the booster, then into the intake... not to say it can't happen though! Probably see some weeping where the two meet, if the master cyl was bad. You've checked all your lines - even at the junction on the firewall under the intake?

This happens more than you imagine. The secondary seal on the primary cup holds fluid from coming out the piston end of the master cylinder. If only this seal is leaking, your pedal will feel normal. The brake booster will fill with fluid before you see any inside the car underneath the dash. The brake booster line will suck the fluid in it, pull the tube off to check as Zardoz mentioned, takes 5 seconds.

But the boost mating area to the master cylinder isn't open to the diaphram to the intake... Just curious, I've seen/changed probably 30 master cylinders and a dozen or so boosters on fleet vehicles and haven't had that happen. If the secondary punches out it'll piss all down the front of the booster, but haven't had it suck through. Granted these are Chevy/Ford, but I'd assume the boosters are built similarly. Otherwise you could loosen you master cylinder and have a wicked vaccum leak...

did you look to see if any of the lines were corroded?