breaks loosing pressure?!? help!

[HaShfIeNd]

okay hopefully someone can help me troubleshoot this..

my breaks started being funky yesterday.. i get about one good pump. and then i slowly loose break pressure all the way until it hits the floor. this has only happend one other time other then this time, on a hot day the exact same symptons accured, but then dissapeared.. and havn't had any problems until yesterday. well today i took'er out and breaks seemed good for about 5-10 maybe 15.. then i started to loose them again.. i checked the fluid and that seemed good.. i am suspecting that the temp. has something to do with it? anyway... feels like master cylinder might be going out or something ugh... what do you guys think? where are some good places to start looking?

*EDIT* we're in the 90+'s degreewise.. 95 today..

[shepherd79]

it sounds like your booster is gone.
so you may as well get booster and master cylinder assembly all together.

[DBMaster]

Actually, it sounds like the master cylinder. This is exactly what mine did at almost precise 100K mile intervals. As the fluid heats up it looses viscosity and slips past the M/C piston seals. Look on the booster where the M/C is bolted. Is there any fluid there? It would be very little and would not cause a noticeable fluid level loss. Replacing the M/C solves the problem. I got a very nice brand new (not rebuilt) one from a local mom&pop auto parts store. It was very good quality and came complete with the reservoir and electrical connectors. Pretty easy job to replace, but you do have to bleed the brakes when you get done.

[mouchyn]

agreed.

master cylinder.

vacuum boosters rarely go bad in hondas.

[charlie89LXi]

okay hopefully someone can help me troubleshoot this..

my breaks started being funky yesterday.. i get about one good pump. and then i slowly loose break pressure all the way until it hits the floor. this has only happend one other time other then this time, on a hot day the exact same symptons accured, but then dissapeared.. and havn't had any problems until yesterday. well today i took'er out and breaks seemed good for about 5-10 maybe 15.. then i started to loose them again.. i checked the fluid and that seemed good.. i am suspecting that the temp. has something to do with it? anyway... feels like master cylinder might be going out or something ugh... what do you guys think? where are some good places to start looking?

*EDIT* we're in the 90+'s degreewise.. 95 today..


My 89LXi does it for 3 years now. It happens on every hot days.
Even when I don't use brakes a lot. I think it's the MC too.
The car still has the original MC. 206K+ miles and counting.

[Versanick]

Vacuum. my b20a with race cams makes no vacuum at idle so I have to pump the brakes like three or four times to actually stop. and then the car sometimes stalls. but that's okay.

Definitely vacuum if not master cylinder. I've never had a master cylinder go on a 3g (many of which I've owned), but if DBMaster's goes every 100k miles then it's worth a shot.

What exactly is the vacuum booster? And where can I get one!

[DBMaster]

Interesting. I have changed my brake fluid every 30K miles as recommended by Honda and I am on my third M/C. I wonder if the people who get theirs to last 200K miles changed the fluid as often. I have also been using the Valvoline synthetic DOT4 fluid for quite a few years now. It stays very clean looking for a long time, but it leaks past worn piston seals just as much. Maybe it has to do with all the stop-and-go driving I do in the hot Texas summers.

I doubt it's the vacuum booster because a problem with that probably would not be temperature dependent.

[HaShfIeNd]

thanks guys -- it definately is slightly better in colder weather, but still not what it was.. when i first take it out in the morning the breaks are great, feels nice to have them normal again... but doesnt take long well, what are some average prices to pay for a m/c..? great to average deal or so is fine, i just dont want to get ripped off.. i appriciate the inpute i suspected the m/c.. but was hoping it might be something a little more simple.. anyways appriciate the input.. think its very dangerous to drive it in this condition?

[mouchyn]

i got my brand new master cylinder with new reservoir for $40 with a lifetime warranty.

[ICEMAN707]

if it's pedal pressure and not brake caliper pressure, then it's not the master cylinder or air in the lines. it's your brake booster. it's vaccuum assisted. if it has a vaccuum leak, that causes you to lose pedal pressure. it happens when the rubber gasket in it softens up over the years. spilled brake fluid also softens up the rubber. the brake booster must be leak-free and sealed. so check that. it's a pain in the ass to get out though. but worth it if you want your brake pedal pressure to get back. i suggest just replacing it with a new one or a good one from the junkyard.

[acranox]

It doesn't sound like a problem with the booster. If your booster was bad you would have to use excessive pedal pressure to stop the car.

Before you replace the M/C you should thoroughly examine the whole brake system. (You should always know the source of the problem before you go mindlessly replacing parts.)

I had a stuck parking brake cable, which was causing the right rear brake to drag which cause the fluid to overheat, so after about 15 minutes of driving the pedal would go to the floor when braking. My M/C was fine, it was just one dragging wheel brake that created the problem.

--Peter

[Blkblurr]

It is definately you master cylinder. In order to maintain the pedal position when you press on the brakes, the oil in the master cylinder cannot slip past the seal. This seal is designed to work in one direction. When it wears, it leaks past it and allows the brake fluid to go back into the reservoir. That's what causes your pedal to drop. This condition can happen without any external leaks at all. All master cylinders will eventually leak like this. I still have my original one with 232,000 miles. It just depends on how much you use your breaks. If it was the vacuum boost, it would cause it to be difficult to press the break pedal but the pedal would not fade.

[Blkblurr]

if it's pedal pressure and not brake caliper pressure, then it's not the master cylinder or air in the lines. it's your brake booster. it's vaccuum assisted. if it has a vaccuum leak, that causes you to lose pedal pressure. it happens when the rubber gasket in it softens up over the years. spilled brake fluid also softens up the rubber. the brake booster must be leak-free and sealed. so check that. it's a pain in the ass to get out though. but worth it if you want your brake pedal pressure to get back. i suggest just replacing it with a new one or a good one from the junkyard.

Brake systems cannot be designed this way. They would not be safe. Assist means just that. It helps out, it does not control the brakes ability to function. It's just like power steering. The ps system only helps but does not do the steering. If your engine stops you can still stop the car and steer it.

[charlie89LXi]

Interesting. I have changed my brake fluid every 30K miles as recommended by Honda and I am on my third M/C. I wonder if the people who get theirs to last 200K miles changed the fluid as often. I have also been using the Valvoline synthetic DOT4 fluid for quite a few years now. It stays very clean looking for a long time, but it leaks past worn piston seals just as much. Maybe it has to do with all the stop-and-go driving I do in the hot Texas summers.

I doubt it's the vacuum booster because a problem with that probably would not be temperature dependent.

Didn't change my fluid as often during that 207K miles. Only a few times.

[TheWatcher]

i got my brand new master cylinder with new reservoir for $40 with a lifetime warranty.
Not from a Honda Dealer. New Master Cylinders cost WAY MORE than $40!

I would go with a new genuine Honda part for the master cylinder. Expensive, but brakes are important.

Peace.

[88eyeguy]

if it was the booster you would feel excessive pressure on the pedal when you applied the brakes. get someone knowledgeable to help you bleed the brakes, or take it to a shop if you don't feel comfortable doing it yourself. that is 100% master cylinder piston bypass.