1994 Honda Civic, no brakes over 40mph

[Jonathan Ganther]

Kinda going crazy here. Got a call about the brake pedal going to the floor on a 94 Civic. After talking with the customer it sounds like a Master, were sure to check for any leaks on wheel cylinders, caliper, lines and hoses. We can't replicate the problem, we drive it do everything but take it on the highway. Customer's friend who's a "tech" talks to me after we can't replicate it and tells me to put a master on. We don't and tell the customer we'll have to come back out and try to replicate it again.

Customer calls back three days later, Master Cylinder got replaced by someone else brakes felt good and then when getting on the highway the same problem occurred. So I send one of my guys out again to check it out. I think maybe a defect reman got put on or whoever installed it didn't bleed it right. We bring a MC with us this time, tech can't replicate it and I really don't want to throw parts at this thing but I told him to try our MC and see if you have the same issue. Sure enough same issue. There are no leaks the loss of pressure only happens when the car is braking at over 40mph, I know this sounds crazy but its truly what is happening. The proportioning valve looks like it was replaced as it is all stripped up with paint pen. I only mention this because I'm at a loss, I can't figure this thing out and neither can my techs. Brakes feel great when driving bellow 40mph at 40mph and over loss of pressure.

[stowintegrity]

Are you seeing "loss of pressure" above 40mph EVERY time, or only intermittently when braking at above that speed threshold?

[Gonzo]

Chances are it's NOT the MC, mainly because hydraulics don't care about speed. You have to ask yourself..."What's different at speed than standing still?" My first thought, engine speed, thus.... vacuum. I'll bet it's a booster problem.

[mmotley]

Agree with gonzo. That's the first thing I thought of when reading your post. Make sure linkage is adjusted properly too if you replace it

[Jonathan Ganther]

Intermittent above 40mph. I thought booster after being told that the problem occurred only at a certain speed, I thought the booster might be the problem causing it. With the pedal to the floor there is absolutely no pressure, doesn't brake, doesn't matter how hard you press that thing. I haven't run into a booster that's gone out and then provides absolutely no brakes. Maybe this is just a first.

Edited December 18, 2015 by Jonathan Ganther

[John Pearson]

I have run in to problems where for some reason the brake pads move away from the rotor and take 1-2 pumps to have brakes after highway speeds.

 

I have seen this caucused buy Rotors, wheel bearings and caliper slides.

[cdhowell]

Wouldn't loss of vacuum cause a stiff pedal not one that drops to the floor? Watch the firewall for flex when the pedal is pushed. Had a Toyota that the firewall moved almost an inch before the piston started moving.

[cdhowell]

Wouldn't loss of vacuum cause a stiff pedal not one that drops to the floor? Watch the firewall for flex when the pedal is pushed. Had a Toyota that the firewall moved almost an inch before the piston started moving.

[Jonathan Ganther]

I don't know I'm stumped. I've had leaking boosters where the pedal would travel far with no resistance but then I would always have pressure at the end and the car would stop.

[Gonzo]

Wouldn't loss of vacuum cause a stiff pedal not one that drops to the floor? Watch the firewall for flex when the pedal is pushed. Had a Toyota that the firewall moved almost an inch before the piston started moving.

Seen both. Most common is a stiff pedal, but I've seen the pedal just fall to the floor and after much head scratching I ended up changing out the booster which solved the problem. I guess after 30 years of this stuff, ya kind a see a few variations ... LOL

[skm]

I would have to lean more towards something causing the pads to be drawn away from the rotor causing a few pumps to get the pedal back up, yes stuck slide,(I have seen one slide stuck on a caliper and the other free causing a low pedal before) wheel bearing, warped rotor, booster possible if a vacuum situation causing a suction through the m/c drawing fluid out of calipers/pulling pistons in, but that is the only way I see a booster since the connection from the pedal to the master cylinder is all mechanical and the booster just assist the pedal effort. too much vacuum on one side you get a grabbing pedal , a leaking booster you get a hard pedal . For the pedal to fall to the floor with out loosing hydraulic pressure the master cylinder would need to be moving away from the booster as you push the pedal.. just my 2 cents. but anything is possible now a days .. LOL

[cdhowell]

Any word on this?

[ajnealey]

From reading the symptoms, I'm thinking this could be caused by a wheel bearing "knock back" issue. Shake down the front end for any excessive play.

 

Also, Toyota had a TSB for certain model year Tundra's where the brake pedal would intermittently sink to the floor. The remedy was making sure the proper shims were installed on the brake pads.

 

AJ

[Mario]

I had a corolla a few years ago that would intermittently lose brakes. Don't remember if it was while parked but definitely happened at speed.

 

I replaced mc no go. Por valve had no moving parts and no leaks so I skipped that. Ran it with vac booster hooked up and off, didn't matter would still lose brakes.

 

Eventually just replaced calipers and problem went away. I can't think of a test to verify problem was caliper because I watched them work when peddle was pressed. I just did it and it was the solution