Yesterday afternoon: While braking, the pedal drops to the floor slowly. If I brake from 70-0, it gets to the floor before I'm stopped, but if I release the pedal and brake again, I can stop all the way. If I apply pressure on the brake while stopped, the pedal drops very slowly, almost all the way, but not.

Yesterday night: I ask my dad to drive it with me to see what he thinks. The car brakes fine.. there's nothing wrong with it at all. I get home and bleed the brakes, but there's no air in the system.

Today: The car still drives fine, brakes feel great.

My question: Will this problem come back? Is it most likely my MC going bad? Should I replace it immediately? Will a 15/16" MC from a 91 ex 4-door work with my 94 si (WITH ABS)?

 

Sounds like the master cylinder is wearing out. As far as the master cylinder from a '91 EX 4-door, I see you read the thread about the upgraded 15/16th's master cylinder. I think it will work on 92-95's, but I'm not positive. Reread the thread because I remember reading someone asking, "will this work on my 98 Civic". The response was "no, this will only work on ..."

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Aphelion &raquo;</TD></TR><TR><TD CLASS="quote">Will a 15/16" MC from a 91 ex 4-door work with my 94 si (WITH ABS)?</TD></TR></TABLE>

Maybe its your abs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kaiba &raquo;</TD></TR><TR><TD CLASS="quote">Maybe its your abs.</TD></TR></TABLE>
My abs light is on and has been on for some time. Would that cause something like this to happen? I didn't think it could affect my braking in this way.

BTW I just looked under the hood, I have a 15/16" mc stock.. I guess it's there because of the ABS, because non abs 94 si's do not have this size, I'm pretty sure.

 

My buddy had that exact problem in his 92cx last week. When it was hot outside, the master-cylinder would allow pressurized fluid past the seal & back up into the reservoir. This would result in a slowly sinking pedal. Then once he released the pedal it sucks the fluid from the reservoir back into the system, and starts over.

If this is the case, you can check it really easily. When it's hot out, remove the cap from the reservoir, and hang it on the side so it's still dipped into the fluid (but you can see inside). Now have a friend press & hold down HARD on the brake pedal (so it starts sinking). If you observe the fluid rise (ever so slightly) when he pushes in, and sink when he lets off, you have found your problem. Now all you have to do is replace your master cylinder...

 

Also, I'm pretty sure the ABS master cylinders have different size brake line fittings. This means you won't be able to use a NON ABS MC in an ABS car.

It's pretty bad *** that you have the ABS Hatchback. They only made those in 94...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">It's pretty bad *** that you have the ABS Hatchback. They only made those in 94... </TD></TR></TABLE>
94-95 SI and EX optional only.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kaiba &raquo;</TD></TR><TR><TD CLASS="quote">
94-95 SI and EX optional only.</TD></TR></TABLE>

You are mistaken. First off, ABS is not an option, it is completely seperate trim level. The 3dr Si w/ ABS is different from a 3dr Si. If ABS is present on any other year EG hatchback, it was added after the car was built, and did not come from the factory...

94 3 door trim selections (click here)
95 3 door trim selections (click here)

 

haha, thanks bro I wish I could get my abs light to turn off o_O

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">

You are mistaken. First off, ABS is not an option, it is completely seperate trim level. The 3dr Si w/ ABS is different from a 3dr Si. If ABS is present on any other year EG hatchback, it was added after the car was built, and did not come from the factory...

94 3 door trim selections (click here)
95 3 door trim selections (click here)
</TD></TR></TABLE>

Wow... really cool. I didn't know that. Hah, learn somthing new everyday on h-t.

 

I just bought a remanufactured MC from advance auto parts, and on a note inside it says "Reuse mounting flange seal from original master cylinder". 94eg, is this the seal that you're talking about? I guess when I go to change it tomorrow I'll just look at the seal and see if it's in good enough condition to reuse.... or should I just go ahead and get a new one?

 

Thats not the seal your having a problem with. You will be okay reusing your old one, but that part is only $3 at the dealership. They should have them in stock too...

It's number 3 in this pic...