don't try to diagnose something as wrong until the entire job is complete.
replacing the BMC and not bleeding the entire system is paramount to rebuilding and engine and starting it before putting oil in it and then trying to figure out why it won't maintain idle.
Get the system thoroughly bled and then we'll go from there.

even more
you're kidding right?
a rubber seal, that is in an engine bay with a widely varying temperature range, that as different levels of vacuum applied to it never goes bad? Wow.
I wonder what I was doing wrong with the handful of boosters that I've replaced. I mean, they quiet obviously wouldn't hold any sort of vacuum, and just whined, and one of them wouldn't release the pressure as it built up until it eventually ruptured.
So yes, boosters do go bad.
perhaps no where near as often as other parts, and is typically not the issue, but they do in fact go bad.

they aren't really working fine when there is no vacuum. You just think they are working because you don't have the same strength as you do when you get the vacuum assist from the booster. When you are using just your foot, no assist, then you can only apply so much force. The pedal will feel firm, and the calipers will engage, some. Which will make you think that it is work.
Then you apply the vacuum assist and it multiplies that force several times. This is what makes the pedal more soft to push on as compared to when there is no vacuum. Now what is happening is that you are compressing the pockets of air in the lines, which is letting the pedal go basically to the floor and not supplying much if any stopping power. Ironically enough, it is the same amount of stopping power that you thought was there when you pushed with just your foot.

now, since you say the pedal moves in relation to engine speed, that would indicate to me that either A) you need to adjust the rod that connects the pedal to the BMC. if it is a bit too short, the brakes will be partially engaged and when the booster fluctuates the amount of vacuum assist it can supply, the pedal will move. and/or B) it would also make me question if the booster was tweaking out and staying engaged itself. Holding too much vacuum.
Did the car sit for a long time?
One the few that I had to replace, the car has been sitting for 6 months to a year.
I got lucky and had a parts car to pull what I needed off of so I've never had to buy a brand new booster.

Also, something to consider, the BMC's you get from advance are re-manufactured units. meaning, they are metric pieces of metal that are torn apart and filled with SAE seals, so they can very well be bad when you get them.

 

My mistake. Doing brake overhauls on two of my cars I had never read about a booster ever going bad but I suppose it would be possible, however rare.

 

Even though I really doubt your booster went bad, I have a spare S14 auto one at my house you can have if infact it did. Now that I sold my car I need to get rid of all this junk anyways.

 

I did get ahead of myself in posting this thread. I don't know what I was thinking. Chome PM me about pricing on that booster if it'll work for my S13 w/ MT

 

pass. rear 1st, drvr rear 2nd, pass. front 3rd and last but not least? iv alwas done it the other way around ....neerest to Master cyl 1st..ect.

 

I've been told by several people to start the furthest away first and that's what I've gone by. Haven't had any problems doing it to this date and haven't been told I was doing it wrong yet either. Who knows.

 

hum .guess it dosent matter then lol

 

it doesn't "really" matter

most people will argue the fact that you are probably using more fresh fluid when you start at the front since you begin to pull some of the fresh fluid from the front, all the way to the back before getting all of the old crap out.
they will also argue that if you start at the front, there is a higher chance of getting air back into the lines because you are "going over" what you have already done. The idea being that the rear typically start at 1 line coming out of the BMC so it is less likely to suck up some air once you have flushed them through.

I don't know how much I believe in all of that. I don't know that it really makes a difference either way. I have always done it from the furthermost point first just because it gives me a pattern to follow. But I also go back and do each one a little bit more once the whole system has been flushed, just in case.
for the average user, using the valvoline 3&4 brake fluid (which is the absolute best "cheap" fluid you can get) It doesn't make much difference. But for the heavy user, that has a need for better brake fluid (i personally use superblue mainly because it has the temps i want, and you can get it blue, or gold, which makes flushing the system easier, in my eyes, just alternate colors) then making sure you get all of the old stuff out is a major issue because just a little bit of old fluid can dramatically lower braking performance.
but like i said, for the average user, just making sure the air is out is good enough.

 

Regardless of my stupidity this thread has good info in it. Sidenote: While changing my fuel filter today I yanked the fuse and as the engine died I heard a hissing noise coming from the drivers side firewall area. It lasted a few seconds after the engine stopped, I'll still be vacuum bleeding the brakes after lunch. Report then.

 

The brakes have been 100% bled, over-bled infact there is nothing but fresh fluid in the system. The brakes are still doing the same thing. I did get a hissing sound coming from the booster on the "up" stroke of the pedal. I tried to record it but I couldn't catch it on the mic.