notoriousB

i originally posted this in the tech section where I got zero responses, hopefully my accord brethren can help me out here.

I'm having some weird brake problems after my car sat for about 6 months waiting for its new motor. The motor's in, running good (except some cold start issues), but now the brakes are screwy. They just go mushy all of a sudden, then they come back when they want to.

car: 1998 accord 4 cylinder (turbo'd)

i went through the "brake booster tests" on pg 19-17 of the helms, once cold, once after a test drive.

the test drive was weird, brakes were ok, then BAD, then ok, went to dunkins for a coffee, brakes were MISSING in the parking lot the whole time (right to the floor), driving down the road it brakes fine again. STRANGE.

functional test:
1: press pedal several times, then press & hold. if pedal sinks, something's leaking or mc bad.

result: hot & cold, doesn't sink at all

2: start engine w/ pedal pressed, if pedal sinks slightly vacuum booster is normal

result: before test drive, sinks slightly. after test drive, sinks to the floor when started.

3: w/ engine running apply brake slightly, if brake pedal sinks more than 3/8" in 3 minutes MC is bad

result: cold, no sinking. after test drive, sinks slowly to floor

leak test:
1: press brake pedal w/ engine running, then stop engine. if pedal rises at all within 30 seconds booster bad

result: cold, no problem no pedal rise. after test drive, once pedal is pumped up and held, motor shut off, no pedal rise

2: with engine stopped press brakes several times. 1st time should be low, pedal height will gradually rise each time after

result: cold & hot, works as expected.

sounds to me like it's probably the master cylinder, especially since it's an intermittent problem. I'm looking for additional experienced opinions, thanks!!

no visible leaks in the system either, and MC fluid level does not seem to be changing.

update 1: bled the brakes, they worked ok for a little while and now they're screwy again. leaning towards master cylinder.

if pressed hard when the car's running the pedal will go all the way to the floor, then when I let it up the car idles up a few 100 rpms, thinking this is the vacuum reservoir refilling itself?

update 2: bought and installed a new master cylinder, completely flushed the system with brand new synthetic brake fluid, and it's still doing the <u>same exact thing</u>.

intermittently goes to the floor, rpms fall if I pump the brakes up, solid as hell one minute, gone the next. oh and if I really pump the brakes up to the point where the rpms drop the ABS light will come on for 1-2 seconds and then go back out once the car gets back up to speed.

I'm totally confused. Brake booster bad? ABS proportioning valve maybe??

help! -B

James

sounds like a master cylinder problem - or it could be air in the system. Maybe you bleed the whole brake system and see what happens. If it does not solve the problem, you can replace the master cylinder and bleed again. If you replace master cylinder, I think it is a good practice to replace slave master at same time, that is if you have manual tranny.

James

Oops, you already replaced MC and bleed the system -- hmmm, yes, it is a weird problem. I am not sure what it can be. Sorry.

drifter_for_life06

since you already bleed and repalced

maybe you have a leak in a line somewhere and your losing the fluid pressure/taking in air?

this one stumps the hell out of me

notoriousB

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drifter_for_life06 &raquo;</TD></TR><TR><TD CLASS="quote">
maybe you have a leak in a line somewhere and your losing the fluid pressure/taking in air?

this one stumps the hell out of me </TD></TR></TABLE>
that definitely could be the case. I did see some fluid around the ABS proportioning valve, but that also could have been spillage from the MC swap or oil from my 2nd blown motor. I cleaned it up yesterday and will be checking it out shortly.

while pondering this problem i thought of one more thing: when I was installing the new MC I put some grease on the rubber o-ring that's around the booster "nipple", and when i touched the booster nipple from the side it released a little bit of air pressure. i did this a couple of times and air leaked a little each time. is that normal? i don't know...

stumping the hell out of me too. and now my truck's making a tapping noise from the valves somewhere. not having much good luck here.

allmotorteg_96

sounds like you might have a brake cylinder leakin in the rear.. or a possible vaccum leak at the brake booster... there is also a little valve that goes bad that is in line with the intake manifold to the brake booster that will go bad from time to time. try these and i'll check with ya later.

Polando83

Well, its possible the you have an intermediate vacum leak. Many times if there is no vacum assist the brakes will get stiff and then if the vacum comes back the power assist make the brakes soft again. I would check for vacum leaks anywhere under the hood. The turbo may also instead of letting the engine draw air from the vacum system, it could be acutally putting pressure on the vacum system which woule make it cancel out the vacum affect. When you rev up the engine do the brakes change? Just a thought.

notoriousB

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by allmotorteg_96 &raquo;</TD></TR><TR><TD CLASS="quote">sounds like you might have a brake cylinder leakin in the rear.. or a possible vaccum leak at the brake booster... there is also a little valve that goes bad that is in line with the intake manifold to the brake booster that will go bad from time to time. try these and i'll check with ya later. </TD></TR></TABLE>
i was just outside under the car, none of the wheel cylinders are visibly leaking and i can't find any visible leaks around the MC or the ABS system. I did check the brake booster check valve, it is drawing vacuum like crazy, and it's closed if I try to blow through it the other way.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Polando83 &raquo;</TD></TR><TR><TD CLASS="quote">Well, its possible the you have an intermediate vacum leak. Many times if there is no vacum assist the brakes will get stiff and then if the vacum comes back the power assist make the brakes soft again. I would check for vacum leaks anywhere under the hood. The turbo may also instead of letting the engine draw air from the vacum system, it could be acutally putting pressure on the vacum system which woule make it cancel out the vacum affect. When you rev up the engine do the brakes change? Just a thought.</TD></TR></TABLE>
interesting. when i went for the test drive a few minutes ago i did have one of my vacuum lines come loose for a second time. I hooked it back up, drove around, brakes worked good, went to park it and they went right to the floor again.

for a moment it was like if I pressed the brakes slowy and softly it would go right to the floor each time.

i will definitely investigate the rest of my vacuum lines further, but I'm pretty sure they're all connected well, as I just put this motor togther in the last month.

come to think of it I'm not sure I checked the problem c.c. vac line after my 2nd test drive. I'm gonna go do that now.

the turbo definitely pressurizes the vacuum lines, but I never had any brake problems before and this car's had the turbo on for 2 years now.

do the brakes change when I rev the engine? not that I've noticed at all. I can't build boost at idle revving it anyway.

the engine rpms change when I pump the brakes tho.

keep 'em coming guys, thank you!!

Chillinlikeamofo

Sounds like it might be a blown wheel cylinder. If the fluid is pretty optimal and doesn't move then it's your power brake booster.

PEACE

JimBlake

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by notoriousB &raquo;</TD></TR><TR><TD CLASS="quote">... when I was installing the new MC I put some grease on the rubber o-ring that's around the booster "nipple", and when i touched the booster nipple from the side it released a little bit of air pressure. i did this a couple of times and air leaked a little each time. is that normal? i don't know...</TD></TR></TABLE>After you shut off the engine, the brake booster should hold it's vacuum. You were letting air in thru that vacuum hose nipple, that's almost normal.

What isn't normal about it is that it sounds like it was real easy to release the vacuum by touching that hose. Try a new rubber grommet for that fitting, maybe it's old, hardened, or loose? The normal motion of a running engine might cause a big vacuum leak at random times, which causes the funky brake action too.

So if you don't touch that hose for an hour or more, THEN you should still have vacuum in the booster. If the vacuum leaks away by itself (when you don't touch the hose), then you can check for a leaky check valve or bad booster.

notoriousB

It was actually leaking from around the "pushrod" in the booster (behind where the MC mounts) when I touched it, not the vacuum line or vacuum fitting itself.

I was talking with my neighbor last night (he's also a mechanic) and he brought up the possibility of the check valve being stuck open at times.

This would almost make sense: if the booster wasn't holding vacuum the brakes would still be OK, but once vacuum returned the vacuum "boost" it gives would make the pedal really soft, no?

I'll be pulling the booster line off the car tonight and spraying the crap out of it with some seafoam deep creep, we'll see if I get any garbage out of it.

Man I want to drive this car so bad!!

JimBlake

Isn't there a gasket between the MC & the booster? The little rubber diaphragm/disk #3 in the picture. Is that where it's leaking?

notoriousB

yep there's a rubber gasket there. it's not leaking all the time, but when I was greasing up that gasket I pressed the "nipple" for the booster to the side slightly and I heard air escaping (or would it be being sucked in, as that's vacuum??).

it's not leaking any vacuum that I can tell with the MC reinstalled.

drifter_for_life06

did you replace that rubber piece?

notoriousB

no. I thought it would be included w/ the master cylinder. I thought wrong. I can't see that being the issue tho.

notoriousB

development: took the booster hose off and ran a crapload of seafoam deep creep through it tonight. let it sit for quite a while with the deep creep in it then sprayed it out again.

put it back in, and now when i hit the brakes (car off) it doesn't build vacuum in the booster at all. perhaps my check valve is screwed. i'll be calling the dealer tomorrow to see if they have one on hand.

JimBlake

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by notoriousB &raquo;</TD></TR><TR><TD CLASS="quote">... put it back in, and now when i hit the brakes (car off) it doesn't build vacuum in the booster at all.</TD></TR></TABLE>It can't develop any vacuum when the car's off. The vacuum comes from the engine in the first place. So I don't understand what you mean here...

Did you leave out that rubber seal disk or did you re-use the old one?

notoriousB

**** good point. I couldn't start the stupid thing last night (different problem - tuning issue)

actually wait a sec, from the helms' brake booster leak test:
2: with engine stopped press brakes several times. 1st time should be low, pedal height will gradually rise each time after

shouldn't the brakes do that? ^^^ they're not now and did before with the car off.

I re-used the old rubber seal disc between the mc & booster.

JimBlake

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by notoriousB &raquo;</TD></TR><TR><TD CLASS="quote">actually wait a sec, from the helms' brake booster leak test:
2: with engine stopped press brakes several times. 1st time should be low, pedal height will gradually rise each time after

shouldn't the brakes do that? ^^^ they're not now and did before with the car off.</TD></TR></TABLE>Yeah, they should do that. What's happening is you're using up the vacuum that's stored in there from when the engine was running. As the vacuum gets used up the pedal gets harder. I got confused when you said it 'doesn't build vacuum'...

In order to do that check, you have to start with vacuum in the booster. You get that vacuum by running the engine. If you can't run the engine, you could pull a vacuum in the booster with a MityVac or something.

So NOW, after you shut off the engine, does the vacuum disappear right away? That could be a screwed-up check valve.

If you re-used the old seal, & it was good, then maybe something else is happening? Sounds like your booster doesn't hold vacuum any more. Leaks thru the check valve? Leaks thru that re-used disk seal? Got it installed backwards?

Another possibility is the MC pushrod length. Did you check the new one against the old one? Look in your Helm book about using that strange measuring tool to adjust the pushrod when you replace the MC.

notoriousB

you're right - vacuum confuses me, when thinking vacuum one has to think totally backwards and it screws me all up, sorry about my wording.

I didn't remove the old seal from the booster, it appeared to be in excellent condition and was well in place.

I'm waiting for a response from my tuner (patiently... c'mon....) regarding the cold start problem I'm having. Once I get it running it runs like a champ, and once warm will start right up. It's something in the AEM EMS, I'm going to mess with the initial injector crank pulse in cold conditions tonight some more to see if I can get it to start up reliably.

I didn't check the MC length when installing, I did read that section regarding the crazy tool, but I don't have that tool.

I did check my Haynes manual for a 2nd opinion and it has a procedure for measuring & setting the rod length without that crazy tool that I can try out. That tool does look like it would make life a lot easier. Not sure where I'd find it tho...

Neither of the local Honda dealers have the booster hose, so I'm screwed for buying/trying that today.

I'm considering just sucking it up and ordering the booster, seal, hose, and proportioning valve and installing all of the above because this sucks and I'm getting nowhere fast. I'll have to pull the MC to replace the booster, so I figure why not install a new proportioning valve at the same time, it's only like $30.

Not to mention my truck has just begun making a very nasty tapping noise from the valves and I fear it is on it's way out as well. This year has not been good for me. I'm just about ready to burn both vehicles to the ground and buy a bicycle.

JimBlake

When I changed MC on my Integra, the pushrod length was exactly the same as the old one. So I didn't have to worry about that tool. The idea is you adjust the pushrod down at the pedal (# 2 & 16?) to account for the difference.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by notoriousB &raquo;</TD></TR><TR><TD CLASS="quote">... I'm just about ready to burn both vehicles to the ground and buy a bicycle. </TD></TR></TABLE>Hey... I LIKE bicycles!