dma251

Well, As I said in a previous post, my brake pedal was at times very soft, and would sink almost to the floor at times. I replaced the master cylinder and it's still happening! Maybe not as far down, and not as soft, but it still has intermittant normal, and then very soft braking.<br><br>What's next? Change the front brake lines?<br><br>

NC_Mog

Does the fluid level decrease? If so, then you have a leak in the system. If not, then this is usually associated with the master cylinder (i.e. pressure leaks around seals in the MC) or you have a bunch of air in the system. Also, did you or whoever the installer was bench bleed the master cylinder? This process bleeds all air from it before installation. Has the system been thoroughly bled?

dma251

No fluid loss as of yet, and it was full before I changed the M/C as well. I did bench bleed the M/C, and bled out all the old fluid and couldn't get any more air out of any of the lines.<br><br>The only other item to mention is that I have some rubbing on my right front brake hose, and am planning on replacing it with a set of braided steel lines soon. It's getting near the inner steel lining of the hose, but not revealing it yet. Before everyone writes about how important it is let me save you some time- I KNOW. But is it causing this intermittant low pedal?<br><br>I am still suspecting a vacuum issue.<br>

Mexstan

The symptoms are that there is some air trapped in the system. Then again, you could have a defective master cylinder. Even tho you have replaced it, it could be a defective unit. Was this a rebuilt master cylinder? Maybe you could go back to where you bought it, explain the problem and see what they reccommend. They may give you another one.

Smokee

I agree with Mexstan. However, the chaffed line may be collapsing internally, producing the effect that you describe.<br>george

BigBlue

I don't know bout collapsing. I was thinking maybe swelling instead. I don't understand how the line could collapse if pressure is always exerted outwards. ???

johnaw

What do the rear brakes look like? Mine were toast so I had them turned all the way off until got around to replacing the shoes and drums. This caused my pedal to slowly but surely &quot;sink&quot; to the floor at stop lights bit scary at times but always able to stop. After replacing the rear brakes all is well. Just a thought

Mexstan

Sorry guys. but I disagree with you that a collapsed/swelling hose or worn brakes will cause the pedal to intermittantly go to the floor. For a brake pedal tp drop it means that fluid is being displaced or lost. In this case I will say it is being displaced internally in the master cylinder. I go back to what I said earlier, you could have another defective master cylinder and to go back to the supplier and tell them the symptons. I also doubt that improper bench bleeding will cause intermittant problems.<br>Keep us posted.

Stamey

If the rear brakes are out of adjustment there is no intermittent to it, the pedal will always be low and stopping power will suffer. I can see the brake pedal going down at the stop light with rear brakes out of adjustment, because they have not hit the drum yet and are just pressing against the spring until they reach the drum.<br><br>As far as collapsed lines, yes it does happen, and when it does, the fluid cannot get back to the master cylinder after the brakes have been applied. This results in the calipers not disengaging and the premature wearing of the front brakes.<br><br>A vaccum problem can go one of two ways. First, if there is no vacuum, or little vacuum, you get a harder pedal. If there is too much vacuum, (I've never actually heard of this happening so this is just theory), the brakes would be applied when the pedal went down. Do you think your brakes are dragging?<br><br>I'm still on board with Mexstan, since there is no other place for the fluid to go if it isn't leaking out. The ABS is just valves and cannot provide a place to hold the fluid without letting it leak out.<br><br>Make absolutely sure the brake system was bled properly, including bench bleeding, and the rear brakes are adjusted properly, then look at the master cylinder again.<br><br>Chris

Mexstan

Stamey, you are correct. I was concentrating more on the intermittant pedal travel then excessive travel. Yes, rear brakes out of adjustment will definitely cause excessive brake pedal travel. One quick way (but not foolproof) to check for rear brakes out of adjustment is to very lightly put the parking brake on. Just enough to cause the brakes to drag slightly. Then pump the brake pedal a few times or drive it for a few minutes. Wait a few seconds and try again. If the pedal does not travel as far this time then your rear brakes are out of adjustment.<br>In theory a spongy flex line could cause intermittant pedal travel due to it restricting the fluid going back to the master cylinder, but one bad line should not cause that degree of a problem.<br>BTW for any of you changing a master cylinder. This is an excellent time to purge the brake lines of old fluid and have new (high temp?) brake fluid in the entire system. Make sure you use the appropriate brake fluid for your system and don't be cheap in quality of the brake fluid.

Stamey

Mexstan,<br>I'm in agreement with you. I was just trying to explain the symtoms of the other theories so others would understand. And not being able to examine it firsthand, we all must theorize a little.<br><br>Chris

Mexstan

Understand and agree.

TXRAM2

Stan and Stamey,<br> I think you are on the correct path. The only thing that I would also check, would be too much runout in the front rotors. Normally when that happens, it may take several pumps of the pedal to move the piston out far enough to feel braking. Although I have never saw this symptom be intermittent. May be worth a look see.<br>my $0.05 HTH

greatwhite

I had this problem with my 93. Turned out to be front wheel bearings allowing runout. I posted this before. Did you check it? Try it in a parking lot. When I twigged to the problem, I was driving to the shop to get a new m/c installed. Stepped on brake to turn into the lot, and the pedal went way down. For some reason, I kept my foot on the pedal and when I straightened out of the turn, the pedal came back up. Kinda threw me off. 1 each new wheel bearings, rotor spindle and stone guard later I was back on the road. Excessive front wheel runout will cause EXACTLY what you describe. Btw I returned the m/c. This was 100,000 miles ago. M?C is stil doing fine.

Mexstan

Nice new slant to this thread. Never thought of that or experienced it but it makes a lot of sense. Very unusual tho. You must have had a lot of bearing slop for this to happen.