I was driving my [93 T4R Manual V6 4WD] yesterday and I was approaching a stop, and my brake pedal went almost to the floor before slowing down the vehicle. I immediately pulled off to the road and inspected my brake lines and master cylinder reservoir finding no apparent leaks or low fluid. I continue driving and the brakes were fine. Another stop, to the floor again. Help! This is what I have found or have done:

1. Reinspected all brake lines again.
2. Bled the brakes: RR, RL, FR, FL. No apparent air coming out of all lines.
3. Removed front tires and inspected pads, rotors and calipers. All ok.
4. Adjusted rear brakes to the point where its almost dragging.
5. Checked vacuum line/s to power brake booster.

And it STILL does it.

I have found, that for whatever reason, when I am slowing down IN GEAR, they work fine, but if I am slowing down with the clutch in, or in neutral, to the floor it goes. Pumping the brakes does not regain pressure (like there was air).

I am stumped. If anyone has any idea of the culprit, please, let me know!

Thanks in advance!

 

sounds like a vacume problem with the brake booster

 

going to be your master cylinder, had it happen on my old 86 a couple of times. very disconcerting when you step on the brake pedal and it goes to the floor.

check around for a supplier that may have a lifetime warranty because it will go out on you again. some folks recommend using a block of wood under the brake pedal to prevent damaging the seal by pumping the pedal all the way to the floor.

good luck, keep us posted.

lee

 

Brake booster or master cylinder are bad, I go with the brake booster first.

 

Why in the world would y'all think it's the vacuum booster (brake booster) ?




Fred

 

If you are unsure of which is bad take it in for a diagnosis by a mechanic. You might want to replace both as it is scary not to have brakes.

Please update when you find out the answer to your problem.

 

The fact he had brakes then all of the sudden didnt, I aint perfect Fred bit replacing both at the same time is a smart move anyways.

 

When the brake booster goes out it does NOT cause the brake pedal to drop to the floor. It's kinda the complete opposite. It makes it very HARD to press the brake pedal.
The vacuum boost (brake booster) is the "power" park of power brakes.
Bad booster = very, very hard brake pedal, not a brake pedal that drops to the floor.

I do fully agree, that if the poster is not familar with the brake system, then take it in and have someone check it out and fix it.
Sounds to me like the master is taking a walk on the wild side.

Also Toyota does something really funky with the PS system and the ABS system, though that should affect or cause the pedal to go to the floor.



Fred

 

Did you have normal pressure, then all of a sudden the pedal went to the floor? If so, I would suspect a sticking caliper piston. It was probably stuck, then midway through your braking, it popped free. Thus losing pedal pressure. Mine does the same ˟˟˟˟˟ every once in a while.

One way to check your pistons: Remove your calipers and take out the pads. You should be able to compress each piston with a set of channel locks (easily). If one is exceptionally hard to compress, it is likely the cause of your problem.

 

I didnt know that, coulda sworn it was the other way around.. MC it is then..

 

I do not believe it has to do with vacuum pressure. If the brake booster is bad, like FredTJ said, it would cause and extremely hard pedal, not a soft one. Any leak in that part of the system wouldn't do that. The master cylinder seems to me like to be most likely the problem. I know it's a two chamber system, however, it would seem like both chamber seals would have to be bad, BUT, I do have full pressure at some stops. ChickenLover's theory could be true, but it is not a "full pressure then loss of pressure." It is one or the other. Any more feedback? I appreciate your thoughts so far, it has helped a great deal. Thanks in advance.

 

When's the last time you did a brake job? I'd replace the m/c, booster, calipers, pads, hoses, etc...money well spent in my book.

 

id say the mc is going bad

 

I had a similar problem and it ended up being worn pads combined with a stuck caliper. The pedal would go almost to the floor if I didn't pump in once before I braked.

 

Leave the brake lines connected to the M.C. and unbolt it from the booster. Look for any sign of brake fluid around the seals, if there is get a new master cyl. as rebuilds tend to be junk. There may also be brake fluid residue on the booster below the master cylinder.
On another thread a guy had a problem with swelling brake hoses causing the same condition, so I would look at those as well.

 

not to say this is the cause, but yesterday when workin on a friends Buick Park Avenue which had no brakes we went and got a nice old master cyl from the scrap yard bolted it on and started to bleed it when we then found a line now that had a pin hole and was sucking air in. with the old master cylinder on i guess there was air in the line and wasnt making this line under pressure and the new one made it, anyways, it was now pissing brake fluid out this leak where before it wasnt. old master cylinder put back on now works fine and makes this line piss fluid before.

was similar to brakes would go to the floor, could get them to lock up back tires but not the fronts, but wasnt losing any fluids at all. replaced front line, and now everythings ok.

try bleeding the system from brake lines and not the bleeders. it should shoot out pretty good if theres on thats weak look for symptom there. also if it is m/c you might want to change the booster as im not sure if the yotas will but some vehicles will suck the brake fluid into the booster.

jeff

 

Found the source...

The grommet's in there are bad, and is letting air come in. Its either buy a new master (which isn't a bad idea, going on 250k+ miles) or pay $10 a piece (there's two in there) at the stealership. Wow, what a rip! Thanks for the input guys!

 

Doctor, you got latex gloves on? Cool!

 

totally needed. lol.

side note, i want ur 69 stang. lol. ok. im done.