Soft brake pedal

[Kidd7]

I was reading through posts, but now I'm heading outside to look things over. 2001 v8 stock Explorer ~90K miles. I don't drive it much, mostly my wife.
Last week got in it and the brake pedal felt wrong. It would go to the floor with less effort than I'd expect. The brake fluid was a little low, so I topped it off and it felt better. I inspected the lines for any leaks, found none. Held pressure on the pedal for a while hoping to expose a leak, no luck. I've not done any brake work recently, so no reason air would be in the lines. Last night we were heading out and it felt soft again, so we took the other car. I'm going to thoroughly check the lines, hoses, pads, calipers, etc. Any suggestions for specific things to look at or ways to narrow down whats going on? Thanks.

 

[974X4BLACKSPORT]

Brake fuild level can go down when the front and rear pads wear, unlike drum brakes that self adjust and the fluid level does not change, with disk brakes the reservoir is larger, and when the pads get low on "meat", the piston moves further in the caliper, this requires fluid from the reservoir to take up the space, that is why you can see the fluid level go down without any leaks in the pressure system, so check all your brake pads first, and maybe think about a brake fluid change.

 

[J_C]

It might be good to flush the fluid just to have that constant, but low fluid in the reservoir, so long as neither side is empty, and pad wear, should not cause this drastic difference in pedal travel. The fluid to compensate for pad wear stays in the lines, is somewhat self-adjusting too.

To what extent did the lines get inspected? I wonder if you have the early onset of a leak and soon enough you'll see enough fluid *somewhere*. If there are definitely no leaks, I'd suspect the master cylinder, unless it is possible that the reservoir did empty and you now have air in the line but bleeding should eliminate that possibility.

 

[Kidd7]

Checked it out. Found no leaks, hoses look good with no soft spots or bulges. Pads show some wear, but plenty of pad left. Drove it today and it feels good while driving and stopping.The pedal will stay firm without vacuum. In park under moderate foot pressure the pedal will slowly go to the floor. I didn't experience this sitting at any light stopped. When I got to my destination and put the truck in park the pedal slowly went to the floor. Placing the tranny back in drive, the pedal does not go to the floor. Seems vacuum related. Thoughts??

 

[J_C]

This is a change, previously it was sinking but now stays firm.

You do not need any vac for brake pressure, it is only an assist. You have some kind of hydraulic compromise for the pedal to travel further than it should. It could be fluid out, or it could be air in the line, or it could be master cylinder wear letting fluid past the seals.

Then again, your description seems a bit vague and back and forth about it. It might be an internet post language discrepancy, but it seems odd that what you stated is that it works better now than it did previously.

Did you bleed the brakes yet? I'd at least do that so we can rule out air in the line (assuming a good full purge of the brake lines);.

 

[Kidd7]

I don't drive it much, yesterday I drove it paying attention to the brakes. Here's the complete situation for clarity.
- Engine off; pedal stays firm, does not go to floor w/o excessive force, really stand on the pedal.
- Engine running, in park, in driveway, pedal does not feel soft, but will go to floor under normal pressure.
- Driving around, brakes feel normal.
- Reached my destination, pulled in driveway, stopped, brakes normal. Placed tranny in Park & pedal slowly went to the floor.

 

[1998Exp]

You have a small leak or a bit of air trapped in the system. If no leak is found and regular bleeding doesn't help, there is some air trapped in the ABS controller. This usually happens when the system is opened or the master cylinder is allowed to go dry at some point. Bleeding the ABS controller requires a fully capable scanner, but I am told that the free Forscan can do it too.

 

[donalds]

Easiest way is to find a patch of dirt road or loose gravel
And slam on the break s to activate the abs push the air out then bleed and bleed again
Or forscan

 

[Caponetta]

Check brake pads, as they wear fluid is displaced into the caliper pistons. If they're OK, I would suspect air in the system and potentially a small leak.

 

[Kidd7]

I have a good amount of pad all the way around. I got Forscan working and was able to run the ABS self test. I have no idea how old the brake fluid is, so I decided to replace it. While I was flushing the old fluid out I can the ABS self test a few times to release any air that may have been in there. Took her for a drive afterwards and feels so much better. Thanks for all the advice.