HELP Brake pedal goes to floor slowly (2 Viewers)

[2fpower]

Facts:

Working on a 97' lx450.
ABS and LSPV removed.
brake proporting valve added by master
master replaced with non-abs unit
replaced the bleed valves
booster was replaced last year.
Bled the snot out of it. Ran it up and sat on hills to try and get air to go one way or the other.


No visible leaks and hoses don't appear to have any bubbles.

The rig was sitting for some time, so ran it last night and the wear on the rotors appears even across all the rotors, (after we found pass rear was not floating) so I am thinking that all calipers are working -- can't tell if any single pot is locked.

Here is what is happening....

Car off, pumps and bleeds great. Pedal does not wander to floor.
Second pump is always better than the first
When car is running it will slowly 5-10 seconds drift down the floor.

Current thought is to replace all the soft lines, pull the calipers and look for any concerns, although hoses are likely only 5 years old, and not seeing cracking.

What am I missing?? Should I swap masters?

 

[jpoole]

Slowly to floor is often a symptom of a Master leaking/failing internally. It may not happen with engine off because the brake booster is not at play then. I've heard of and have had new/remanufactured masters show issues like this out of the box so it's possible that you got a bad unit and/or that issues developed while you were bleeding the snot out of it

I think that most other possible causes of a pedal that keeps falling like that would result in fluid loss though there are a few like a ballooning and then contracting brake hose that wouldn't necessarily, although pedal feel would be poor and you'd likely notice degraded/soft hoses.

Before I dove into replacing more parts though I'd do additional testing (in case you haven't already) and in particular would see if the pedal travels further down only after driving or even after you've pumped many times, with force, while sitting still. A test like that would help rule out a loose bearing or warped rotor pushing a pad out, etc. that may lead to excessive pedal travel after you drive a bit.

 

[BILT4ME]

Slowly to floor is often a symptom of a Master leaking/failing internally. It may not happen with engine off because the brake booster is not at play then. I've heard of and have had new/remanufactured masters show issues like this out of the box so it's possible that you got a bad unit and/or that issues developed while you were bleeding the snot out of it

I think that most other possible causes of a pedal that keeps falling like that would result in fluid loss though there are a few like a ballooning and then contracting brake hose that wouldn't necessarily, although pedal feel would be poor and you'd likely notice degraded/soft hoses.

Before I dove into replacing more parts though I'd do additional testing (in case you haven't already) and in particular would see if the pedal travels further down only after driving or even after you've pumped many times, with force, while sitting still. A test like that would help rule out a loose bearing or warped rotor pushing a pad out, etc. that may lead to excessive pedal travel after you drive a bit.

I agree completely.

 

[cruisermatt]

Yep, trying a different master cylinder would be the first thing I'd do and I've seen this exact issue before.

 

[2fpower]

Slowly to floor is often a symptom of a Master leaking/failing internally. It may not happen with engine off because the brake booster is not at play then. I've heard of and have had new/remanufactured masters show issues like this out of the box so it's possible that you got a bad unit and/or that issues developed while you were bleeding the snot out of it

I think that most other possible causes of a pedal that keeps falling like that would result in fluid loss though there are a few like a ballooning and then contracting brake hose that wouldn't necessarily, although pedal feel would be poor and you'd likely notice degraded/soft hoses.

Before I dove into replacing more parts though I'd do additional testing (in case you haven't already) and in particular would see if the pedal travels further down only after driving or even after you've pumped many times, with force, while sitting still. A test like that would help rule out a loose bearing or warped rotor pushing a pad out, etc. that may lead to excessive pedal travel after you drive a bit.

I totally agree with you.. at this point I am just throwing parts at it because nothing seems to point to the issue.

Is this what you are referring to trying? Car driven around yard for a few minutes then let it sit, engine still running, for a couple minutes. First pedal so-so, second pedal much better, but putting force on it, drifts down over 5-10 seconds.

 

[jpoole]

@2fpower

"putting force on it, drifts down over 5-10 seconds"

this points pretty strongly towards the master cylinder leaking internally

"First pedal so-so, second pedal much better"

This indicates the possibility of an additional, common problem with your brake system that my post drive brake testing vs. static brake testing was related to.

This second issue could be caused by the brake pads getting pushed back/away from the rotors too much while driving, which increases pedal travel required to push the pads back into contact with the rotors. Causes for pushing the pads back/away from the rotors could be loose wheel bearings, warped rotors, etc. Symptoms of this issue would primarily be that after you drive the first brake pedal depression goes further than immediately following brake pedal depressions. If this "driving induced" issues is present then if you were to depress the brake pedal multiple times without driving in between (regardless of the passing of time) the pedal travel would remain consistent, assuming there aren't other issues in the system.

The first/main step that I would take regarding this second issue of the longer initial brake pedal travel would be to lift each tire/wheel off of the ground (one at a time is fine) and check for bearing looseness. You basically grab the tire with one hand on the top tread, one on the bottom, and try to lever the top of the tire in and out of the wheelwell. Repeat this at the 9 oclock and 3 oclock positions and check all 4 wheels. If your bearings are loose it's usually very easy to feel the slack/bump as you switch push/pull directions. You may also want to remove the tire/wheel on each corner and check the torque of the caliper bolts and inspect for any visual movement/weird wear patterns. At this point I just assume that an 80 has loose wheel bearings, front in particular, so it's always a good thing to check.

This second issue of the first pedal depression being deeper than following depressions could possibly also be related to an MC or other components that aren't functioning that well. We are getting into tricky territory here but my rough theory is that using the brakes could bring pressures up, flare the little internal cups/seals out a bit, etc. and lead to better subsequent braking in the system. Anyway, when you are trying to troubleshoot systems like these the imagination can become active but fortunately there are a handful of common issues you can focus on initially before you have to get too creative.

 

[2fpower]

@2fpower

"putting force on it, drifts down over 5-10 seconds"

this points pretty strongly towards the master cylinder leaking internally

"First pedal so-so, second pedal much better"

This indicates the possibility of an additional, common problem with your brake system that my post drive brake testing vs. static brake testing was related to.

This second issue could be caused by the brake pads getting pushed back/away from the rotors too much while driving, which increases pedal travel required to push the pads back into contact with the rotors. Causes for pushing the pads back/away from the rotors could be loose wheel bearings, warped rotors, etc. Symptoms of this issue would primarily be that after you drive the first brake pedal depression goes further than immediately following brake pedal depressions. If this "driving induced" issues is present then if you were to depress the brake pedal multiple times without driving in between (regardless of the passing of time) the pedal travel would remain consistent, assuming there aren't other issues in the system.

The first/main step that I would take regarding this second issue of the longer initial brake pedal travel would be to lift each tire/wheel off of the ground (one at a time is fine) and check for bearing looseness. You basically grab the tire with one hand on the top tread, one on the bottom, and try to lever the top of the tire in and out of the wheelwell. Repeat this at the 9 oclock and 3 oclock positions and check all 4 wheels. If your bearings are loose it's usually very easy to feel the slack/bump as you switch push/pull directions. You may also want to remove the tire/wheel on each corner and check the torque of the caliper bolts and inspect for any visual movement/weird wear patterns. At this point I just assume that an 80 has loose wheel bearings, front in particular, so it's always a good thing to check.

This second issue of the first pedal depression being deeper than following depressions could possibly also be related to an MC or other components that aren't functioning that well. We are getting into tricky territory here but my rough theory is that using the brakes could bring pressures up, flare the little internal cups/seals out a bit, etc. and lead to better subsequent braking in the system. Anyway, when you are trying to troubleshoot systems like these the imagination can become active but fortunately there are a handful of common issues you can focus on initially before you have to get too creative.

Great info. Will start diagnosing tonight. I keep an extra master around, so will swap it out if bearings look good and see if the rotor action looks odd. Good thing is I have a collection of calipers I can swap on to eliminate possible reasons for this.

 

[2fpower]

frustrated.... when not running, hard as a rock, with no movement. when running pedal drifts to floor.

1. no front bearing issues/movement,
2. used pry bar to move pad away from rotor and had someone pump the brakes, watched each individual pot push, all seemed reasonable pressure and movement.
3. swapped master, no change.
4. pulled out the proportioning valve. no change
5. cussed a little
6. I had bought some plugs, so tried to isolate front and rear circuit to see if we can narrow down the issue. Plugged front first and rear seemed better, but still drifted. We swapped out all rear soft lines, no change.
7. changed vacuum hose to power booster.
8. plugged both front and rear at master. Hard as a rock with no pedal drift.
9. opened front circuit and plugged rear, had drift still, so changed out all front soft lines.. same issue.

Put it all together and after all this really no change. So power washed it to see if we can see any evidence of leaks.

I know it makes no sense, but really thinking about swapping out the power booster. I don't understand how both front and rear can be leaking (thinking that when i put a plug in and isolated a side the issue persisted)....

Thoughts?

 

[jpoole]

That's a lot of effort to have no change and I'd be frustrated too. You must be close though, there's not a whole lot left to replace at least.

Regarding the pedal drift, is it a constant rate pedal drift where the pedal will travel all the way to the end of the stroke at a fairly consistent pressure/speed of travel? An alternative way the pedal could drift down out may be the pedal travel only drifting through part of the stroke (as compared to when you are bleeding) and/or ramping up in terms of effort taken as the pedal goes deeper into it's travel. This second feel of pressure increasing would be more likely related to air in the system that is being compressed. Either way the differences in feel can be subtle but if you are noticing anything about the how the pedal feels as it drifts it may be helpful to share it here.

While seeing the fluid run out will help find/diagnose any external leak large enough to let the pedal fall like your describing should show up pretty quickly in the fluid level dropping in the reservoir.

Did you replace all of the soft hoses? I believe that there are 7 with an ABS system like you had though you may have changed a few things.

With the information that you've shared I'd be focused on:

-searching for leaks, like you are doing, particularly around all connections that were recently redone with abs/lspv removal, line changes, etc.
-on getting a really good bleed while seeing if the feel changes after bleeding efforts, potentially changing your bleeding techniques to see if different approaches yield improvements
-reviewing the changes that you made with the abs and lspv removal to make sure that there isn't a plumbing issue there causing this
-doing the FSM tests on the booster to see if you can rule it out and save you the hassle/worry of replacing it

Hopefully taking a few days break or someone else chiming in here will lead you to the eureka moment and help you get your brakes fixed without too much more effort. At the end of this process it seems like you will be an expert on your 80s brakes at least and well prepared to keep them happy for the life of the truck.

 

[2fpower]

pedal travel...... To be clear, when car is not running, it is solid. Feels good. When running, it goes about halfway and brakes will stop vehicle decently, then the pedal slowly drifts to the floor.

Yes, all 7 soft lines are new now.

I use a clear tube for bleeding and watch until no bubbles, then do a few more times to make sure it is clear. Starting at furthest point and working to nearest... then doing again sometimes. Used 2 quarts of fluid yesterday.

Good thoughts on the FSM on booster. I don't know how to test for that.

 

[ppc]

You stated that you swapped the master. Was this new OEM, remanufactured or swapped from a parts truck? From your description it just keeps pointing back to the master.

 

[2fpower]

You stated that you swapped the master. Was this new OEM, remanufactured or swapped from a parts truck? From your description it just keeps pointing back to the master.

New in box, non abs master. A1 cardone.

Reading the FMS for testing the booster makes it sounds like there could be vacuum leak. Need to see if i still have a pump to create and gauge vacuum.

 

[Peluo]

I had the same thing happen to me on my other truck, a Ford Ranger. I don’t know if it is relatable but the fix was a new brake booster. The symptoms were the same ie: slowly the brake pedal would go to the floor.

 

[satchel]

What peluo said, I've had the same thing before. Seems like a MC issue, but basically the booster is leaking it's vacuum and not applying it to the brakes, going around the seal. So it leaks until it gets to the point of applying brakes then it feels firmish. You'll know for sure if you hear any hissing.

 

[2fpower]

I had the same thing happen to me on my other truck, a Ford Ranger. I don’t know if it is relatable but the fix was a new brake booster. The symptoms were the same ie: slowly the brake pedal would go to the floor.

I did the FSM test on the booster, and it tells you what it should do, but not what it should not to say the booster is good. The second test is to pump three times to see if the distance from the floor to the pedal gets better... well it does of course, then it drifts down to the floor.

With your info @Peluo, I am going to swap out the booster -- after I confirm we have good vacuum. nothing else makes sense.

 

[White Stripe]

Did you bench bleed the master?

 

[2fpower]

Did you bench bleed the master?

Yes, with clear lines, so I could see when all air was out.

 

[BILT4ME]

@2fpower :
Everything you've done to this point as well as current symptoms point to a bad booster. I think you could be confident in that change.

 

[White Stripe]

Pinch the front and rear brake hoses off and see if it still does it

 

[2fpower]

Pinch the front and rear brake hoses off and see if it still does it

Good point..... uh... when I plugged the front and back ports at the master, it did not drift to the floor.