97 xlt brake issue update

[IMINYOURCHAIR]

Okay, I have a brake issue.

symptom: brake pedal goes about 30% deeper than normal before any stopping force is felt. this is intermittent between when the pedal is pressed/released and pressed again. most often it does this when coming to a red light. i get normal pedal when I make the initial brake effort, then when I stop and try to creep forward and re press the pedal it sinks further in before doing anything.

Test/diag: tonight I tried something. I pulled into my drive way and re created the pedal softness then let it roll to some speed then floored the pedal. the rear brakes locked up instantly. tried it again with normal pedal and it stopped quickly with no lock up (abs disabled due to rust-frozen dead WSS)

Conclusion: there is something mechanical stopping the front brakes from getting pressure. I have already bled the system even though it was never opened or ran dry prior to this starting. and the fact that the pedal becomes firm even without pumping says the lines are air free.. the right rear tire was replaced the day it started but I feel that is not relevant to the problem.

The next thing I want to try, is to put an abs bypass in. Why? I suspect one of the internal valves is failing/failed. It seems to explain the random nature of the problem. I have no information on actually doing that, although, I have heard it mentioned with some f-150 trucks of the same vintage but no actual install results. I will try it on Saturday and hope it works. I want to get my AC installed sometime

 

[IMINYOURCHAIR]

Also, to add, I truly appreciate any help I get with this. It's really got me stumped.

Thanks to each and all of you!!

 

[FordandPolaris]

I would replace the master cylinder. Sounds like the seal inside of the cylinder has gone bad allowing for mushy brake feel. I had the same issues and replaced the master cylinder, made a world of difference.

Just make sure to bench bleed the new cylinder before putting it in. If you still suspect the ABS, remove the ABS fuse and see if the condition is still present. If it is, it has nothing to do with ABS.

 

[bedrck46]

ABS fuse is #25 in the fuse box under the dash

 

[IMINYOURCHAIR]

I have already pulled the fuse. I've got a bad wheel speed sensor and it's rusted to the place it is in. I guess I will try the master cylinder and cross my fingers that works. If the problem still persists what would you believe to be the next possible cause to the problem. I don't really want to throw parts at it if I don't need to

 

[FordandPolaris]

I have already pulled the fuse. I've got a bad wheel speed sensor and it's rusted to the place it is in. I guess I will try the master cylinder and cross my fingers that works. If the problem still persists what would you believe to be the next possible cause to the problem. I don't really want to throw parts at it if I don't need to

Like I said, if the ABS fuse is pulled, the system is completely disabled and therefore not having any input into the braking process. So bypassing the ABS would be categorized to me as just throwing parts at it. Not trying to be mean, just trying to clarify. If the ABS is disabled, the wheel speed sensor should have no input on anything. Braking is all hydraulic and has no electronic components except for the ABS.


I still think the master cylinder is the culprit but you can check the vacuum lines leading to the brake booster (big circular piece that the master cylinder mounts to) and see if they are in good condition. Usually with the master cylinder going bad, you will feel better brake pressure if you keep pumping it, as it builds a little pressure each time. Hopefully that helps.

 

[IMINYOURCHAIR]

I understand. I know the effects of pulling the abs fuse but as I have read, there is a possibility of a failed valve internal to the abs module which would effect the brakes regardless of the fact that the fuse is removed. I think what I meant by not throw parts at it. was to not throw the expensive parts first. and on another note. i may be wrong, but wont putting a new master cyl in require the abs module to be bled anyhow?

 

[FordandPolaris]

I understand. I know the effects of pulling the abs fuse but as I have read, there is a possibility of a failed valve internal to the abs module which would effect the brakes regardless of the fact that the fuse is removed. I think what I meant by not throw parts at it. was to not throw the expensive parts first. and on another note. i may be wrong, but wont putting a new master cyl in require the abs module to be bled anyhow?

I never did that when I replaced my master cylinder. Only bled the cylinder itself. Like I said I didn't mean to insult you, its hard to convey that typing sometimes. We have several Expeditions in my family, and two of them have needed the master cylinder to be replaced. I have never worked on the ABS module on any of them. I think I paid about $90 for a master cylinder from O'Reilly so they are not terribly priced, and its not like the money is wasted. Brakes are the best things you can sink money into anyways.

 

[hooraah]

Possible you have a swelling soft line on the front? An old brake line that swells under pressure can easily give you a soft pedal, and I dont think that would affect bleeding the fluid.

It might be difficult to find unless theres a really obvious bubble.

 

[toms89]

Okay, I have a brake issue.

symptom: brake pedal goes about 30% deeper than normal before any stopping force is felt. this is intermittent between when the pedal is pressed/released and pressed again. most often it does this when coming to a red light. i get normal pedal when I make the initial brake effort, then when I stop and try to creep forward and re press the pedal it sinks further in before doing anything.

Test/diag: tonight I tried something. I pulled into my drive way and re created the pedal softness then let it roll to some speed then floored the pedal. the rear brakes locked up instantly. tried it again with normal pedal and it stopped quickly with no lock up (abs disabled due to rust-frozen dead WSS)

Conclusion: there is something mechanical stopping the front brakes from getting pressure. I have already bled the system even though it was never opened or ran dry prior to this starting. and the fact that the pedal becomes firm even without pumping says the lines are air free.. the right rear tire was replaced the day it started but I feel that is not relevant to the problem.

The next thing I want to try, is to put an abs bypass in. Why? I suspect one of the internal valves is failing/failed. It seems to explain the random nature of the problem. I have no information on actually doing that, although, I have heard it mentioned with some f-150 trucks of the same vintage but no actual install results. I will try it on Saturday and hope it works. I want to get my AC installed sometime

The rear brakes will always lock up first assuming the antilock function is disabled. The weight transfers to the front during braking, how much depends on how hard you brake. The front also has more weight on it than the rear normally.

The fact that your rear brakes locked up during your test and the front did not is meaningless to me. In fact I would expect it to do exactly that. I think you are reading too much into it.

Just my opinion... Since your anti lock brakes have been disabled I would suspect the master cylinder, air in the lines, leak somewhere or bad hoses before I would suspect the anti lock brake system itself. I believe you have far more occurrences of master cylinders going bad than the latter.

 

[JUST4FUN]

the master controls the front and rear brakes seperately to stop a total failure most likely the front brake has a bad seal/o-ring.This will cause spongy brakes as the fluid bypasses the o-ring
https://www.youtube.com/watch?v=523fHbmbdsQ

 

[IMINYOURCHAIR]

just4fun, you nailed it. that describes it exactly.

basically what has happened is that seal is erratic thus the pedal goes in further before giving pressure to the rear brakes at what feels like a new threshold. the seal seems to reset if i release the pedal and allow it to go all the way back up and press the pedal again. which explains why the rear wheels locked up (more work for two wheels and they are rear most as well) and why no wheels locked up when it was "reset" (load was balanced over four wheels compared to the rear only so it stopped before they could lock up)

thank you all for the advice I will re read and possibly edit my post after I finish the repair tomorrow. I am writing this after a 14 hour shift today..

 

[IMINYOURCHAIR]

I never did that when I replaced my master cylinder. Only bled the cylinder itself. Like I said I didn't mean to insult you, its hard to convey that typing sometimes. We have several Expeditions in my family, and two of them have needed the master cylinder to be replaced. I have never worked on the ABS module on any of them. I think I paid about $90 for a master cylinder from O'Reilly so they are not terribly priced, and its not like the money is wasted. Brakes are the best things you can sink money into anyways.

No insult taken. I agree, brakes are the first thing to put money into unless you're upping their size then rims to make clearance for them would be first

good to hear the abs shouldn't need to be bled for the master cyl replacement fingers crossed

 

[IMINYOURCHAIR]

The rear brakes will always lock up first assuming the antilock function is disabled. The weight transfers to the front during braking, how much depends on how hard you brake. The front also has more weight on it than the rear normally.

The fact that your rear brakes locked up during your test and the front did not is meaningless to me. In fact I would expect it to do exactly that. I think you are reading too much into it.

Just my opinion... Since your anti lock brakes have been disabled I would suspect the master cylinder, air in the lines, leak somewhere or bad hoses before I would suspect the anti lock brake system itself. I believe you have far more occurrences of master cylinders going bad than the latter.

I understand where you are coming from on the weight shifting and rear being lighter etc.. you'd really have to feel how the pedal is doing to understand me, I know it sounds weird, just4fun pretty much explained it for me. the front brake seal internal to the master is failing thus all the brake pedal effort is going to the rear brakes which made them lock when i hit the pedal. when I released and retried the pedal it was normal and the truck actually stopped rather than sliding.

 

[IMINYOURCHAIR]

y'all were right it was the master cyl. I didn't even have to bleed the lines. I did bench bleed the new one though and everything went together smoothly. took about 20 mins to do.

 

[FordandPolaris]

Glad it fixed the problem! Spongy brakes can be nerve-racking.

 

[IMINYOURCHAIR]

same here, I was surprised at how easy it was to do. the only problem I had was the bolts on the booster are doing this number \_/ but only about 1mm out at the tip compared to the base. a quick tap with a hammer resolved it. I was expecting to have to bleed the whole thing after I got it together but the bench bleed took care of that for me. as soon as I bolted things down the pedal was firm.