BARELY THERE BRAKES

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cc72red

cc72red

Joined
Apr 9, 2013
Threads
14
Messages
94
Hi Everyone.
Just the other day, all of a sudden, while driving, my brakes gave away. When I realized that my brakes were not slowing me down, I pushed to floor. Finally about the last 1/2 inch they grabbed. When returning pedal and trying to stop again,,, same thing. There is obviously a lack of fluid pressure build up., but where? Can't find and external leak anywhere,
Started inspecting all wheel calipers and lines. Had someone pump brakes to build up fluid and find a seep... nothing! The pedal will pump up with car off but once pumped up it gradually goes to floor as if you are bleeding the brakes.
Found the passenger caliper with a wetness on it but not WET. THought that maybe seals were bad, So, put a new caliper on. Same with the left back.... Problem still arises. Replaced the master brake Cylinder. Still same problem. No leakes to e seen. Even hosed off underneath with a bit of pressure to see if we could see any fluid leaking. Nothing.
Im at my wits end...
Could there be a problem with the ABS where the fluid is just bleeding back into that?
or the Proportioning valve? Just have no clue!
Please Help!
Cindy
 
Is the actual fluid level in the master cylinder going down?
 
You've checked the lines, calipers, MC, all good. Next logical step is the booster.
 
Sounds like maybe the Brake Master Cylinder is bypassing fluid internally past the piston seals if you're not losing hydraulic fluid from the reservoir or the wheel calipers or line connections. This would explain having a very soft pedal that collapses until the last little bit, which could be a constriction in the bore.

When the Brake Booster goes out, your pedal stays at the same position, it just requires every ounce of strength in your legs plus a young priest and an old priest to bring the vehicle to a safe stop. You may also need a new steering wheel, as yours will be bent upward. Oh, and a thorough cleaning of the drivers seat may be needed, too.

My bet is the Brake Master Cylinder. I don't have much luck with rebuild kits, and would replace the whole assembly as it comes from Mr. T.
 
LongDuck said:
Sounds like maybe the Brake Master Cylinder is bypassing fluid internally past the piston seals if you're not losing hydraulic fluid from the reservoir or the wheel calipers or line connections. This would explain having a very soft pedal that collapses until the last little bit, which could be a constriction in the bore.

When the Brake Booster goes out, your pedal stays at the same position, it just requires every ounce of strength in your legs plus a young priest and an old priest to bring the vehicle to a safe stop. You may also need a new steering wheel, as yours will be bent upward. Oh, and a thorough cleaning of the drivers seat may be needed, too.

My bet is the Brake Master Cylinder. I don't have much luck with rebuild kits, and would replace the whole assembly as it comes from Mr. T.
Click to expand...
Says he replaced it.

OP what year is the truck? Does it have rear drums or disc?
 
Grandlooser said:
Says he replaced it.

OP what year is the truck? Does it have rear drums or disc?
Click to expand...

The question is what did he replace it with? And remember the 3rd rule of diagnostics is a new part doesn't = a good part.
 
cc72red said:
Could there be a problem with the ABS where the fluid is just bleeding back into that?
Click to expand...
Yes
"IF" the master is good and "IF" your not actually loosing fluid, you may have an issue with your ABS.

There's a valve in your ABS called a dump valve, if this is leaking will allow fluid to push into a chamber called an accumulator. The symptom is the same as a bad master. This is not uncommon on high mileage abs systems. ABS was one of my specialties in the shop. I've diagnosed quite a few over the years including my Cruiser. The fix is replace the unit or bypass it. I chose the latter. There are no serviceable parts in it.
 
I have a decent one waiting for you if that is the case, however I agree with the latter option of removal myself. Some will obviously come in and mention all the lives they saved having ABS.:meh:
 
leonard_nemoy said:
The question is what did he replace it with? And remember the 3rd rule of diagnostics is a new part doesn't = a good part.
Click to expand...
We put a new MC on it the other day. However, The old one was only 4 years old.
So next step is to power bleed the brakes and flush and replace the fluid for ruling out boiled fluid. Also reinstalling old master cylinder after bore inspection.
After all that, The ABS is next by process of elimination.
Thank You for all of your suggestions and information. We are using it all!
 
smritte said:
Yes
"IF" the master is good and "IF" your not actually loosing fluid, you may have an issue with your ABS.

There's a valve in your ABS called a dump valve, if this is leaking will allow fluid to push into a chamber called an accumulator. The symptom is the same as a bad master. This is not uncommon on high mileage abs systems. ABS was one of my specialties in the shop. I've diagnosed quite a few over the years including my Cruiser. The fix is replace the unit or bypass it. I chose the latter. There are no serviceable parts in it.
Click to expand...
How
smritte said:
Yes
"IF" the master is good and "IF" your not actually loosing fluid, you may have an issue with your ABS.

There's a valve in your ABS called a dump valve, if this is leaking will allow fluid to push into a chamber called an accumulator. The symptom is the same as a bad master. This is not uncommon on high mileage abs systems. ABS was one of my specialties in the shop. I've diagnosed quite a few over the years including my Cruiser. The fix is replace the unit or bypass it. I chose the latter. There are no serviceable parts in it.
Click to expand...
I'm not familiar with the ABS bypass. Simple or hard? What's the plumbing for that? I'm just a girl that needs my rig working again. So, hoping it wont be out of my mechanical knowledge. :)
Thank you!
 
Grandlooser said:
I have a decent one waiting for you if that is the case, however I agree with the latter option of removal myself. Some will obviously come in and mention all the lives they saved having ABS.:meh:
Click to expand...
What are you asking for the unit?
 
So.. In process of doing bypass with the ABS. Since we are doing that,, we are gonna wait on reinstalling old MC.
IMO once the brakes are bled again with Pneumatic brake bleeder after the ABS bypass, this will be the tell all. If brakes work , then obvious ABS issue. If not, then will have to look further. I will inform once the ABS is bypassed and brakes bled again.
Thanks to everyone!
 
cc72red said:
I'm not familiar with the ABS bypass. Simple or hard? What's the plumbing for that? I'm just a girl that needs my rig working again. So, hoping it wont be out of my mechanical knowledge. :)
Thank you!
Click to expand...

Sorry, didn't log in until now. It looks like you have it handled.

cc72red said:
I'm just a girl that needs my rig working again. So, hoping it wont be out of my mechanical knowledge. :)
Click to expand...
Some of my students are girls. Its fun watching them out diagnose the guys.
 
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