?HELP? - Brakes won't bleed - 2018 Durango SRT MC/Booster/4 Calipers on 1972 Chassis

[Imperialist1960]

I have a 1972 Imperial. I drive it fast on road rallies and eat people in little vintage EuroTrash cars when I do.
Had a problem where I burned 3 of the 4 brakes off the car while intimidating an Austin Healy just west of Lake Tahoe.

So I redid the car's stoppers and am stumped:

Inventory
2018 Durango SRT Master Cylinder, Booster, Calipers, and Rotors.
My plumbing, Stainless lines to f wheels and rear axle.
ABS module and anything else that was on the Durango otherwise is deleted

• Pedal is firm and GREAT when the car is off.
• Pedal is soft and slowly sinks when car is on.

Brakes function when car is on, but very spongy and no feel to the pedal - wheels can lock on slick painted floor at low speed (so brakes clamp, right?) but pedal is sinking to the floor meanwhile.

I have bled by vacuum, pulling fluid out of the calipers.
I have bled by pressure, forcing fluid up from the calipers.
I have cracked the fittings at the MC while the pedal was depressed.
I have used pressure with the MC off the booster, tilted at an angle so that the lines are inclined to promote bubbles going UP and not flat where they might hide in a pocket.
Removing the MC from booster while car off, even long time, there is a hiss as the seal between MC and booster breaks - vacuum remains until MC is pulled, so booster ?not? leaking down.

• -Is the MC side of the booster supposed to have zero vacuum when MC is pulled?
• I have had same results with two different used boosters. Perhaps both were bad? -I doubt it strongly.

Only variance from stock application is that the Durango has a tilted plane on the firewall, with the MC inclined.
My firewall is vertical flat. I modded the reservoir to be flat and it is not part of the problem/no leaks, etc.

I have put at least a gallon of brake fluid out of spite and stubbornness, but still get the same outcome.

I don't think that it is an air bubble, but have no other explanation that I can imagine.

Bench Bled, that didn't seem to help - the number of fittings at the MC makes timely, effcient reassembly a challenge.


What do you think?


Kenyon

 

[1971demon]

I have a 1972 Imperial. I drive it fast on road rallies and eat people in little vintage EuroTrash cars when I do.
Had a problem where I burned 3 of the 4 brakes off the car while intimidating an Austin Healy just west of Lake Tahoe.

So I redid the car's stoppers and am stumped:

Inventory
2018 Durango SRT Master Cylinder, Booster, Calipers, and Rotors.
My plumbing, Stainless lines to f wheels and rear axle.
ABS module and anything else that was on the Durango otherwise is deleted

• Pedal is firm and GREAT when the car is off.
• Pedal is soft and slowly sinks when car is on.

Brakes function when car is on, but very spongy and no feel to the pedal - wheels can lock on slick painted floor at low speed (so brakes clamp, right?) but pedal is sinking to the floor meanwhile.

I have bled by vacuum, pulling fluid out of the calipers.
I have bled by pressure, forcing fluid up from the calipers.
I have cracked the fittings at the MC while the pedal was depressed.
I have used pressure with the MC off the booster, tilted at an angle so that the lines are inclined to promote bubbles going UP and not flat where they might hide in a pocket.
Removing the MC from booster while car off, even long time, there is a hiss as the seal between MC and booster breaks - vacuum remains until MC is pulled, so booster ?not? leaking down.

• -Is the MC side of the booster supposed to have zero vacuum when MC is pulled?
• I have had same results with two different used boosters. Perhaps both were bad? -I doubt it strongly.

Only variance from stock application is that the Durango has a tilted plane on the firewall, with the MC inclined.
My firewall is vertical flat. I modded the reservoir to be flat and it is not part of the problem/no leaks, etc.

I have put at least a gallon of brake fluid out of spite and stubbornness, but still get the same outcome.

I don't think that it is an air bubble, but have no other explanation that I can imagine.

Bench Bled, that didn't seem to help - the number of fittings at the MC makes timely, effcient reassembly a challenge.


What do you think?

View attachment 166647
Kenyon
www.imperialclub.com

Above my pay grade...when @ BULL wakes up...he should be able to help..he knows everything about brakes....

 

[BULL]

I have a 1972 Imperial. I drive it fast on road rallies and eat people in little vintage EuroTrash cars when I do.
Had a problem where I burned 3 of the 4 brakes off the car while intimidating an Austin Healy just west of Lake Tahoe.

So I redid the car's stoppers and am stumped:

Inventory
2018 Durango SRT Master Cylinder, Booster, Calipers, and Rotors.
My plumbing, Stainless lines to f wheels and rear axle.
ABS module and anything else that was on the Durango otherwise is deleted

• Pedal is firm and GREAT when the car is off.
• Pedal is soft and slowly sinks when car is on.

Brakes function when car is on, but very spongy and no feel to the pedal - wheels can lock on slick painted floor at low speed (so brakes clamp, right?) but pedal is sinking to the floor meanwhile.

I have bled by vacuum, pulling fluid out of the calipers.
I have bled by pressure, forcing fluid up from the calipers.
I have cracked the fittings at the MC while the pedal was depressed.
I have used pressure with the MC off the booster, tilted at an angle so that the lines are inclined to promote bubbles going UP and not flat where they might hide in a pocket.
Removing the MC from booster while car off, even long time, there is a hiss as the seal between MC and booster breaks - vacuum remains until MC is pulled, so booster ?not? leaking down.

• -Is the MC side of the booster supposed to have zero vacuum when MC is pulled?
• I have had same results with two different used boosters. Perhaps both were bad? -I doubt it strongly.

Only variance from stock application is that the Durango has a tilted plane on the firewall, with the MC inclined.
My firewall is vertical flat. I modded the reservoir to be flat and it is not part of the problem/no leaks, etc.

I have put at least a gallon of brake fluid out of spite and stubbornness, but still get the same outcome.

I don't think that it is an air bubble, but have no other explanation that I can imagine.

Bench Bled, that didn't seem to help - the number of fittings at the MC makes timely, effcient reassembly a challenge.


What do you think?

View attachment 166647
Kenyon
www.imperialclub.com

^^^^Trying to absorb this and not misread it...

I had a '99 V10 2500 Ram PU that had a vaguely similar problem.

LONG story short, it WAS in fact a stubborn air pocket in a very high spot in the brake lines/automatic proportioning valve that truck had above the rear axle it used to change brake proportions when it was loaded down.

Trying essentially the same things you have done, including "fast" bleeding to get that bubble to try and move, the ONLY thing I was able to do to get that bubble out was to crack the fittings at that valve and bleed at that location insteadof the calipers.

I realize you don't have these components, but the lesson here is that air bubbles can be persistent in some cases.

I am purely guessing here, but with a custom system, maybe you've got a similar "high" spot as a result of a custom system.

I've got one more thought I'll share, but I'll let you respond to this first with possibilities.

 

[BULL]

Teaser on next piece

I use a customized version of this to bleed from the MC to the calipers...

But there are important techniques to know

https://www.amazon.com/Motive-Products-European-Bleeder-Pressure/dp/B0002KM5L0

 

[BULL]

BTW, i removed your website linkage due to a Trend virus warning.

What's up with that shit?

 

[72 440 Barracuda]

Beautiful car! You don't see many of these on the road much less ones that are done up like yours ! Nice job !

 

[Imperialist1960]

I did more internet looking meanwhile, and I suspect that the problem is the Booster or MC.
I am tempted to purchase a rebuilt booster (I have two eBay used ones that behave the same) and a new MC.

I can wait for BULL or anyone else.

^^^^Trying to absorb this and not misread it...

I had a '99 V10 2500 Ram PU that had a vaguely similar problem.

LONG story short, it WAS in fact a stubborn air pocket in a very high spot in the brake lines/automatic proportioning valve that truck had above the rear axle it used to change brake proportions when it was loaded down.

Trying essentially the same things you have done, including "fast" bleeding to get that bubble to try and move, the ONLY thing I was able to do to get that bubble out was to crack the fittings at that valve and bleed at that location insteadof the calipers.

I realize you don't have these components, but the lesson here is that air bubbles can be persistent in some cases.

I am purely guessing here, but with a custom system, maybe you've got a similar "high" spot as a result of a custom system.

I've got one more thought I'll share, but I'll let you respond to this first with possibilities.

_____________________________

I concur about persistence in air bubbles - I'm living the dream as I type, obviously.
That is a well phrased point, so I'll reconsider and inspect, but the system is incredibly simple.


Well, the pressure bleeder you referenced looks a lot like what I've got, but mine is hand-cranked.

https://www.amazon.com/Phoenix-Syst...cphy=9032042&hvtargid=pla-2281435177898&psc=1

The V system pushes a significant volume on each stroke, so popping it 8 times rapidly ought to be ballpark to the pressure pot that you point out.

I have also used the vacuum bleeder that runs on compressed air, and the symptoms NEVER vary - it's not like continued effort has shaved 5% or something - always the same persistent sink rate.

---

MC is highest point, then down to the frame and very horizontal from there.
Kicks up to go to the rear end, so I suppose that's a high point that I could crack open.
$3 says that no air comes out of there, but it's on the lift and accessible, so I'll try it.

There just isn't anything else in the system.....
Um except the rear circuit bias valve.
I guess I can crack the fittings on that too, but no, can't be that - it's on a flat run...

<<BUT>>

If the pedal resistance is correct and delightful when engine off, and ONLY sinks when engine on, and I have been truly savage about bleeding the fluid to avoid having to ask someone else after 40 years of doing this stuff, then I must conclude that the air bubble would be detectable in the pedal w engine off and no vacuum to the booster.

Ergo I conclude booster that I got from mysterious origins on eBay may be suspect and I should toss $250 at a reman unit just to see.
A replacement MC is only $80, so why not both at the same time?

There are tales online of a sinking pedal only with power being a firm symptom of a failed booster. Alternate theory is that the increased pressure forces fluid between the two chambers of the MC, but I'm not as hot on that idea.

Thank you for considering my plight.