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Discussion Starter #1
Folks, I have a brake problem like I have never experienced before.

Problem: Brake pedal not firm, will go to the floor on first push. Brakes do work, will stop the vehicle, but the pedal goes to the floor. Even if you pump the brakes and get about half a pedal, it will sink to the floor if you push it down with the engine running.

96 Dodge Ram 2500
2WD, Rear Wheel Antilock
8800 GVWR
5.9 Diesel

A few weeks back the brakes on my truck felt mushy. I replaced both rear wheel cylinders and adjusted the shoes until they rubbed the drums. I have verified several times that no slack exists between shoes and drums.

While bleeding, I let the master cylinder run dry. Rookie mistake, but it happened. So I began to bleed the air out of the entire system. Initially I let the system gravity bleed until each cylinder / caliper had fluid. After that point, with a helper siting in the truck, I started with the lines at the master cylinder, then the lines at the proportioning valve, then the lines at the RWAL solenoid valve. From there I moved to the RR wheel cylinder, LR wheel cylinder, FR caliper and finally the FL caliper. All this was done carefully to not produce aeriated fluid. With no bubbles coming out anywhere, I have a pedal that will sink to the floor with the engine running. Without the power assist, the pedal feels fine. The truck will stop, but I don’t like a pedal that goes to the floor.

So I broke out the mighty vac, and vacuum bled the system at all 4 corners, pulled somewhere between 3 and 4 quarts through. I did initially seem to get some air, but with a vacuum bleeder it is hard to know if you are sucking air past the bleeder screw threads, even with them wrapped in Teflon tape. I tapped the lines and valves as I bled to dislodge air. I even removed the right hand side, hardline to rubber line bracket, so the upside down “U” bend was horizontal in case air was trapped there. No joy, still same pedal issue.

Next, I replaced the master cylinder with a reman. Bench bled it per the instructions with the plastic plugs. Installed it, bled the connections at the master cylinder. Same issue. Made some hardline bleeders from brake tubing and performed the conventional master cylinder bench bleeding making sure the lines were submerged in brake fluid. I did get a little air out. So I thought I had found the problem. Nope, same issue.

Bought another reman master cylinder. Same procedure, same issue.

Ok, so I am thinking air is entering the system somewhere. The calipers are old, I disassemble one of them and find light gouges in the piston. Thinking this is allowing air to enter as the piston retracts, I buy two reman calipers and install them along with new pads. Gravity bleed them, then with a helper, pressure bleed and vacuum bleed them. Same issue with the pedal.

I am hard headed, this feels like a master cylinder that is leaking internally .Back to the parts store and this (third) time buy a new master cylinder. Bench bleed it with my custom hardlines, install it. Same issue.

Next I try pressure bleeding from the bottom up. Buy more brake fluid, a new one gallon garden sprayer and attach my clear hose to the stalk of the sprayer and the other end to the bleeder screws. With a helper watching the master cylinder, I pump up the garden sprayer, prime it to remove all air from my new pressure bleeder and introduce clean brake fluid into the bleeder screws one at a time at each corner and fill the master cylinder 4 separate times with this method. No air bubbles appear in the master cylinder. Same brake pedal issue.

So to recap, up to this point, Rear wheel cylinders, Front calipers, Master cylinder and front Pads all replaced. All three rubber brake lines are one year old. Proportioning valve is centered. No evidence of leaks anywhere I can see. Brake shoes are slightly dragging against the drums and the front pads are in contact with the rotors. Pedal goes to the floor, although the truck has brakes that stop it ok, something is still wrong. Somewhere within the system a full stroke of the brake pedal is being absorbed.

Has anyone ever had this issue??? And how did you correct it?

Thanks! Not sure what to do next....:frown2:
 

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Had that exact issue and it was the hard line that runs up near the front of the motor that rubbed and got a slight hole. Tore my hair out trying just about everything you did. It just barely seeped and the leak didn't look like anything other than the typical 12v drool, so I ignored it. Fixed that and it bled in 2 minutes by myself with the truck off.
 

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Discussion Starter #3
I had not considered that a brake fluid leak could be masquerading as an oil leak. That line on my truck has taken a beating over the years. Maybe I will just replace it and see. Thanks for the information!
 

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Discussion Starter #4
I've checked a number of things, fabbed up some test connections and replaced some stuff:
Checked the Master cylinder to see if it was leaking out the rear into the power brake booster. Nope, dry.
I did notice that the power brake booster pushrod/piston and seal were dry and dirty. So I cleaned both and applied silicone grease. Hopefully this will address a typical lazy power assist I have at first cranking each morning.
Made plugs from brake tubing for the front and rear ports of master cylinder and for the tee-fitting for the crossover tube at the front.
Checked pressure at master cylinder.
Front portion (rear brakes) easy to obtain and hold 400 to 600 psi with a plug in rear portion (front brakes) of the master cylinder, this is without power assist.
Rear portion (front brakes) as soon as 400 psi is obtained, the pressure immediately starts going away. Tried additional bleeding, both pressure and looped line back into reservoir to no avail. Therefore master cylinder (yes it is new) is bad. Replaced master cylinder and with plugs in it, have rock solid pedal and steady pressure at each port.
So, I now have one item, master cylinder that checks good.
Moved down to the proportioning valve and discovered it is now leaking out it's sensor port. Don't know if it was leaking when all this trouble started, I had bled it a few days back by removing the large nut, and that may have damaged it's internal seals. Went to the pick a part salvage yard and found a 3/4 ton, V-10 truck, same year as my cummins powered truck, with what visually looks to be the same RWAL solenoid block and proportioning valve. Checked the resistance of both solenoids, one was 1.7 ohms and the other was between 4 and 5 ohms, just like my original solenoids. Installed both the proportioning valve and RWAL solenoid block as an assembly. Plugged the outlet of the proportioning valve to the front brakes, bled the air out of master, prop valve, RWAL. Rear brakes are rock solid pedal. Yeh! I have isolated the issue to the front brakes.
Hooked the front brake line back to the proportioning valve and bled the air out at this fitting.
Plugged the tee fitting at the top of the rubber hose on the driver side to remove the crossover tube and passenger front brake from the system. Obtained a good pedal. So now the problem is either the crossover tube or the passenger side brakes.
Hooked the crossover tube back up to the driver side tee fitting at the rubber hose.
Went to the passenger side front wheel well and unhooked the crossover tube from the rubber hose. Took an old rubber hose for that side and cut off the hose from the brass end, cleaned and tinned and soldered up the fitting to have a way to pressurize the crossover tube. Then realized my pressure gage would screw right into the crossover tube. So I installed the pressure gage instead. Bled the air. Had my helper stab the pedal. 1600 psi! and steady! This was with the engine running and power assist.
Hooked the crossover tube back up to the passenger side rubber hose.
My new metric tap set arrived today, good timing. Took a piece of aluminum round stock and drilled and tapped it for M10x1.5 to attach the end of the rubber hose to it as if it were the caliper. Bled this joint. Good pedal to this point. Therefore the passenger side caliper is suspect.
Disassembled the caliper and found multiple impact marks across the sealing surface. It is obvious that this is a new chrome plated piston in this newly installed reman caliper, but someone was very rough with it. Removed the square cut seal and found steps in the bottom of the seal groove where maybe the caliper had a repair attempt during reman? Anyway I suspect the impact marks &/or step is allowing air to enter during retract. There was no evidence of a pressure leak, so it must be drawing in air. That is my theory at this point.
Tomorrow I will replace the caliper and see.
 

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Discussion Starter #5
Caliper replacement did not fix the issue.
The replacement caliper had a nice new chrome plated piston, no impact marks. However the groove for the square cut seal has the same step in it. Perhaps this is an intentional design feature. Although I have never seen this in other calipers.

Since it will stop, I will drive it until my stainless flex lines arrive and see if driving shakes any air out.
 

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Discussion Starter #6
Stainless flex lines did not fix the issue. They did make the pedal stiffer however, which is a step in the right direction.
I tested the master cylinder with plugs.
First with the pedal at the top, will not budge with the plugs installed.
Then tested it by stroking to 1/2 pedal movement and then having the plugs tightened, just thinking there might be some problem / port / scratch in the master cylinder allowing fluid to transfer between the two pistons within it. Nope, master cylinder is firm as soon as the plugs are tightened.

Testing will continue...

Anyone ever had this issue?

Thanks!
 

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I replaced basically everything you replaced and my brake pedal goes to the floor if I press it hard. I hate the brakes and steering on this truck and I'm actually probably going to replace it with a newer truck that has rack and pinion steering and a brake system that doesn't want to kill me. I'm driving our company's 2017 Dodge 3500 dually right now and it's light years beyond my '96. As much as I really like this 12v, I'm pretty much done messing with the truck that surrounds it.
 

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I had a 97 12V and never had a moment's issue so it's not the truck - just find the problem.

Have you pulled the factory service manual on how to properly bleed the system? Have you used a vacuum bleeder like a Mityvac?
 

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Buy a pressure bleeder, they are not expensive, it’s really the only way to ensure all air is out of the system, while pressurized you can also go over all connections and lines looking for leaks.
 

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You could also make your own pressure bleeder by attaching a fitting to your master cylinder cover and cutting a hole in the rubber diaphragm, regulate the air pressure to 5lbs or so, use a tie down to secure the master cylinder cover. Don’t let the master get empty. Use clear tubing at each bleeder so you can se fluid flow and air bubbles.
 

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Discussion Starter #11
Update: I tested the RWAL solenoid block with a cut off q-tip. Removed the rubber cover from the accumulator port and inserted the q-tip up until it contacted the accumulator piston. Then had my helper crank the engine and apply the brakes. He could feel the pedal slowly sinking to the floor and continued to apply the pedal until it reached the floor. The accumulator piston did not move. So I guess this means my solenoid valve for the accumulator side of the RWAL solenoid block is sealing correctly.

To answer some questions, yes I have tried vacuum bleeding with a mighty vac. I pulled over a gallon of brake fluid through the system. Did not affect the sinking pedal. I also tried reverse pressure bleeding from each corner back to the master cylinder. While this did not affect the sinking pedal, I must say I really like this method of bleeding the brakes.

Testing will continue, I have borrowed a pressure bleeder for the master cylinder and it is one of a few things I hope to try over the next week as time allows.

Thanks to everyone for the input to this perplexing issue.
 

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Do you have a factory service manual for your truck? I'm sure you can find one online.

there are some here: https://www.dropbox.com/sh/81mtpw6h29nct9h/AADFUT79CVpu_LcpdZOLxp5ja?dl=0
Thanks for the service manual links. Yes I do have a factory service manual. The brake bleeding procedure is very standard stuff, as if it did not have RWAL. Just normal brake bleeding starting at the RR wheel.

Yesterday I engaged the RWAL repeatedly on wet roads. This has thrown the brake light to come on the dash. Maybe this will shed some "light" on this subject! I have to see if my code reader will work on this vehicle.
 

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Curious about what the outcome was. I have a similar problem without a resolution. Right now I am also thinking about the removal and inspecting the proportioning valve and RWAL. If you had some direction before this next step it would be great.
 

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Curious about what the outcome was. I have a similar problem without a resolution. Right now I am also thinking about the removal and inspecting the proportioning valve and RWAL. If you had some direction before this next step it would be great.
I had replaced my RWAL / Proportioning valve with a junkyard part and it made no difference. I also mechanically deactivated the accumulator in my RWAL by machining a steel dowel rod to hold the accumulator piston bottomed out in its bore, thinking one of the valves might be allowing brake fluid into the accumulator....because this is pretty much what my problem "feels" like. It feels like brake fluid is flowing somewhere other than the ground--nope, into the power brake booster--nope. Strangest thing, no loss of fluid, but pedal sinks to the floor under a steady high load.
Since I originally posted this I have also replaced the Vacuum Booster (it went out) and the front calipers began sticking and they were replaced "under warranty" along with new brake pads. Neither of these two things affected the original problem.
The problem persists. I think the only "mechanical thing" I have not replaced is the check valve to the rear brakes.
I plan to get back to trying to resolve this later this summer, I have a Wilwood proportioning valve sitting on the workbench and plan to remove the anti-lock apparatus along with the original proportioning valve and plumb in the Wilwood valve to the rear brakes.

Please post here if you resolve your issue!
 

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I would eliminate the RW load sensor gizmo instead of "fooling" it . with a rubber brake hose .
I did my 02 that way .
 

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I just got the sinking pedal yesterday, talked to my stepdad who used to be a mechanic, then read through everything on here.

I found the front reservoir to be out if fluid today, and rear reservoir was definitely low. Just pouring in more fluid, I was able to get more resistance in the pedal with the engine on, but also with reduced braking. At idle, I had to jam the pedal down hard to keep it from moving, and the pedal would still sink to the floor. With the engine off, I can pump the pedal, and build some pressure, but it isn't going hard like I would expect. I didn't see any fluid on the ground, or wheels. I did open the reservoir again, and the fluid looks brown in there now. My suspicion is the master cylinder has a bad seal somewhere, but it isn't at the booster, because I pulled it off the booster and had no fluid there. Brake pedal still sinks to the floor, and I have a new master cylinder that I ordered tonight before reading through all this.
 

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Yesterday I engaged the RWAL repeatedly on wet roads. This has thrown the brake light to come on the dash. Maybe this will shed some "light" on this subject! I have to see if my code reader will work on this vehicle.
After making the RWAL work on the wet road. Did you bleed the brakes again right after? Had a issue similar to yours on my 98 GMC 6.5. Mushy pedal going to the floor.
Air got into the anti lock valve body and could not get it out with normal bleeding. Had to force the antilock work an number of times on a dirt road. This pumped the air out of the anti lock valve body. I blead it out again with my Vac bleeder soon as I got home. Brakes were fine after.
 

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See answer below
 

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After making the RWAL work on the wet road. Did you bleed the brakes again right after? Had a issue similar to yours on my 98 GMC 6.5. Mushy pedal going to the floor.
Air got into the anti lock valve body and could not get it out with normal bleeding. Had to force the antilock work an number of times on a dirt road. This pumped the air out of the anti lock valve body. I blead it out again with my Vac bleeder soon as I got home. Brakes were fine after.
That never occurred to me to bleed after activating the anti-locks. Thanks for the information! I have bled the system since then when I replaced the front calipers, but that was maybe a year afterwards, but I like your suggestion and will take that to the next level and bleed all fittings the next time I activate the anti-locks.
 
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