2nd Gen Non-Engine/Transmission Brake Pedal Sinks to floor- engine on 96

[CWeaver]

Hello, I've seen similar questions asked on this and other forums, but frighteningly... no solutions!

On my 96' 2500 4wd (RWAL- rear wheel anti-lock) ram I started loosing brakes driving home with no load the other night. I would have weak brakes and at stops the pedal would Slowly sink to the floor. if I repeatedly pump the pedal it would come up, but would then slowly sink back down. After another half dozen miles I parked the truck at my mechanics shop where my wife's car was and talked to him about it. The trunk was down to a quarter of the normal brake fluid in the master, and we couldn't find any leaks- with the truck on or off with brakes applied.

He said: that sounded like the master cylinder was internally failing and fluid could be leaking past the valves/seals into the brake booster? I should replace the master cylinder(MC) and empty out the brake booster and should be good. We topped up the fluid so I could drive it slowly home.

The next morning I followed my friends gen 1 flatbed home just in case. We stopped at the parts store to get a MC and came out to a puddle under the front right of the truck. the hard line went by the frame.

We replaced and hardline, still pedal issue, replaced MC still issue, in trying to bleed brakes ended up with rusted broken bleeders: replaced the right front Caliper and both rear wheel cylinders and rear hard lines to center.

Power bleed brakes- still weak and sink to the floor.....
Some folks online said line to rear was bad & mine looked ugly. Ever since I got the truck the fuse was pulled for the anti-lock brakes and the solenoid or parts under the distribution block under MC look rusted and awful. I removed the antilock valve/block and ran new hard line from proportioning valve to a new rear flex line. So all the rear lines are now new.

I let it gravity bleed a while, but ran out of daylight to do any more...but initial pedal feel is the same. I plan to bleed it fully tomorrow. Has anyone seen this problem and resolved it?

Some of the threads I've seen on this are from almost ten years ago, I would think someone must have fixed it by now!!!!

 

[petersonj]

You said, "I would have weak brakes and at stops the pedal would Slowly sink to the floor. if I repeatedly pump the pedal it would come up, but would then slowly sink back down."

You have done a lot of work on your truck brakes and sometimes troubleshooting gets difficult when many things are being replaced or repaired. Initially you indicated that you could make the pedal firm, but if your foot remained on the pedal, the pedal would sink to the floor. Only three things can cause this on your truck: an internal leak inside the master cylinder, an internal leak in the anti-lock brake system (fluid leaking into the accumulator), or an external leak anywhere which may or may not be visible. It looked like you found the cause when you saw brake fluid on the ground and replaced the offending brake line.

Later in you post you said that the brakes are "still weak and sink to the floor". Do you mean that they are behaving exactly like you said earlier in the post, or do you mean that you just have a low brake pedal? If you just have a low pedal condition, it means that you have air in the system somewhere or your rear brakes are out of adjustment, or both. If you can get a firm pedal by pumping the pedal and it still sinks to the floor, then you should be looking at the three above-mentioned causes.

When you figure it out, let us know the solution.

- John

 

[BigPapa]

Look at the rear line that runs along the frame behind the fuel tank for leaks. Very common for them to rust out.

 

[CWeaver]

Thanks for you responses guys:

Before I had this issue I only had to push my brake pedal about a inch maybe to start substantial braking, three inches would be a lot of brakes and the pedal would stay at that height sitting at a stop. Now, even after the new MC, I have to push the pedal at least half way 3-4 inches to feel any braking and then the pedal sinks right to the floor. If I repeatedly pump the pedal I can build up pressure so the pedal is closer to the normal height, but as soon as I hold it, it starts sinking down. So the issue is the same... maybe slightly better.

I also read that the rear brakes set the pedal height, so we adjusted the rear brakes so the drums barely fit on.. used a hammer to tap them on they were so tight. This didn't help or effect the pedal height / feel.

I did the new rear hardline from the proportioning valve to the rubber flex line to rear axle Sunday night, and will bleed it tonight and see what I get. The line I replaced was rusty where I could see it & I didn't see what it looked like behind the fuel tank as I fished a new line back their and left the old one there.

You stated the three culprits could be: an internal leak inside the master cylinder, an internal leak in the anti-lock brake system (fluid leaking into the accumulator), or an external leak anywhere which may or may not be visible.

Master Cylinder is new, not rebuilt, lines are new or look good, Anti-lock block under MC is removed.
" anti-lock brake system (fluid leaking into the accumulator) " has me lost?? Is this accumulator part of the rusted block I removed?


Could it be anything else?
maybe bad front flex hoses or Caliper (both replaced 5-8 years ago)? not sure what else?

 

[petersonj]

" anti-lock brake system (fluid leaking into the accumulator) " has me lost?? Is this accumulator part of the rusted block I removed?

It sounds like you have removed the dump valve / accumulator portion of the rear wheel antilock system. My understanding of this system is that the dump valve opens and fluid going to the rear brakes is redirected to an accumulator as the rear wheels approach a lock up situation. When the near lock up event is over, the accumulator returns the fluid back to the reservoir. If the dump valve leaks fluid into the accumulator during normal braking operation, this would cause a sinking pedal. If you have removed this hardware (which it sounds like you have), then you can disregard this cause.

So, in my mind, this leaves only two situations that would cause a the brake pedal to sink to the floor - an internally leaking master cylinder (even though it is new) or an external leak that has not been found yet.. I would be suspecting an external leak.

Try this as a process of elimination. Remove fluid from the master cylinder reservoir until the level reaches the dividing wall between the front and rear chambers. Put the cap back on and operate the brake pedal, purposely pumping, holding, and letting it drift to the floor several times (the more, the better for this test). Now recheck the reservoir. If the level remains the same, then you have a master cylinder leaking internally. If the level has dropped, you have an external leak and you should be able to see which axle circuit is leaking by tracing the lines from the chamber with the lowest level in the master cylinder.

Hope this helps,

- John

 

[CWeaver]

Saturday I Blead the brakes and had no success. I pulled the driver side caliper to try compressing it with a clamp to be sure it was free and didn't have air in it. It was rusty and fought a little so I replaced it (everything else is new right!) blead the brakes and this didn't seem to help. I tried gravity bleading, then made a new metal plate for my power bleeder and power blead the brakes, still no luck.. when bleading I tapped the calipers and line mounts on the frame with a hammer to try to knock free any bubbles. Still spongy brakes...


I disconnected the power bleeder and instead hooked up a good size vacuum pump to the hose. When hooking up the vacuum pump I accidentally broke the gauge so I couldn't watch how much vacuum I was pulling, but I let is run for 40-60 minutes while tapping the brake calipers, line mounts, master cylinder, proportioning valve and shook the flex lines around while pulling vacuum. The taping did produce bubbles. I also tried slowly pumping the pedal and even running the engine while under vacuum.

Although I think this got air out, it did not resolve the problem or even seem to make it much better....

 

[CWeaver]

Sunday: Today I talked to Mechanic friend who said he once had a 96' 1 ton that did this and had to install two master cylinders before it was resolved. So I bought another new MC and installed it on the truck, but this time a friend loaned me a little kit with the thread in plastic plugs and hoses to "bench bleed" the master on the truck the old school way. I remember when this is what MCs came with to blead them. He said this way you can't compress the piston to far into the MC and hurt it when doing it on the truck vs, on the bench. I S L O W L Y pumped the brake pedal until the MC was blead and there were no more bubbles produced. I then hooked up the system and power blead the lines at all 4 wheels again, but I still have the same pedal feel...

With the engine still running I decided to do the test again.... I hate to do it, but I grabbed the vice grips and went to the top section of the front flex hoses (where the lines have double thick padding) and clamped the lines to close the front brakes off. I then let the engine run a moment, and tried the brakes, the pedal was now only about a inch to low- if that and drops super slowly... This sure seems to point to the front brakes.... ???? The new rebuilt Calipers and New Flex Hoses from Advanced Auto.

The hoses were only $19.99 and $24.99 with a business account, could the hoses just be crap (expanding that much) right out of the bag? It seems unlikely they would be that bad when new? Especially since there is zero load on them now. If so I guess I could go to braided hoses.... or is there really air in my lines somewhere.....

 

[CharlieFoxtrot]

I'm sure my recent posts were included in the search results you read, and I still don't have an answer either.

Thoughts:

Always bench bleed a MC. I don't know if it always matters, but if you don't do it, you won't know if that's your problem. I used a big syringe from NAPA to bench bleed and it was AWESOME! I will never do it any other way again. Part # NMC P105551MCB or similar elsewhere.

Adjust your rear brakes often, and do it before starting this job.

While multiple junk master cylinders are a possibility, IMO if you don't find fluid inside the booster, that makes a bad MC less likely. You can confirm your MC is good by blocking both outlet ports with brass fittings (you'll need a well-stocked parts store and a helpful counterman), then pushing and holding the pedal. If it stays hard, you have no MC leakage.

While pressure bleeding, open every fitting, in top-to-bottom order at the MC, prop valve, and ABS (if equipped).

If you have used a vacuum bleeder, follow up with a pressure bleeder. Any sort of bleeding machine can move much more fluid than you can by pushing the pedal and can quickly remove air pockets that you'd never get out with the pedal.

The ABS, when it's not activated during brake lockup, does not have any effect on the system. So my concern about air trapped in the ABS causing my soft pedal was unwarranted.

IMO, once you have replaced the rubber hoses with new rubber, you have removed nearly all the softness that lines can cause. I would not be concerned with braided now.

My pedal isn't as firm as it should be, but my truck is much better than it was, and this is what I have learned or the opinions I have formed in the process.

Good luck!
kevin

 

[Missouri Mule]

Does the brake pedal stay firm when you first start driving and then goes soft and to the floor. If so your rubber brake lines going to the front discs need to replaced.
When the high pressure rubber brake lines get old the inside collaspes when the brake fluid gets hot causing the brake fluid to keep appling pressure the the front discs.

I had this happen to my Moose (Freightliner) I had to have all my high pressure lines replaced (hydraulic disc all the way around) it cost me a fortune but i did front and back at different times.

 

[CWeaver]

I don't start driving because when I brake the pedal goes right to the floor, but I've already replaced the flex lines....

After talking to another mechanic last weekend we decided to check the proportioning valve...... after dissecting I decided to replace it. I tried ordering one and found out they are no longer available. I got another valve from a boneyard (94 Ram 2500 gas) truck, and installed it. I have bleed the brakes several times with no improvement.... Any new ideas?

 

[petersonj]

Any new ideas?

Since this has not been mentioned, but is possible, I thought I would throw it out there. Over the years I have known some Dodge vehicles to have front brake calipers that could be physically mounted on either side of the front axle. It they were mounted on the incorrect side, the bleeder valves would be located on the bottom of the caliper. In this case, it is impossible to remove all of the air.

So, are the bleeder valves on top?

- John

 

[CWeaver]

Yeah bleeders are on top, we even tried leveling the truck so it has a factory style rake to it (a touch nose down).

Last night I tried reverse bleeding the front end. Used the power bleeder to push about a liter and 1/2 af fluid up each front line to master to push any air out. Started with 15 psi and then went to 20, did not seem to help (actually pedal feels softer) May do the rear today just to try it. View attachment 95867

 

[CWeaver]

Catching fluid from MC at top......

 

[Missouri Mule]

Are you loosing brake fluid?

 

[CWeaver]

I don't believe I'm losing any brake fluid anywhere, but it's had to say. It's been humid and rainy for weeks so I've been bleeding with fresh brake fluid once or maybe twice and then discardin it. I've already used gallons of the stuff on this project.

Yesterday I reverse bleed the rear brakes and the pedal feel was no better. Then I set up the power bleeder the normal way and bleed the power front brakes. The pedal feel was firmer, but not right. Today I'll power bleed it normally a couple times.

 

[CWeaver]

When I stopped working yesterday midafternoon 2ish? I left the Motive pressure bleeder pressured up, just went out today at a little after 10AM and it's still got 10psi. That would suggest no big leaks I guess...

The pressure bleeder is limmeted by how well it seals on the top of the plastic MC.


Rebleed once so far, no go....

 

[fest3er]

You've done everything, replaced everything usually associated with soft pedal. It's beginning to sound like something is misaligned, as though the four brakes do not engage at the same time. Or the rear ABS is permanently engaged.

• Have you adjusted the rear brakes out so they provide a little resistance? Until I did this with mine, most braking was from the front. (Come to think of it, my front brakes seem to be holding out better now that the rear brakes are doing more work).
• Have you verified that the brakes (shoes and pads) apply evenly and 'squarely'?
• Have you verified that the height-sensing adjuster between the rear axle and the frame works correctly? If set wrong, it could adversely affect rear braking.
• Have you *definitely* inspected the ABS system and verified that it operates correctly, that it does, in fact, properly disengage? When ABS engages on many of these 2nd gen trucks, 90% of braking is eliminated. It is most disconcerting; one moment the truck is slowing rapidly, and the next moment you're standing on the pedal with it on the floor and the truck is barely slowing down. (I'm surprised the NHTSA never got involved and that there was never a recall.)

 

[Missouri Mule]

Reading the fsm it stated that a master cylinder leaking internally could cause pedal to go down. But you said you replaced master cylinder.

Reading over your first post did you empty the power brake booster of brake fluid?

 

[CharlieFoxtrot]

Where are you bleeding from? Just the bleed screws on the caliper? The biggest inprovement I got in my pedal came from pressure bleeding and opening the outlet fittings on the MC, then the inlet fittings on the prop valve, then the outlet fittings on the prop valve, then the inlet fittings on the ABS, then the outlet fittings on the ABS, then the wheels. I had a lot of air in the prop valve!

What kind of pressure bleeder are you using? I have the Motive pump bleeder with their big aluminum plate MC top, and I can't get it to stop leaking fluid out of the top of the reservoir while I bleed. It's messy and wasteful. Would love to know if there's a secret...

 

[CWeaver]

What kind of pressure bleeder are you using? I have the Motive pump bleeder with their big aluminum plate MC top, and I can't get it to stop leaking fluid out of the top of the reservoir while I bleed. It's messy and wasteful. Would love to know if there's a secret...

I'm using a Old Motive Pressure bleeder with the Plastic top plate. It didn't seal well so I cut a metal plate to go on top, then put a strip of wood on the top center (oriented to the side that leaked) and added a welding clamp to add more even pressure on the top. Adding a top clamp or two really helps!