Soft brake pedal

[Ozymandias]

Interesting. So, it looks like your brake pedal operates the same as @Ozymandias. Where the heck is the brake fluid going?! Is this supposed to be normal brake pedal operation? It sure doesn't seem like it should operate that way - but, who knows.

- John

I've no idea right now as I proved that it isn't going into the ABS reservoirs. They stay empty.

The behavior is so weird pressure wise. You push the pedal with a rising force of your leg, so far so good, operates like we expect it. But at a certain point you reach a force that just let the pedal plummet to the floor without raising the force of your leg.

Sidenote here, I checked the pedal assembly too, works as desired. The brake rod moves fine into the booster assembly.

 

[User113]

The behavior is so weird pressure wise. You push the pedal with a rising force of your leg, so far so good, operates like we expect it. But at a certain point you reach a force that just let the pedal plummet to the floor without raising the force of your leg.

Ozzy, that would scare the heck out of me. If you make the pedal sink to the floor on a steep incline (or with the truck in "D") does it begin to roll?

I don't have the updated PS Pump in mine, I'll test it tomorrow.

 

[Ozymandias]

No it holds fine, don't misunderstand me it does not "sink" like with a broken MC or so, steady pressure keeps it at its level. Reread my last post, it explains.
It's a non-linear behavior the pedal. It acts more like an air-brake of a semi then a hydraulic system.

 

[User113]

I tested my brake pedal last night. To the best of my knowledge, I still have the original power steering pump, etc. My truck has 300K miles on it, so I don't have any idea about the brake lines, calipers or master cylinder either, all I know is that I have not changed them since 2014.

Engine off, it pumps up hard and firm, third pump probably only moves 2-3 cm.

Engine on, it moves significantly farther down. Three pumps and it is probably down 8-10 cm. But it remains firm at that point even with heavy pressure. I can make it bounce at the end of travel, so it is not traveling far enough to touch the floor or any other obstruction.

 

[User113]

It would be interesting to put a brake pressure gauge on it to see what is happening to the pressure when your pedal bottoms out.

 

[Ozymandias]

I tested my brake pedal last night. To the best of my knowledge, I still have the original power steering pump, etc. My truck has 300K miles on it, so I don't have any idea about the brake lines, calipers or master cylinder either, all I know is that I have not changed them since 2014.

Engine off, it pumps up hard and firm, third pump probably only moves 2-3 cm.

Engine on, it moves significantly farther down. Three pumps and it is probably down 8-10 cm. But it remains firm at that point even with heavy pressure. I can make it bounce at the end of travel, so it is not traveling far enough to touch the floor or any other obstruction.

Thank you for your input, I think that is like mine behaved with the old PS pump. But that's years ago and my memory in this case could be wrong.

The idea with the pressure gauge is a good one. I'll dive into that and do my research.

 

[CVR222NV]

Thanks you very much, so I've a second input. Yours behave the same as mine.
Let's see if we get more people to walk out to their truck and fo the test.

In the end I spent a 1000$ for fixing what's not broken.

Well I'll be darned! Finally got my truck back home and decided to test it and with the truck off the brake pedal travels a couple of inches and holds hard. With the truck running and constant pressure to the pedal it goes straight to the floor. My power steering pump is out of a 2009 truck. I'm thinking this might be normal.

 

[Ozymandias]

Well I'll be darned! Finally got my truck back home and decided to test it and with the truck off the brake pedal travels a couple of inches and holds hard. With the truck running and constant pressure to the pedal it goes straight to the floor. My power steering pump is out of a 2009 truck. I'm thinking this might be normal.

Thank you for testing, with every input here the picture clears up a bit.
For now it looks like RAM gave us an easteregg with the upgraded pump and it's slightly higher pressure.
Let's see if more people are willing to walk out their trucks and check.

 

[Ozymandias]

@sag2 question to a pro, is there any information out from RAM that they mention in connection with the upgrade of the PS pump? Additional parts that needs to be changed or something like a TSB or what so ever? Workshop instructions? Anything?

 

[CVR222NV]

Thank you for testing, with every input here the picture clears up a bit.
For now it looks like RAM gave us an easteregg with the upgraded pump and it's slightly higher pressure.
Let's see if more people are willing to walk out their trucks and check.

Ozy, I had the SIL check his 2007 5.9 stock truck and his pedal goes down and stops hard about half way both running and not running. Is the only difference the power steering pump and if so why would that cause this issue?

 

[petersonj]

It seems to me that the only way the brake pedal can continue down to the floor is if there is a mechanical issue (which seems very unlikely), or hydraulic brake fluid is going somewhere that is either intended or unintended.

@Ozymandias mentioned that he checked the accumulators in the hydraulic part of the ABS and saw no fluid entering during the pedal application to the floor. So, is it possible there is a regulating / relief valve inside the master cylinder? It doesn't seem likely, but it is possible. If there is one, could it be possible that the two different power steering pumps operate at different pressures and the higher pressure one overrides the that regulating / relief valve?

Sure would be interesting to find out just what is going on.

- John

 

[Ozymandias]

Ozy, I had the SIL check his 2007 5.9 stock truck and his pedal goes down and stops hard about half way both running and not running. Is the only difference the power steering pump and if so why would that cause this issue?

2007 has a different MC if I remember correctly. Also the HB is slightly different.

I didn't disassembling the old MC, I might should have..