Weird issue with brake pedal feel and PS pump

[Haggar]

NIsaacs,

 

I think i am getting where you are at.  I am sorry, it is truly a problem with many of our engineering descriptions...  the language is not always robust enough...  Hydro-pnumatically the names are the same and you have to know from the system what the function is.... (and I hope we are not getting hugely technical in the fact of whether it is "flow control" or "pressure control" and some of the side arguments associated with that...) 

 

Ok  The "relief valve" you may be picturing is like on our air compressors or water heaters.  These are designed to "relive" to prevent catastrophic failure to other components in the system.  They are also there BECAUSE something unrelated to the NORMAL operation is present.  In the case of the air compressor, the pressure regulator could fail allowing the compressor to keep pumping.  In the hot water system, normal system pressure is supplied by the city, county or your well pump. If the heating elements stick on and don't stop heating at the right temperature, we could boil the water, and the resultant volume expansion is catastrophic.  (our waste gates on the turbos,  burst discs on a supercharger  etc.)    In all of these cases, system pressure is set by something else in the system.  (notice almost all the things we just talked about were compressible fluids....)

 

The "relief valve" on our power steering pumps, SETS the system pressure.  (and should more properly be called a "pressure regulating valve"... but there are other reasons it is not called this....)  If you can visualize it,  our PS positive displacement pump output is directly connected to the "relief valve".   When you start the car, the power steering pump immediately begins pumping fluid.  Whether we have a "pressure relief valve" or not, the pump would build pressure.   Since (in our case) we are not presently using any of the pressure (our foot in NOT on the brake, nor are we turning the steering) the pump would very quickly dead-head. (dead-head is the point where there is no flow and usually result in maximum system pressure...)  Since power steering fluid is relatively in-compressible, and the efficiency of the vane pump fairly high, the pump would completely stall (lock up in this case) causing belt slippage break things etc.    Since we have this "relief valve" "in line with" the hose that feeds the presently closed valves ( brakes not being used, steering not being turned) the pump does not stall, but all the fluid is forced through the restrictions and returned to the reservoir.

 

When we then step on our brakes and hold, some fluid is allowed to fill the hydroboost force multiplication reservoir.  the system pressure will immediately drop (we have opened a "large" cavity of low pressure fluid) the "relief valve" will close and the pump pressure goes to the hydroboost and it recieves the pressure.  the pressure builds until the hydroboost reservoir is at system pressure and the "relief valve" opens again, recirculating fluid into the pump reservoir, and maintaining system pressure.     The same cycle happens when you turn the steering wheel.  As soon as you begin turning the wheel, system pressure drops and actually stays dropped until the wheel quits moving, or the flow of the pump is greater than the speed of turning the wheel.  (any of you/us guys with big tires notice that when in a bind you can turn your tires in little spurts?  or you lose your turning strength momentarily when you touch the brakes?  or speed up the engine and it will turn?) 

 

Edit:   So to answer your last question.  Yes.  The pressure lines at the exit of our pump all the way to the hydroboost then to the power steering sector are at a pressure ( I hesistate to says it is 1500psi at idle without checking.... but it is at what pressure the PS pump can make at the speed (idle) that it is running.)    system flows and heads make diffferences in the actual pressures, but your pump starts pulling Horsepower the minute the engine is on.

 

I hope this helps!

 

Hag

 

 

Edited August 29, 2018 by Haggar
better direct answer to the question

[Mopar1973Man]

@Haggar that was a wonderful explanation of the power steering system...Could I get you to post this in the 2nd Gen articles, please!?

[NIsaacs]

Hag, thank you again, that is an amazing description. So the way I understand the pump description, it is always pumping against the relief valve and is using power? Is this type of hydraulic system (power steering) a unique system differing from other hydraulic systems? If this were the case, a large system would not allow the engine to even turn over/start. For example a log splitter.

 

I just went on a quick 3 mile round trip to load my dump trailer, slow 1st gear road and let it idle while I unloaded. I checked temps on the system. The pump was 135*, hydro boost 135, lines 105 and the gear box was 114....interesting.

 

 

[Mopar1973Man]

2 hours ago, Haggar said:

(any of you/us guys with big tires notice that when in a bind you can turn your tires in little spurts?  or you lose your turning strength momentarily when you touch the brakes?  or speed up the engine and it will turn?) 

 

Another great example of the impact of larger tires and leverage forces it takes to overcome bigger wheels. Since work is going to show up as heat this one reason I don't have these issues with heat and fluid breakdown since I ditched the 265's long ago and dropped to 235's. Now here soon I'll be dropping the 235's (31.7") for 245's (30.5") reducing the leverage forces even more. 

[KATOOM]

FANTASTIC discussion.....!  This is what these forums should be for, not arguing.

 

Also, I have more to add to my thread in regards to the hydroboost and brakes.  The cooler is clearly helping as the hydroboost lines are staying much cooler.  Nice...

 

But I need everyone to put on their thinking caps one more time.  Remember, the initial reason I started the thread was because I was concerned about the "feedback feel" within the brake pedal and described it as a slight shudder.  In saying that, this is not an accurate description because what it truly is should be described as a slight "bump" in the initial pedal movement.  Almost as if theres a small gap between the hydroboost rod and the master cylinder rod.  Then as I hit the brakes abruptly the gap is noticeable in the form of a bump in the pedal movement.  NOTE: It doesnt happen if I depress the pedal in a easy normal braking fashion.  ONLY if I hit the brakes more abruptly.  And it typically will only do it during that initial braking event, not repeatedly.

 

OK, now hopefully you're all understanding what I'm feeling in the pedal...because I also noticed when I jacked up the front axle to allow easy unrestricted movement of the tires while turning the tires lock to lock bleeding the hydroboost system, the tires were more difficult to spin by hand than I remember.  Thinking this may have been because its was sitting for weeks and I was messing with the brakes a lot while its been sitting, I looked passed this as an issue.  Well maybe I should revisit it because I took some laser temp readings on the rotors while driving over the past couple days and it seems that the drivers side is consistently running about 25* hotter than the passenger side.  I know thats not much of anything in regards to disc brake temperatures but still shows that there's slightly more drag on that side.  I even jacked the axle off the ground again and compared each side and sure enough the passenger side is slightly easier to spin by hand.  Not a whole lot but noticeable.

 

So...have I noticed something related?  Because I'm very curious as to what this bump in the brake pedal is.  There is no braking pull to either side, and they work fantastic too.  I'm stumped and wondering if there's something else going on in the master cylinder or possibly the ABS system which would cause a feedback issue in the brake pedal or allow a caliper to not release completely.  NOTE: I do not have the 4 wheel ABS either.  Just the rear axle.

 

I'm sure this isnt anything anyone will have an answer for either so I wont be disappointed if there's a lot of shoulder shrugging...

[Haggar]

Great pictures!

 

Yes, in the wood splitter hydraulic circuit, when the spool is in the center position, any flow from the power unit returns directly to tank.  If you watched the pressure gauge shown, it would only show a few PSI.  Just the resistance of the flow in the tubing and the spool to return the fluid to the tank.

 

In our system there is this in the bottom of the pump....

 

The "fluid under pressure" is the pump output.  This circuit allows the "pump output"  to cycle back to the "pump inlet" under certain pressure and flow conditions.  (but at the cost of small passages causing heat from work)  But all the green dots coming out of the "pressure hose fitting" are under pressure when the pump is turning (engine is rotating)

 

This is a parasitic loss.  Probably a 1/4 to 1/2 hp at idle and up to 5 or 6 hp max.  (engine full speed etc)   This is why there has been a move to "electric steering"...  cafe standards don't look at battery charge during the driving cycle.  its just like VW, our car design is being forced by the almighty mileage standard and the numbers it puts up....  (is electric steering better safer?  are electric air conditioning compressors better safer?)   they can probably store more electricity so the steering works anytime, but only recharge the battery when there is excess energy available (during a coasting section etc.) 

 

anyway  that's my $0.02.  

 

Hag

 

 

Katoom,

 

Interesting.   Well you could have one wheel bearing dragging a bit more than the other.  another thing to not forget, our Dodges are NOTORIOUS for internal failure of the front flexible brake lines, causing a resistance in the return flow.   I have on my truck, and a couple friends trucks, experienced this.  (of course we didn't catch it early as you may have...)  

 

I have a couple thoughts on your "slackness" under certain conditions.  (I was truly hoping you find a bit of slop in the input rod or something.)   I will try to orient those thoughts in a semi readable form.  (while stream of consciousness writing is fun, it is really hard for someone else to follow....)

 

Hag

 

Edited August 29, 2018 by Haggar
added front flexible to Katoom section

[KATOOM]

Looking forward to hearing what you conjure up...

 

In regards to the brake lines, if thats the problem, does anyone have a source fro SS braided lines?

[NIsaacs]

On ‎8‎/‎27‎/‎2018 at 5:10 AM, Haggar said:

Yes our PS  systems get hot fast.  The reason is, it is always making pressure.  It is not demand sensitive.  So the pump is always fully loaded.  When there is no mechanical work to be done, it is all that horsepower going into heat.  (the pumped fluid has to go through the small orifice in the pressure relief constantly.)

 

I am going to add a PS cooler soon.  I have a manual transmission, so the area Not occupied by a transmission cooler is the perfect spot for me.  I am going to use the oil cooler from a Ford truck.  It is not perfect.  As I am going to add it to the return side of the power steering.  So my cooling will only be when the truck is being steered.  long idles, it won't cool.  (most of the factory systems worked this way, on the return line.  It is the simplest place, as the pressures are very low.)

Hag 

 

 

Thanks for the excellent flow diagram...why couldn't I find it, I have been all over researching this conversation, lol

 

I am still having a hard time wrapping my head around the above quotes. So there is no fluid flow from and to the pump when there is no input on the brake or steering? That the return line has no flow when the system is at rest so to speak? That the brake booster and gear box spools block all the flow until there is input? That the pressure line is pressured up at all times and the relief valve is reliving at all times so the pump can turn without locking up?

 

On my old mid 70's Fords with a belt drive pump, any time the belt got too loose it would squeal/stop turning when you turned the wheel. Is that a little different system than our Dodges?

 

Thanks again, Nick 

[Mopar1973Man]

4 hours ago, KATOOM said:

what it truly is should be described as a slight "bump" in the initial pedal movement.

 

This could be an ABS function kicking in quickly. So if the brakes are dragging a bit on one side then there would be a possible offset of left to right speed signals. Which the ABS might be jumping and bumping the electric pump to offset the left to right pressures to keep even braking. I would break down the calipers and inspect them. It's possible the pistons are caked with brake fluid and binding up. With the seals out the piston should fall to the bottom of the cylinder without being pushed. If they are hanging the pistons are caked with brake fluid. You can replace the pistons or just lightly sand them with fine grit sandpaper to get them back to size. 

[KATOOM]

1 minute ago, Mopar1973Man said:

 

This could be an ABS function kicking in quickly. So if the brakes are dragging a bit on one side then there would be a possible offset of left to right speed signals. Which the ABS might be jumping and bumping the electric pump to offset the left to right pressures to keep even braking. I would break down the calipers and inspect them. It's possible the pistons are caked with brake fluid and binding up. With the seals out the piston should fall to the bottom of the cylinder without being pushed. If they are hanging the pistons are caked with brake fluid. You can replace the pistons or just lightly sand them with fine grit sandpaper to get them back to size. 

 

I may try that but I think I'm going to order some SS brake lines first.  They cant hurt and its possible the drivers side rubber line is compromising return fluid flow.  Also, I dont have the 4 wheel ABS so the system couldnt know if either front is not working correctly.

[Mopar1973Man]

5 minutes ago, KATOOM said:

Also, I dont have the 4 wheel ABS so the system couldnt know if either front is not working correctly.

 

So you got the RWAL which is just going to guard the rear axle has no function on the front axle. ABS system doesn't care if the brakes are working or not it all based on speed signal and rate of change of the speed signals. In a nutshell as soon as the switch is closed for the brakes the ABS computer is monitoring the speed sensor(s) for a balanced change of speed. 

 

5 minutes ago, KATOOM said:

may try that but I think I'm going to order some SS brake lines first.  They cant hurt and its possible the drivers side rubber line is compromising return fluid flow.

 

The only reason you would have any line issues is that your brake fluid has degraded from lack of fluid changes. As brake fluid is hygroscopic which means it absorbs water from the air. As the moisture is absorbed by the brake fluid the boiling point falls quickly as well. Being water has oxygen in it then it has the ability to oxidize metal parts and degrade the rubber parts. This is why brake fluid turns dark to black in color. 

[Haggar]

Nissacs,

 

Here is a great article I found.   It has the best drawings for how the hydroboost control valve position moves and what ports are exposed.

http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/

 

In the hydroboost, the control valve blocks the return (but keeps the pump input connected to the power steering gear)  so there is no return during "no brake" operation other than the leak around the control valve.  (this means that a leak in the control valve CANNOT self apply the brakes....) 

 

It is hard to imagine, if you have not seen a system like this.  Otherwise it is similar to some of the more simple hydraulic systems, it is more a function of system response time. 

 

Our steering gear works similarly.  The control valve does not apply power to help turn one direction or the other until it is told to.

 

There will be "some" return flow.  These valves leak by a little bit internally.

 

HTH

Hag

[Mopar1973Man]

Right out that article... 

http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/

 

Quote

Power Steering Flush
In addition to requiring the correct pressure, it is also critical that the fluid be clean. The tolerances in the moving parts inside the hydro-boost are such that only a small amount of contaminates can cause a malfunction. This is especially true of the spool valve. The tolerances necessary to form a metal-to-metal seal are quite small and any contaminates or tarnish buildup can prevent smooth operation of the spool valve. Since the spool valve controls the flow of fluid into and out of the power chamber, it is critical it functions properly.

2

 

[KATOOM]

OK, classroom comparison...  Here's a short short clip of what my brake pedal feels like when the engine is off.  You can clearly hear and see the movement which seems like there's two rods not touching and the gap is recognizable.  Does yours do this with the engine OFF?  I'll be checking again today with the engine ON but just wanted to get this out in the thread.

 

https://www.youtube.com/watch?v=glNGhUoRqMo&feature=youtu.be

[Mopar1973Man]

No. Mine doesn't do that at all.

[KATOOM]

Update, I tested with the engine running and the slack is pretty much all but gone.  So I cant explain whether or not thats simply the hydroboost rod not returning as fast as normal due to the lack of hydraulic pressure or if there's something else going on I havent figured out yet.

 

Also, crisis averted with the dragging caliper too.  Last night I took the front brakes apart and cleaned things up.  Cycled the calipers with no pads and greased up the slide pins.  Put it all back together and they work so good its silly...  Not only can I spin the tires almost completely free of rotational drag but the temperature of the rotors is much much cooler.  So...lesson learned that even though you're not daily driving your vehicle, they still need attention.

[dripley]

 Mine has the little play like yours in in the vid and is gone with engine on.  Engine off my pedal travels like yours but maybe not quite as far.

 The only thing holding the pedal up is the rod from the hydroboost must be a little play in there that shows up without hydraulic pressure maybe???

 

[Mopar1973Man]

3 hours ago, KATOOM said:

Also, crisis averted with the dragging caliper too.  Last night I took the front brakes apart and cleaned things up.  Cycled the calipers with no pads and greased up the slide pins.  Put it all back together and they work so good its silly...  Not only can I spin the tires almost completely free of rotational drag but the temperature of the rotors is much much cooler.  So...lesson learned that even though you're not daily driving your vehicle, they still need attention

 

That's a project I've got to do in the near future before winter hit and lube the slide pins and check the piston operation. I've replaced my rear calipers last winter because of a weeping brake fluid issue past the piston seals. Not to mention the rust really took hold on the rear calipers. 

 

Might have to check mine on the way home with a seat of the pants feel with my finger test for warmth or dragging issues. Might be a good idea with all the miles I put down.

[NIsaacs]

7 hours ago, Haggar said:

Nissacs,.

There will be "some" return flow.  These valves leak by a little bit internally.

HTH

Hag

Thank you for the link, I saved it!

 

Just did an install of a power steering cooler, it is a little large but I had it new on the shelf. I bought it for my old Ford (auto tranny) and then bought a new Dodge instead, (1991) so it has been on the shelf a long time.

 

I also wanted to check return flow...on my truck, with the steering box return line pointed at my oil drain pan, I had my wife start the truck. The flow was massive and emptied the reservoir instantly. Granted, it only holds about a pint, but in about 2 seconds the fluid turned to foamy air. If I remember right, when I would change the fluid it only required a little less than a quart. The system now holds 1.250 quarts, a good thing. Here are a couple of pictures.

[KATOOM]

2 hours ago, NIsaacs said:

Just did an install of a power steering cooler, it is a little large but I had it new on the shelf.

 

What, are you trying to show me up with a "size matters".....

 

Dont forget to post some temperature readings in relation to ambient temperature when you get a chance.  I'm curious to see how much cooler yours is.