Auto Park Brake converted to Manual Lever

[the_dieter]

Tropical:

The system that I envision would be far less expensive and would have no pull cables or the need to crawl under the coach to release the brake.

Best regards, Jack

Ps: I say "envision" because I am retired and have no intention of producing a system or criticism for anyone who works to replace the existing system.

[tropical36]

Originally Posted by the_dieter

Tropical:

The system that I envision would be far less expensive and would have no pull cables or the need to crawl under the coach to release the brake.

Best regards, Jack

Ps: I say "envision" because I am retired and have no intention of producing a system or criticism for anyone who works to replace the existing system.

Eventually they will all disappear. Either the rig or the system, just as you have done with your version. As for me, I have no plans so far, other than to keep it in repair and you must admit that it's great when not giving you any problems.
The later J72 AP's seem to be doing well and pretty much problem free, so there's another possible conversion that you don't hear much about. I mean there's so much hype, that all you have to do, is mention AP and no one even asks, which version. Most will also assume that a RGS is always present with these different systems.
As for envisions and producing, I don't even know how Brazel's does it. I mean anytime you take on such a feat as this, you also take on a huge liability as well.

[max49]

Great information guys, thanks. Can that actuator rod be pried or winched back in case it won't come out on it's own long enough to get the angle iron into place?

[iRV4FUN]

Great Thread -- for a hugh problem that has yet to get the attention of the NHTSA! I wish GRAINGER carried the RGS replacement. If they did, 80% of the system problems would go away.

The RGS is the part that needs to be upgraded. Why can't we find a better switch? The NHTSA could make this happen! We are so lucky nobody has been killed or killed someone else due to a known defect

[iRV4FUN]

Here’s a few bits and pieces of the RGS:

The thread is a 3/8 24 - - a straight thread, not tapered like a pipe thread.
The switch closes at 1200 psi and opens at 1600 psi

[the_dieter]

Interesting that the pressure is over 10 times as high as air brake pressure. I have designed pressure switches for Aerospace applications but they were expensive and in low quantity production. This one needs to be inexpensive, not cheap like the corrent one.
To get approved, the 90 year old, 90 pound lady would have to be able to crawl under the coach to release the brake. (Bad joke)

Best regards, Jack

[tropical36]

In response to some of the questions and issues presented here, mackpeteno says he can release his brake in about 10 minutes using a ratchet type strapping tool. I have one that is cable only on board and will keep it in mind. This is a lot of force in that direction and pulling on the AP actuator cable, but may allow one to insert the angle iron cage.

Not much chance of NHTSA attention here, as there is next to none, any real evidence of bodily harm associated with the AP. Just a lot of aggravation.

As for the RGS, I've never seen one that wasn't OEM, no matter where you got it or what you paid for it. Question is, who made the OEM and doubtful that GM made their own. No one else is going to make a better one for after market as there isn't any real money in such an adventure. I even talked to some pressure sw. manufactures to see if they had anything that would meet the specs. and it was always with some interest and then never hearing from them again. For the RGS's odd thread pattern, a machined brass adapter would be in order and not all that hard to make, if another sw. can be found and if it's expensive of aerospace quality, so be it.

As for the pump pressure, it is very high and the reason that the RGS has a reputation for eventually bursting when it's failure is ignored, causing a loss of fluid and lockup. This is required for collapsing the heavy spring that actuates the brake by default, making it fail safe with proper adjustment and parts that aren't worn out.

[the_dieter]

Being the curious type, I wanted to learn more about air brakes. There is a huge amount of info on the Internet.

I had to learn that what I though were "spring loaded diaphragms" are called "spring brake cylinders "...go figure. There are a bazillion of off the shelf at the very low price as I expected. This is to be expected because of the billions in service. They operate at around 120 psi which is about as much as a two iiter plastic pop bottle will hold, not that I would use one.

Using air really lowers the stress on the components compared to hydraulic and the resultant cost.

Now, I have to get off this cotton-picking computer and finish my electrical wiring...the grass is starting to green up.

Best regards, Jack

PS: I love my Kindle Fire!

[the_dieter]

Tropical:

They could have cut the pressure in half by simply doubling the piston area (not diameter). Since the piston is not inside the spring, that would have been simple. By the way, the operating pressure of the system may be pushing the limits of the gear type pump.

Best regards, Jack

[the_dieter]

I couldn’t stop thinking about the question posed by iRV4Fun about the possibility of replacing the RGS with a better one! The figures of 1200 and 1600 PSI agree with the Workhorse Motor Home Chassis Guide for the closing and opening pressures of the affectionately named RGS.

That caused me to question why the system pressure is so high so I decided to do some fundamental calculations:

I measured the OD of the pressure cylinder and estimated the wall thickness at .250 in. This gave 2.020” OD and 1.520” ID.

The area of the piston comes out to be 1.815 square inches.

Multiplying the subject pressures times the area gives 1.815 X 1600 = 2904 lb., 1.815 X 1200 = 2178 lb.

I am missing the actual force required to compress the spring but I would be surprised if it is as much as 500 lb. which, if true, indicates that the hydraulic force is ridiculously over designed. This could be measured for assurance.

Looking at those figures led me to believe that the wall may be thicker than I had estimated so I decided to take the end cap off of the wildebeest and measure the actual wall thickness. I found that I was only off the thickness of a human hair so the above calculations are correct.

It appears to be possible to reduce the system pressure simply by substituting a pressure switch that gives say 2 times the force required to compress the spring (1000 lb. if the spring turns out to be 500 lb.).

This yields a pressure switch with 550 and 730 PSI pressure range with the same 25% dead band as the original switch. This is what I would do if I were still plagued with the RGS but I am not suggesting that anyone else should do it as this is just a flight of fancy by a retired “expert” that needs something to stimulate his mind.

Note to self, “try to find out how much force it takes to compress the spring”.

Best regards, Jack

[the_dieter]

I tried to extend the actuator rod with a pry-bar and was unable to move it. This implies that the spring installed load is far more than I or reasonable design principles would require.

Since the mechanical hand brake lever has about six-to-one ratio and from 5-10 pounds force on it will hold the coach in low and reverse, I can conclude that the force of the spring is grossly over what would be a reasonable requirement, putting unnecessary stress on all of the system, encouraging failure of the components.

Apparently a different spring would be required to be compatible with a lower system pressure...it just gets more and more complicated by an error that was made in the force requirement to operate the brake.

Note to self, "Do not attempt to disassemble the spring housing, it may be dangerous!".

Best regards, Jack

[max49]

Originally Posted by the_dieter

I tried to extend the actuator rod with a pry-bar and was unable to move it.
Best regards, Jack

I did the same thing yesterday, I had about a 3' pry bar and I was very surprised at how hard it was to move a 1/2" or less. I stopped trying because I feared the bar would slip off, or even worse if it didn't slip off , I may break something in the actuator.
I don't understand how it has the power to compress that spring but it must be pushing against the spring; not pulling on the actuator rod.
It is a great idea OUB had with the angle iron to hold it in the released position, if the actuator will work long enough to get the spacer in place.
I've been thinking about what kind of tool, or grab hook to make to go around the rod lock nut but after feeling how stiff the spring is, I'm thinking I may need my 2 T cable come along winch puller. This seems like it could do a lot of damage if not pulled straight.
I wish I could see a picture of how you can safely winch that rod out of the actuator.
The spring does set the parking brake really tight, I've been on a lot of steep boat ramps and even winching the boat on the trailer and the PB holds. So if it ever locks up on me, there's no way my 8.1 would be able to power through it.
Maybe it is way over built with lots of weak links.

[the_dieter]

Max:

Agreed that the actuator rod must be pulled straight without putting a sideload on it.

The hydraulic piston pushes in the same direction that we are trying to pry it and the spring is just super strong. And that is in the lowest load position, with the rod retracted in my case! (No hope for this puppy)

Best regards, Jack

[tropical36]

Originally Posted by the_dieter

I tried to extend the actuator rod with a pry-bar and was unable to move it. This implies that the spring installed load is far more than I or reasonable design principles would require.

Since the mechanical hand brake lever has about six-to-one ratio and from 5-10 pounds force on it will hold the coach in low and reverse, I can conclude that the force of the spring is grossly over what would be a reasonable requirement, putting unnecessary stress on all of the system, encouraging failure of the components.

Apparently a different spring would be required to be compatible with a lower system pressure...it just gets more and more complicated by an error that was made in the force requirement to operate the brake.

Note to self, "Do not attempt to disassemble the spring housing, it may be dangerous!".

Best regards, Jack

This is where that Mountain Gorilla I was speaking of comes in...
This automatic force is why a 90lb, 90yr old lady is able to apply it with the same pressure as anyone else. It also allows for a lot of fatigue down the road and in which case it'll still hold very well and that's assuming that there will be eventual fatigue.
The stress I see on the system is mostly in the high pressure lines and proven by the RGS woes and don't know how it withstands it at all. The gray sw. for the warning light is subjected to high pressure as well and they seldom go bad. Now take into account the pump itself, especially the Parker, which is next to bullet proof and proven by how many times it's been overheated and cut in and out by it's built in thermal overload. This is what happens as soon as the RGS shorts across and continues to do so (run intermittently), while the warning light is being ignored. Many will go for miles and miles before the RGS ruptures with pressures that are now out of sight, resulting in fluid reservoir loss.
Sorta reminds me of the man who fell from a building's 20th floor? As he was going by the 10th on his way down, he said, everything's OK so far.

You can disassemble all you want, as long as you do so with the brake in default on. I would probably install the AI cage, knock out the lever pin, then remove the cage before proceeding. As always, block the wheels before doing anything.