This article was not done by me (Oemy), but I thought it should be made availible for those that have the Autopark feature. All the information and photos are the work of Roger Haag AKA-oldusedbear. This article is just for information only and if you need help in solving a J71 Autopark problem you need to contact Roger by Email email@example.com or you can check out his web site www.rvautopark.com
If you Email oldusedbear please include the following in your email:
The current OEM version of Autopark (J72) is not addressed in this article. But, Roger may be able help should you have a problem. You may also what to download the J72 pdf document in the download section.
Comments from the AutoPark Library and oldusedbear
June 23, 2013
Many of the best ideas for "Living with AutoPark" show up on IRV2. Sometimes though, we see something that we don't understand, or maybe even disagree with. Sometimes we think there is simply more to be added. Our following comments are directed towards various viewpoints or information contained in this particular thread, as well as to all of us with an interest in the general subject of auto apply parking brakes. Everyone who contributes to these discussions is trying to help, and technical disagreements should not be translated into criticism of anyone for their ideas or suggestions. We apologize for the length of the following post, and hope it is found useful.
Our comments will (hopefully) be directed to contents of the thread as they serially appear. Readers can sort through the entire thread and figure out "who wrote what" if that is of interest to them, but the important thing is to kick around the ideas - - not the authors.
Remarks and conclusions:
The RGS is an interesting (at least to me) design. The choice of materials, along with pressures and temperature, no doubt doom it to failure at some point. The plastic diaphragms that are exposed to system pressure, are always deformed, hard and brittle in the failed switches we have autopsied. I'm convinced that the ravages of time, temperature, and pressure, along with polymerization of the plastic diaphragms, will almost always account for switch failure. At time of writing, you can still get a new RGS from Amazon for about thirty bucks. The longer lived and better quality pressure switches are far more expensive from what we hear. Value of the tradeoff between the lo priced and hi priced ones has got to be up to the coach owner. As a matter of technical interest, the trigger pressures of the RGS are not determined by the plastic diaphragm (s) in the RGS, but by a steel "oil can" type diaphragm. The stiffness of this steel diaphragm is what determines the switching pressures.
Our best advice based on experience to this point: Build and install your own Genie Lamp setup. Very inexpensive and can save your bacon. You would not likely care to drive a coach that didn't keep you aware of engine oil pressure or lack thereof, and potential lockup of the parking brake, should be about the next thing below that on your list of concerns. The Genie Lamp will give you a big improvement in your safety margin in that respect. Carry a spare RGS, a spare gray Light Switch (looks like the RGS but gray in color), a spare relay, and some spare ATF. Pump up your knowledge base on the parking brake system. To this end, help from the AutoPark Library continues to be available (free) from firstname.lastname@example.org
J71 - Theory of Operation
Autopark Library Misson Statement
If your AutoPark is giving you trouble, or you're afraid that it might, we will try to give you some help
The AutoPark Library is basically a collection of information. It consists of factory manuals, drawings, pictures, and papers we've written on various aspects of the system. We have some great assistance from four other forum members who help me with both general and specific problems. There is additionally a huge contribution made by many other forum members who have sent us all sorts of valuable information.
We are particularly anxious to help those who want to do their own repairs. On the other hand, if you are trying to just educate yourself, or prepare to deal with a service outlet, that's OK too. In either case, we'll do what we can.We would stress that we are in no way trying to compete with commercial repair outlets and have no financial interests in any part of the process.
In almost every case, we will need to exchange several emails to complete the diagnosis and repair. I usually check my email several times a day, so we normally respond pretty rapidly. It goes without saying that prompt replies on your part will speed up the process. Not ALL RV'ers are retired though and we understand that many of you just can't drop everything to work on the motorhome.
We surely hope that our information is accurate, but can make no guarantees to that effect. Simply stated, we will do our best to help those who ask.
Obviously, anyone who undertakes their own repairs has the responsibility for the outcome - - including considerations of safety. For those who have reservations in this regard, we strongly suggest they utilize a competent commercial service.
Patience and persistence seem to be the key words in this process. Where people are willing to "keep looking and trying," our success rate is very high. Hopefully your case will be no exception.
We always welcome comments and questions.
We'll look forward to hearing from you and helping with your AutoPark problems.
Roger - - At the AutoPark Library
Which Version Do I Have?
The purpose of this write-up is to help with the determination of "Which version do I have?"
The J71 AutoPark systems built between approximately 89, and 94, all utilize the power steering pump as a source of hydraulic pressure. They have a "PARK position" on the gearshift lever that actuates the automatic apply parking brake. Most of these units also have a manually applied foot pedal, located to the left of the steering column, that will also apply the same brake, a drum type brake located on the driveshaft right behind the transmission.
We have arbitrarily labeled this configuration, "Version I."
Within the Version I timeframe, there are a small number of units that DO NOT have the foot applied brake, but instead have a yellow knob on the dashboard that will apply the parking brake. As with all the other Version I units, the brake can also be applied by putting the shift lever into PARK. We see very few of these, and simply refer to them as "Version I with the yellow knob."
Sometime during 94, (the date is a little soft), use of the power steering as a source of hydraulic pressure was discontinued, and a dedicated pump and reservoir were added. We call these "Version II." They also have the foot pedal for application of the parking brake, as well as the PARK position on the gearshift lever.
Around 98 or 99, The current OEM took over the chassis manufacturing from Chevrolet. They discontinued the provision of the foot pedal for application of the parking brake, and went back to the "yellow knob on the dashboard." We call these "Version III (J72)."
HOW DO WE TELL WHICH VERSION WE HAVE?
All Version I systems have some rather sophisticated valves and tubing under the floorboard. We've attached pictures of these. Presence of these valves is a sure indicator of Version I.
Version II has the pump and reservoir located under the coach, on the passenger side of the transmission and slightly aft - - up against the right hand frame rail. The reservoir can be seen thru a cutout in the metal box that shields it and the other AutoPark goodies. We've attached a picture of the reservoir. If you have this reservoir, AND a foot applied parking brake pedal, you have a Version II.
Version III (J71) is on the OEM chassis. It has NO FOOT PEDAL for application of the parking brake, and instead has the yellow knob on the dashboard.
RGS - Rotten Green Switch
The following legend goes with the drawing of the RGS. This drawing is not to scale in any respect. The whole idea is to show the basic principle of how the RGS functions.
A. This is the inlet port for the pressurized ATF.B. These are pieces of some sort of plastic film that are maybe .010 of an inch thick, amber in color and look like camera film in many respects. There are two layers of this material acting as the diaphragm against which the pressure pushes. It doesn't look like it would hold 1600 psi, nor does it look like it would effectively seal between the and cap "G" and the washer "C." But it apparently does all these things up until the time it fails, causing the RGS to stay closed "switch ON." Having the ATF leak into the rest of the switch, and eventually leaking out past the electrical terminals where the RGS is connected to a push-on connector normally follow this.
The same plastic film is on both sides of the convex "oil can" diaphragm. In this application though, I think it acts more as an anti-friction device.
C. This washer, while the diagram does not properly show this, is tightly sandwiched against the amber film diaphragm. It is compressed in that position by the rolled crimp "N."
D. This piston moves to the left when the system is pressurized. This right-to- left movement is what causes the steel diaphragm "E" to "oil can" to the condition depicted by "F."
G. This is the steel outer can of the RGS. The rolled crimp "N" is what holds all the inner components (except the piston and the steel diaphragm) tightly in place.
H. This is a raised circular ridge on the inner face of the end cap "I" - - It has a very important function in that it is what the steel diaphragm "E" presses against when the piston moves to the left. The pressure from "H" is what causes "E" to "oil can" to the position shown by "F."
I. This is the other end cap, which is held in place by the rolled crimp on "G."
J. This is the bright green plastic enclosure for the switch contacts and terminals. It is held by a separately crimped aluminum sleeve - - not shown.
K. These are the two terminals exiting the RGS - - They connect to the control circuit of the AutoPark system.
L. This is the actuator rod that transfers the movement of the steel "oil can" diaphragm, to the switch. Normally, this rod is to the left, causing the switch to be ON. When the steel diaphragm "oil cans" to the right, the rod moves with it - - thus allowing the switch to open.
M. These are the switch contacts.
N. This is the rolled crimp, which keeps all the components tightly sandwiched and held in place within the RGS.
So - - when 1600 psi is applied at port "A," the amber film "B" is deflected to the left, where it pushes on the piston "D." The piston moves to the left, and presses the steel oil can diaphragm against the circular ridge "H." This causes the steel diaphragm to "oil can" to the condition depicted by "F." The actuator rod "L," moves to the right with the diaphragm, and allows the switch contacts to OPEN.
We expect that the textbook RGS failure occurs when the amber film diaphragm somehow ruptures and allows the pressurized ATF from port "A" to get past the washer "C" and into the rest of the switch. At some point in time, the fluid makes its way out past the terminals "K" and ends up on the ground.
None of this information, including the illustration, is cast in marble. It is just our best estimation at the time of writing.
RGS - Disassembled
Roger took the time to disassemble a RGS and annotate the photos.
DIY J71 Autopark Replacement
Jerry Peck from IRV2 had 3 Autopark failures and decided to fix the poor autopark design. So, he disigned a system using 12 volt DC linear actuator. So, if you are a DIY type person there is a complete "How TO" document in the Downloads section.
Link to DIY Autopark Brake Replacement.
Note - This is a fairly large PDF file (5.4 meg)
Be sure to read the disclaimer on the last page of the document before starting this project.
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