J71 Autopark

1. Autopark Library Mission Statement 2. Which Version Do I Have?
3. Rotten Green Switch (RGS) 4. RGS Disassembled
5. DIY J71 Autopark Replacement

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 oldusedbear@oemys-performance.com or you can check out his web site www.rvautopark.com

If you Email oldusedbear please include the following in your email:

  1. Your email address. This is important in cases were you are using and alternate Email address. IE - Your using you moms computer.
  2. Year, Make & Model of your RV. This is important as he needs to ID the version of Autopark you have.
  3. Your forum ID. IE - RV.net=rvonthego or IRV2.com=gorving
  4. A discription of the problem as best you can describe it.
  5. A phone number.. Land line and/or cell. Normally this is not necessary but there are times when it is the only way.

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.

  1. "There is no pressure relief on the pump." BOTH the Parker pumps and the MTE pumps DO HAVE pressure relief valves. The pressures to which they are set, may be questionable, but both pumps do have these valves. Pictures and info available to those interested.
  2. While not discussed in the thread, the Parker pump additionally has a thermal safety switch on the pump motor. It will shut off the motor if the pump is stalling. It automatically resets after a short interval. The MTE pump does NOT have such protection to the best of our knowledge. Additionally, the Parker has a thermal relief valve. We have lots of documentation showing that the thermal motor switch works. We don't know much about the thermal valve, but know it is indeed there.
  3. In our opinion, the likelyhood of twisting a motor shaft off, is extremely low. We have never seen that happen, but that does not mean it is impossible. We HAVE seen failure of the little coupling that connects the pump to the motor. They are pretty dinky, and have been intentionally hardened to absorb the mechanical punishment of use. I'd guess that some have been OVER hardened to the point of becoming brittle. When we make replacements for these, we harden them first, then draw down some of the hardness so they are hopefully tough, but not brittle. I've broken a couple of OEM ones while changing out bad motors. The motor torque is a long way from being awesome - - or capable of twisting off the ~ 5/16 shaft - - just my opinion.
  4. "It will fail at around 2300 psi." Referring to the RGS. Possibly true, but the system will not ever get to 2300 psi UNLESS the RGS has already failed. Normal working pressure (while you are going down the road) is going to be less than 1600 psi if the RGS is still functioning as designed. The RGS will shut off the pump at 1600 psi, but in the fraction of a second that it takes the one-way poppet valve to close, the pressure will drop some. So, the system exposure to 1600 psi is very brief. This all translates into RGS failure at something less than 1600 psi most actual cases.
  5. "The worst case is you will blow the fuse etc." The fuse in question is a fusible link - - about 60 amp rating in most cases. We've never seen or heard of one blowing. I think we would have heard because the damned thing is usually hidden and hard to find. We've seen the relays burn up on a regular basis, and even a few motors become totally toasted (not many Parker motors, mostly MTE because THEY lack the thermal protectors). In the Parker motors, we know of several where the thermal protector has burned up - - luckily, they can usually be replaced at a fraction of new motor cost. The autopark control circuit fuse is a whole different subject. It does NOT blow directly as a result of motor issues. The biggest offender is the Light Switch (mounted on a tee fitting at the back of the actuator). Light Switches are quite similar to the RGS in principle, BUT they are also prone to internally shorting to ground - - which the RGS almost never does. This toasts the control circuit fuse and the parking brake immediately applies. EVERYONE, should locate their fuse for this circuit and carry spares. The shorted Light Switch can simply be disconnected (electrically) and you can continue driving after fuse replacement. The Light Switch can be replaced at your convenience later.The control circuit fuse will also pop from a shorted solenoid coil. In this case, you disconnect the coil, and also disconnect the cable to the parking brake drum. You'll be chocking your wheels until you can repair the solenoid situation. Fuse replacement again necessary to keep the control circuit operating.
  6. "I installed a sun brand cart relief, jump the RGS to force the pump to run etc." The RGS will 99 percent of the time fail "locked on with the pump running or trying to run." To meaningfully "jump" the RGS, it will have to be first disconnected - - which means you will be under the coach to do this if your rig is a mid-94 to mid-2001 year model. On mid - 2001 and later coaches equipped with J 71, the pump will be up front under the utility hood - - much easier to reach. If you're gonna have to crawl under the rig, you might as well take an additional two minutes or so to replace the RGS - - Carrying a spare should be just about mandatory - - again my opinion. Manual switching of the pump involves many considerations - - People who really understand their system can make this work - - For many though, it could be a source of real danger - - almost a totally different subject to explore.
  7. "I'll go with the original RGS plus cart relief - - because the cart relief protects them all." If the cart relief is set at 1950 psi, the RGS is still going to fail at a pressure considerably lower than that. The best you can hope for, is IF you (the driver) are not aware that you have a problem (EVERYONE SHOULD HAVE A GENIE LAMP TO TELL THEM WHAT IS HAPPENING WITH THE AUTOPARK SYSTEM), is that you are less likely to ruin the relay or somehow damage the motor (especially in the MTE system). _That is a plus for the pressure relief valve _tho - - If you are NOT paying attention, it could prevent some damage to the relay or motor system. The pressure relief idea SHOULD NOT be an excuse to tool on down the road with the pump motor spooling up - - You'll still end up with trouble if you do that.
  8. "The overall system reliability can be vastly improved by lowering the hydraulic operating pressure." I'm guessing that statement is based on the assumption that the system would still work. The author of that idea bases this on "actual tests and calculations." On my benchtop J71, the actuator shaft starts moving at about 500 psi, and is completely extended at 600 psi. Having the RGS open at 600 would not leave the shaft fully extended as there will still be pressure lost as the one-way poppet closes to seal the system pressure. The loss will be less than if the RGS opened at 1600 psi, but there will still be loss. (I'll try to simulate that with the bench unit and see what actuals turn out to be.) Admittedly, things happen so quickly when you try these experiments, that it is hard to get exact numbers
  9. My abacus says there is about 1070 lbs. of pressure required to fully extend the actuator shaft - - that is with ~ 600 psi of pump pressure. . Assuming those numbers are approximatel correct, an RGS with a 600 psi opening pressure, would have ZERO pressure cushion to keep the brake released. Totally unworkable. To have ANY SAFETY MARGIN AT ALL, the RGS will have to open at substantially higher pressures.

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 oldusedbear@oemys-performance.com

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
c/o oldusedbear@oemys-performance.com

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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)."


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.

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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.

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RGS - Disassembled

Roger took the time to disassemble a RGS and annotate the photos.

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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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