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Why do J71 AutoPark parking brake actuators fail?

Why do J71 AutoPark parking brake actuators fail?

This data sheet is new, and is written to address an AutoPark parking brake  problem that has become quite prevalent in just the last few months.  In the first ten years or so that we’ve been attacking AutoPark failures, we have encountered almost NO leaking actuators.  However, the last few months has seen this problem expand to the point that it has become a major issue.

The failure itself, is not very complicated: We’ve always known that “rubber products,” go downhill with age.  This is true of tires, belts, and the various types of seals that are used in our RV’s and other vehicles. All indications are that AGE is the primary factor in the failure of these seals, but HEAT (especially from an exhaust system component) may also weigh into this equation. For sure, if BRAKE FLUID is added to the AutoPark reservoir (instead of the required ATF), you will see rapid destruction of the hydraulic cylinder seal, and subsequent leaking.

IN MOST CASES – – these leaks tend to start small and slowly get worse.  It is pretty unlikely for a seal to create a sudden and major leak which would cause the parking brake to apply.  Usually, it starts with mild seepage from the hydraulic cylinder, and over time the leak becomes large enough to cause cycling of the pressure pump and maybe a noticeable drop in the fluid level of the AutoPark reservoir. In many cases, the seal has lost all of its flexibility and can look pretty bad before it starts leaking. This gives rise to a situation where you may have a very marginal seal, but still no outward signs that would indicate this.

So – – We feel pretty comfortable with saying that we’re addressing a situation which will normally involve some options. Unlike many AutoPark malfunctions which require immediate attention, in most cases of leaking seals, or potentially leaking seals, we have some choices:

  1. Based strictly on the age of your coach, you might choose to proactively replace the seal – – on YOUR time schedule and at your convenience. More on this later.
  2.  If there are already signs of leakage, then you will definitely want to address this on more of a priority basis. Unless it is a big leak where you see the reservoir getting low, you still probably have some wiggle room on how soon the repair needs done.
  3.  If the leak is so bad that you can’t keep the reservoir topped off for any length of time, then you know the seal needs immediate attention

There is a pretty widely held opinion, that our RV tires should be replaced at around seven years of age. People knowledgeable in the seal business, tell us that seals, like tires, also go bad with age and temperature.  Our experience with the seals we’ve replaced to date, seems to strongly support this theory. By the time the seal is ten years old, it is pretty hard and starts to get crumbly.  The nature of the piston and cylinder design is such that the consistency of the sealing material can be pretty bad before the cylinder starts to leak – – so that is in our favor and it is good to have this as a bit of a safety margin.
In conclusion, we feel pretty comfortable with the following:

  1. If you can see any evidence of a leaking AutoPark actuator cylinder seal, get it fixed at the earliest opportunity.
  2. If you cannot see any evidence of a leaking seal, but your coach is around ten years old or older, you may want to consider seal replacement on a proactive basis, and at your convenience – – like during the Winter months or between trips.

The good news is that this is yet another AutoPark “fix” in which you can participate and save yourself a bunch of money. If you’re an OK shade-tree mechanic, with a pretty normal toolbox, you can remove the hydraulic cylinder portion of the actuator (the larger portion which contains the BIG spring can remain in the coach – – no need to fiddle with cables etc.), and get the seal replaced. There are several options open to you as regards the repair of the AutoPark actuator cylinder seal once you’ve removed the cylinder.

If the above information is raising some questions for you, feel free to contact us for further enlightenment.  We have several data sheets on this subject – – pictures etc.

Questions and comments are always welcome, oldusedbear

Posted in: Category 7 - - AutoPark Actuators, type I, II & III': acuator troubleshooting and repair, example auto park actuator pictures with anotations and operational illustrations.

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