Do-it-yourself AutoPark parking brake actuator repair?

Do-it-yourself AutoPark parking brake actuator repair?

In general, we encourage coach owners to do just about any of the procedures that it takes to keep their AutoPark system up and running properly.  The exception to this is the seal replacement in the hydraulic cylinder for the actuator.  There is no question that some owners might have the equipment and ability to do this job, but in most circumstances this may not be the case.  We have a small but fairly complete machine shop here at the AutoPark Library and without that to fall back on, I’d not feel comfortable about doing this particular repair.  Some examples – –

We’ve made a single purpose VERY STRONG spanner to remove the end cap of the cylinder.  It is about sixteen inches long, and by itself is adequate for about a third of the cylinders we open.  In the worst cases however, it is supplemented by a FOUR FOOT cheater bar to crack the tightest cylinders we encounter.  The vise we use in this process required a LOT of  extra anchoring to a bench that probably weighs nearly a thousand lbs.  We tore a couple of vises off our benchtop getting to this point.

Removal of the old seal requires some special attention.  It is really easy to mar the surface of the piston in this process.  We frequently encounter pistons that have been damaged (by improper technique) to the extent we need to chuck them up in the lathe and clean up the buggered surfaces.  Failure to do so will keep the seal from holding the high pressure (1600 psi) that are present in normal operation.

Sometimes, for whatever reason someone has used the improper hydraulic fluid, and we find a lot of corrosion in the cylinder.  In the more severe cases, this will require honing the cylinder – – much like a regular brake job.

Most actuators have a factory placard of some sort on them, which points out the danger (potentially considerable) of opening up spring loaded actuators.  It can be VERY dangerous and should not be undertaken without some working knowledge of these devices.

Finally and (we think) very importantly, we have a complete J71 Autopark system which has been converted to a benchtop test station.  It has been modified with a pressure gauge and changes in the valving and wiring which enable us to use it for rigorous testing of the repaired cylinders.  With this setup, we pressurize (at 1600 psi) the cylinder assembly for a minimum of 24 hours and we can detect even the slightest loss in pressure or any fluid loss.

All of the above does not mean that there are not coach owners equipped to make these repairs.  It only means that we do not encourage this in most cases.

If we have not already done so, ask us to send you the data sheets on the actuator removal and repair process.  It pretty well describes what is involved for the coach owner to participate in this repair – – saving a LOT of money compared to going to the average service outlet.

Comments and questions are always welcome, oldusedbear

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