Auto Park Brake Sytem, warning

[Free Bird]

Having owned my first Class A motorhome a little over a year now, a 2001 Forest River Georgetown 32' gas powered, on Work Horse chassis, I suddenly found out how little I know about parking brake, and would like to advise anyone who does not already know, how expensive it could get by not maintaining it properly. My advice, Study the system and get very familiar with it.
While leaving the last campsite, I noticed a slight squealing noise as I pulled out. Not any drag, or problem. drove 300 miles home and backed into driveway and put it in park and jumped out. Guess what, it rolled away. my first thought was the tranny was shot, Oh God.
Turns out, with tthe amazing help from "oldusedbear" on this web site, I found out that: 1. Because I had a leak in actuator pump, I lost all fluid in reservoir. 2. ( I never even knew, nor did any literature tell me I even had a reservoir) I though "Park" was in the transmission, GUESS WHAT, IT's NOT. 3. Drove home 300 miles with autopark brake on. 3. Result: burned park brake, major job, 3-4 hundred dollars in parts, sending actuator away for rebuild, 2 weeks wait, 3 days of my labor, all needless. I must also add, that the autopark warning light in instrument panel is invisible on sunny day and cannot be noticed.
MY ADVICE!!! If you have Auto Park System, study it carefully and maintain it regularly. God Bless "oldusedbear" it would have run close to 2 grand to take it in to the dealer.

[frankdamp]

Autopark was one of the reasons we didn't even look at anything on a Workhorse chassis. The Bosch service brakes debacle was the other.

I was very glad I read this forum and RV.ney regularly before we bought our current rig.

[Free Bird]

Quote:

Originally Posted by frankdamp Autopark was one of the reasons we didn't even look at anything on a Workhorse chassis. The Bosch service brakes debacle was the other. I was very glad I read this forum and RV.ney regularly before we bought our current rig.

Re: My earlier post on AutoPark System:
Don't get me wrong, it is a great system, just everyone should know it's operation and maintenance proceedures. They just don't tell us before hand. Better than having a " Transmission parking pawl" to break.
free Bird

[DaveFL]

This sounds like a holdover from the chevy chassis, as my 1998-9 chevy chassis has an auto brake. What specific maintenance are you planning for a future free of maintenance issue problems. I am in the middle of brake work, in cleaning the old brake fluid from the reservoir and using a mirror to see the bottom of the tank, not only does it need emptying it also has to be wiped out, black stuff in the bottom. Next step will be bleeding from all wheels starting p rear, d rear, p front, d front.

[DriVer]

Quote:

Originally Posted by frankdamp AutoPark was one of the reasons we didn't even look at anything on a Workhorse chassis. The Bosch service brakes debacle was the other..

Workhorse discontinued the auto park on the majority of their fleet in 2006. This device was carried over from GM in 2001 and is still in wide use today on a number of commercial vehicles that use hydraulic brakes. Workhorse did re-engineer the brake to a J72 which was much more reliable and simple and not prone to failures by pressure switches like the J71.

If you have a 24K or 26K F Series Super Duty Chassis, don't look now but you will also have Bosch brakes - the same as Workhorse.

[Free Bird]

Auto Park brake is a seperate entity from the hydraulic brake system. The regular hydraulic system should be flushed and fluid replaced every couple of years. The Auto Park however, is pretty much a mechanical brake shoe on the drive shaft at rear of transmission. Used when in "Park", or with manual park brake knob. Fluid reservoir, and Actuator pump and prssure switches on mine are in a steel box on passenger side frame rail just aft of transmission. Just keep reservoir full, and check often for leaks.

[JohnRR]

If you do not service the fluid in the reservoir it can retain moisture and it will freeze in colder temperatures locking the brake shoes in what ever position they were in when the cold came (on/off)

[frederick w]

Free Bird
Who did you send the pump to and how hard was it
to replace the pump?

Glad you got thru it all.

Fred Rubio 2000 Flair
work horse chassis

[Free Bird]

Fred, Actuator pump itself, was not too difficult, 'oldusedbear", on this web site was of tremendous help. Without him, I would have been in deep trouble. When we detemined that it was not the fabled RGS switch, I looked further and found the leak. He recommended, and I sent it to: PRECISION REBUILDERS" of St. Claire, Missouri. He was right, they were great and reasonable. I replaced the brake while at it.

[Thumper221]

We have a 1993 Airstream LY that we have had for 6 years, its on a Chevy P30 chassis with a 454 in it. Most all the auto breake setups are powered by the Power steering pump. A few use a seperate reservoir and a electric pump to develoupe the 300 Psi for the system. You can get into real trouble if you ever let it run low on fluid, I found that out the hard way heres why. The Hyd cylinder that releases the spring tension on the breake unit is Hyd actuated and spring return, NO LINE BACK TO THE PS TANK. To make matters wost, its a large diameter cylinder so when the hydralic pressure is droped off to let the internal springs apply the brake it sucks a fairly large amount of Oil out of the system as it pulls the piston back to the end of its stroke. If you are low on fluid or have a broken line like we did and dont know it, and keep going from park to not park, all that happens is you are sucking air into the system. The air that gets into the auto park cylinder cant het out because with no return to tank, its traped. A good indication of this is power steering and hydroboost work untill you take it out of PARK! The only way to fix this is to bleed the autopark break cylinder. It has a cable comming out of it on one end going to the other two camles from the foot brake and the autopark break drum brake arround the drive shaft. The other end has the hydralic line comming into it fron the control valve. On that end, just above and ontop or the cylinger is a standerd bkeaded fitting, just like the one used on break calipers. Thats where you must bleed it at, the same as you would with regular breaks. You have to be careful to not have the bleeder valve open at the wrong time or you will suck more air back into the cylinder. Once you get all the air out of the cylinder your breaks and power steering will work with the auto park break released.
If you ever have to tow one, Dont take the clevis pin out of the cable relay box, Its a nightmare to get it back in and then you have to readjust two of the three cables! Best thing to do is to disconnect the universil joint closes to the rear differntial and tie the driveshaft up, Then have it towed. I am not trying to be a know it all, just want to share what Iv learned and know with people I have something in common with -
Pat

[Thumper221]

Auto Park Actuator Layout

[oldusedbear]

A few comments which might be useful for "autopark owners."

I'd guess there are many more of the later J71 systems with the dedicated pump and reservoir, than the earlier power steering versions. They've been built since about mid 94 until 2007. So roughly 13 years of the J 71 as opposed to the power steering version which I believe appeared in 89 and was used until mid 94 - - about five years.

There is a pressure regulator in the Bendix relay valve that controls the operating pressure in the earlier AutoPark units to about 130 psi - - quite a bit less than the power steering and the Hydroboost portions of the system.

Pat is correct about letting the fluid get too low - - you will introduce air into the system if you empty the reservoir. The most frequent cause of air ingestion however, is overtravel. Overtravel occurs when the actuator travels more than about 1.5 inches, and will cause air ingestion every time the AutoPark is cycled. No amount of bleeding can fix this problem. It is absolutely necessary to adjust, or maybe even replace the parking brake shoes, as well as adjust the cables in order to reach the optimum 1.25 total travel of the actuator.

Reconnecting the cable at the clevis is best accomplished by having a TRUSTWORTHY helper in the driver seat, who can sit there with a foot applying the service brakes while the engine is running and the shift lever is in NEUTRAL. This will pressurize the actuator and give you all the slack you need to reinsert the clevis pin. Needless to say, wheels should be well chocked and all precautions taken so as not to run over the poor guy under the coach. An alternative method if you have no helper is to back off the cable adjustment at the actuator until you can replace the pin in the clevis - - then readjust the cable connection to get the slack back out of the cable.

An observation: The earlier system like Pat has, seems to be a lot more reliable than the newer systems. With proper maintenance, they give very little trouble with the distinct advantage of "NO ROTTEN GREEN SWITCH."

oldusedbear

[DriVer]

Thank you Old Used Bear!

Wishing you a very Happy New Year!

[Thumper221]

oldusedbear - Thank you for the positive comments. I would like to share some things with others that helped me feel more at ease and comfortable while driving our coach. The service manual says the break is " spring aplied and hydralicly released". Now ours is " spring applied and cable released " Right in between the drivers seat and the Dog house cover there is a floor mounted hand opreated break handle that you grab with your right hand and pull up to release the auto break. The cable sheath and cable in it go to the auto park relay box - in thru the drum brake side. It hooks to the bottom, long end, of a pivot bar setup. The other end of the pivot bar, the short end, is were the Brake drum cable hooks to. There is also in the box a adjustable stop for travle on the pivot bar to get the 1.5" travle you need to enguage and disinguage the break. and a roller head type limit switch that senses park position. The pivot bar is necessary to reverse the action of the hand break and with the hand break cable tied to the long end of it it gives some mechanical advantage to the hand break. The park pressure switch has been disconnected and wires ran to the new switch in the pivot bar setup. When you pull the break release handle up it allows the top part of the pivot bar to move in away toward the rear of the coach and compress the drum break springs and release the brake. To enguage press the release button on the hand brake lever and let it go to the floor. This takes tension off the drum and sets the brake. The drum springs will push the pivot bar back as long as therse slack in the hand brake cable for it to do so. I later went back and put a spring from the bottom of the pivot bar to a fixed I bolt to help it along. The wires from the autopark enguage pressure switch not go th the limit new limit switch that senses park. When you release the brake now there is no lag, the park light goes out right away.. I know it works backwards but it has several advantages over the old system. Once its installed its simple and easy to maintane. If the autopark light comes on you know its on for sure because the switch that detects it is now on the auto brake drum cable itself. If it comes on the cable has moved in farther than you set it for. If it moves far enough the break will set. An other big advantage is if you loose your service freakes you can get breaking action by feathering the break handle up and down. I did this on the storage facility property after I compleated the Mod. I had no problens with it for 3 Years till we sold it and upgraded at retirement a year ago. If any one wants layout and Pix I will post them if requested to do so. Another good thing is you dont have to PULL THE CLEVICE PIN to tow or push it!

Pat - KB5EGN