Get ready for some good reading! ;D
Let me start by saying that I feel I have a good knowledge of how the J71 Auto Park Brake works on my Workhorse P32 chassis (2000 Winnebago Brave 32T). When I purchased this coach about two weeks ago, the original owner knew that there was a mysterious delay in the application of the Auto Park Brake once the coach had been driven long enough to reach normal operating temperatures. Therefore, chocks were always used by him and I planned to do the same.
I drove it about 100 miles (80-90 of which were highway) from the previous owner's home to my home and all was well. The Auto Park Light was off when it was supposed to be off. However, when I parked the coach (i.e. put it into Park with the gear shift as well as pulled the yellow Park Brake knob on the dash) the Auto Park Light did not illuminate nor did the Auto Park Brake engage. So I hopped out and chocked some wheels and went on my way. The next time I drove the coach (the next day) when I fired it up the Auto Park Light was illuminated and the Auto Park Brake was indeed engaged. When I pushed in the yellow dash knob then moved the shift lever into D, I heard the Auto Park Brake hydraulic pump kick in and within five seconds the Auto Park Light went out.
I drove the coach across town to a friend's location, perhaps 2 miles. I did not shut off the engine when I arrived. When I shifted into Park the Auto Park Light illuminated and the Auto Park Brake definitely engaged. Of course the coach really didn't have time to reach normal operating temperature in the short 6-8 minute drive. My friend joined me in the coach and we ran the genny with the galley A/C and had a good chat for about 15-20 minutes. Then he stepped out, I killed the genny and the A/C and prepared to drive 2 miles home. When I pushed in the yellow dash knob and shifted into D, again I heard the hydraulic pump kick in and within a few seconds the Auto Park Light went out. So I began to drive.
On the way home the Auto Park Light began to flash on and off and by the time I got home it was on but dimly lit. I parked the coach and could immediately smell that the brake pads were starting to burn. The short drive home was never over 30MPH and I drove maybe a half mile with the Auto Park Brake dimly lit, so I don't believe there was enough heat buildup to cause permanent damage to the brake or pads. When I shifted into Park and pulled out the yellow knob on the dash, the Auto Park Brake remained dimly lit.
So I began reading everything I could find about the wonderful Auto Park Brake system. It was obvious to me that I needed to replace my "Rotten Green Switch" so I ordered a few from Amazon and waited. The existing switch was definitely faulty and had fluid starting to pass through it to the electrical contacts. It took me about 20 minutes to install the new switch after which everything went right back to how it was when I acquired the coach. That is, the pump engaged as expected when shifting out of Park and pushing in the yellow know, the Auto Park Light went out as expected, and the brake released as expected. I tested it on a hill a few blocks from my home, probably 6-8% grade, parking both up hill and down and the Auto Park Brake engaged and held as expected. Keep in mind that I was just a few blocks from home and therefore nothing was up to normal operating temperature yet.
Then I drove around a bit, about a mile of surface road then two miles of freeway, then another mile of surface road. This was enough to bring the coach up to normal operating temperature. And when I shifted into Park and pulled the yellow knob, the brake did NOT engage and the Auto Park Light did NOT illuminate, exactly like it was when I acquired the coach. So I decided to do more digging, and I engaged expert Roger Haag (oldusedbear) at www.rvautopark.com. He suspected that perhaps the Auto Park Brake cable was becoming bound/stuck when warm and I initially agreed since my cable makes contact with the back of the engine block right where the tranny bell housing connects. But then I realized that if the cable was merely stuck, the Auto Park Light would still immediately illuminate when it was supposed to (when shifting into Park or pulling out the yellow knob). The Auto Park Light doesn't illuminate until the hydraulic pressure is released and drops (so that the actuator spring can decompress and pull the cable to engage the brake). After the coach sits and cools off for about 5 minutes (and you can almost set your watch by it), you can hear the Auto Park Brake engage over a 15 second series of pops and creaks.
So Roger and I are a little stumped on this one. I considered the possibility of a bad relay, but that should only effect whether or not the pump engages. It should have nothing to do with the release of pressure. The "Rotten Green Switch" just tells the pump to come on if it senses less than 1,200psi of pressure while the shift lever is in Park and the yellow knob is pressed. Once the shift lever is in Park and/or the yellow knob is pulled, the pressure should be released.
To add a little more to the mystery, I drove the coach about 80 miles round trip to a campground at a nearby lake and everything was as expected (i.e. Auto Park Light stayed off while driving, engaged only after 5 minutes of "cooling off" period once parked). But then the next day, a particularly hot day (95F) I drove it to a scale house owned by one of my clients (14,540lbs with 3/4 tank of fuel, empty fresh water and holding tanks, a little bit of camping gear). On the drive back, as soon as I got off of the highway and had less than a mile to go to get home, the Auto Park Light began flashing. I continued home (less than a mile, less than 30MPH) and parked and again could smell the brake pads starting to burn. ARGH! It had only been 100 miles since I replaced the Rotten Green Switch so I figured I somehow blew through another one, perhaps due to over-pressure by the hydraulic pump.
So I let the coach sit for a day or two before I got curious again and fired it up. This time it was in the evening and probably closer to 80F. I drove around town for about an hour and the Auto Park Light never illuminated while driving. I parked several times to see if it would illuminate and engage the brake but the same delay was present. So I ended up parking it in a lot in a public park and just sitting there with the engine and dash A/C running. I chocked the wheels even though I was on a level spot and the coach didn't try to roll. After about five minutes of sitting with the engine running (and therefore maintaining normal operating temperature if not a bit higher than normal due to lack of air flow), I heard the brake engage through the usual 15 second series of pops and creaks. So the delay really doesn't seem to have anything to do with engine compartment heat but rather heat or pressure build up at the hydraulic pump.
So to all of you experts out there who are still insane enough to be interested in reading this... What the Hell is going on? I believe the hydraulic pump is shutting off once there's enough pressure to compress the actuator spring and release the brake. Why isn't the pressure being relieved as soon as the shift lever is back in Park and/or the yellow knob pulled? Why does it take several minutes of operation to get to this condition whereby a five-minute delay is needed for the hydraulic pressure to release? And of course, why would the Auto Park Light come on again while I'm driving but then stay off the next time I drive? I have 13 days to get this and a few other issues resolved.
--Kevin
Let me start by saying that I feel I have a good knowledge of how the J71 Auto Park Brake works on my Workhorse P32 chassis (2000 Winnebago Brave 32T). When I purchased this coach about two weeks ago, the original owner knew that there was a mysterious delay in the application of the Auto Park Brake once the coach had been driven long enough to reach normal operating temperatures. Therefore, chocks were always used by him and I planned to do the same.
I drove it about 100 miles (80-90 of which were highway) from the previous owner's home to my home and all was well. The Auto Park Light was off when it was supposed to be off. However, when I parked the coach (i.e. put it into Park with the gear shift as well as pulled the yellow Park Brake knob on the dash) the Auto Park Light did not illuminate nor did the Auto Park Brake engage. So I hopped out and chocked some wheels and went on my way. The next time I drove the coach (the next day) when I fired it up the Auto Park Light was illuminated and the Auto Park Brake was indeed engaged. When I pushed in the yellow dash knob then moved the shift lever into D, I heard the Auto Park Brake hydraulic pump kick in and within five seconds the Auto Park Light went out.
I drove the coach across town to a friend's location, perhaps 2 miles. I did not shut off the engine when I arrived. When I shifted into Park the Auto Park Light illuminated and the Auto Park Brake definitely engaged. Of course the coach really didn't have time to reach normal operating temperature in the short 6-8 minute drive. My friend joined me in the coach and we ran the genny with the galley A/C and had a good chat for about 15-20 minutes. Then he stepped out, I killed the genny and the A/C and prepared to drive 2 miles home. When I pushed in the yellow dash knob and shifted into D, again I heard the hydraulic pump kick in and within a few seconds the Auto Park Light went out. So I began to drive.
On the way home the Auto Park Light began to flash on and off and by the time I got home it was on but dimly lit. I parked the coach and could immediately smell that the brake pads were starting to burn. The short drive home was never over 30MPH and I drove maybe a half mile with the Auto Park Brake dimly lit, so I don't believe there was enough heat buildup to cause permanent damage to the brake or pads. When I shifted into Park and pulled out the yellow knob on the dash, the Auto Park Brake remained dimly lit.
So I began reading everything I could find about the wonderful Auto Park Brake system. It was obvious to me that I needed to replace my "Rotten Green Switch" so I ordered a few from Amazon and waited. The existing switch was definitely faulty and had fluid starting to pass through it to the electrical contacts. It took me about 20 minutes to install the new switch after which everything went right back to how it was when I acquired the coach. That is, the pump engaged as expected when shifting out of Park and pushing in the yellow know, the Auto Park Light went out as expected, and the brake released as expected. I tested it on a hill a few blocks from my home, probably 6-8% grade, parking both up hill and down and the Auto Park Brake engaged and held as expected. Keep in mind that I was just a few blocks from home and therefore nothing was up to normal operating temperature yet.
Then I drove around a bit, about a mile of surface road then two miles of freeway, then another mile of surface road. This was enough to bring the coach up to normal operating temperature. And when I shifted into Park and pulled the yellow knob, the brake did NOT engage and the Auto Park Light did NOT illuminate, exactly like it was when I acquired the coach. So I decided to do more digging, and I engaged expert Roger Haag (oldusedbear) at www.rvautopark.com. He suspected that perhaps the Auto Park Brake cable was becoming bound/stuck when warm and I initially agreed since my cable makes contact with the back of the engine block right where the tranny bell housing connects. But then I realized that if the cable was merely stuck, the Auto Park Light would still immediately illuminate when it was supposed to (when shifting into Park or pulling out the yellow knob). The Auto Park Light doesn't illuminate until the hydraulic pressure is released and drops (so that the actuator spring can decompress and pull the cable to engage the brake). After the coach sits and cools off for about 5 minutes (and you can almost set your watch by it), you can hear the Auto Park Brake engage over a 15 second series of pops and creaks.
So Roger and I are a little stumped on this one. I considered the possibility of a bad relay, but that should only effect whether or not the pump engages. It should have nothing to do with the release of pressure. The "Rotten Green Switch" just tells the pump to come on if it senses less than 1,200psi of pressure while the shift lever is in Park and the yellow knob is pressed. Once the shift lever is in Park and/or the yellow knob is pulled, the pressure should be released.
To add a little more to the mystery, I drove the coach about 80 miles round trip to a campground at a nearby lake and everything was as expected (i.e. Auto Park Light stayed off while driving, engaged only after 5 minutes of "cooling off" period once parked). But then the next day, a particularly hot day (95F) I drove it to a scale house owned by one of my clients (14,540lbs with 3/4 tank of fuel, empty fresh water and holding tanks, a little bit of camping gear). On the drive back, as soon as I got off of the highway and had less than a mile to go to get home, the Auto Park Light began flashing. I continued home (less than a mile, less than 30MPH) and parked and again could smell the brake pads starting to burn. ARGH! It had only been 100 miles since I replaced the Rotten Green Switch so I figured I somehow blew through another one, perhaps due to over-pressure by the hydraulic pump.
So I let the coach sit for a day or two before I got curious again and fired it up. This time it was in the evening and probably closer to 80F. I drove around town for about an hour and the Auto Park Light never illuminated while driving. I parked several times to see if it would illuminate and engage the brake but the same delay was present. So I ended up parking it in a lot in a public park and just sitting there with the engine and dash A/C running. I chocked the wheels even though I was on a level spot and the coach didn't try to roll. After about five minutes of sitting with the engine running (and therefore maintaining normal operating temperature if not a bit higher than normal due to lack of air flow), I heard the brake engage through the usual 15 second series of pops and creaks. So the delay really doesn't seem to have anything to do with engine compartment heat but rather heat or pressure build up at the hydraulic pump.
So to all of you experts out there who are still insane enough to be interested in reading this... What the Hell is going on? I believe the hydraulic pump is shutting off once there's enough pressure to compress the actuator spring and release the brake. Why isn't the pressure being relieved as soon as the shift lever is back in Park and/or the yellow knob pulled? Why does it take several minutes of operation to get to this condition whereby a five-minute delay is needed for the hydraulic pressure to release? And of course, why would the Auto Park Light come on again while I'm driving but then stay off the next time I drive? I have 13 days to get this and a few other issues resolved.
--Kevin