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Old 03-06-2014, 04:17 PM   #1
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Okay ... I SOLVED THE AUTO PARK BRAKE PROBLEM!

Okay ... I SOLVED THE AUTO PARK BRAKE PROBLEM!

We have owned our 1998 Chevy chassis motorhome for about 2-3 years and have suffered the Dreaded Auto Park Failure While Driving three times. I had to come up with a permanent fix to that problem as I do not like repeating failures twice, much less three times, and I know from my research that many others have suffered the through the same Dreaded Chevy Auto Park Brake Failure While Driving.

I want a fix which would keep the auto park brake where it would be automatically engaged/disengaged based on the factory vehicle wiring.

My redesign also solves the auto park brake shoes dragging on the drum problem along with solving the insufficient park brake holding problem (my park brake never had much holding power when the brake shoes were adjust to no drag on the drum and overheat).

My redesign is a much less complicated mechanism that Chevy put in there - go here for a description and photos of my project: http://www.irv2.com/forums/downloads.php?do=file&id=275

The project been completed and put back into service, and has been tested on several camping trips.

All I can say is ... it operates beautifully, holds the park brake very tight, is so simple and is fully automatic with the factory vehicle systems engaging and disengaging the parking brake.

I was asked this question:
Q. Does your version automatically engage the parking brake when the vehicle is put in PARK?

A. Absolutely. It automatically does everything the original unit did automatically.

I made no changes to the wiring or controls on the vehicle or the wiring harness to the unit, I even adapted the original wiring connectors from the original components to the new components so the connections would match the original wiring connectors from the chassis to the auto park brake unit.

The only thing that is different is that the brake cable is pulled (engaged) and pushed (released) by a 12 volt linear actuator instead of the hydraulic cylinder linear actuator.

When you are driving, shifting in and out of Park, the park brake operates on its own just as the factory unit did.

My chassis manual states that the factory unit takes 5-6 seconds to fully engage/disengage. My redesigned unit takes about 7 seconds to fully engage - not much different than the factory unit.

I put a label on the instrument panel, under the speedometer, stating that the park brake takes about 6-8 seconds to fully engage/disengage. This is just for information of others who may drive my motorhome, the factory never had a label stating it could take 5-6 seconds to fully engage, that information was buried in the chassis manual.

Once the engaging starts you could walk away from the motorhome as the linear actuator will continue to pull the park brake tight until its internal limit switch for retraction is met; when disengaging the disengaging starts immediately and the park brake shoes keep getting pushed farther from the drum until the internal limit switch for extension is met. It is ready to move almost immediately but I wait the 6-8 seconds before driving away.

When driving off, all you do is shift out of park and the park brake releases just like the factory unit does.

When parking, all you do is shift into park and the park brake engages just like the factory unit does.
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Old 03-06-2014, 04:25 PM   #2
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Wow, now that is a full description with accompanying pictures from start to finish. Great job.
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Old 03-06-2014, 06:12 PM   #3
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My hat is off to you. What a great job design and documentation.
A couple questions:
1) page 14 - What forces are on the 'intermediate support' aluminum bar? With one attachment to the side, is there enough to warrant an attachment to the bottom of the steel enclosure (90 degree angle and added bar to the bottom)?
2) page 28 is the tool - Why did you pull against the spring in the 'hydraulic cylinder' vs. removing the 'hydraulic cylinder' and using the 'DC Linear Actuator' to pull/release the APB cable?
Once again - fantastic engineering feat.
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Old 03-06-2014, 07:23 PM   #4
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My hat is off to you. What a great job design and documentation.
A couple questions:
1) page 14 - What forces are on the 'intermediate support' aluminum bar? With one attachment to the side, is there enough to warrant an attachment to the bottom of the steel enclosure (90 degree angle and added bar to the bottom)?
2) page 28 is the tool - Why did you pull against the spring in the 'hydraulic cylinder' vs. removing the 'hydraulic cylinder' and using the 'DC Linear Actuator' to pull/release the APB cable?
Once again - fantastic engineering feat.
A. to 1):
- Very little forces at all. I thought about a vertical support down to the bottom, but between the rear mount to the back of the box and front mount to the brake yoke, to the all thread, to the cable connector, there was really no forces when in retract as it pulls everything tight. This is when the greatest force of the linear actuator are in play.
- When in extend and pushing the cable to release, the linear actuator does not require much pushing force and I only observes about an 1/8" or so of uplift on the actuator laying on that support. I added the two black cable ties to hold the actuator to the support so it would not move even that little bit.

After a few more camping trips I will raise the motorhome up, remove the side panel, and check on that support. If all is well, I will leave it, however, if it appears to be loosening due to stresses then I will add that vertical support (which will be easy to do).

A. to 2):
- The reason I made that tool and pulled against the hydraulic cylinder was to determine the maximum stroke length of the hydraulic cylinder and what kind of stroke length I would need to order for the actuator. That means I had the brake unit out to measure the stroke length, then had to set it aside while I ordered the actuator with the stroke I wanted, or could have had a custom stroke length made if needed (but the stock 3" stroke was just what I needed).

The cylinder has an internal spring and the spring is under pressure, I could have gone to lots of effort to remove the spring and check the stroke length, but I would not have known if the stroke length was affected by the spring - so I just made that tool to pull the cylinder out tight against the spring and measured the effective stroke length (I have no idea what the stroke length of the cylinder itself is, but it did not matter either).

I am glad everyone likes it - there is no difference in driving or using the motorhome than with the original park brake unit ... everything is still done automatically.

No more worrying about it failing while driving and applying the park brake, and now it actually grabs the brake drum and holds tight.

I have two nice little hills in our neighborhood, one I tested the brake on and it held quite nicely, I am guessing it was about a 6% grade but I will check the % grade next time I have the motorhome out.

The other hill I am going to test it on to see how it holds is much a steep angle, probably over a 30% grade (it is steep, but short). When I do test it there I will post whether it held or not and the % grade it was.
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Old 03-07-2014, 06:01 AM   #5
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Great write up with plenty of pictures, like the way you tied it in to the factory wiring so everything operated the same. I have an 1989 chassis and don't know if it is set up the same but switching over to your method is something I'm going to look into.

The only thing I might do different is to skip the factory wiring due to the age of my chassis and wires going bad and just wire a new switch and indicator light mounted on the dash that you would have to operate manually, I'm a old truck driver so manually operating the parking brakes is something I'm used to,

Again a Great write up...
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Old 03-08-2014, 05:47 AM   #6
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Thank you for the answers. This kind of creativity always amazes me.
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Old 03-08-2014, 05:51 AM   #7
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Thank you for the answers. This kind of creativity always amazes me.

Yah! What he said!
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Old 03-09-2014, 09:20 PM   #8
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The grade (hill) I have already tested it on and it holds excellent is a 4.1% grade.

I will test it on a steeper grade the next time I have it out, which should be in the next 2-3 weeks for our camping trip.
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Old 03-26-2014, 08:50 PM   #9
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brake holding on grade

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Originally Posted by JerryPeck View Post
The grade (hill) I have already tested it on and it holds excellent is a 4.1% grade.

I will test it on a steeper grade the next time I have it out, which should be in the next 2-3 weeks for our camping trip.
Here are the results of my brake holding test on various grades:

- I first tested its holding power on a 4% grade in our neighborhood - held perfectly, couldn't have held better;

- I then tested it on an 8% grade in our neighborhood - same as the 4% grade - held perfectly;

- I figured I would test it the slightly steeper upslope grade opposite the downslope 8% grade I was on as that would test the holding power front facing downslope and rear facing downslope in case there was a difference - held perfectly on that 10% upslope grade.

My redesigned Chevy P30 parking brake holds with no strain on a 10% grade, and that is with parking brake shoes which went through my last parking brake failure while driving ... I could smell the brake shoes overheating. To get to the parking brake brake shoes I have to remove a multi-section drive, then the parking brake drum - I didn't make time for that, figured that I could address the shoes if needed later ... looks like there is no need to address those brake shoes if they hold on a 10% grade with no creaking, no creeping, and hold tight.
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Old 08-24-2014, 12:40 PM   #10
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auto park

Hope to try your fix once we get towed home autopark engaged 14 miles from home today!! Was it expensive to do?
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Old 08-25-2014, 06:05 AM   #11
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Hope to try your fix once we get towed home autopark engaged 14 miles from home today!! Was it expensive to do?
I have a post somewhere here where I listed the approximate costs, can't find that post right now, but as I recall the cost for the parts (I did the work) was less than or around $400 for everything I bought/used.

You will feel relieved after you make the changeover and no longer worry about the Auto Park Brake being applied unexpectedly and without warning while driving.

I tried to make sure I documented each step, let us know if something is different as there are a few different models of the Auto Park Brake out there, some which have the hydraulic pump separate (up by the engine, I think) - the redesign should cover those other styles because there is no chassis wiring change and you are eliminating the differences anyway.
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Old 01-09-2015, 12:18 PM   #12
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After reading these posts re: Autopark, I am wondering what chassis they were on and what years? Are they only on the Workhorse chassis? And for what years? And when did Workhorse stop making chasis?
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Old 01-09-2015, 02:17 PM   #13
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After reading these posts re: Autopark, I am wondering what chassis they were on and what years? Are they only on the Workhorse chassis? And for what years? And when did Workhorse stop making chasis?
The original "autopark", known as J71 AAPB was a GM design for its P32 chassis. Workhorse bought the chassis business from GM in 1999 and continued making the P32 with the J71 thru the 2004 model year. WCC came up with an "improved" AAPB called the J72 and used it for the 2005 model year P32 chassis and the newly introduced W24/25.5 series chassis.

2005 was the last year they made the P32, and then W series got a tranny upgrade for the 2006 model year which eliminated the need for the J72.

None of the W20-W22 series chassis ever had an AAPB of either design.

The last model year for WCC built chassis is 2011, after which the company was closed down by Navistar.
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Old 01-09-2015, 02:32 PM   #14
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Thanks Edgray,
I am considering a 2003 36' on a Workhorse. Should I be concerned?
OK, I just checked, It is on a W22 chassis.
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