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Old 10-11-2013, 07:34 PM   #1
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AutoPark problem - not the drum brake though.

At the shop, I'm working on a 2005 National RV "Dolphin" with an auto park like I've never seen. It's a front engine gas and the transmission is an Allison 2001MH. This auto brake is completely hydraulic with no linkage. It does have a large contraption bolted on the back of the tranny with nothing but a hydraulic line going to it. The transmission range selector in the cab has a "park" button so according to Allison, this is a unit with what they call "park pawls".

Our customer complaint is that it holds some, but not good. I certainly would appreciate any info, links, etc. to help me diagnose this one. I don't know the specific WH chassis model but I can find out in the morning and I'll let you know.
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Old 10-11-2013, 11:15 PM   #2
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AutoPark

Sounds like a J72 system. This is a package made by Carlisle. Sadly, we know almost nothing about it here at the AutoPark Library. Several people have had problems and have had to pretty much bootstrap things to get going. Maybe one of these owners can report on their experiences.

From what we can tell, it is a pretty good system but apparently lacks support from the builders and Workhorse - - not unlike the j71 in that respect.

oub
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Old 10-12-2013, 05:05 AM   #3
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Thank you Bear. I would sure like to know what's inside that thing before unbolting it. There's gotta be a big spring that could come flying out along with who knows what else. The only thing I've done so far is loosen the fluid line to make sure it wasn't holding pressure when it shouldn't.
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Old 10-12-2013, 07:29 AM   #4
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It is the J72. It is a hydraulic cylinder in the shape of a donut. The drum is not gripped on the out sides like a drum/shoe style system It is a flywheel surface on the inside, also has a spring (looks like a concave washer) and a friction disc that is steel with a sintered iron friction material(looks more like a clutch disc). The disc is splined on the inside radius to couple with the outside radius of the output yoke.

The hydraulic pressure (when applied) overcomes the concave spring releasing the friction disc and allowing for movement. The release or lack of pressure allows the concave spring to clamp against the drums face locking the drive line.

This is what I have so far for info. I do have the nomenclature for the internals but can not find it yet.

I have had to deal with this issue on my own coach as well.
Attached Files
File Type: pdf j72 autopark.pdf (361.5 KB, 112 views)
File Type: pdf Driveline Brake.pdf (108.6 KB, 110 views)
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Old 10-12-2013, 07:39 AM   #5
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My J72 applied at highway speed. (Common failure according to FCCC). The unit mounted on the transmission it toast at that point. The J72 APP system as a whole was removed. Allison installed a park pawl in the transmission and a new control panel. Then a drum/shoe driveline brake system installed.

If the brake does not hold the brake unit on the transmission is bad. It probably was driven partially engaged, overheated the concave spring (making it weaker) and destroy the friction disc.

Oh, sorry I did not say but the unit consist of
Splined Yoke
Drum
Friction Disc
Concaved Spring
Piston with one o-ring
Cylinder Base housing
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Old 10-12-2013, 07:52 AM   #6
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Here are some pics.
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Old 10-12-2013, 09:14 AM   #7
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Quote:
Originally Posted by rgreen45 View Post
At the shop, I'm working on a 2005 National RV "Dolphin" with an auto park like I've never seen. It's a front engine gas and the transmission is an Allison 2001MH. This auto brake is completely hydraulic with no linkage. It does have a large contraption bolted on the back of the tranny with nothing but a hydraulic line going to it. The transmission range selector in the cab has a "park" button so according to Allison, this is a unit with what they call "park pawls".

Our customer complaint is that it holds some, but not good. I certainly would appreciate any info, links, etc. to help me diagnose this one. I don't know the specific WH chassis model but I can find out in the morning and I'll let you know.
Most likely that you're working on a W24 chassis, the sixth vin character will be an "A". If the PB has a yellow knob on the dash, the PB is the J72 AAPB, and there is NOT a park pawl in the tranny, which is a 2100MH (not the number you posted). The REASON they used the J72 AAPB is because there is no pawl in a 2100MH.

Hopefully the file provided above tells you what you need to know about this system.
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Old 10-12-2013, 10:01 AM   #8
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J72

Looks like MRV8 has a pretty good handle on the J72. Maybe he would let you work directly with him. I'm sure there are others out there too who have some hands on experience with this parking brake.

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Old 10-13-2013, 06:44 AM   #9
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MRV8, thank you for the information. I'll see if the links you have offer dis assembly info before I attempt to tear this thing apart. If I'm unsure, I'll suggest replacing the cylinder as a whole.

EdGray, I had the right numbers, just wrong order. Thank you for all you do!
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