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Workhorse Chassis, J72 auto apply brake

Workhorse Chassis, J72 auto apply brake

Postby ia2391 » Wed May 08, 2013 6:54 pm

Hello everyone

Have a W18 chassis (2007) with the J72 auto apply brake. When in PARK, and the yellow button is pulled, no problem, auto apply brake is on. As soon as I move out of PARK and/or push the yellow button in, go into R N D 3 2 or 1, the AUTO PARK FAIL lights up on the dash under the speedometer and the alarm sounds, but, the brake goes off fine and the RV is driveable. Have checked the fluid level, perfect, just a gnats whisker under MAX. Cannot find any leaks whatsoever. Anyone got any ideas? If it was electrical, say fuse or relay, surely the system would not work?

Live in the Isle of Man and need to get (safely) to Signature near Wolverhampton, 3 1/2 hour ferry journey plus 125 mile drive, don't want the brake 'locking up' en route!

I am not the best technically, but will try checking anything. Cheers.

Richard
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Re: Workhorse Chassis, J72 auto apply brake

Postby Damon3272 » Fri May 10, 2013 8:29 am

Hi I have had a similar problem on a P32 Workhorse chassis.
I think you sensor is telling you that you have too much slack in the park brake cable,if you check in your Workhorse Chassis guide it will tell you the exact amount of travel the cable has,if its to slack adjust it and it should solve your problem.
What you need to do to check is chock the wheels so the rv cant move then lay under the RV and measure the cables operation length ie when the park brake is off and then apply the park brake and measure the total amount the cable travels during operation,then adjust accordingly.
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Regards Colin

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Re: Workhorse Chassis, J72 auto apply brake

Postby paulH » Mon May 13, 2013 3:48 pm

Is your park brake a round drum on the propshaft

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Re: Workhorse Chassis, J72 auto apply brake

Postby Damon3272 » Mon May 13, 2013 4:23 pm

Yes Paul its a transmission brake that operates on the prop shaft,they are all virtutually the same in operation.
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Re: Workhorse Chassis, J72 auto apply brake

Postby paulH » Mon May 13, 2013 4:55 pm

I have had this happen to me and the brake is hydrolic spring loaded,and the oil pressure holds the brake off the only adjustment is to slaken the brake shoe off the drum, you know when this go,s wrong as the brake locks on and you can,t move the Rv, you have to lie under the brake box and slaken the cable chock he wheels first then carry chocks till its fixed as you have no park brake
Theres two micro switches the green on sticks but its best two replace them both if you go on a P30 forum in the states theres plenty of info, the swiches cost about £20 each from a Chevy dealer

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Re: Workhorse Chassis, J72 auto apply brake

Postby ia2391 » Tue May 14, 2013 11:36 am

Hello good people

I will try and give the correct information here, but don't 'bank' on it. I am no technician but do understand, thereabouts, how things work!

The J71 and J72 and both similar in operation, the brake is mounted on the back of the gearbox and 'locks' the propshaft. On the J71, I believe the reservoir etc., plus two switches are mounted underneath the RV and to the right hand side of the gearbox and not very accessible. One of the switches, the green one, does play up from time to time (it is known as the RGS, rotten green switch) and if you have a J71 brake that is giving trouble, this may be the cause. Also, the yellow pull switch on the dashboard on the J71 is connected to a cable and this cable can become a little stretched, hence why it has been mentioned it may need adjustment.

I have scrabbled about under my RV and there is no reservoir, switches, etc., underneath for the auto apply brake. My manual explains the J72 auto apply brake mechanisms, the actuator, pump, switches, ECM (electronic control module) etc., are mounted to the side of the radiator (under the bonnet, or hood if you like), drivers side. This has some coloured switches too. The UK Workhorse agents (Signature at Wolverhampton) reckon one of my switches is faulty, and it is this switch that is bringing the 'auto brake fail' and 'alarm' on because if it was the other switch, the brake would not work. The brake works fine either with the gearbox put into park, or the yellow dashboard knob pulled on. The 'fail' and 'alarm' stop when in park and come on when in any gear. Damn annoying. Oh yes, there is definitely no fluid leak from the reservoir. And one other thing to mention, at the back of the yellow dashboard knob, there are two wires connected to it, not a cable.

I am booked into Signature next month for a repair and only hope the 'fail' warning and 'alarm' don't drive me mad on the 120 mile journey!! Fingers crossed then.

Richard (Isle of Man)

PS - I hope you don't mind me quoting below three remarks from US websites, all relating to J71 or J72 brakes

(i)Workhorse service centre narrowed 'auto brake fail' and 'alarm' to electrical, replaced a circuit breaker that affected the 5 amp fuse circuit, didn't know why! (I suspect this was a J72 brake)
(ii) Cable adjustment. Cable that connects autopark hydraulic cylinder to brake mechanism, cable had 'stretched' causing autopark alarm. Used adjustment (under motorhome) to 'tighten' the cable, now no alarm. (I suspect this was J71 brake)
(iii) Brake locked on miles from home, removed relay which reset engine electronics, lasted 50 to 100 miles. Did it a few times, but got home ok. (I suspect this was a J72 brake)
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Re: Workhorse Chassis, J72 auto apply brake

Postby Damon3272 » Tue May 14, 2013 9:35 pm

I would check to length of cable movement first,this was my problem with the buzzer sounding and the light coming on warning of an overtravel(as Workhorse describe it) of the brake cable.
I think the total movement from on to off was supposed to be 39 to 45 mm,check this as its the easiest way out to start with,just measure the amount the cable moves from turning the park brake on then off.
Remember to chock your wheels before you get under the RV and releasing the park brake.
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Re: Workhorse Chassis, J72 auto apply brake

Postby ia2391 » Fri Jul 19, 2013 9:01 pm

Hello everyone

It is a couple of months since I last mentioned the problem with the J72 autobrake on our Itasca. I am hoping the problem, if there was one, is solved!

Well, this is a tad embarassing! You will remember we were booked into Signature Motorhomes near Wolverhampton in mid June, en route to Holland and the Lake District for our summer holiday. Believe this or not, but I drove the RV a few hundred metres up the road and the 'autobrake fail' light went out and the 'alarm' stopped. Don't ask me why 'cos I don't know. However, I felt it was still important to have the braking system checked at Signature which they did. They checked the system and said it was functioning normally, and there were no 'fault codes' showing when hooked up to the computer. The electrical guy there said that sometimes, this can happen especially when the ignition is not fully on and sometimes, it is to do with the alarm system immobiliser. At least my mind was at rest and I could get on with our travels. They also said it is rare to get a problem with the J72 brake and they could only remember one in the past.

However, one or two other things have happened since but I will cover those in other threads.

Sorry for the delay in being able to finalise this thread but we only got back last weekend.

It's a bit hot folks!!

Richard
(Isle of Man)

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Re: Workhorse Chassis, J72 auto apply brake

Postby Mrtibbs » Sun Jul 21, 2013 4:30 pm

Thanks for the update Richard, better late than never matey :)
Glad to hear that everything was OK in the end, great stuff...

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