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johnhicks · 07-03-2017, 02:38 PM

Hi folks.

1993 HR, Oshkosh chassis, Cummins B and Allison.

Preparing to drive, I push the yellow parking brake knob in and it pops back out. Again and again. Of course the brake is applied when knob is out. It will disengage when pushed in and we roll freely but if I let go it pops out. Everything was normal when I parked two days ago, and I can't see anything dripping or spraying under the engine or transmission.

The MH has a Hydroboost system for steering, hydraulic brakes and presumedly the parking brake. Steering and service brakes feel normal.

Ideas?

Of course this is July 3 and I'm in a state park on the backside of bfe in central-east Georgia. Coachnet has worked it all day and kept in touch; Freightliner refuses to work on it, they found another guy who might get me in on Wednesday, and I've asked them to check with Cummins Augusta.

MorganT69 · 07-03-2017, 03:16 PM

Sounds like an air leak or not enough pressure, you MUST have around 75psi for the knob to stay in.

MorganT69 · 07-03-2017, 03:19 PM

Most likely a brake Chamber or Diaphram, or could be as simple as a valve stuck in the open position, water and trash in the lines could cause that. Air Brake Chambers & Diaphrams at Trailer Parts Superstore
I am not endorsing this company only showing what the part looks like.

MorganT69 · 07-03-2017, 03:21 PM

Wait I just reread this are you sure you dont have Air Brakes instead of Hydraulic brakes, the yellow knob is consistent with Air Brakes.

johnhicks · 07-03-2017, 03:51 PM

This is hydraulic over hydraulic. No air.

MorganT69 · 07-03-2017, 04:02 PM

P30 Automatic parking brake

johnhicks · 07-03-2017, 06:46 PM

I was looking at P30 and it's somewhat similar. There's no autopark; I simply push the knob and hydraulic pressure releases the spring brake.

johnhicks · 07-05-2017, 04:08 PM

I got towed the 70 or so miles to Rush Truck Augusta today; my contact here at the shop was telling me what the problem is when I walked in the door.

Neither Freightliner or Cummins Coach Care would work on it.

The tow operator had a bear of a time removing the drive shaft. It's short and the locked brake eliminated free play.

Kudos to Coach Net. I called them Monday morning July 3; they worked the problem but had a hard time finding anyone answering the phones. Coach Net tech Pat worked it on July 4 and called me this morning to tell me where we were going.

MorganT69 · 07-06-2017, 09:54 AM

Im glad you are getting things worked out, stay safe.

johnhicks · 07-07-2017, 06:22 PM

And now for the rest of the story...

We're finally out of Camp Parking Lot Friday afternoon, July 7.

A technician worked for quite a few hours in a gravel lot amid a bazillion ants and 97F heat to get the drive shaft back in yesterday. The drive shaft ultimately won; he called in sick today.

Today we got a new guy who had worked at Freightliner. I showed him where the cable went and what I thought he was looking for and he said "I'll find it!"

Sure enough two hours later he found it and fixed it. What he found is that there's a bracket that holds the cable up against the valve and that bracket had not one of the four bolts and nuts still attached. None. I'll bet that there's one last rusty bolt laying in the middle of our site at Hamburg SP. Without the bracket of course the cable freely flops.

Again, Coach Net, the C&C Towing driver and Rush Truck Center Augusta went way beyond the call of duty to help us.