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Topic: 89 U280 Park air brake wont release (Read 420 times) previous topic - next topic

89 U280 Park air brake wont release

Hi,

Never had this situation and don't find a similar situation in the archives.

My 89 U280 has been sitting on permanent site since mid summer.  With the winter weather hitting us last weekend I was going to back her in the shed for winter.  Fully aired up and park wouldn't release.  Button stayed in with a slight force for about 5 seconds then popped back out.  Did this over and over again for a morning.  Called a friend that runs a few semis and he said ice in the system probably.  It was borderline 32F and had been down to upper 20's overnight.  ok, sounds reasonable.

Ok, came back today and in mid 40's.  aired her up and same thing.  Can here the air going out under the dash and then after about 5 seconds pops out.

Ideas on what to check?  I'm not overly familiar with air systems but I guess I'm gonna learn.

TIA. 
Dan 1989 U280 40'

Re: 89 U280 Park air brake wont release

Reply #1 –
How high was your air pressure the button won't stay in until you have around 60 lbs. air pressure
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: 89 U280 Park air brake wont release

Reply #2 –
Do you have a air system schematic for your coach?  It is much easier to figure out air system problems if you have the diagram.

If the parking brake knob won't stay in, that indicates the parking control valve is not seeing "adequate" air pressure.  You need to have around 50-60 psi at the control valve for it to stay in.  From the brake air tank to the parking control valve is 1/4" plastic brake line.  For some reason air may not be getting to the valve.

If the knob does not stay in, then the parking control valve will not send the proper pressure signal to the spring brake control valve.  If that valve does not open then it will not send air pressure to the spring brake relay valve.  If that valve does not see air pressure, it will not send air pressure to the rear axle brake chambers, and the spring brakes will not release.

Lots of 1/4" air line involved in the parking brake release process, and many places ice might form.  I don't know how long it would take to melt, even at 40 degrees, because the lines are hidden up under the coach where the sun don't shine.

If you need to move the coach right away, you could cage the rear brakes to release the springs.

https://www.youtube.com/watch?v=XVmRCPSVQrM
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: 89 U280 Park air brake wont release

Reply #3 –
Thanks Chuck for posting that video, I'd seen "caging" in other posts but didn't know how so you saved me a post.  I'm sure my threads are as nice and clean as those in the video!  I got a feeling the 1/4" hose is going to be the issue somewhere,  uggggh. sigh.

Old Guy,  120 psi give or take.  full air.
Dan 1989 U280 40'

Re: 89 U280 Park air brake wont release

Reply #4 –
You have more than enough air. You could have an air leak or a blown air blader. Build up the air and then shut off the engine push
in the park brake button and and then listen for an air leak. It should only take a couple seconds to fill the bladers with air and
then there should be no air loss. Listen and watch the air gauge. The air gauge should remain constant.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: 89 U280 Park air brake wont release

Reply #5 –
I can't recall for sure, but I'm thinking you may not need that 5" long "special" socket (shown in the video) to cage our Meritor brakes.  I think you can just use a box end wrench to turn the nut.  You'll quickly know the answer when you crawl under and look.  Somebody with more experience on our brakes can tell you for sure.

SAFETY FIRST!  Chock the wheels before you release the parking brakes!  Don't want the coach rolling away with you under it.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: 89 U280 Park air brake wont release

Reply #6 –
Old Guy,

I hear the air going out from somewhere in front of dash when I push the button.  Definitely lose pressure.. about 3 times pushing the button and it popping out about 5 seconds later drops it about 30 psi.  So bladder, 1/4" hose, etc.  gotta big leak somewhere.

Gonna try the caging thing and get her backed inside for winter, then have 6 months to get it fixed.  Sure hope I don't wait....#1 priority is to get her inside..  Can do a lot of things under a roof.

Probably more questions to come before spring.

Thanks guys!!
Dan 1989 U280 40'

Re: 89 U280 Park air brake wont release

Reply #7 –
If you cage it you will still have front and rear brakes.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: 89 U280 Park air brake wont release

Reply #8 –
Dan,

Let us know when you get the coach moved inside.  We always like to hear about a solution to these problem threads, even when the fix is only a successful temporary work-around.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: 89 U280 Park air brake wont release

Reply #9 –
Quote from: craneman –
If you cage it you will still have front and rear service brakes.

If you choose to use an offset box end wrench, keep all body parts away from the path that bolt will take if it should come free.  An unsung benefit of the 5" deep socket is containment.  With a box end wrench you could put an eye out, with the socket a big bruise or a black eye.

If you have the "S" cam brakes you can also back off the slack adjuster.  Then you will have no rear brakes.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
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AA1OH (H)e who must be obeyed.