Rear brakes

[Towboy]

Have a 2018 holiday rambler endeavor on a freightliner xcm chassis. Stopped in marathon Florida for fuel started heading south toward home Summerland Key, just before the 7 mile bridge (no shoulder) my speed dropped from 45 to 25 instantly no alarms air pressure 130 both gauges thought maybee fuel / filter issue pedal to metal got back to 45 drove the 7 miles over bridge motorhome started filling with smoke (brakes) finally got to a safe pull off location. While waiting to cool inner left tire explodes from heat. Cooled down so i layed under to try and cage brakes to see if i could get off roadway only 1 key so called tire guy to change tire, tow truck which his heavy duty wrecker was broke told if he could bring me a cage key for other chamber. Hid did arrive caged other brake and had service brakes ( no parking brake though) drove to 20 miles home had excessive brake chatter guess shoes cracked or drums warped anyway after all that i will have to check for a leak but weird thing is never lose air pressure. Any ideas?? Brake shoes only show 1 option bendix k098129. 16 1/2 x 8.625
Mulitiple brake drum options has anyone come across only 1 particular brake fit only? Looking at eaton 4726 esII shoes 16 1/2 x 8.625 just wondering if anyone else found compatible shoes these are 23k linings

Sorry for long post just wanted to share my day with you all.
John

Cannot figure how parking brakes engaged without pressure loss on gauges any ideas?

[Skip426]

I'll have to go through my air brake training manual but JMHO . I wouldn't trust those rear dual chambers.

Have you confirmed that both rear brakes were locked up ?

Was the caging bolt hole, rubber cover plug in the chamber missing on either side ?

[Towboy]

Yes, both sides were locked up. Rubber caps on both chambers were in place, and 1 t bolt was missing.

John

[Towboy]

It's home able to drive with both chambers caged. i will remove caging bolts and listen at the chambers for leaks, but if one is bad, would it deflate both? I am looking at air brake schematic to see if check valves between 2 spring brake chambers to prevent that scenario.

John

[twinboat]

Parking brake button pulled or defective.

Inversion valve failed. It uses the parking brakes to stop when psi is low but not yet ctitical.

That's about it, with no tank air loss.

One leaking chamber can lock up both wheels. Your supposed to stop when brakes are failing.

Now your grease seal are cooked, ABS sensors melted, if equipped and you melted one tire and I'd suspect the one on the other side is damaged.

[Towboy]

It was either block the south lane on the 7 mile bridge in marathon florida and cause an accident or drive to a safe pull off location. No, the parking brake valve was not pulled.

[Skip426]

Without an air system diagram for your chassis , I have to refer to my Freightliner diagram , and that shows a single pressure line from the dash to the rear of the chassis , split to provide pressure to both chambers .
So a leak in one chamber would cause both spring brakes to engage.
Internal leakage through the diaphragm should have blown out the rubber plug. .

[Towboy]

Both rubber plugs were intact. it's on blocks today. I'm going to get under and check for leaks hopefully tomorrow. i attached a schematic downloaded fron dtna connect for my chassis via vin number. I appreciate your help! Bought an extra long 1 1/16 deep socket to make it easier to uncage the brakes to listen for leaks


John Air brake shematic.PDF
Attachment 394583Attachment 394584

[Towboy]

Looks like attachment didnt workAir brake shematic.PDF
Attachment 394582

[Skip426]

Attachment is fine in both posts .

Man things got way more complex when Daimler got involved .
Of course my chassis and diagram are 20 years older.

I'll look things over and re-post later.

[Towboy]

Thanks, one thing was odd. When i caged the left brake, I had a hard time getting the key in and had to go in at angle, so I'm thinking maybe the diaphram did blow changing the position inside for the key??

[Towboy]

Found air leak this morning combo valve up inside rear crossmember leaking from bottom exhaust valve the valve feeds lower parking brake valve.

Thanks again for your help John

[Skip426]

Ok , after downloading and blowing up your air system diagram ; I'm confused .
I cannot figure what the engineering department was trying to accomplish ; besides making the system overly complex. BUT ,I did see that when Daimler was involved with Chrysler when I was still working.
I cannot figure why they decided to supply pressure from both front and rear ( red & green ) brake systems to the rear combination valve . That's one major difference that jumped out comparing my 1999 diagram to yours.

Also no indication of where the pressure sensors for system ( front & rear )are located , in particular the sensor for spring (park) brake release pressure . Or brake light switches. All are shown in my 1999 diagram.
I guess a parts list would help to determine what all the item , line markings and modification notes are about.
Tank drain valves or auto ejectors not shown.

I even went back to my air brake training manual ( of course it's 13 years old )so dated to be sure but no help figuring things out.

When you get to testing your system , if you find no leaks in the spring brake chambers or their supply tubing , you're going to have to talk to a mechanic who's worked on this particular system ; someone who may have a good idea of what happened to allow the spring brakes to apply ; particularly with no alarm, or indication of air loss.

[Skip426]

Originally Posted by Towboy

Found air leak this morning combo valve up inside rear crossmember leaking from bottom exhaust valve the valve feeds lower parking brake valve.

Thanks again for your help JohnAttachment 394620

OK , glad you found a problem ( and posted while I was typing up my last post ) .

I'm wondering why you got no warning ; light or alarm ; that the release pressure to the spring brakes had dropped .