Well have been having trouble to say the least with my brakes MCI7. Last trip coming home I was wondering on what I would hit to stop ( not that bad but close). Well so far I have had all brakes relined, drums turned, ( they are all within specks) and shoes surfaced to fit the drums, new brake springs and waiting on a 85 PSI pressure regulator. All brake pods are working and all BRAKES ARE ADJUSTED PROPERLY. When we took it out for a test drive a few weeks ago everything seemed good. Backing down the drive the brakes would not completely hold it. Had 110 PSI of air. Parking break would not hold it still either. After letting it sit for a hour or so pulled it back up the drive and the breaks held. Now we have pulled the tires back off to check everything out again and to make it easier to install the 85 PSI valve. Now one rear driver break pod was replace a few years ago and the other one looks great plus all the break pods work great. While setting there I thought less bleed the air out of the system, so I started pumping them down to see it the parking breaks come on, got the air down to 15 PSI and they didn't. When we took the 85PSI valve off the emergence breaks slammed on. So any thoughts. the breaks are adjusted correctly and everything else has been done the correct way. Sorry for this long post but I am at my wits end. We want to go north for 5 weeks.
You need to check and be sure the exhaust valve and drain slot are pointed down the DD-3 will only work half @$# if the valve is pointed up ,then check the pressure at the tank that supplies the DD-3 it should have a separate tank rust and crap can plug the valve
You have dd3 brakes, not a spring brake system.
Your testing methods, as you have seen, don't produce the results that a spring brake system would.
How old is the relay valve and treadle valve? Is the desired air pressure being delivered to the chambers by those two valves?
Were the linings/shoes matched to the drums? Were new linings properly burnished?
You say the brakes are "adjusted"... by what method, and what measurement are you getting with applied pushrod stroke? ...
" back it off a half turn" doesn't expose worn mechanical parts, which can quickly take up valuable push rod stroke.
Keep at it, you'll get it sorted out!
Happy coaching!
Buswarrior
On YouTube there are numerous videos on adjusting DD3 brakes.
To bad he owns a MCI spring brakes makes life so easy and simple ,I don't think the adjustment is his problem he has a air supply problem ,the DD-3 has 80% of parking braking power compared to stopping brake and they need at least 75 psi to apply the 80% and lock in place
If the parking brake doesn't hold, is there any chance there is a problem with the DD3 parking brake mechanism itself?
Were the cans properly lubricated? Did they ever get wet inside?
What's the condition of the air system? Oil in the lines/cans blocking up the works?
The brakes are properly adjusted, but what's the condition of the S-cams and their bushings?
Intermittent brake problems has to be a air supply problem on a 3 axle dual air system ,the relays have a cracking psi like 4 psi for full air pressure something he is not getting.ED spent all the money redoing the brakes again (I think he did brakes about 2 years ago) with his problem I would start at the foot pedal and work from there
We spent a whole lotta time on inferior brakes a while back on our 4104, just service brakes - no spring nor DD3 and the main issue was the threadle valve. Now it stops on a dime with 9 cents change so to speak...
Thanks Cliff that is what I am doing now. The inversion valve was changed three years ago, the 65 PSI air pressure in the front tank was just changed waiting on the 85 PSI valve to put that in. To all who have replied, cams and all else are adjusted by the MCI 7 maintenance manual. I have a good mechanic. Thanks all will let you know what we find out. The air compressor was changed 2 years ago as was the air drier.
Quote from: edvanland on June 20, 2021, 08:38:24 AM
Thanks Cliff that is what I am doing now. The inversion valve was changed three years ago, the 65 PSI air pressure in the front tank was just changed waiting on the 85 PSI valve to put that in. To all who have replied, cams and all else are adjusted by the MCI 7 maintenance manual. I have a good mechanic. Thanks all will let you know what we find out. The air compressor was changed 2 years ago as was the air drier.
Plus you don't cut corners except on your beer brand
Ed did you change out your E-8 or higher rely valve in the back?
no not yet Luke is sending me one. Is the the 85PSI valve?
Luverbus. Agreed now drink Millers instead of Coors. Got to cut corners somewheer
Quote from: edvanland on June 20, 2021, 02:17:00 PM
no not yet Luke is sending me one. Is the the 85PSI valve?
Ed the E-8 is the foot valve for dual air systems
Check air pressure when activating brakes with an air pressure test gauge at the chambers. Temp. tee it in.Also, make sure slack arm is at 90° angle to chamber pushrod upon brake application.
The pressure regulator for the parking brake is not going to do anything for the service brake performance.
Is that what you mean by 65 lb valve?
Not sure what you mean by 85 lb valve for an mc7?
Check under the driver, with an assistant flexing the brake pedal, that the linkage between the foot treadle and the actual treadle valve is not flexing due to age/rust/deteriarated structure, and is fully acting on the treadle valve.
Happy coaching!
Buswarrior
Not the foot treadle I was talking about the E-8 or maybe his is an E-14 rely valve in the rear. Looks like a spaceship on the back of the bulkhead in the wheel well. across from the inversion valve.
You can find them here Ed
https://www.anythingtruck.com/category/htp-brake-air-valves.html
Quote from: Dave5Cs on June 20, 2021, 07:44:59 PM
Not the foot treadle I was talking about the E-8 or maybe his is an E-14 rely valve in the rear. Looks like a spaceship on the back of the bulkhead in the wheel well. across from the inversion valve.
You can find them here Ed
https://www.anythingtruck.com/category/htp-brake-air-valves.html
Relays are usually marked with R,you need to match the crack pressure when replacing those it will vary from 0 to 4 psi,the 1/4 inch line is the control that sends the pressure to the brakes through the relay
Yep R-14 relay valve mine is still the R :^-8
https://www.anythingtruck.com/category/htp-brake-air-valves-relay.html
Well just received the rear break crack valve ?, the 85PSI valve which will be installed tomorrow then for a test drive stopping check if all is good then leave 4th for Durango, Colorado springs, Colorado then Wyoming, Idaho, Wyoming, Washington, Oregon ( do some deep sea fishing), Nevada then home to Arizona
Quote from: edvanland on June 29, 2021, 10:59:26 AM
Well just received the rear break crack valve ?, the 85PSI valve which will be installed tomorrow then for a test drive stopping check if all is good then leave 4th for Durango, Colorado springs, Colorado then Wyoming, Idaho, Wyoming, Washington, Oregon ( do some deep sea fishing), Nevada then home to Arizona
What are we talking about ED a 85 lb crack valve I am going to use the ? mark too you lost me
yep I'm lost also. Ok the Rear break relay valve, I read in the maintenance manual should have a crack pressure ? of 0 to 4 PSI, you think I can find that sentence now? so I bought a new one. The 85 psi valve is a pressure regulator coming from the front push-pull control valve in line with the inversion valve. Cliff you mentioned on June 20th about the relays having a cracking pressure of 4 psi. After today just about everything on the breaking system will have been replaced. The front and tag break chambers have not been replaced nor has the foot valve, but they are working like they should.
ED who adjusted the brakes ? the reason I ask is because I adjusted the brakes on a MCI Monday a guy did from a utube video and they had adjusted the brakes wrong by turning the slack adjuster bolt in the wrong direction.A easy to tell if the rod starts to extend from the chambers you are going the wrong direction that rod does not move when adjusting the brakes only the s/cam moves it was a simple fix on his and I hope yours is too
Thanks Cliff he knows how to adjust the brakes, but good question. He worked on trash trucks for a few years that had the same brakes I have. I will know in a few hours, he is on his way over, how they are going to work.
Thanks