DD3 Parking Brake Won't Release (Again!)

buswarrior · July 09, 2018, 07:42:17 PM

Knowing the orientation of the brake chambers on other bus models can also be good for a busnut's creativity when considering a spring brake upgrade.

Look under a late model 5307 and dream how to use those longer shaft units...

Don't let the existing orientation restrict your thinking!!!

Happy coaching!
Buswarrior

chessie4905 · July 09, 2018, 08:03:53 PM

Ok,4104's, 4106's,and 4905 with bogie removed.

gus · July 10, 2018, 07:57:49 PM

Thanks guys for all the comments - but nobody addressed my question about brake linings? I guess this is a good sign:)

I had decided to start my diagnosis with linings but if nobody ever had a problem with them I'll skip that part.

As I remember there is a separate 65psi tank for setting the park brake and for emergency application. This is a lot different system than my 4104. I'm going to check is mine still has one.

The 4107 DD3 is really a weird setup according to the manual which makes installing spring brakes even more complicated than converting a 4104.

Yep, it sat for most of the year but has never ever given any problems in the past after long sitting.

I never greased the rollers because I didn't know it was possible. After some research I think it is supposed to be a special grease, not chassis.

My brakes have, up until now, operated super smoothly. To set all I ever did was pull the button, never had to use the service brake. To release, 99% of the time all I had to do was push in the button and, after a short pause, the brakes released. Who could ask for more?

When the weather is halfway decent I'm going to try again to get them to release by holding the SB longer after pushing the button in. In the past, when it was necessary, I only had to use the SB for an instant to release.

buswarrior · July 10, 2018, 08:17:38 PM

The parking tank will be at system pressure, with the regulator feeding the brake circuit the lower pressure.

If the whole tank was at 65 lbs, there would be less volume of air available.

Loose or tight brake parts, the chamber stroke is going to draw all the loose slop up on application, the chamber isn't going to notice any difference when it comes time to release.

Don't be too worried about the grease type, the days of wonky grease are long gone. Whatever quality product you use will be sufficient.

happy coaching!
buswarrior

luvrbus · July 11, 2018, 04:04:43 PM

Probably if you pull the DD3's and clean the racket they will last for ever, they build up a lot of rust setting you not knowing to grease the DD3's helps with the build up

gus · July 11, 2018, 07:35:36 PM

Quote from: buswarrior on July 10, 2018, 08:17:38 PM
The parking tank will be at system pressure, with the regulator feeding the brake circuit the lower pressure.

If the whole tank was at 65 lbs, there would be less volume of air available.

Loose or tight brake parts, the chamber stroke is going to draw all the loose slop up on application, the chamber isn't going to notice any difference when it comes time to release. Thanks. My thinking is that as the brake linings wear the rod will go farther and farther out of the chamber until the rod no longer can move out the tiny bit required to release the rollers. I always had my brakes adjusted before every trip so this may not have ever happened, it was just a though.

Don't be too worried about the grease type, the days of wonky grease are long gone. Whatever quality product you use will be sufficient.

happy coaching!
buswarrior

gus · July 11, 2018, 07:38:32 PM

Quote from: luvrbus on July 11, 2018, 04:04:43 PM
Probably if you pull the DD3's and clean the racket they will last for ever, they build up a lot of rust setting you not knowing to grease the DD3's helps with the build up. Thanks. I was hoping not to have to do that. I don't have a very good place to work underneath.

chessie4905 · July 12, 2018, 04:35:39 AM

Maybe 40 years old. You should pull them, and rebuild them or install replacements. I did mine and with manual, they are pretty easy to do. I got my parts from Mohawk. About $200 bucks for everything, including new pancakes, rollers, etc. You will need to disassemble and clean first. Sometimes main parts can be so corroded, you need to replace unit. Easy to remove and reinstall.
Better than having one not release in a bad location.

bevans6 · July 12, 2018, 10:42:09 AM

"Thanks. My thinking is that as the brake linings wear the rod will go farther and farther out of the chamber until the rod no longer can move out the tiny bit required to release the rollers. I always had my brakes adjusted before every trip so this may not have ever happened, it was just a though."

This is called "over-stroking" and is why you adjust the brake slack adjusters - to take up slack as a consequence of normal wear and use. DD-3's have an allowable extension of 2 1/2", and a normal extension under full brake application of around 1 1/4". You adjust the slack adjuster for this amount of extension.

gus · July 12, 2018, 05:10:26 PM

Quote from: bevans6 on July 12, 2018, 10:42:09 AM
"Thanks. My thinking is that as the brake linings wear the rod will go farther and farther out of the chamber until the rod no longer can move out the tiny bit required to release the rollers. I always had my brakes adjusted before every trip so this may not have ever happened, it was just a though."

This is called "over-stroking" and is why you adjust the brake slack adjusters - to take up slack as a consequence of normal wear and use. DD-3's have an allowable extension of 2 1/2", and a normal extension under full brake application of around 1 1/4". You adjust the slack adjuster for this amount of extension.

I've kept them adjusted so this is probably not my problem