Just had a thought (Rare!).
Could excessively worn brake linings allow the shaft to extend so far forward that it won't unlock?
I had this thought just before I spend $1100 on rebuilt brake cans!
I suspect rusted/contaminated rollers since I use the bus so seldom anymore, but the only way to test this is by removing and taking them apart - I'm getting too old for this! Brake linings are much easier to check.
Thanks
There is a grease fitting to add lube to shaft locking rollers. Extended sit time and infrequent lube service can cause rollers to stick and not release from corrosion. Be glad you were able to get rebuilt ones. They're getting scarce. Now you also have new brake diaphragms also.
Whens the last time you moved the bus?
Also worn "S" cams will do it. You can get rebuilts for around $450.00
A friend of mine had a 4107 with DD3's. If he didn't reduce the air pressure to 90 to 100 psi by repeatedly applying the service brakes BEFORE he applied the DD3's he would on occasion not be able to release them. Once he always got used to reducing the air pressure before applying the DD3's he never had any problems releasing them.
Re: Bill's comments above
Check the pressure setting of the regulator feeding the parking portion of the DD3.
If the regulator is allowing too high a pressure, there is less pressure differential for the service brake to squeeze and take the force off the locking rollers.
But, these machines need lube and need to be used.
A sitting coach makes its own trouble!
Happy coaching!
Buswarrior
In Joe's bus there was no regulator. None shows on the manual for a 4107. We looked all over the place and read all the books and none exists.
Adding an 80 psi regulator would be a good upgrade. The parking brake diaphragm on the DD3 is roughly 80% of the size of the service brake diaphragm, so produces less application pressure than the service brake diaphragm so allowing a FULL pressure application enough oomph to push out the push rod that tiny bit and release, but reducing the maximum pressure available to the parking brake is always a good thing. Remember also that the locking port needs the same air pressure applied to it before it will release, supplied by the inversion valve - is the inversion valve in good working order, supplying air pressure to the locking port? I had to replace my inversion valve (and all the rear brake hoses) when I did my rear brakes.
MCI always regulated the DD3 parking portion.
Different pressures for different models at different times, the last of 'em were on the heaviest coaches, and had the highest pressure, IIRC...
MCI was completely DD3 committed, GM, a somewhat rare option. GM was counting on the differences in diaphragm sizes for the strength differential to unlock, MCI wanted more insurance?
Lost to the sands of time...
even in the captivity of a build or storage, a busnut should fight hard to run the coach systems somehow, to whatever extent possible, with some frequency.
These old coaches only keep going reliably, if they keep going. Park it and forget about it, stuff stops working right, stuff gets stuck, stuff corrodes, and life gets miserable, cuz now you have to go find the fix to more problems that you had before...
As FF always said, 100 miles, once a month...
Happy coaching!
Buswarrior
X2 on the inversion valve.
Should be as standard a replacement job on a new to you coach, as changing the fluids.
Few inversion valves have EVER been changed out on any PM schedule.
It is the Master to your slavery, when it comes to your DD3 parking system.
Your choice, at home in the driveway and never think about it again... or at the mercy of the roadside...
You will likely need all new hoses at the same time,another investment in PM...
Put anti-seize on all mating surfaces, you will thank yourself in 20 years when you can actually get the fittings apart again...
Happy coaching!
Buswarrior
Measure if the 4107 is like a 4106 you have enough room to install spring brakes and you can toss the DD3 brakes,if like a 4905 it takes some fab work but doable for spring brakes,I have done spring brake conversions on both,using the MGM rotatable spring brakes chambers 300 bucks for a set and you are done
The Buffalos need the rear baggage compartment notched 3or 4 inches to get the maxis to clear. Afaik, 4104 is only GM that they will fit. Be careful if you convert, there are a lot of components back there if it has the dual braking system. I just completely rebuilt all of my braking system, tanks, valves, components, lines, hoses. Did it over the winter. I'll post pictures once I'm sure you don't have to pecker around to get them to fit size wise.
Quote from: chessie4905 on July 09, 2018, 10:57:01 AM
The Buffalos need the rear baggage compartment notched 3or 4 inches to get the maxis to clear. Afaik, 4104 is only GM that they will fit. Be careful if you convert, there are a lot of components back there if it has the dual braking system. I just completely rebuilt all of my braking system, tanks, valves, components, lines, hoses. Did it over the winter. I'll post pictures once I'm sure you don't have to pecker around to get them to fit size wise.
Quote from: chessie4905 on July 09, 2018, 10:57:01 AM
The Buffalos need the rear baggage compartment notched 3or 4 inches to get the maxis to clear. Afaik, 4104 is only GM that they will fit. Be careful if you convert, there are a lot of components back there if it has the dual braking system. I just completely rebuilt all of my braking system, tanks, valves, components, lines, hoses. Did it over the winter. I'll post pictures once I'm sure you don't have to pecker around to get them to fit size wise.
Take a peek at Tom and Doreen Caffey 4106 Ted at Bus Maintenance in Ca installed his spring brakes and I copied it since he is the number 1 guru on GM buses and works like a charm with the right spring brake chambers 8)
Ok, 4104 and 4106's. Def not buffaloes
Quote from: chessie4905 on July 09, 2018, 04:59:53 PM
Ok, 4104 and 4106's. Def not buffaloes
There was plenty of room on Bills 4905 his had the bogie removed but I did make a bracket for something and forgot what for I need to dig the photos out
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
Ok,4104's, 4106's,and 4905 with bogie removed.
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.
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
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
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
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.
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.
"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.
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