DD3 Parking Brake Won't Release (Again!)

gus · July 08, 2018, 04:07:49 PM

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

chessie4905 · July 08, 2018, 05:19:19 PM

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.

opus · July 08, 2018, 09:09:44 PM

Whens the last time you moved the bus?

Dave5Cs · July 08, 2018, 09:55:49 PM

Also worn "S" cams will do it. You can get rebuilts for around $450.00

Bill Gerrie · July 09, 2018, 06:27:07 AM

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.

buswarrior · July 09, 2018, 06:36:23 AM

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

Bill Gerrie · July 09, 2018, 07:10:30 AM

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.

bevans6 · July 09, 2018, 08:00:16 AM

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.

buswarrior · July 09, 2018, 08:01:32 AM

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

buswarrior · July 09, 2018, 08:08:21 AM

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

luvrbus · July 09, 2018, 08:46:35 AM

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

chessie4905 · 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.

luvrbus · July 09, 2018, 11:14:43 AM

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

chessie4905 · July 09, 2018, 04:59:53 PM

Ok, 4104 and 4106's. Def not buffaloes

luvrbus · July 09, 2018, 07:22:27 PM

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