Question for Buswarrior ( or other DD3 expert)

JackConrad · September 12, 2007, 04:57:33 PM

I have to replace a service diaphram on the driver's side DD3. Here is my question: Since the DD3 locks the shaft in the applied position, can I simply disconnect the air lines, remove the band the holds the service diaphram chamber, remove the back half of the DD3, install the new diaphram, and re-install the chamber on the DD3? Jack
PS: while I have the back 1/2 of the DD3 off, I plan to go ahead and replace the aux. diaphram also.

Jerry Liebler · September 12, 2007, 05:57:53 PM

Jack,
Yes. I just did the left side of mine. I took the can out by removing the air lines, pin and 2 nuts. mainly so I could clean up the parts before reassembly. Be sure to mark the pieces so you get the lines oriented the same in reassembling. Don't make the mistake I did, recheck the lines, it's easy to swap the front and rear.
Regards
Jerry 4107 1120

buswarrior · September 13, 2007, 06:55:21 PM

Hello Jack.

As Jerry said.

I suspect you want to leave it mounted in the coach.

For ease of re-assembly, back that brake's adjustment off all the way so there is less pressure on the return springs. And be ready for the parts to jump off on disassembly.

For those whose fingers aren't what they used to be, one of those cheapie cargo straps with the ratchet is a handy tool to rig up to help pull the pieces back together and hold them while you mess with the bands and fasteners.

And for the casual viewer, Jack already knows to properly block the suspension and block the wheels to prevent personal misadventure. And a DD3 is not a spring brake. It does not have the big power spring in it that will kill you if you mess with them!

happy coaching!
buswarrior

FloridaCliff · September 14, 2007, 03:58:11 AM

Hi Jack,

When I did mine I didn't remove the air lines, keeps the can or section hanging out of the way off the ground.

As BW said, it is easier to back the adjustment off. I did it without, but sounds like an easier way.

If you don't back it off, after you get the service diaphram in and can straped on, push it in by hand to make it easier to get the park diaphram and back on.

Edit: I am by NO means an expert on DD3, but have BTDT on all phases of my air brakes and have a qualified opinion.

Cliff

JackConrad · September 14, 2007, 05:12:00 AM

Bus warrior,
Yes, I did plan to replace the diaphrams without removing the unit from the mounting bracket. Looking at the photo of the cut away DD3 from your presentation at Bussin' 2006, it looks like if I leave the parking brake applied, the rollers will hold the shaft, keeping the return spring compressed?

buswarrior · September 14, 2007, 06:07:05 PM

Hello Jack

The spring layout in that mock-up is not quite right.

The builder of that cut-away took a small liberty on correct pieces, as the focus was to show function to drivers, not teach technicians. I didn't think it important...until now!

Check the cut away picture in the MCI manual, and you will see that the spring layout is somewhat different than the one in those pics I used. The spring more closely matches the cone shape of that piston and fills the cavity a little better.

Hmmm, that cut-away must be nearing the end of its useful life at its fleet...I'm due for another visit!

happy coaching!
buswarrior

JackConrad · September 15, 2007, 04:52:36 AM

Thanks Ewen,
My new DD3 diaphragms arrived yesterday from MCI. I hope to get them changed today. I will do as you say and back off the slack adjuster. I decided to go ahead and change all the brake diaphragms while I am at it (much easier in my shop than along the road). I removed the front diaphragms yesterday to find both must have been replaced right before I bought the bus, they are look brand new. Jack