Bad DD3 Diaphragm Symptoms???

Highway Yacht · February 15, 2011, 04:34:25 AM

I was wondering if there are any specific symptoms of a bad diaphragm on DD3 Brakes? I am having a problem with air escaping out of the little rubber boot on the Brake Application Valve up front in the spare tire compartment of my MC-9, but only when the park brakes are applied. When I release the park brakes, the air escaping from the application valve stops. Whatever it is, it only does that when the park brakes are applied. If a bad diaphragm would cause this, is there anyway to determine which canister has the bad diaphragm??

buswarrior · February 15, 2011, 08:02:18 AM

Yes, that is a classic DD3 leaking diaphragm symptom.

Best to consider preventive maintenance and do them all, but to find the offender...

pinch, or disconnect, the service line from one chamber and see which end of the pipe the air escapes from, or which pinched side makes it stop.

happy coaching!
buswarrior

Highway Yacht · February 19, 2011, 04:15:07 PM

What all is involved with doing preventive maintenance on the DD3 brake system once you get into the brake canister?? Is there a parts kit available or is it mainly just changing the diaphragms out with new ones??

buswarrior · February 19, 2011, 05:40:08 PM

an occasional light squirt of grease to the zerk on the chamber, very occasional and very light.
This is one that I would use a manual gun so you can feel what's going on.

Every busnut needs to know the age of their inversion valve. If you don't know yours, just change it and be done with it.

The rubber boots need to stay intact on the DD3 push rods. Dirt up into there is not our friend.

If you have to do a diaphragm, just do them all, both sides, and then it is done.

As for complete dis-assembly... I don't recall a busnut sharing that they did that. If there are problems with the locking rollers, that's a trigger for trade for fresh re-builds. It takes some experience to make the determination as to whether the core is worthy of fresh parts or scrap.

I am a big advocate of using anti-seize on all mating surfaces of airline fittings, so you have half a chance of being able to get them apart again for the next time, rather than cutting the lines and replacing it all.

happy coaching!
buswarrior

John316 · February 19, 2011, 05:58:43 PM

Jimmy,

Did I mention that I want to go to spring brakes

. Just kidding. The DD3's really are just fine. So far ours have done great, with very few problems.

God bless,

John

Highway Yacht · February 19, 2011, 06:32:49 PM

Quote from: John316 on February 19, 2011, 05:58:43 PM
Jimmy,

Did I mention that I want to go to spring brakes . Just kidding. The DD3's really are just fine. So far ours have done great, with very few problems.

God bless,

John

John.. Most importantly my brakes are stopping the bus just fine right now but I do have other problems with the braking system. First off, the air pressure build normal up to about 60 to 65 psi and then it takes forever to climb from there up to 120 psi. If I release the park brakes when I have enough pressure, the pressure will start to rise a lot quicker up to full 120 PSI capacity. Once I stop the engine and apply the park brakes, the air pressure will drop very fast from 120 PSI down to about 65 PSI (in less than 10 minutes). After the pressure quickly drops to 65 PSI, the pressure drop slows way down to maybe a 10 PSI drop per hour. Also, I've had a time or two that my Park Brakes didn't hold after the pressure drop and allowed the bus to roll a few feet.. That's not good... With all that said..I only build pressure slow and lose pressure fast when the Park Brakes are applied. Once I have enough air pressure that I can release the park brakes, my troubles go away until I need to set the park brake again.

buswarrior · February 19, 2011, 06:35:30 PM

Yes, fix your diaphragms.

happy coaching!
buswarrior

Highway Yacht · February 19, 2011, 06:46:23 PM

Quote from: buswarrior on February 19, 2011, 06:35:30 PM
Yes, fix your diaphragms.

happy coaching!
buswarrior

Suppose to have a friend here next weekend to work on it. He is bringing some Diaphragms with him so hopefully they will be the right diaphragms.. He has never worked on a bus braking system before but does brake work on Semi trucks and trailers everyday where he works. If the diaphragms he brings won't work, I will have to order some and put it all back together the following weekend. I wonder if these diaphragms be purchased at NAPA if the ones he brings does not fit.

buswarrior · February 19, 2011, 06:50:23 PM

He has to bring DD3 diaphragms, or he's wasting his time.

"regular" diaphragms don't come close.

Most truck folks have never seen or heard of a DD3 brake chamber.

And that isn't going to get better.

happy coaching!
buswarrior

Cary and Don · February 19, 2011, 08:03:09 PM

We had a truck mechanic destroy one of chambers before he figured out that it wasn't like the truck chambers. Napa can order the diaphragms for you. The brake application one runs about $30, the park diaphragm was about half that. They are really easy to change, just kind of a pig to get to. The chambers don't even have to come off to do it.

Don and Cary
GMC4107
Neoplan AN340

Highway Yacht · February 19, 2011, 09:37:38 PM

Quote from: Cary and Don on February 19, 2011, 08:03:09 PM
We had a truck mechanic destroy one of chambers before he figured out that it wasn't like the truck chambers. Napa can order the diaphragms for you. The brake application one runs about $30, the park diaphragm was about half that. They are really easy to change, just kind of a pig to get to. The chambers don't even have to come off to do it.

Don and Cary
GMC4107
Neoplan AN340

I was wondering if NAPA could get them for me. I did a little searching on the Napa website using the Bendix Part Numbers but got "0" results. I'll stop by my local Napa Monday and see what they say. I know they have gotten lots of other stuff for me for the bus. I hope I do have the correct part numbers. I got them off the Bendix DD3 Type 30 Technical Sheet.
These are the numbers I searched for on the Napa Site with no luck:
Bendix Service Diaphragm Part # 246371
Bendix Auxiliary Diaphragm Part # 246675

I did find these on a DD3 google search but these have the vendor's part numbers and not the Bendix numbers.
The Service Diaphragm there is $80.15 and the Auxiliary Diaphragm is $23.89 but they don't disclose wheather these are Type 30 or Type 24.
http://store.valueweb.com/servlet/busfixx0/Categories?category=Brake

buswarrior · February 20, 2011, 06:07:58 AM

everyone has their own part numbers for pretty much everything.

Cross referencing is what separates a real parts guy from a boob.

I expect that they will be type 30's. There may be a type 24 in theory, but pretty rare out here.

Mohawk is a popular source, and it doesn't hurt to price MCI.

http://www.mohawkmfg.com/
1.800.323.7652

http://www.mcicoach.com/parts/parts.htm
U.S. 800-323-1290
Canada 800-665-0155 (English)
800-546-3457 (Français)

Remember, many motorcoach fleets are small mom & pop operations, so they are used to helping folks who need some help and buy limited quantities.

happy coaching!
buswarrior

Tom Y · February 20, 2011, 11:00:12 AM

I also tried NAPA before with no luck. Tom Y

Cary and Don · February 20, 2011, 11:16:31 AM

Our Napa has a heavy vehicle department. I took in my manual and they found the right one, even after I argued it didn't look right. Not all the Napas have that department. I would think that the others could make a phone call though and find them.

Don and Cary
GMC4107
Neoplan AN340

gmbusguy1 · February 20, 2011, 04:40:20 PM

Just call Luke at US Coach and you will have all the correct parts and FREE advice that is the best available

then you will know how to do this job

Chris