Brake diaphragms....

[Iver]

When I first acquired our MC-9 I wondered if the previous owner had done any work on the brakes among other things.  Unfortunately he passed away before I was able to get much info on the coach so it has been a challenge to discover all about the wiring,  plumbing, mechanical etc.

As mentioned in an earlier post, I am replacing the seal and brake shoes on the tag axle.  And thanks again to all who helped with information.

And after looking at Craig's (Gumpy's) site I thought I should check the brake canister diaphragm.   I guess I also should have clued in before when a front wheel diaphragm failed on the drive home from the previous owner's.

First of all, the bolts holding the clamp were impossible to remove.  Bad sign about any previous repairs.  So a quick cut with an angle grinder removed them and I pulled out the diaphragm.  On the surface it looked in good shape, but bending back the lip showed an almost continuous split all around the inside.  I suspect it could have failed at any time.

So now I am planning to check and service all the wheels because I just don't know their condition and I have no service records.

Rubber diaphragms......5 bucks ea.  I got 6.

Iver.

[JackConrad]

Iver,
  Did you make sure you got the right sizes? the front a axle, tag and drive axle use different sizes. If you have DD3s on the drive axle they require diaphragms that are specific to DD3s (and qite a bit more $$$).  Jack

[gumpy]

What Jack said!

Also, it's a good idea to go through all axles and repair/replace anything that looks suspect. Shoes, drums, bearings, seals, pins, lug studs and nuts, airbags, airlines, diaphrams, leveling valves, etc.

I know it's time consuming and expensive to do this, but far cheaper than the consequences of having a failure on the road. Failure of some of those parts could
lead to very severe consequences under the right circumstances.

[rv_safetyman]

OK guys and Gals, every time this subject comes up I ***TRY*** to convince folks to change the WHOLE chamber.  Each time I mention our test lab experiences, so here we go again.

Gates used to make air brake diaphragms and I ran the test lab at one time.  We had a huge bank of brake cans that cycled several times a minute.  The cans were opposed to each other and worked again the opposite can.  Occasionally the brake canister would fail from fatigue and it was not pretty.  One time one let go just as a tech was inspecting the unit next to it.  He could have gotten pretty badly hurt if he had been a little closer to the failed can.

Here is my point.  Our brake cans are typically pretty old and have seen a ton of fatigue cycles.  Worse yet, they have been exposed to terrible road conditions that could weaken the can via corrosion. 

The failure mode of a rubber diaphragm is usually a small leak at first.  With that condition, you still have some breaking.  If a can fails, you have TOTAL loss of braking in that circuit (major flow loss).

Brake cans are cheap.  This is not the place to try to save a dollar or two.

Jim

[bevans6]

I agree.  the regular cans on the tags and steers are so inexpensive that I can't imagine taking them apart, replacing the wear parts, media-blasting them, cleaning them, repainting at the least and replating them if I was in a mood to do it right, new clamp ring,  new gaiters, and finally new diaphragm.  This is a good time to upgrade to long stroke cans as well.  All the above goes double for spring brake cans.  Even DD-3's I would replace in preference to rebuilding.

Brian

[gumpy]

Jim,

I don't understand all you are saying here. What kind of brake cans were you testing?  Were they DD3's or spring brakes?  What kind of failure of the can did you encounter?  I'm having
a hard time envisioning a DD3 failure that could cause an injury. Obviously, failure of a hose or diaphram in a DD3 could leave the wheel without braking power and potentially could deplete
air reserves.

As for cost, have you checked prices on DD3's lately?  Last I checked, they were several hundred $$$ or maybe even over a thousand $$$ for a single drive axle canister. I may be completely
off base here, though, as I haven't had to buy one.

craig

[Iver]

Thanks everyone for your input....
  But I have ordered six diaphragms and have only picked up one so far.  I did take the old one out from the tag and got it matched at the parts store.
My book says the cans on the front and tag are identical but I will still match the parts before I will use them.
I have only started on this brake project and this first wheel gets new shoes, a new seal and now a new diaphragm.

I will be starting on the drive axle next and will check all wheels as I go, one at a time.
My plan is to do as Craig suggests and repair/replace anything that looks suspect.
As Craig says, the DD3 cans are not dangerous.  But they are very expensive.  I saw a tag axle can for sale for over $500.00

I appreciate the suggestions to replace everything with new but I simply can't throw away and replace parts which are still in very good condition.
However,  having said that, I have a friend who is a mobile diesel mechanic who will check anything for me which I am not sure about.

I agree totally with the safety issue.  I think we are all on the same page there.

       Thanks,  Iver.

[gumpy]

My book says the cans on the front and tag are identical but I will still match the parts before I will use them.

That is correct. Same cans on the tag and steer. They are very simple. No rollers or locking mechanism, just a diaphragm and pushrod.

I'm not positive, but I think the parking brake diaphragm in the drive can may be the same as the tag and steer, too, but have it matched, just in case. It's been a few years since I did
that.

You're doing the job correctly. Rebuild what you can. Replace what needs to be replaced.

All the best to you...

craig

[luvrbus]

Iver, when needing brake parts I found www.ryderfleetproducts.com to have the best prices most of it is free shipping I just ordered some diaphragms (3 bucks ea) and s cams from there


good luck

[mikelutestanski]

HELLO    Dont forget Luke he has stock parts and he uses OEM parts.
     As far as the DD3s I found one site on ebay that has new cans @ approx 550 each.
    I rebuilt my cans 10 years ago and just last month changed the first diaphragm which was the park brake side which developed a crack.  It was a midland part . SO 10 years and approx 60000 miles.  THe symptom was a leaking R-6 valve which I changed then found out the leak was actually coming from the dd3 can. Luke provided the rebuilt R-6 valve which was starting to deteriorate from previous salt exposure so it may have lasted longer but now I know the rebuilt valve  should last as long as I need it to.
    I examine all the parts during a rebuild go from there.
  When I grumble to the wife about the parts and if I shuld spend the money she always says the same thing. That is that I need to be comfortable when I get behind the wheel. So if I have done my best then the trip is enjoyable without having nagging worries about some part going south.  THe trips and the highways have enough distractions and worries to think about. 
   FWIW   
    Good luck   
     REgards and happpy busssin     mike

[rv_safetyman]

Craig, we were using the actual brake cans from the company we were making the diaphragms for.  The name Midland Ross sticks in my mind, but that may have been the pump manufacturer who uses similar diaphragm technology.

It has been a ton of years (~~'78), but I seem to recall that they failed with a fatigue crack at the maximum curved surface where the metal was displaced the most.  The crack would start as a short rupture, but the system would function just fine.  Fairly quickly the crack would propagate and then the outer part of the can would open up completely (many separating with some significant force.

The front and bogey/tag cans are the type we tested.  Would test different sizes at different times.  We did not test the DD3 or spring brake cans.  The thought of the failing cans was still so vivid in my mind (including the look and reaction of the tech that almost got hurt) that I changed all of my cans including the spring cans.  

As we all know the DD3 is expensive and getting harder to get.  I think they might be a cast construction for the air chamber (not sure about that).   If it is a cast can, they would probably be more fatigue resistant (just a guess).  You would just have to use your judgment.  If you have dual air system and both  front and bogey/tag brakes, you will have some decent brakes to slow you down if you loose a DD3

Iver, it sounds like you have made the decision to use your old cans.  That is an individual decision.  However, PLEASE very carefully wire brush both the outside and inside of the cans and ***CLOSELY**** check for cracks.  If your cans are over 10-15 years old, you might be pushing your luck.  If you have any suspicion that they might be the original cans from 1979, please give a second thought to your decision.

Jim

[gumpy]

Jim,

Thanks for the update and clarification. I see now how the failure could have caused concern. Pressing a can out of sheet metal could certainly fatigue the metal sufficiently
to allow a crack to form, and eventually a failure to occur, and with 120 psi of air in there, rapid failure of the chamber would be like a mini-bomb.

Certainly a close inspection is warranted during the rebuild process. Catching a potential failure before it happens is the ultimate goal for all maintenance items.

However, in the 10 years I've been reading these boards, I don't recall a single incident where a DD3 brake can has failed catastrophically on one of these buses (aside from the
diaphragm failures). Maybe someone will correct me on this if I'm wrong. I just don't think the risks are that high to justify the added expense of replacing good working cans.

But this is an individual decision that every bus owner has to make for himself. I've replaced my share of good parts on mine just for peace of mind.

[rv_safetyman]

Craig, just a couple of corrections.  The forming of the can does not damage or "fatigue" it.  What it does do is to create a thinner spot where the fatigue action of the cycling of the pressure can concentrate the loading and begin the failure process (takes many thousands of cycles). 

Next, we did test at some pretty high pressures that would simulate a full panic pressure application.  However, the actual pressure we apply for most of our stops seldom gets over 40% of that.

I too,  have never heard of any can failure (DD3 or other).   Replacing the DD3 is probably not necessary as long as folks keep a close eye on the condition of the can. 

My main point was that the cost of the non-DD3/spring cans is not all that great, and we should really think about replacing the whole can.  Again, this thinking is based on our older buses that have seen a bunch of cycles and terrible road conditions (corrosion) in some cases.

Probably just my conservative (paranoid?) nature.  But when you see one fail, it gets your attention.

Jim