Troubleshooting big air brake leak

Nova Eona · February 28, 2020, 08:31:46 AM

Hi all, so up here in New England we're finally starting to thaw out - was testing some things on the 4104 recently and discovered the following air leak; only when holding down the brake pedal, there's a significant and constant air leak coming from the front, probably the driver side but it's tough to tell. This leak is not audible at all when not applying brakes or when the park brake is engaged(maxis in the back), and it's not coming from the foot valve or anything in the tool compartment under the driver. I've read that this can happen if the valves get some junk in them, but a few hard stomps on the pedal did not fix it.

Right now the ground is too mushy to safely get under the bus, but my plan at present is to wait until it firms up, block it up, and wiggle under to find the leak and repair or replace whatever's going on. Might be that that's all I can do, but I figured I'd ask you all and see if there are any suggestions to try or check in the meantime.

Raymond smith · February 28, 2020, 01:52:41 PM

You might have a hole in the diaphragm on the front brake pot. Easy to change if it is not too rusty

chessie4905 · February 28, 2020, 01:55:29 PM

If the diaphragm is leaking, just replace both front chambers. They are pretty cheap and Luke can get them. One item done and never need fooling with again.

buswarrior · February 28, 2020, 04:46:10 PM

Quote from: chessie4905 on February 28, 2020, 01:55:29 PM
If the diaphragm is leaking, just replace both front chambers. They are pretty cheap and Luke can get them. One item done and never need fooling with again.

X2.

Just swap 'em both when you find it leaking.

Preventive maintenance. Fresh air lines to get full marks.

Happy coaching!
Buswarrior

chessie4905 · February 29, 2020, 04:45:13 AM

Yes, the connecting hoses are common item and also inexpensive. Do them also. You can get those most any truck parts supplier just match length and thread size on ends on hoses. Or Luke also.

Nova Eona · February 29, 2020, 07:44:19 AM

Makes sense, I'm very much in favor of replacing things I'll probably never have to replace again, particularly safety bits. Now I've just got to lay eyes on it to figure out part numbers and lengths. Thanks

chessie4905 · February 29, 2020, 10:15:44 AM

Forget part numbers. Just remove hoses and take them to a hd truck pparts place and match them up. Fortunately it is one of the common items used on coaches.

Raymond smith · March 01, 2020, 06:30:08 PM

Might as well change the slack adjusters too

buswarrior · March 02, 2020, 04:54:25 AM

Quote from: Raymond smith on March 01, 2020, 06:30:08 PM
Might as well change the slack adjusters too

There's nothing to age in a slack adjuster, they may be re-used until their mechanical condition dictates replacement.

I would certainly confirm they are tight in their moving parts, and go at them with lube, to make up for any oversite of previous owners. Disconnected, i'd run the adjuster as lube is being applied.

Doubt they are ASA on this old bus.

Replacing parts with rubber in them is always good preventive maintenance, replacing mechanical parts for no reason gets pricey in a hurry.

We have to keep the greenhorns from spending all their ca$h in one place?

Happy coaching!
Buswarrior

neoneddy · March 02, 2020, 06:48:31 AM

Mine is in the same boat, replaced the one, going to do the other as well. With an Air Impact wrench it went quickly.

Nova Eona · March 02, 2020, 02:07:37 PM

Quote from: buswarrior on March 02, 2020, 04:54:25 AM
We have to keep the greenhorns from spending all their ca$h in one place?

Oh I assure you, I'm spending all my cash in many places!

Jim Eh. · March 03, 2020, 08:22:18 AM

If you go the route of just replacing the diaphrams, have some baby powder on hand. Lightly coat the edges of the diaphram with baby powder to help "settle" the diaphram into position during re-assembly and make sure the steel bits of the brake chamber are ... you guessed it, "clean as a baby's bottom"!

Nova Eona · March 08, 2020, 07:21:44 PM

Okay! So I got my new ramps built and the bus up on them

so I could wiggle under and see what's leaking. As expected, it's the passenger side brake chamber. Now, I'm a newbie to air brakes and am not sure exactly what to call this type of chamber - seems both DD3 and Spring refer specifically to the rears, not sure if the fronts present any of the same hazards but have no intention of opening the chamber anyways. So, question is, what's the proper way to remove these bad boys? Is it as simple as unhooking the air line, knocking the clevis pin out, then removing the two bolts?

Also, looks like I have manual slack adjustors here if I'm not mistaken, I imagine this would be a good time to upgrade to autos? The current adjuster has some port-starboard slop as well, seems that probably shouldn't be there.

dtcerrato · March 08, 2020, 09:21:33 PM

NICE!

richard5933 · March 09, 2020, 04:20:32 AM

I believe you are correct - spring brakes/DD3 are rear brakes. Fronts are usually simple brake cans.

If this were mine I'd just swap out the brake cans. They're not that expensive and they are pretty simple to R&R. You've got enough rust on those that I wouldn't bother trying to rebuild.

They are as simple to R&R as you describe, based on what I've seen on Scott's videos on BGM. Luke should have replacements that you could have delivered by the end of the week.

Not sure I'd swap to automatic slack adjusters - the manual ones have been working for more than a few decades, and it's unlikely you'll put on enough miles to make auto adjusters worth the effort/expense.

If there is slop in the adjusters, it might be a good idea to pull the wheels & drums to see if your brakes need attention. I'm wondering the state of the S-cam bushings, as well as other things that can add slop.