Combination spring and service brake chamber rebuild

[Justino]

My combination brake chamber on the front of my center axle is leaking on my 923, I've searched but all I can find much info on is regular service brake chambers. Has anyone rebuilt one of these and if so do you have any pictures or illustrations? Does any body know the part numbers for the diaphragms, boots, seal, etc?

 

[73m819]

location requires MORE then UNITED STATES

 

[Csm Davis]

You can sometimes tighten the clamp a little and they will quit leaking but unless you are sure you can fix one and not kill yourself just buy a new one the spring in these are as big as a small car coil spring. And as you are asking how it is done I will say that if you want to learn this procedure go to a big rig shop and have them show you.

 

[73m819]

I am sure -24p-1/24p-2 will have the numbers and pictures you are looking for.

 

[Justino]

Its leaking through the parking side diaphragm, I was planning on caging it, draining the air, cracking it open and replacing that
diaphragm. What I really wanted to know was, is there a return spring, what size is the diaphragm 16 or 12, and is there a seal or does the diaphragm accomplish that through being sandwiched between the sides of the case.

 

[quickfarms]

Its leaking through the parking side diaphragm, I was planning on caging it, draining the air, cracking it open and replacing that
diaphragm. What I really wanted to know was, is there a return spring, what size is the diaphragm 16 or 12, and is there a seal or does the diaphragm accomplish that through being sandwiched between the sides of the case.

It is very very dangerous to use the caging bolt to compress the spring to replace the diaphragm. The ears can snap off the caging bolts.

 

[Ferroequinologist]

Honestly for just a few more dollars than the diaphragm, you can buy a whole take out unit from several sources. I took one apart once and I don't want to ever have to do it again. It was like working on something with a cobra right there coiled and ready to bite.

 

[Justino]

I am sure -24p-1/24p-2 will have the numbers and pictures you are looking for.

Thanks I found just about everything I was looking for.

 

[Vintage iron]

The civilian units are made so they can not be rebuilt on the spring brake side. Yes they are very dangerous.

 

[73m819]

The civilian units are made so they can not be rebuilt on the spring brake side. Yes they are very dangerous.

YES dangerous but can be done SAFELY, I have repaired/rebuilt many over the years, ONE thing use a NEW caging bolt if you rebuild, just to cage, use the USED supplied bolt, If you need to replace the spring, there is a SPECIAL long release bolt/tool, plus a cage (retaining device) to use to contain a mishap. NO MATTER WHAT NEVER, NEVER get in line of either end, side work only while caged, also KNOW WHERE the spring or bolt will go if the gage becomes UNCAGED, a flying spring/bolt/part/ect. ricocheting off something will cause a lot of hurt and damage.

Now with all the above said, as cheap as rebuilt/new cans are these days, unless you are stuck somewhere and a rebuild is required to get going, just buy a new/rebuilt can, you will be ahead just in cost of your time let alone the rebuild hassle.

 

[Jakelc15]

Be careful. Not too long ago I was rebuilding a specialty can for a driveline parking brake that decided not to cooperate. I put in the 100 ton shop press to hold it together while I removed the ring of bolts that held it together. Then I slowly released the press letting the spring pressure off. The spring wanted to push out sideways. After after clamping, chaining, and fighting with it, I found the pig tail of the coil was broke off which made the coil push sideways.
Threw that in the scrap bin, should have saved time and frustration and ordered a new one to begin with.

 

[Justino]

YES dangerous but can be done SAFELY, I have repaired/rebuilt many over the years, ONE thing use a NEW caging bolt if you rebuild, just to cage, use the USED supplied bolt, If you need to replace the spring, there is a SPECIAL long release bolt/tool, plus a cage (retaining device) to use to contain a mishap. NO MATTER WHAT NEVER, NEVER get in line of either end, side work only while caged, also KNOW WHERE the spring or bolt will go if the gage becomes UNCAGED, a flying spring/bolt/part/ect. ricocheting off something will cause a lot of hurt and damage.

Now with all the above said, as cheap as rebuilt/new cans are these days, unless you are stuck somewhere and a rebuild is required to get going, just buy a new/rebuilt can, you will be ahead just in cost of your time let alone the rebuild hassle.

I've checked around and found the A3280E6817 piggyback assembly for $125-200, which doesn't seem too bad. Does anyone know of a source for the rebuilt piggyback assembly or an alternative part number for equivalent civilian models. I've seen T16 spring/T12 service piggybacks for even less than the Meritor part but I'm not sure about some of the particulars such as stroke length, line fittings, and non-pressure housing compatibility.

 

[peter34668]

I've checked around and found the A3280E6817 piggyback assembly for $125-200, which doesn't seem too bad. Does anyone know of a source for the rebuilt piggyback assembly or an alternative part number for equivalent civilian models. I've seen T16 spring/T12 service piggybacks for even less than the Meritor part but I'm not sure about some of the particulars such as stroke length, line fittings, and non-pressure housing compatibility.

I too am in the need of the same part and spent my day calling 22 different suppliers all stating that although this is a good part number no one in the country has one. If you have been able to source one please let me know where and I will be eternally grateful

 

[Jakelc15]

I'm not sure your looking for the right part.
I have numbers nsn: 2530 01 125 6076 part: x76-3276-L-12 meritor Alternate pn: ta-0011sba and 84tc266

They are pricey but can be found. Those #'s are for the spring brake can.

The non spring can (front) is nsn: 2530 01 091 7814 pn: E3276-L-12

 

[Justino]

I'm not sure your looking for the right part.
I have numbers nsn: 2530 01 125 6076 part: x76-3276-L-12 meritor Alternate pn: ta-0011sba and 84tc266

They are pricey but can be found. Those #'s are for the spring brake can.

The non spring can (front) is nsn: 2530 01 091 7814 pn: E3276-L-12

Nsn: 2530 01 125 6076 part: x76-3276-L-12 is the complete assembly and includes the entire non-pressure side.

Cage code 78500 (Meritor) A-3280-E-6817 HOUSING ASSEMBLY, BRA BRAKE CHAMBER is just the piggyback unit and comes caged with all internals and the center section that the lines attach to.

Ref.
TM9-2320-272-24P-1 Unit, Direct and General support parts and special tools manual for the M939 series truck. 1 of 2. Feb 1999
Page 251-251.1 Figure 251
Item #6 (7,8, and *a) Piggyback
Item #5 (6-15, and *b) Complete unit without mounts or lock nut

Unless you had some sort of impact, or something crazy happened, you should only need the piggyback and a size 12 diaphragm to do a good rebuild on this unit.

 

[juanprado]

check ebay seller foxholejoe as he has new nos

 

[Justino]

That part number is correct for just the piggyback. If you are leaking air out of your caging hole or your outer or center housing sections are cracked this will do the trick. Find it parts dot Com should have them in stock for $184, jbr17llc dot com also shows it in stock but they didn't respond to my email when I tried to find out what all was included with it.

If you google A-3280-E-6817 (make sure to include the dashes) you should see several sources (i.e Brooks & Maldini, CTG) ask for a quote one of the suppliers that comes up on the search has them for $125.

***Disclaimer***DON'T TRY THIS IT'S DANGEROUS!!!!

If your diaphragms are just leaking you can rebuild this unit yourself, you will need an unhealthy balance of B$%ls and common sense, a size 12 and 16 diaphragm (3 bucks a piece), a good caging bolt, and a new 1/2" to 1" longer bolt and new nut for the big deadly side clamp (actually I think the longer bolt was for the little side cause the clamp is hard to close enough for the original).

With air in the truck, the E-brake off, and wheels triple chocked, cage the chamber then drain the air. Open the little clamp (closest to the wheel) and pull out the old diaphragm and clean out the rust or other crap inside. Replace this with the #12 and bolt it all back up (you just did the service brake).

Now if you still want to continue get out from under the truck and reach in between the wheels from the outside for the mid axle or around the wheel for the back.

Make sure brake is still caged!!!

Unbolt the deadly big side.
DO NOT UNDER ANY CIRCUMSTANCES position yourself so you are in front of the the open end or in front of the caging bolt.
Always work from the side of the chamber.
Know where the parts will fly to and bounce off of it stuff goes bad.
After the big deadly side is unbolted slide it down, the safety ears wont let it come straight off.
Put the #16 in the big can and slide it back on don't bother cleaning this side too risky.
Put the bolt back in and crank her down, fire up the truck to give the brake air, and have a beer.
If nothing falls off uncage the brake and your good.

Your done.

I've done five of these in the last month, it's kind scary but I need a little risk in my life now that nobody shoots at me or tries to blow me up.

 

[doghead]

FHJ, How did that saying go?

 

[peter34668]

Thanks for everyone's help. I have been a lurker here for about a year and in the past I have always found the answers I need via the search option. I currently have 5 military trucks, It started with a 53' M37 I bought just as a yard truck. I loved it so much I I did a bit of repairs to it and decided I need bigger. I then found a 72' M35A2 and drove that around as my grocery getter and wheeling truck. I once again wanted bigger and found a mint freshly rebuilt Tan 85' M923. When I went to pick it up a noticed the guy had 3 other trucks that were equal in quality. Luckily the guy was getting out of military trucks so I made him an offer on 2 more. I now also have the camo 83' M923 and the crown jewel to my collection a 91' M936A2 wrecker. Everytime I get a new to me truck I start with a good cleaning, change all the fluids and filters and go through the with a fine tooth comb. I also happen to have a class A CDL license. I don't drive for a living but many years back I completed the schooling and decided not to pursue that field. I did keep the license all these years however. There seems to be loads of comments as to if a CDL is needed or not but I have one nevertheless.