Air tank size- would a FMTV benefit from a much larger tank?

[Reworked LMTV]

I was thinking about how quickly the air tanks run out of air with repeated braking. While I have never driven in ice or snow in my truck, might a larger tank allow you to pump the brakes a lot more before no air (assuming no antilock brakes) and thus be safer? Maybe I'm missing something.

 

[doghead]

Is your air system fully serviced and operating at full capacity?

 

[wheelspinner]

They are air hogs with repeated braking. I am parting one out and plan to use a tank or two for additional capacity.

 

[Suprman]

Compared to a M939 truck single piston compressor, the dual piston one in the lmtv is great. I can recommend rebuilding your unloader in the compressor head and turning up the air governor a few psi. That might make a noticeable difference. If you hold your brake pedal down and your air gages go down slightly and then dont recover or keep slowly going down then you have an air leak somewhere.

 

[Reworked LMTV]

yes

 

[Tga]

The brake systems are designed to have enough capacity under most situations. The components are engineered to be compatible with each other, meaning the compressor is sized to be able to push enough air to efficiently and effectively keep the proper sized tanks pressurized to the proper psi. Different vehicles have different/more/less brake chambers that require different air reserves. While adding capacity may seem like a good idea, it is not. Additional capacity equals additional recovery time. In a situation where you have a leak in the system the compressor will not be able to pump enough volume (cfm's) to hold the psi needed to operate the system, leading to activation of the emergency brake system. The systems are also a dual tank system that somewhat isolates the two air supplies from each other to decrease low air situations. Bottom line is...if you're having issues with holding pressure in the 90-120psi range during normal operation you have other issues that need to be addressed. Basic rules for air loss are as follows (start tests with system fully charged to 110-120psi). I am referring to tractor only.
1. Emergency side: chock wheels, engine off, apply air (by pushing in your yellow park brake button), don't not apply foot pedal, if air loss equals 2psi per minute or more you have an unsafe condition and repairs should be made before operation of vehicle.
2. Service side: chock wheels, engine off, apply air (same manner as emergency side), apply full brakes via foot pedal and HOLD, if air loss equals 3psi per minute (after initial pressure drop) or more you have an unsafe condition and repairs should be made before operation of vehicle.
3. Recovery time: chock wheels, start engine, release brakes (as before), pump brake pedal until pressure falls to 85psi, with engine running at operating rpm's (1600-1800 rpm) pressure should recover from 85psi to 100psi in no more than 45 seconds. If it does not you have an unsafe condition.

 

[1951M1078]

What about just adding another tank ? Maybe something that will only fill when the system is topped off ?

 

[fjdedrick]

The brake systems are designed to have enough capacity under most situations. The components are engineered to be compatible with each other, meaning the compressor is sized to be able to push enough air to efficiently and effectively keep the proper sized tanks pressurized to the proper psi. Different vehicles have different/more/less brake chambers that require different air reserves. While adding capacity may seem like a good idea, it is not. Additional capacity equals additional recovery time. In a situation where you have a leak in the system the compressor will not be able to pump enough volume (cfm's) to hold the psi needed to operate the system, leading to activation of the emergency brake system. The systems are also a dual tank system that somewhat isolates the two air supplies from each other to decrease low air situations. Bottom line is...if you're having issues with holding pressure in the 90-120psi range during normal operation you have other issues that need to be addressed. Basic rules for air loss are as follows (start tests with system fully charged to 110-120psi). I am referring to tractor only.
1. Emergency side: chock wheels, engine off, apply air (by pushing in your yellow park brake button), don't not apply foot pedal, if air loss equals 2psi per minute or more you have an unsafe condition and repairs should be made before operation of vehicle.
2. Service side: chock wheels, engine off, apply air (same manner as emergency side), apply full brakes via foot pedal and HOLD, if air loss equals 3psi per minute (after initial pressure drop) or more you have an unsafe condition and repairs should be made before operation of vehicle.
3. Recovery time: chock wheels, start engine, release brakes (as before), pump brake pedal until pressure falls to 85psi, with engine running at operating rpm's (1600-1800 rpm) pressure should recover from 85psi to 100psi in no more than 45 seconds. If it does not you have an unsafe condition.

Excellent!

Sent from my VS995 using Tapatalk

 

[wheelspinner]

All good information and I understand it all completely. In normal operation it is true, the air supply is fine. When off roading, with a lot of down hill braking I have several times run out of air, and additional air would have been nice to have. Having to stop mid-travel and wait for air again was not my idea of fun. Although this is an extreme outlying need, it was a need. But just to be sure, I will again go through leak down testing on the truck before any mod is made.

 

[Reworked LMTV]

The brake systems are designed to have enough capacity under most situations. The components are engineered to be compatible with each other, meaning the compressor is sized to be able to push enough air to efficiently and effectively keep the proper sized tanks pressurized to the proper psi. Different vehicles have different/more/less brake chambers that require different air reserves. While adding capacity may seem like a good idea, it is not. Additional capacity equals additional recovery time. In a situation where you have a leak in the system the compressor will not be able to pump enough volume (cfm's) to hold the psi needed to operate the system, leading to activation of the emergency brake system. The systems are also a dual tank system that somewhat isolates the two air supplies from each other to decrease low air situations. Bottom line is...if you're having issues with holding pressure in the 90-120psi range during normal operation you have other issues that need to be addressed. Basic rules for air loss are as follows (start tests with system fully charged to 110-120psi). I am referring to tractor only.
1. Emergency side: chock wheels, engine off, apply air (by pushing in your yellow park brake button), don't not apply foot pedal, if air loss equals 2psi per minute or more you have an unsafe condition and repairs should be made before operation of vehicle.
2. Service side: chock wheels, engine off, apply air (same manner as emergency side), apply full brakes via foot pedal and HOLD, if air loss equals 3psi per minute (after initial pressure drop) or more you have an unsafe condition and repairs should be made before operation of vehicle.
3. Recovery time: chock wheels, start engine, release brakes (as before), pump brake pedal until pressure falls to 85psi, with engine running at operating rpm's (1600-1800 rpm) pressure should recover from 85psi to 100psi in no more than 45 seconds. If it does not you have an unsafe condition.

Thanks for the exceptionally thorough reply.

 

[porkysplace]

The brake systems are designed to have enough capacity under most situations. The components are engineered to be compatible with each other, meaning the compressor is sized to be able to push enough air to efficiently and effectively keep the proper sized tanks pressurized to the proper psi. Different vehicles have different/more/less brake chambers that require different air reserves. While adding capacity may seem like a good idea, it is not. Additional capacity equals additional recovery time. In a situation where you have a leak in the system the compressor will not be able to pump enough volume (cfm's) to hold the psi needed to operate the system, leading to activation of the emergency brake system. The systems are also a dual tank system that somewhat isolates the two air supplies from each other to decrease low air situations. Bottom line is...if you're having issues with holding pressure in the 90-120psi range during normal operation you have other issues that need to be addressed. Basic rules for air loss are as follows (start tests with system fully charged to 110-120psi). I am referring to tractor only.
1. Emergency side: chock wheels, engine off, apply air (by pushing in your yellow park brake button), don't not apply foot pedal, if air loss equals 2psi per minute or more you have an unsafe condition and repairs should be made before operation of vehicle.
2. Service side: chock wheels, engine off, apply air (same manner as emergency side), apply full brakes via foot pedal and HOLD, if air loss equals 3psi per minute (after initial pressure drop) or more you have an unsafe condition and repairs should be made before operation of vehicle.
3. Recovery time: chock wheels, start engine, release brakes (as before), pump brake pedal until pressure falls to 85psi, with engine running at operating rpm's (1600-1800 rpm) pressure should recover from 85psi to 100psi in no more than 45 seconds. If it does not you have an unsafe condition.

Well what about tractor versions ? I haven't looked through the parts TM but I am betting they use the same compressor as the cargo version . With various trailers of 1, 2, 3 axles ect. , the additional air capacity comes from additional air tanks on the trailers.

 

[Suprman]

They all have the same compressor and tanks on the truck

 

[porkysplace]

They all have the same compressor and tanks on the truck

Well then adding tanks shouldn't effect air recovery any more than adding a trailer with more tanks.

 

[Tga]

Well then adding tanks shouldn't effect air recovery any more than adding a trailer with more tanks.

Except maybe when you add a trailer to your already added to air system? It WILL effect the recovery rate even without a trailer....will it effect it enough to put it out of spec? I don't know...depends on how big/many tanks you change/add. If the compressors are indeed the same it may give more leeway on an lmtv vs. an fmtv. The point I was trying to make is that there are many things to consider/understand before you start modifying your braking system. The OP asked if a "much larger" tank would help and if he was missing anything....merely trying to throw some things out there that could/should be considered and invoke a little more thought.

 

[porkysplace]

Except maybe when you add a trailer to your already added to air system? It WILL effect the recovery rate even without a trailer....will it effect it enough to put it out of spec? I don't know...depends on how big/many tanks you change/add. If the compressors are indeed the same it may give more leeway on an lmtv vs. an fmtv. The point I was trying to make is that there are many things to consider/understand before you start modifying your braking system. The OP asked if a "much larger" tank would help and if he was missing anything....merely trying to throw some things out there that could/should be considered and invoke a little more thought.

Well here in michigan we regularly switch from 2 axle trailers to 8 axle trailers ( more with JoeDogs and permits) without any problems . So whatever the tractor version is rated to pull ( it seems 3 axle trailers at least ) adding a air reserve to a cargo truck with the same system isn't going to effect it.

 

[Suprman]

If one of the check valves by the steering box, or your tractor protection valve have a cracked diaphragm then you will drop pressure faster when braking.

 

[snowtrac nome]

I cant speak for your driving style but I spend a lot of time off road and on un improved roads even in the winter I have never had a lack of air pressure. I'm betting if you do your airbrake test you will find you have a leak the other problem can be excessive stroke in the air cans because the auto adjusting feature isn't working.

 

[dmetalmiki]

My 530C has 3 tanks standard and an extra I fitted to assist in the air power steering. Everything works fine. And it is quite possible to turn the wheels lock to lock stationary. (with a 'quite satisfactory(hiss)). Sound.