M1083 Howls like Godzilla got kicked in the clockweights

[M1083]

Hi fellas,

I am not a mechanic, and I don't know what most of these parts are called or what they look like, so you'll have to be really untechnical with me. I have been trying to work the bugs out of this MTV for over a year for work. It is a fire truck now. It pumps the tires up when you start it like it should, but every 15 minutes or so, and every time it is shut off, it lets out this godawful scream for a few seconds up to a few minutes. The sound is coming out of the 2 exhaust manifold things over the rear axles. They each have 2 hoses going to the rear wheels, and it looks like they are connected to each other, and both fed from the same hose that goes towards the front of the truck somewhere.

The HWY light blinks most of the time. Not sure if it is related, but the rear tank gauge shows 120, while the front tank gauge only tops out around 105 or so. We have been able to fix all the air leaks that we found, so there are none that we area currently aware of.

Any help would be appreciated. Thanks guys!

 

[coachgeo]

Hi fellas,... Any help would be appreciated. Thanks guys!

if you have not done so yet..... get the TM's for all the diagnostic test info. (technical Manuals). If it is an A0 then all the manuals are on this board. (see TM section on front page of Steelsoldiers. If it is an earlier A1 then you can now get all those on CD or thumb drive via a fellow on Facebook. (minus branching software that allows one to input results of diagnostic test.. that part not released to public... just the manual is released)

 

[M1083]

Not sure how to tell which truck we have. I have downloaded and read good chunks of both volumes of the 1800 page Manual. It's frustrating, because any real problems it just tells you to take it to a mechanic.

 

[coachgeo]

Not sure how to tell which truck we have. I have downloaded and read good chunks of both volumes of the 1800 page Manual. It's frustrating, because any real problems it just tells you to take it to a mechanic.

what year is the truck?

The Vin number is the closest clue to what you have A0 or A1....... if it starts with an:

"A" then it is an A0.
"A1" then it is an A1...

say "closest clue"; cause on occasion a truck is updated so no matter what the VIN it may be a bit of a hybrid though mostly one or the other... hmmm....... then again...... guess I'm assuming here that an updated truck keeps its original vin. and that may be a wrong assumption. Those in the Know..... when a truck got updated like a few that has been auctioned... do they change to a new vin on those trucks? I doubt it.... but again that is an assumption.

https://www.steelsoldiers.com/showthread.php?123737-FMTV-VIN-Decoder

 

[M1083]

what year is the truck? also the Vin number is the closest clue..... if it starts with an "A" then it is an A0....

A1's..... start with "A1"...

say "closest clue"; cause on occasion a truck is updated and may be a bit of a hybrid though mostly one or the other.

https://www.steelsoldiers.com/showthread.php?123737-FMTV-VIN-Decoder

Not sure where to find the VIN on the truck, but the registration shos the VIN starting with BT. It is a 1997.

 

[gimpyrobb]

Your best bet is to post a pic of the offending parts.

 

[Suprman]

Sounds like ctis quick release valves. Do your tires go flat fast when sitting?

 

[Ronmar]

What superman said. The quick release valves connect between the CTIS pressure control unit(PCU) and the wheels. They also have a large port to dump air quickly from the tires. There is one for each axle. dump valves have a sliding valve core.

When you supply air from CTIS it flows thru these valves to the wheels.

If you drop the CTIS side pressure down to about 8-10 PSI, the valve core shifts partially and connects the wheel side to that vent port which vents the air from the wheels out that port very quickly and loudly.

If you drop the CTIS side air from wheel pressure to 0, the core should shift rapidly to the closed position. This does cause the valves to dump/vent/burp very briefly whenever the system vents, like after it checks tire pressure every 15 minutes.

So I think one or two things are happening. 1. The valve cores are sticking and not closing smartly. 2. The CTIS is not venting smartly/quickly. This happens when the control solenoid on the PCU(behind passenger kickpanel) de-energizes. The air flows out thru a hose that goes thru the floor right behind the passenger grill. If the solenoid valve is sticking or the line is plugged the system cannot vent quickly. If it were this though the QR valve for the front axle(located beside transmission) would also be acting this way. So maybe the rear axle valves are sticky... I guess a pinched kinked or plugged line back to the rear axles, causing only them to have a longer than normal burp when the system vents...

 

[M1083]

Sounds like ctis quick release valves. Do your tires go flat fast when sitting?

No, the tires do not go flat while sitting. They seem to lose some air while its doing its Scream and Shout route, but that is all.

 

[M1083]

What superman said. The quick release valves connect between the CTIS pressure control unit(PCU) and the wheels. They also have a large port to dump air quickly from the tires. There is one for each axle. dump valves have a sliding valve core.

When you supply air from CTIS it flows thru these valves to the wheels.

If you drop the CTIS side pressure down to about 8-10 PSI, the valve core shifts partially and connects the wheel side to that vent port which vents the air from the wheels out that port very quickly and loudly.

If you drop the CTIS side air from wheel pressure to 0, the core should shift rapidly to the closed position. This does cause the valves to dump/vent/burp very briefly whenever the system vents, like after it checks tire pressure every 15 minutes.

So I think one or two things are happening. 1. The valve cores are sticking and not closing smartly. 2. The CTIS is not venting smartly/quickly. This happens when the control solenoid on the PCU(behind passenger kickpanel) de-energizes. The air flows out thru a hose that goes thru the floor right behind the passenger grill. If the solenoid valve is sticking or the line is plugged the system cannot vent quickly. If it were this though the QR valve for the front axle(located beside transmission) would also be acting this way. So maybe the rear axle valves are sticky... I guess a pinched kinked or plugged line back to the rear axles, causing only them to have a longer than normal burp when the system vents...

I'll dig into this today, time permitting. Thanks for the detailed reply. I have not looked at the front one at all, so I don't know if it is venting as well.

 

[M1083]

I'll dig into this today, time permitting. Thanks for the detailed reply. I have not looked at the front one at all, so I don't know if it is venting as well.

Also, should there be oil in this system? There is a little coming out of those exhaust valves. Thick, like gear oil.

 

[Ronmar]

NO! The system should be completely dry. This indicates bad CTIS axle seals out in the hub between hub and spindle, allowing gear oil to be admitted to the system. Oil in the QR valves could cause them to gum up and not shift properly...

A bad CTIS wheel seal should also force air into the axle while the system is inflating the tires. You can look for air venting out an axle vent line while CTIS is inflating or checking pressure, which may point you to a specific axle(or axles) that has a seal issue.

 

[M1083]

NO! The system should be completely dry. This indicates bad CTIS axle seals out in the hub between hub and spindle, allowing gear oil to be admitted to the system. Oil in the QR valves could cause them to gum up and not shift properly...

A bad CTIS wheel seal should also force air into the axle while the system is inflating the tires. You can look for air venting out an axle vent line while CTIS is inflating or checking pressure, which may point you to a specific axle(or axles) that has a seal issue.

You are my new best friend! That makes perfect sense to me.

 

[Suprman]

Bad hub seals

 

[M1083]

OK, update. The front QR does not have oil in it like both rear ones do. The front one does release air and squeal like both back ones do. I disconnected an airline going into each of the rear QR's and filled them with brake cleaner to try to remove some of the oil and at least temporarily stop the noise - no joy. When I shut it off just now it screamed for several minutes until the tires were about half flat. The fact that the front one is also doing it, while free of oil, seems to me to point back to the solenoid under the passenger grille referred to by Ronmar in an earlier post. Yes, those hub seals I'm sure need replacing, but don't seem to be the cause of the noise, if I am thinking right. I will have to continue this hunt tomorrow.

 

[M1083]

I am guessing this is that solenoid?

 

[Ronmar]

Since they are all doing it, it is probably in that Pressure control unit you pictured. If you remove that grey cover on the bottom you will find 3 solenoids, control, supply and deflate, usually labeled C, S and D.

C actually vents the manifold/system plumbing INTO that grey cover which is plumbed by that line on the right out thru the cab floor. I suspect either the C solenoid is sticking(bad o-rings inside?) or that line out the floor is plugged...

Could be as simple as some bug decided to winter over in the vent port behind the grill...

 

[M1083]

Since they are all doing it, it is probably in that Pressure control unit you pictured. If you remove that grey cover on the bottom you will find 3 solenoids, control, supply and deflate, usually labeled C, S and D.

C actually vents the manifold/system plumbing INTO that grey cover which is plumbed by that line on the right out thru the cab floor. I suspect either the C solenoid is sticking(bad o-rings inside?) or that line out the floor is plugged...

Could be as simple as some bug decided to winter over in the vent port behind the grill...

HO-LEE-SHE-AT!!!! That vent was plugged....it works!!!! Thank you for taking the time to help me. Huge! This has been a pain for over a year. If you are ever in the Jacksonville area, I owe you a beer.

 

[coachgeo]

Glad you got the noise solved and it was easy. Still got to do rear axle CTIS seals to keep oil where it belongs. For some odd. Reason oil migrating away from where it should not be is a bad thing lol. Check your all your front and rear axle fluids. You may be low.