My coach sat in heated storage without exercise for 3 months. As a rule we try to get it out once a month but I've hurt my back and am scheduled for fusion next month.
Last week we started it up to take it out for a couple of hours. It took longer than normal to air up and for the air dryer to purge. Once it did I backed it out, foot on the brake. At that point the low pressure alarm went off, both tanks dropped to 60 pounds and the brakes got mushy. I managed to stop, took it out of gear and applied the parking brake. Again, it took a while to air up and purge. Once it did I put it back in the garage and parked it.
I found a good mobile diesel truck mechanic to come change the D2 Governor. The old one rattled to I expected this was a good fix. My D2 is set for 125PSI as was the old one.
We tried again today. Once aired up I press the brake all the way down. The air dropped a little then stopped. I then pumped the brakes and the pressure on both tanks dropped like a rock to 60 pounds. I feel that if I continued the tanks would have dropped to zero.
I aired back up and shut the engine off. I walked around the coach listening for an obvious leak and didn't hear anything.
Unfortunately with my back injury I have limited mobility. I can't get under there and crawl around.
Any suggestions from the experts would be greatly appreciated! Where should I start?
Thanks all,
Jeff
Edited to add: Leveling is not effected. The coach stays up.
Get another person to listen outside while coach is running, especially near the air dryer and go from there, can you somehow make
sure he put the D2 on correctly.
See page 8, "Test Air Leakage Rate".
"Test Air Leakage Rate. With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving.
Check Air Compressor Governor Cut-in and Cut-out Pressures. Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut-out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise."
I also found this useful, "The In Cab Air Brake Test".
The In-Cab Airbrake Test | Layover.com (https://www.layover.com/trucking-news/page/48/the-in-cab-airbrake-test-)
No, what he is describing is NOT normal. If this only occurs when the service brake is applied, there may be a bad diaphragm in one of the brake chambers or bad air line going to one of them.
But, both gauges dropping at the same time due to a massive air leak-- wonder if a check valve is also suspect?
I don't understand this statement. Jeff's coach is
not acting "normal" when he says:
"Once aired up I press the brake all the way down. The air dropped a little then stopped. I then pumped the brakes and the pressure on both tanks dropped like a rock to 60 pounds. I feel that if I continued the tanks would have dropped to zero."
The pressure should
not drop like a rock to 60 psi. The air compressor
should cut in at about 90-100 psi and recharge the air tanks.
It sounds to me like the new D2 was not installed correctly, and/or is not properly sensing the wet tank (RES) pressure. I would suggest some more experimentation to determine at exactly what pressure the air compressor is cutting in and out. Jeff knows from past experience how his air compressor should work, and what readings are "normal" on the dash air pressure gauges.
From what I read if he steps on the brake pedal and holds it the pressure stops dropping. When he pumps the brakes continuously it drops. If a diaphragm or airline is bad it would drop while holding the pedal down. The compressor will not keep up at idle if you keep pumping the brakes. Jeff needs to get the pressure up and hold the brake, it should drop a little then come back up while he holds the brake pedal. Next when the pressure is up count how many times and in how short a period he is pumping the pedal. A relay valve would be more suspect to me.
Thanks Craneman, I'll give it a try.
Have someone go to each wheel while you push the brake pedal . The leak is post pedal , could be the pedal itself if both tanks show pressure loss .
Thanks Mike
Just a thought. What about ice in the air lines. Is it cold were you are?
We are in heated storage to no ice.
Jeff, any updates on the leak?
Not yet Craneman. I ordered trailer hitch/safety stands that arrive today. I hope to head to storage tomorrow with a friend that will pump the brakes while I look for the leak. I also want to find the D2 on my DD 6V92 to see if that was installed correctly. I have old one, I want to compare and make sure correct ports were used on the replacement.
At least, this is the plan, depending on my back.
If you start it up and don't touch the brakes does the governor shut off the air compressor and dump air through the drier at 125 psi? if so it is working properly.
The air line from the wet tank goes to one of the bottom ports. The air line going to your air compressor goes to one of the middle ports. Top port is exhaust.
Haldex D2 Governor Service Data (http://beamalarm.com/Documents/haldex_d2_governor_service_data.html)
Thanks Chuck. Is it possible to connect incorrectly?
Yes, but it will not function if the lines are hooked up wrong. It only controls the cut in and cut out of the compressor. Nothing to do with the brakes.
X2 what the other Chuck said.
If the 2 air lines were swapped at the D2, it would not function at all.
I think in that case your air compressor would never receive the "unload" signal, and would continue to compress air until something let go.
Hopefully it would be the safety relief valve on your wet tank at around 150 psi.
Just to circle back it wasn't the D2 (replaced it) and it's not the brakes. We couldn't find any air leaks in the brake system today.
The Mechanic feels the issue is that the compressor (original) is taking too long to air the coach up or the braided air line from the compressor to the air dryer is bad.
I was losing air when pumping the brakes until the emergency brake deployed at around 40PSI. The coach would air back up slowly, eventually to 125PSI and the air dryer purges as designed.
When driving about a mile around a large, flat parking lot today, using the brakes to make the turns PSI didn't get above 70 PSI until I parked it and waited a while.
The mechanic will make another house call to replace the braided air hose next week. If that doesn't solve the issue he will replace the compressor.
Edited to add, the braided hose does look crimped at the compressor connection.
I do like this guy and he has a great reputation and has a very busy Deisel shop here in town. He doesn't want to take my money until it's completely resolved. He charged me $80 to replace the D2. He wouldn't accept any payment today. He traveled an hour each way and spent two hours under the coach.
Sounds like you have a solid mechanic. Hard to find guys like that. Sorry you are having issues and can get them resolved quickly.
When the mechanic does replace the braided hose, can you get a part number to share? It looks like a teflon lined hose. I do not need one now, but like to be prepared.
Will do, DayDreamer. It should be next week.
When I was at the Granvention last October I was told by Mark Crick that he spends a lot of time repairing or replacing check valves that are leaking and most people do not test for leaking check valves.
We 'checked'. There are no air leaks in the brake system.
Mark and his family are awesome. We met his parents as well. We met last year, he did some work on my coach in South Dakota
Does anybody have a good strategy for testing the check valves?
Since both service tanks on our coach will drain when the wet tank is drained via the water drain, I am assuming the check valve on the inlet to the service tanks has failed. I intend to replace them and will see if the service tanks hold air when the wet tank is drained. Is this a good way to test the service tank inlet check valves?
Any thoughts on how to test the wet tank inlet check valve, the shuttle valves on the service tanks, and the pressure protection valves on the service tanks? Any more of them?
1. Yes. What you did is the gold standard test for those check valves. They have failed. Either clean them & reuse, or replace them.
2. No. If in doubt, take it off and inspect it. If condition is doubtful, replace it.
3. No. If in doubt, take them off and inspect them. If condition is doubtful, replace them.
4. It is possible to check the protection valves by doing the following:
a. Pressure up the wet tank to about 100 psi.
b. Open (disconnect) one of the air lines
downstream of the protection valve on
one of the brake tanks.
c. While the air pressure is escaping from the open line, watch the pressure gauge for that tank.
d. If the protection valve is working properly, the pressure in that tank will stop decreasing at about 50-60 psi and hold.
e. If the pressure in the tank keeps falling to zero, that protection valve has failed.
f. Then do the same test for the protection valve on the
other brake tank, starting from Step A above.
#2 loosen the airline at the compressor with the engine off, no air should be there if the inlet check valve is good on the wet tank.
Just to make it easier to swallow when you write the check;
Without these valves working properly you have given up the safety of dual breaking circuits i.e if one circuit has a "blow out" you would automatically lose the other circuit.
There should also be a pilot operated valve to supply bulk air to each brake chamber. I'm looking forward to learning more about testing those at your expense. ^.^d
On our (air disk brake, non-ABS) coach there are six valves dedicated to the operation of the brake system:
1. Treadle valve (brake pedal)
2. Parking control valve (parking brake knob)
3. Quick release valve (front brakes)
4. Spring brake control valve (rear brakes)
5. Service brake relay valve (rear brakes)
6. Spring brake relay valve (rear brakes)
I have rebuilt one of them - the parking control valve:
Bendix PP-1 Repair Kit (https://www.foreforums.com/index.php?topic=27892.msg229649#msg229649)
I have not messed with the others, cuz they are still working properly (I guess...) on our coach. They are all up in dirty cramped hard-to-get-to places under the coach, so I am putting that project off as long as possible.
Seems like I have been writing a lot of checks lately! Been salivating at the paint jobs others are getting done, but definitely need to focus on getting it safe first.
By pilot operated valves are you referring to the SPS valves on the drawings? Took me a while on Google to determine they are Skid Protection Sensitive valves that work with the ABS system.
ABS coaches are different than older models without ABS. The SPS valves in your diagram must be part of the ABS systems. It looks like they take the place of the Quick Release valve (front) and the Service Brake Relay valve (rear) on older non-ABS models.
I edited my post above to only pertain to non-ABS systems.
No. In order to obtain quick response on a pneumatic system, it is customary to place a pilot operated valve near the load, that way when you send a signal it goes through a smaller line that operates the pilot operated valve which moves the bulk air into the device.
You have ABS? Cool! I hope they got it right. When the railroads tried ABS in an attempt to eliminate flatted tires, commuter trains ended up rolling though stations without enough air left to set the brakes. I'm sure they got it right on your rig. ;D
Actually, the ABS systems on Foretravel coaches, although they seem to work OK,
have caused some problems for our Forum members.
There is a particular "sensor" at each brake unit that is prone to going dead. When it does, owners have a hard time finding a replacement. In some cases, it is unobtainable... I don't know all the details cuz we don't have ABS, but anyone interested in this subject can search the Forum for more info.
It's the rear ABS sensor on late 90's coaches. OEM size and style not available. The new part number that replaces it does not fit those coaches.
1998 U 270 rear ABS sensor source and part number (https://www.foreforums.com/index.php?topic=29227.0)
Replaced the check valves on both service tanks today with new Haldex KN23000 check valves. They are working great. Now when I drain the wet tank, both service tanks hold air! Hope I never have to rely on them, but feeling a little safer. Looks like you can also get just the internals as part RN10Y, but it is not that much cheaper.
Also replaced a leaking regulator on the step with one from Home Depot. Still have some minor air leaks to find/fix, but only lost 4 psi over an hour.