BAC Forum
General Boards => Technical Support => Topic started by: Keith Moffett on September 01, 2015, 11:24:02 PM
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I freely admit that in my persuit of repairs before things break down, I sometimes see problems that dont exist. This may be one of those.
When we got this coach the air ride seemed real solid while traveling. I barely noticed bad road. Now it bounces three or four times on the front and the air pressure is down to 90 lbs or so. It also seems to take longer and longer to recover.
Interestingly the same problem exists in the brakes. Months ago it seemed I used the brakes while manuvering several times and lost 10 - 15 lbs. The other day while parking the coach in a tight spot the air alarm went off and it took several minutes to rebuild.
All that said, we often park and just leave the air up. We dont have air leveling just ride. Never the less it goes two days losing only 10 lbs or so one time and next time it will be down to 90 lbs over night.
What do you all think? Ride height valve? Air can? How does one check an air can? Anyone use those air flow control valves on the air bags?
Thanks
Keith
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Keith,
The ride bounce usually means shocks but I guess it could be the air suspension losing air. The air loose and recovery sounds like you have a big leak somewhere. Build up the air to compressor cut out and shut off the motor get out and listen and see if you can hear air leaking, if not then apply the service brakes (pedal) and have somebody listen around for air escaping. With all the air systems on these things it could be anywhere.
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Keith, the first question is your air system building up to 120 PSI and than hearing air dryer pop off.
Second question, when you pull yellow button out, to apply parking brake does the air at valve ( one
yellow button is pulled ) seems like the air takes longer to stop hissing sound. Third air pumped up and
air dryer poped off, with engine shut off does the pressure gauge on dash go down and is it more than
( 1 ) pound per minute. The answer to above questions will tell a person if you have a problem or not.
The first question you have to have min 120 PSI when air dryer pops off, answer should be yes.
Second question applying park brake ( pulling Yellow Button out ) hissing sound is longer than normal.
answer be no, if answer is yes you have a pancake bad on your spring brake on rear axle.
third question with air supply pumped up and air dryer pops off at 120 Psi, watch pressure gauge on
dash if needles are going down more than ( 1 ) pound per minute. this will give a idea if there is
something going on with vehicle air system. Dave Atherton Retired Cat Mechanic
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Keith,
If you have the original Bilstein shocks and around 75K miles or so on the coach, the shocks are probably bad, causing the "porposing". I recently replaced mine with Konis at 93K. The Konis give a good ride but IMHO, not improved enough to justify the added cost compared to the Bilsteins. Shock Warehouse has some fairly good prices and free shipping.
Steve
S
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Keith,
If you have the original Bilstein shocks and around 75K miles or so on the coach, the shocks are probably bad, causing the "porposing". I recently replaced mine with Konis at 93K. The Konis give a good ride but IMHO, not improved enough to justify the added cost compared to the Bilsteins. Shock Warehouse has some fairly good prices and free shipping.
Steve
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Steve, are you saying that if the shocks are bad the travel on the air ride valve is using more air when hitting a bump?
I have looked at Koni and am not convinced either considering the cost! What physical indicator shows a shock to be bad?
Thanks
Keith
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http://www.motoringabout.com/when-to-replace-shock-absorbers/
and I would augment these with a seventh item... when a shock absorber is leaking oil.
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Keith, the first question is your air system building up to 120 PSI and than hearing air dryer pop off.
Second question, when you pull yellow button out, to apply parking brake does the air at valve ( one
yellow button is pulled ) seems like the air takes longer to stop hissing sound. Third air pumped up and
air dryer poped off, with engine shut off does the pressure gauge on dash go down and is it more than
( 1 ) pound per minute. The answer to above questions will tell a person if you have a problem or
Dave
The air drier was rebuilt last year with a kit. It does build to 120 and the over pressure release valve activates but not as noticable as it was before rebuilding.
When applying the park brake there is very little air release with the button, just a quick 'cht' sound.
With the air ride at full pressure and the engine off the guage might show a small loss over night.
thanks
Keith
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David
I appreciate the input. Over the years I have come to believe I know some things about mechanics. Working on these MH's things are a bit different. I usualy find t better to confirm what I believe I know to be true.
I do have some diving on curves and vibration through the steering wheel and ratteling noise on rough roads. That said, the air ride may be minimizing a shock problem so it hasnt been as noticable as it might have been.
I am not so sure that this can account for greater air loss on rough roads and longer recovery times.
Keith
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Keith,
Sometimes you might see oil leaking but my experience has been ride quality. When it starts bouncing or shaking, shocks are normally the chief culprit and with 75-100K miles, you've gotten your $ out of them anyway. Might be that air system but from your ride symptoms, I'd put shocks at the top of the suspect list.
Steve
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Gentleman, with Keith first posting I half way agree with the bounce going with shocks worn or
bad. However where My thoughts going down the road with only 90 PSI showing on air pressure
gauge tells me there is a problem within the air system. Pressure should be running 120 PSI in the
Air system and air tanks. With the rear spring brakes locking up wheel at 50 PSI and system pressure
at 90 PSI only few pumps on brake pedal and your out of air before spring brakes apply.
( Note the rear brake chamber one for each wheel have a big spring inside of brake housing and is
Released with air pressure you build up pushing yellow button and unlocking each wheel.) wheels
with release at 60 PSI . Keith you mentioned loosing 10 to 15 PSI just applying brakes than the light
came on. Sounds like air governor needs adjustment. But my first post my first question what is your
pressure on gauge in cab. Dave Atherton Retired Cat Mechanic
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Dave and Keith,
The suspension in these coaches use a lot of air while traveling and my air gauge cycles between about 90lbs and 115lbs about every 20 seconds to perhaps a minute depending on the tilt of the road, wind, and bumps. It cycles back quickly at road rpm, so although we use a lot of air, the recovery rate is quick due to the relatively small size of the reservoir tanks when compared to the air quantity being used. I have done leak down tests and the air system is good.
The issue with the alarm when braking multiple times while idling and maneuvering is you can use more air then is being generated at low rpms. That is normal and is a driver awareness that needs to be monitored. I was thinking that the coaches were set up for 90 to 115lbs possibly for a reason so I have not messed with mine. I have never thought of the 90lb cut in pressure as any problem. Wondering if 90lbs to 115lbs is normal for most of us with this chassis?
Even with a change to 100 to 125lbs things will not change much regarding how much air we use and our reserve while driving, braking, at idle speed.
Later Ed
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Ed, we both agree air pressure needs to recover and maintain 120 psi, point of concern many air
systems slow to recover can present problems. Been involved in many out of service ( vehicle Tagged
out of service, air compressor slow recover and air pressure bleed off with engine shut off that exceeds
more than 1 pound per minute.) there is a standard that pertains all vehicle with air systems with D.O.T.
When we worked on air systems that standard,had to be followed. when I see post with air systems
something is out of place means Safety. In most states, motorhomes drivers are exempt from having a B class
( air brake endorsement ) driver license but it is clearly spelled out. Our mechanics were required to have air brake
inspector endorsement including myself working repairs with on road trucks. We had to sign off on
repairs that fell in line with D.O.T. Reg's. Anything to do with air systems cause for a big concern to myself.
Dave Atherton Retired Cat Mechanic
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Dave,
I was not implying that an air system should not be leak free to a standard. I would not be happy with one pound per minute leak down and mine is tested periodically by me and surely does better than that. The pressure build time at idle with a tight leak free system is such that you can use more air feathering the brakes and rocking while rolling in a campground then can be generated at idle. Just a fact of life the driver needs to be aware of. I do not know if 90 to 115 is right or 100 to 125psi is better. We should see what others have and debate that one a little maybe.
Later Ed
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With mine I have never seen the gauge pressure change much going down a road, even with curves ànd rolling bumps. Air pressure will hold for two or three days if leveling is turned off.. I do have a leak in the rear on the leveling system I will find when we get home in a week.
System cut in 92 cut out 121 psi.
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My cutin seems to be about 100, cutout 120. I don't see any variation in the air gauge while driving down the road. When I first bought the coach I noticed an "air" light flashing on the dash when bouncing over bridges and such. Haven't seen that in over a year though, no idea what it was.
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Jerry thanks, guys are beaten up on me today, I have Googled or maybe I bugle you, but called for
backup and they sent me kermit the frog from sports bar down the street and by his croaking. think he was sitting on his lilly pad way too long. I have to agree, this is where I was coming from, even
broke out the good book ( Air Systems Troubleshooting ). The nice part here with BAC Forum we all
learn from each other and no view is a bad view. Dave
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Jerry thanks, guys are beaten up on me today, I have Googled or maybe I bugle you, but called for
backup and they sent me kermit the frog from sports bar down the street and by his croaking. think he was sitting on his lilly pad way too long. I have to agree, this is where I was coming from, even
broke out the good book ( Air Systems Troubleshooting ). The nice part here with BAC Forum we all
learn from each other and no view is a bad view. Dave
Is it the Elk thing again?
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I have the SMC era Magnum chassis although in 2002 the called it a Roadmaster. If you folks with later era chassis do not use air driving down the road that is a curiosity to me. I know my air use is heavily modulated by the road conditions and wind so it is suspension responses that consume large amounts of air and not leaks.
Later Ed
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I have the SMC era Magnum chassis although in 2002 the called it a Roadmaster. If you folks with later era chassis do not use air driving down the road that is a curiosity to me. I know my air use is heavily modulated by the road conditions and wind so it is suspension responses that consume large amounts of air and not leaks.
Later Ed
I suppose it could be a gauge thing. I watch the air gauge, especially after I lost all air going down the mountain on I 77. It only seems to go down when I use the brakes. I hit some pretty rough roads (for Interstates) on that last rip too. My chassis is a Roadmaster Magnum also. I'm going out for a few days next week and I'll keep a closer eye on it. I'm curious now.
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Jerry , climbing tall Mts. and air is real thin, googled a few times than tried to bugle,
Getting very hard to google and bugle while climbing. Dave
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Dave
On only a couple of occasions the pressure would not climb past 110 lbs. Normaly the dash guage reads 120 or so.
The coach has been sitting now for almost three days and the air still reads 95 lbs.
I have not had time yet to air it up completely and listen for leaks.
I did find a source for a governor. My main concern is the slow recovery time so baring finding a leak at a brake or the tag axle lift then I am going for the governor as it is fairly cheap.
Shocks may take a bit longer depending on the results from the check of the AS.
Thanks again
Keith
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Keith, my first suggestion would be adjust your air governor on your air system. Something that
you can do. It should be mounted in the back on air compressor or remote mount close by. We can
get better location from one of our C-12 owners. All that is needed is a little 7/16 wrench and a short
flat blade screw driver. before adjustment pump brake pedel and release air from system ( this takes
air pressure off plunger on air governor ) On air governor one end there is a Plastic cap that covers
the adjustment nut and threads, remove by unscrewing cap. what you will see is nut with threads sticking
up about 1 inch with a slot for screwdriver. This is the adjustment for air governor. Hold threads in
place with screw driver in slot than loose the nut with 7/16 wrench.loosen the nutup about 3/8 inch
note : location of the slot on the threads Turn screw out 2 complete turns and tighten the nut. this will
increase your air pressure on gauge inside. start up engine build up air pressure between 120-125 #.
you should be real close to correct pressure on dash. If pressure is still low but increasing on gauge,
shut off engine and pump air off system with foot pedel and loosen nut holding screw in place and than
turn 1/2 turn out screw than lock down. ( this will increase air pressure in small amount ) when correct
pressure is reached tighten nut and put plastic cap back on. Just remember to let air off system to allow
easy movement of adjustment rod with threads. If you have any problems or questions give me a
call 605 999-0720 air bleed off very slow while sitting engine off ( 3 possible spots ) air leveling
rod not centered by possible wear and looseness believe you have 2 leveling rods, than check
bottom of your air dryer purge valve on bottom, when the purge valve along with water and oil mist
many cases that area will weap a little air. this can be checked with a little soap bubbles like checking
a gas connection. Dave
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Dave
The local CAT shop says the replacement governor is no longer adjustable. I will look to see which mine is. As I posted earlier the guage usualy reads 120 plus so do you still feel I should adjust it higher?
Ed
We have essentialy the same chassis. By your last post it seems yours consumes air like ours does. Funny thing is I am real certain ours was no where near this bad two years ago. If I am right then it is at least mostly curable. I dont know about you but I sure dont like traveling and looking down to see 95 pounds on the guage especialy now that it takes longer to rebuild.
Having given it further thought, I bet that the shocks were good two years ago but older and now can no longer compensate for the air system.
When replacing the shocks, does one relieve all the air in the system (via the four rear valves) first, or just put supports under the frame?
Thanks to all
Keith
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Keith and Ed, hard to believe Cat would say that because they do not build the air compressor. I'm
Looking on my Cat program and so far cannot find anything applying to that non-adj air governor.
Before we go too far would pump up air and check leveling valves not centering ( even everything
Is working ) you may be dumping too much air and leaking from not all the way centered. Possible
Rod loose or worn just a little, would be hard to hear small air leak under back. Will check back in
And let you know what I find out why Cat is telling about no adjustment on air governor. There has to be
Adjustment at this point. Dave
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Keith and Ed, getting back with Info on AC for C-12. What you should have on your engine is a
Air Compressor Model EL-740 which is made by Midland and yes the governor is a off parts house
shelf and can be adjusted.
Cat has a new model built Bendix Duraflo 596 which replacees the Bendix TuFlo 1400 but you do not have
that model because if you do air pressure is different and fast recover air flow. possible Mod 1400
Going back on a few thing to check to make sure problem is not with the air flow and delivery on
your Air Compressor. ( slow recover rate air delivery ) dirty filter for Air Compressor, carbon buildup
in discharge line that is connected to air compressor ( that is the Steel braided air Line about 2 feet
long. air pressure time to build air from 85 psi to 110 40 seconds or less. compressor cut-in 90 psi,
compressor cut-out 120 psi these are thing that would make for slow air recover.
Reason you do not have the new style Bendix 596. the governor cut-out is 130 psi, governor
cut-in at 110 psi, air pressure time to build air from 85 psi to 110 psi 25 seconds. you need to get air compressor model number off tag on a/c/ this moder has a different type of air governor that
only be replaced and not adjusted in the field, very unlikly you have this updated model.
What information I found about troubleshooting is for a Cat C-12 2KS S/N with your air system off
Cat Service Information System. Again first thing to look for can you build air from 85 to 110 in 40 sec.
I mentioned yeserday about carbon build up in the discharge line off A.C. ( need to remove both end
of hose) and the air filter for A.C. this will tell you what you need to find problem. last thing the Air
governor for your A.C. can be adjusted. If perhaps you do have the new updated Bendix Mod 596,
than air system will need to be reset. Dave
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Keith,
Usually with shocks you would support the frame at the best working height to be able to access the top and bottom bracket bolts. The shocks will extend as needed to adapt to the frame hole positions.
You have a tag that adds another need for air so we are not exactly the same. I bought the coach six years ago with 28K miles and it used a lot of air then and a lot of air now. I have done leak down tests for the parking brake chambers and the brakes and they are fine. I did replace the rear brake chambers due to a leaking diaphragm on one side a few years back. Each time the coach leans, hits bumps, is hit by cross winds you can see the air gauge respond. When you are sitting still, either once the brakes are held on or off it holds air well. I think it is just the nature of the beast in the design to compensate and enhance the ride. Perhaps stiffer shocks like the Konis might reduce the air use some by limiting the coach travel movement over bumps. If you are sitting still, feather the brakes until the compressor kicks on and if you held the RPM at say 1350, how long is the air rebuild time. If you record that you would have a baseline. It is hard to judge if it is building air OK while consuming air which is always a variable.
Later Ed
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Dang Dave, that was alot of research and effort on your part for this. Thanks a bunch. I am going to look over the AC hose and filter. The entire engine compartment was nearly an inch thick in dirt from a PO. Had I known there was a filter it would have been changed already. You say this is available at a standard parts house?
After 3 days of sitting on air ride alone, the coach was listing tothe passanger side a fair amount. Part of this is due to the site but mostly not. What would an air leveling rod look like if it were worn slightly. What if it were off center, how does one tell.
I am not a big fan of climbing under the coach to work on the air system since I am not set up for good blocking. Small steps I guess.
Will check on air recovery time and report back tomorrow. I have a feeling that this thread may help any number of folks so I appreciate the time spent by both you and Ed.
Keith
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Keith, back again, doing more digging on problem for you and Ed. this may be a new twist.
Pubication date 01/08/2001 and updated 09/10/2001 Systems Operations Bendix Duraflo 596 Air Compressor. It is very possible you have that compressor on your engine and if that is the case
I think the MFG set up air system at wrong values that are to low for your air sysrtem and air
recover rate. I kinda put the info. on my last post in the middle at that point 2 other model Air
compressors were used on the S/N 2KS
Looking at spec's Synchronization valve Cut-in Rate ( 110 PSI ) Cut- out Rate ( 130 PSI ) Can only
use Bendex SV-1 Synchronization valve with the Bendix Duraflo 596 Air Compressor Rating 110 to 130 psi. recovery time from 85 psi to 110 psi 25 seconds Synchronization is preset
Bendix D-2 Air governor was also used with Bendix Duraflo 596 Air Compressors that can be
serviced and adjusted. Again here is where I pick up on problem Cut-In pressure ( 110 psi ) and
Cut out pressure ( 130 psi ) recovery time from 85 psi to 100 psi less than 40 seconds
This information and setting may have fall through the cracks and answer some questions
for you. Dave
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Keith and Dave,
Keith there is no air filter per say on our C12 compressors. If you look at the head on the compressor there is about a 3/4 inch line that comes over the top of the engine between the two valve covers. It is tied into the intake manifold so I think that is the air supply for the compressor. That would mean that that the compressor starts with filtered turbo boosted air that has been cooled by the intercooler. I think this is right but I reasoned it out from looking at the plumbing so maybe Dave or Gerald can confirm that.
I still am not sure if we were all set up for 90 at the low end to somewhere between 115 to 120PSI on the high end for a reason and that is correct for these coaches. Hard to know and nobody with C12s has piped in on the subject to share the air pressures their coaches are running. I have not heard 110 to 130PSI before.
Later Ed
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Keith and Dave,
Keith there is no air filter per say on our C12 compressors. If you look at the head on the compressor there is about a 3/4 inch line that comes over the top of the engine between the two valve covers. It is tied into the intake manifold so I think is the air supply for the compressor. That would mean that that the compressor starts with filtered turbo boosted air that has been cooled by the intercooler. I think this is right but I reasoned it out from looking at the plumbing so maybe Dave or Gerald can confirm that.
I still am not sure if we were all set up for 90 at the low end to somewhere between 115 to 120PSI on the high end for a reason and that is correct for these coaches. Hard to know and nobody with C12s has piped in on the subject to share the air pressures their coaches are running. I have not heard 110 to 130PSI before.
Later Ed
I posted earlier that I think my cutin is around 100, maybe as low as 90. Hard to tell when driving. Cutoff is 120. I think my coach air is rock solid at 120 going down the road unless I use the brakes. I will verify next week on a short trip and post. When I first go out to the coach with no air in the tanks I'm guessing they fill and cut off in 2-3 minutes.
Jerry
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Ed, the intake is in pipe coming from air filter for engine this correct location. Question number two,
information is stright off Cat SIS about air pressures and Spec's with air compressor. this information
is used for on-road trucks and that standard is D.O.T. ,standards that truck repairs have to comply
with. Does the Motorhome have there own standards ? starting to wonder because Buses use the same
air ssystems as trucks. let touch again about the Bendix Duraflo 596 it has one D-2 air governor that
can be adjusted. Than the Bendix Duraflo 596 with a synchronization valve that is preset at 110 psi and
130 psi and cannot be adjusted. Point I made very clear, Keith made call and found air governor had
to be replaced because it could not be adjusted. this tells me if Keith has the synchronization valve of
which party Keith called assume that than air pressures on his motorhome have to fall with in the higher
air pressures. This Question can only be answered when Keith finds what air compressor he has on his
Cat C-12. Some thing else they do sell new sychronization valves ( why is this because possible problem
having to do with air pressure with this valve.
I have presented Fact from Bendix Air System Troubleshooting and Cat SIS information that
pertains everything with the C-12 engine. And again Ed may be the motorhome people are
exempt from standards same as not having a CDL license to drive a motorhome.That is about
all I can do to help you guys out. Dave Atherton Retired Cat Mechanic
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Gentleman, I just made a reply about location of intake for the air compressor. but somehow it got
lost. it is in tube from air filter. At this point I do not have anymore current resource to get information
from. What I have used is the Bendix Air Systems Troubleshooting, and Cat SIS information that is
also current. D.O.T. has set a standard that all repairs have fo fall within there rules for on-road trucks.
Maybe motorhomes are exempt from D.O.T. standards because I'm begining to think so. we seem
to question the information on the synchronization valve pressure that is preset and cannot be adjusted
if your C-12 has that valve than that is where pressure will be, but we do not even know if Keith has this
new style valve. The party Keith called seem to think he does because of statement have to replace
air governor because cannot be adjusted. You guys have better infomation on the subject than I do
so I'm going to back out of this. Dave Atherton Retired Cat Mechanic
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Dave,
There is no piping from the air filter chamber to the compressor. There is a pipe from the intake manifold on the other side of the block, as I mentioned, so that seems like the source for the compressor air inlet.
Later Ed
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Ed, there are 3 ways the Air compressor will gets sourse of air from. Number 1 from a air filter on
air compressor housing itself. Number 2 from pipe connected into air filter and engine turbo charger.
Number 3 air compressor gets air supply from intake manifold on engine via of 1 inch hose. while
on subject I have seen all three systems on motorhomes, There seems to be no standard when builder
puts house over the motor. Again answer to your question, It may not be the same for others as yours.
The engine S/N number plays a big part in where you going with this. Different S/N will change how
add-ons location will be different from engine to engine. Mounting of the fuel filter is a good example
to play with. Cat C-9 engine the air governor is remote from air compressor to upright support on
right side of engine in back . Engine Data Connector another good example, some models along inside
of right frame rail to above rear back of engine. last the big air filter it self, different locations mean
different mounting of add-ons. I answered your three fold as way Cat SIS lays out info for many different
locations of add-on . again there is not one standard set in stone. Dave Atherton Retired Cat Mechanic