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Topic: "rear" air gauge shows zero psi (Read 906 times) previous topic - next topic

"rear" air gauge shows zero psi

Rear air gauge on dash shows zero psi & have air leak somewhere.(bad enough that the 12 v pump cannot keep up when parked)
 And the DW says she can hear a warning dinger (like a door ajar)when we are driving
all air bags air up but go from 95#'s on front gauge to 60#'s in about 30 min with engine shut down.
The slide air is shut off due to massive hole in bladder. (  Maiden voyage will be to HWH in Moscow IA.)
Any ideas as to where to start looking with a soapy spray bottle?

thanks

red
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: "rear" air gauge shows zero psi

Reply #1 –
Start with one of the easy ones - make sure the tank drains are closed. 

Do you have the air schematic for your coach?  It would be in the Owner's manual if you got those with the coach. 

Besides the usual suspects, the transmission retarder has an air valve on it that's fed from the rear brake tank.  Several members have had to replace it due to a significant leak so it's another easy check

Replacing transmission retarder valve (split from What did you do to your coach)

Big Air Leak Hydraulic Accumulator
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: "rear" air gauge shows zero psi

Reply #2 –
Red,

You have '02 model with slide, so there are considerable differences in air system between your coach and ours.  That being said, I think the HWH systems on both coaches work in a similar manner.  Looking at my air diagram, I don't think it would be possible to drive our coach with ZERO air pressure in the "rear" air tank.  There are some air components that can be fed from both brake tanks, but the front and rear 6-packs, for instance, can only be served by their respective tank.  If you really have zero pressure in your rear tank, I don't think the rear air bags would ever inflate.  Also, you would not have rear service brakes.  I'm not even sure if the spring brakes would release.

If the "rear" tank has zero pressure, the "wet" tank would also have zero pressure, and the engine air compressor would never unload.  If the "wet" tank never builds pressure, then the "front" tank would not receive any pressure.  See how they all relate?

What I'm saying is, I would first suspect a problem with your "rear" tank GAUGE.  One thing you could do is rig up a pressure gauge on the drain line for the rear tank - see what it reads.  Or, you could pull the air line off the back of the "rear" gauge, and see if you have air coming out the line.  If you do, try swapping the air lines on the two gauges.  If the rear gauge still reads zero, then the gauge is broken.

You undoubtably have some air leaks that will require attention, but first you need to verify the correct operation of your gauges.  Then, based on the two posts linked above, the "retarder valve" certainly sounds like a good place to start your search!
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: "rear" air gauge shows zero psi

Reply #3 –
Hijacking the thread just to say that the reference to the previous writeup had a post from Tim F. about the value of having the manufacturer still in business was priceless and I just have to agree. I've called FOT many times and either James or one of the other old-timers "happens" to remember my coach and gives me a specific fix. Kinda makes me tear up.  :))
Larry
1996 U295 36'
Build # 4805
Actually we sold it but just like to lurk

Re: "rear" air gauge shows zero psi

Reply #4 –
If you didn't have any air pressure at the rear your brakes would lock up unless the maxi's had been keyed.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: "rear" air gauge shows zero psi

Reply #5 –
Quote from: craneman –
If you didn't have any air pressure at the rear your brakes would lock up unless the maxi's had been keyed.
True, I'm thinking that it may be the sender for the gauge, may have "blown it's top" so to speak, looking at the schematic of the air system, I just have to get the coach raised and blocked then just go from there.
Being "tone deaf" doesn't help at all trying to find air leaks, so just have to work around that challenge.
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: "rear" air gauge shows zero psi

Reply #6 –
Quote from: saddlesore –
True, I'm thinking that it may be the sender for the gauge...
OK, electronic gauges - good point.  I'm always thinking in terms of mechanical gauges, cuz that's what I have.  But the objective remains the same: get your pressure gauges working before you try to do any leak remediation.  I would also suggest rigging up a gauge that reads "wet" tank pressure.  Easy to do - it can be plugged into the "tire filler" hose with a quick-connect.  Once you can see the air pressure in all 3 tanks, much easier to diagnose leak locations.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: "rear" air gauge shows zero psi

Reply #7 –
also if you go under block the coach up
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: "rear" air gauge shows zero psi

Reply #8 –
Quote
Besides the usual suspects, the transmission retarder has an air valve on it that's fed from the rear brake tank.  Several members have had to replace it due to a significant leak so it's another easy check

Is the retarder valve an issue when the engine is not running?
Royce & Denise, MC #17410
'01 U320 4220 ISM450 Build #5895 SOLD
Toad: '10 Honda CR-V

Travel makes one modest. You see what a tiny place you occupy in the world. - Gustave Flaubert

Re: "rear" air gauge shows zero psi

Reply #9 –
Quote from: John S –
also if you go under block the coach up
Yup, Had a local steel outfit cut me 8  2x2x11" square tubes yesterday, $56, so got that covered.
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: "rear" air gauge shows zero psi

Reply #10 –
You could crawl underneath and see if both tanks have good pressure when opened. You also could swap senders to see if the problem goes with it. Possibly it is a wiring or connection problem so you could just swap the wires on the senders first.
Jim Frerichs
2002 U320 42'

Re: "rear" air gauge shows zero psi

Reply #11 –
Quote from: saddlesore –
And the DW says she can hear a warning dinger (like a door ajar)when we are driving
quote]

I am sure your coach is different than mine, regards the warning.  There is probably a sounder of some type behind the dash for a warning of several things like low air pressure, low oil pressure, not in travel mode, antenna up, turn signal, etc. etc.  When I purchased my coach, I found that a prior owner had placed a piece of tape over the sounder to silence it rather than fix the problem which was with the antenna up switch.  This also negated all the other really important aural warnings; the warning lights would still function, but air and oil pressure are important.  I could not hear the  warning, but my wife could.  Have DW  check behind the dash.  There is also a very small volume control next to the sounder on my coach that I have adjusted to max volume.
Jerry Whiteaker former owner 96 U270  36' #4831 Austin,TX-Owner Mods LCD TV w/front cabinet rebuild - LCD TV bedroom - Dual Central AC, either can cool coach w 30 amp - Skylights at roof AC openings - Drop ceiling for ducting of AC - Shower skylight white gelcoat/wood/epoxy frame - Air Springs/Shocks replaced - 2014 CRV - 8K Home Solar - Chevy Volt

Re: "rear" air gauge shows zero psi

Reply #12 –
Didn't find any significant air leakage @ the rear bogies, 6 pack had several with tiny bubbles showing and the wet tank's over pressure fitting had a small amount of bubbling but that's all I could find at that end..
Will git after the front end tomorrow.

'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: "rear" air gauge shows zero psi

Reply #13 –
Every so often when coming up to travel height, our air pressure alarm drops to a very faint beep and we have to concentrate to hear it. Doesn't seem to be a problem in that all systems look good and she drives OK. Usually goes away in a couple of miles. Thinking it is the sensor sticking just a bit.
Larry
1996 U295 36'
Build # 4805
Actually we sold it but just like to lurk

Re: "rear" air gauge shows zero psi

Reply #14 –
FOT parts are awsum! 
Called FOT for a part # on air pressure sender for our coach.....Our coach has Stewert-Warner gauges and senders have Packard electrical connectors, not VDO
They looked up our coach specifics and gave me the SW part # so called a buddy of mine @Summit Racing..... Have them in stock... 2 senders for $113.44... That price I can do.....and free shipping for anything over $99.

now searching for shower controls and fittings....
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: "rear" air gauge shows zero psi

Reply #15 –
2 more items checked off...
Summit sent the gauge senders, put them in and waalaa! both gauges agree.
chased down the issue with the shower... after tearing everything apart .... vacuum breaker was kaput..... all goodder now.
Back to the air loss thingy
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel