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Topic: How much brake hissing is normal? (Read 1897 times) previous topic - next topic

Re: How much brake hissing is normal?

Reply #25 –
You have it right.
'Supposedly' can be serviced in place, but its a whole bunch easier to pull it - and not that hard...
I rebuilt mine in the driveway after the purge valve blew apart. I would buy a reman again. The cost and hours for a full rebuild aren't cost effective in my opinion.
 
I believe it to be the 'least serviced' critical component for a motorhome...
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: How much brake hissing is normal?

Reply #26 –
From Matt's email
 
Quote
"I could not ID the old dryer, so I followed Brett's advice.  Upside - same day R&R, pro rebuild, updated and improved equipment.  Downside
- just some dollars."

I removed and rebuilt the dryer on my 1999 U-270 when it was acting up.  The rebuild kit was cost effective solution.  If I was to do it again, on my 2000 U-320 I would buy a factory remanufactured unit and just do a remove and replace.  Not big a cost differential, and greater piece of mind.  ALWAYS block the coach anytime you are under it, especially when you are working on the air system.........
 
FWIW, the truck places around here do not rebuild the units, because by the time the technician rebuilds the units the shop labor charge on a rebuild about equalizes the cost as compared to a re-manufactured unit.  If you rebuild your self and your labor is free, the cost side favors using the rebuild kit and doing it yourself.
 
Three choices - each progressively less expensive
 
Pay someone to do it (my current approach) and use a new of factory re-manufactured unit Do it your self and replace old unit with factory re-manufactured unit
 
Do it yourself, buy a rebuild kit, and rebuild your unit on the bench to reinstall
 
To each their own, good luck, and if you need to go beneath your coach be safe and cautious.  They can, will, and have killed owners and technicians.
Tim Fiedler    2025 LTV Unity MBL on Order
2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
1985 Citroen 2CV6 Charleston
Murphy Rebel on wheels with 175HP Titan
Cessna P337
1980 48' Westport MY (!/4 Share)

Re: How much brake hissing is normal?

Reply #27 –
A really dumb question,....where would I locate this dryer on a 1997 U270?  Should I automatically service it every 2 years or is there a way to determine if service is required?

Thank you.
Morris and Janice
1997 U270 36'

Re: How much brake hissing is normal?

Reply #28 –
Guess if helps to have a idea of what to look for.  but don't ask me where exactly to look.  should be near the one of the air tanks maybe.

And no question is dumb!!!  Except the un-asked ones!
1994 U225
build #4514

Re: How much brake hissing is normal?

Reply #29 –
I still question whether there is a problem if the coach occasionally makes the pssst noise frequently but builds and keeps good air pressure both when running and with the engine off.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: How much brake hissing is normal?

Reply #30 –
Quote from: Kent & Peggy Speers –
I still question whether there is a problem if the coach occasionally makes the pssst noise frequently but builds and keeps good air pressure both when running and with the engine off.
It has to frequently do what you describe.  But when it starts building up to 150 lbs or more and starts releasing from the tank release instead of the air dryer or governor that the problem becomes extremely serious.
1994 U225
build #4514

Re: How much brake hissing is normal?

Reply #31 –
So am I correct that the dryier is functioning OK if the air pressure builds to 115-120 psi and it vents, then does not vent any more??
Morris and Janice
1997 U270 36'

Re: How much brake hissing is normal?

Reply #32 –
If yours works like both of mine, some days the dryer releases frequently and sometimes occasionally. It just depends of the humidity and cleanliness of the air. As far as I know if it builds pressure to about 120 and holds pressure unless you use the breaks, it is working ok. My U225 held working air pressure for up to 10 days when not in use and my U300 holds air pressure for several days. Someone correct me if I am wrong.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: How much brake hissing is normal?

Reply #33 –
So let us define frequently and normal.  In my case it was about every ten seconds, which just didn't seem normal to me.  In an eight-hour drive that would be 2,880 vents.  If it had been every ten minutes, I would have suspected nothing and considered it normal. 

What say you?

Matt B
1994 Grand-zilla
Matt B
1998 u-320

Re: How much brake hissing is normal?

Reply #34 –
With an air suspended coach, you have more air usage maintaining the coach level. So the air pressure cycles more often than with a 225/240/ORED
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: How much brake hissing is normal?

Reply #35 –
Quote from: oldmattb –
So let us define frequently and normal.  In my case it was about every ten seconds, which just didn't seem normal to me.  In an eight-hour drive that would be 2,880 vents.  If it had been every ten minutes, I would have suspected nothing and considered it normal. 

What say you?
I would call that excessive provided the air system works like they do on a Class 8 rig.  Are you losing air pressure when parked overnight.  Could be looking at a air leak, bad governor, or re-build dryer.

As Dave pointed out, a air suspension coach will do it more frequently, just because the compressor has to work more.
1994 U225
build #4514

Re: How much brake hissing is normal?

Reply #36 –
Quote from: PatC –
Quote from: oldmattb –
So let us define frequently and normal.  In my case it was about every ten seconds, which just didn't seem normal to me.  In an eight-hour drive that would be 2,880 vents.  If it had been every ten minutes, I would have suspected nothing and considered it normal. 

What say you?
I would call that excessive provided the air system works like they do on a Class 8 rig.  Are you losing air pressure when parked overnight.  Could be looking at a air leak, bad governor, or re-build dryer. 

What would you consider normal for our coaches that have air bag suspensions and the HWH leveling?  Thank you.
Morris and Janice
1997 U270 36'

Re: How much brake hissing is normal?

Reply #37 –
My 95 U320 had its governor replaced and the dryer rebuilt w/in the last 9 months. I would say on average the purge valve cycles every 10 to 15 minutes.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: How much brake hissing is normal?

Reply #38 –
Quote
I would call that excessive provided the air system works like they do on a Class 8 rig.  Are you losing air pressure when parked overnight.  Could be looking at a air leak, bad governor, or re-build dryer.



Prior to the repair, pressure would drop from 120 to 60ish in two days.

Matt B
Matt B
1998 u-320

Re: How much brake hissing is normal?

Reply #39 –
Quote from: oldmattb –
Prior to the repair, pressure would drop from 120 to 60ish in two days.

Matt B

What is it doing now?  And how often is the air releasing?
1994 U225
build #4514

Re: How much brake hissing is normal?

Reply #41 –
OK, I read it three times. Did I interpret it correctly that the purge valve can activate as often as every 15 to 30 seconds under certain circumstances. That is approximately the frequency at which mine cycle on occasion.

Matt, dropping from 120 to 60 psi in two days seems excessive to me.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: How much brake hissing is normal?

Reply #42 –
For those of you that have the money a rebuilt air dryier is the way to go.  I speak from the experience of replacing the purge valve kit in mine and it was a real hassle.  It turned out that it was hard to find parts for it even in Houston (it took three days of looking).  I did eventually find the Bendix dealer and got his last purge valve kit which includes all the gaskets needed for reassembly.  The most challenging problem was trying to torque the bolts with the air dryer sitting on the floor of my garage because I could not mount it in my vise.  I also had the issue of trying to get the dryer out of the chassis as it seemed that it had never been done so there was 15 years of dirt and rust making my job harder.  It also did not help that I had to do it in the storage lot which has some very rough broken concrete fill in the area of the engine bay.  And then there were the fire ants!
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP