air brake pressure drop

[RKL2]

I noticed today that with full air pressure (130#)when I apply the brake pedal the pressure drops to about 105#..then builds back up to 130# If I stop and keep my foot on the pedal, no further air is lost...I haven't noticed the amount of drop before and don't know what is considered normal drop...Does any one know if this is normal?
I also did the air brake sysem checks per the manual and everything test ok, in fact I have very little air bleedoff if any.
Also, the drop off in pressure occurred when I had only driven apprx 4 miles or so.
Should I be concerned with a 20 to 25# initial drop when I hit the pedal easy about 40mph?
Hitting it a second time drops it to about 100#. thanks RKL

[RKL2]

I noticed today that with full air pressure (130#)when I apply the brake pedal the pressure drops to about 105#..then builds back up to 130# If I stop and keep my foot on the pedal, no further air is lost...I haven't noticed the amount of drop before and don't know what is considered normal drop...Does any one know if this is normal?
I also did the air brake sysem checks per the manual and everything test ok, in fact I have very little air bleedoff if any.
Also, the drop off in pressure occurred when I had only driven apprx 4 miles or so.
Should I be concerned with a 20 to 25# initial drop when I hit the pedal easy about 40mph?
Hitting it a second time drops it to about 100#. thanks RKL

[Zimectrin]

Have not experienced that much of a drop on our rig.

Not qualified to know if that drop is severe or within specks.

Am qualified to know that you should persue this inquiry. Maybe drop a note to Freightliner? Be sure and let us all know what you learn.

Good luck.

[smlranger]

RKL:

Drove mine home from service this past Friday. Since I had seen your post, I paid careful attention to mine and it does about he same...drops about 20- 25 psi with first application of brakes...holds steady. If I pump brake once more, drops to about 100 but immediately starts to climb after that. Guess it is normal

[RKL2]

smlranger...From what I learned by talking to several service managers of shops that work on air brake systems what we both are experiencing is normal...
If it was a hose leak, the pressure would quickly drop to 0...Both service guys mentioned that if your slackers are not adjusting the brakes properly, then the air pressure drop increases as the piston must move further distance...
20 to 30 # intial drop is ok so they said...thanks for the response...RKL

[wagonmaster2]

Speaking of air pressure drop, I've noticed that when my coach sets for 2-4 days the front air gauge will be just below 60# which sets off the alarm but the rear gauge us usually still at around 100# or so. Is there some reason the front air drops more just setting or do I possibly have a small air leak in the front system someplace? Is this enough to be concerned about? I haven't checked it day by day yet to see if it does a little each day or all the first day. The front gauge will be just barely below 60#, no further, just enough to set off the alarm. This is on a 2004 Freightliner XC chassis. There are so many if, ands, & buts with these deisel chassis I don't see how anyone can keep on top of things. Thanks for any ideas.
Wagonmaster2

[RKL2]

wagonmaster2.....both my front and rear guages drop equally to about 60# after several days...I don't think you have a problem unless after 3 or 4 days the front end is lower than the back end of the coach......RKL

[mopargo]

I noticed while returning from a trip yesterday that both of the needles on the guage were dropping together, then at 100 lbs they went back up as they should, the difference was that the front needle normally hardly moves and the back one drops and returns. After a few miles the guages returned to normal, but any stop and they both go down for a few miles, then back to normal. The brakes are working fine, but I don't understand the change.