Keith Browning Posted November 6, 2009 Share Posted November 6, 2009 Customer concern: "Losing 30 PSI from air brakes over night, when the pressure gets down to 90 PSI you can hear a leak." I get this truck in, it had air in the tanks. Before I went home I set the pressure to 85 PSI. This morning the gages were in the same place. The service manual states "System Leakage - With the engine stopped and the air reservoirs charged to governor cutout pressure (897 kPa [130 psi] maximum), the rate of pressure drop shall not exceed 7 kPa (1.0 psi) per minute with the service brakes released and spring brakes applied." Am I wasting my time with this or what? I will continue to monitor... Quote Link to comment Share on other sites More sharing options...
LARRY BRUDZYNSKI Posted November 6, 2009 Share Posted November 6, 2009 Customer concern: "Losing 30 PSI from air brakes over night, when the pressure gets down to 90 PSI you can hear a leak." Am I wasting my time with this or what? I will continue to monitor... Keith, the customers states they hear a leak. Can they give you a general area that they are hearing this leak? I would suggest running the truck and getting a full charge of air pressure and giving a good looking at. I think you will find either a valve or possibly a line with a small leak. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted November 6, 2009 Author Share Posted November 6, 2009 Been there done it. Quote Link to comment Share on other sites More sharing options...
dieseldoc Posted November 8, 2009 Share Posted November 8, 2009 If you can hear the leak you should be able to find it. Get your squirt bottle out with water and a bit of dish soap in it. Start spraying the area you hear the leak coming from. If you cant hear the leak it will be almost impossible to find. I wouldnt worry too much about 30psi over night, that is a seriously slow leak. However if the customer is concerned I guess you have to go looking. The general common areas on trucks I have found are at the air dryer purge valves, and my nemesis push together air fittings. I hate those cheap plastic things. They may cost a bit more but a good old brass ferrule fitting is so much better. What engine is in the truck Keith, also what air dryer is on it? Trucks with Cummins engines have a turbo cut-off valve that can cause some wierd issues. Good luck Quote Link to comment Share on other sites More sharing options...
dieseldoc Posted November 11, 2009 Share Posted November 11, 2009 How did your air leak turn out keith? Quote Link to comment Share on other sites More sharing options...
LARRY BRUDZYNSKI Posted November 11, 2009 Share Posted November 11, 2009 +1 ?????? Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted November 11, 2009 Author Share Posted November 11, 2009 Well, I personally like to see a system hold air. I never did verify this one and it held for me. According to Ford's specifications even 30 PSI over night is acceptable so unless I can easily find something... maybe it is intermittent and will show up again with a real leak. Quote Link to comment Share on other sites More sharing options...
sam Posted March 29, 2010 Share Posted March 29, 2010 i dont do any air brake work, but this morning i have one come in with a air brake concern and i am the only one who is "certified" to work on it. I found that there is a leak at a pressure switch on the brake pedal assy. not sure what its called, (yc3t-18737-aa) is the part number on the switch. have one coming. The air is leaking thru the switch and coming out the elec. connector side. easy find since it was leaking so bad. hope this might help someone in the future. Is there anything i should look for other than bleeding the air press before removing the switch? Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted March 29, 2010 Share Posted March 29, 2010 Does it leak when the brake pedal is pressed, or all the time? If it's all the time, it's probably a 60PSI safety switch for turning on the light/buzzer. An internet search confirms this. Pump the pedal down and change it, no big deal. Good Luck! Quote Link to comment Share on other sites More sharing options...
Alex Bruene Posted April 1, 2010 Share Posted April 1, 2010 I know it's an old thread, but I might add that I've seen a few that have the water drains leak after draining the tanks. You have to wiggle the valves to get them to stop leaking. But they'll usually drain the supply completely overnight. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted April 2, 2010 Share Posted April 2, 2010 Well, I personally like to see a system hold air. I never did verify this one and it held for me. According to Ford's specifications even 30 PSI over night is acceptable so unless I can easily find something... maybe it is intermittent and will show up again with a real leak. Going back through some really cloudy memories.... At one point in time, I was the proud owner of a 1976 R700 Mack. This wonderful machine (the "winter package was a toque and an ice scraper) had a brake apply pressure guage. I don't recall ever seeing anything over 45 PSI even in a panic stop.... Back to Keiths concern... The truck loses 30 PSI overnight. This is within Fords Guidelines... This 08 750 is likely expected to be covered under warranty? One of two scenarios come to mind... "cannot duplicate customer concern"... or.... "FMC engineers have determined that customer concern is normal system condition". You can't fix anything if it isn't going to act like it's broken. One might consider using an "ultrasonic leak detector" to check for air leaks.... background noise can can affect the performance of the tool I am familiar with. A length of rubber hose can help identify suspect areas with audible leaks... But we also need to be wary of customers with overly enthusiastic expectations or customers looking for anything they can get for free (over in the monkeyhouse, it is common to see "have you had all the TSBs done?"). When all else fails. look the customer in the eye and say "show me". Quote Link to comment Share on other sites More sharing options...
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