seyser Posted July 22 Author Share Posted July 22 Yes the driver side looks pretty new but the passenger side one looks like it could be original. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555678 Share on other sites More sharing options...
Popular Post fjh Posted July 22 Popular Post Share Posted July 22 pull the line off the service side and see if there is air coming out of the chamber with the brakes released! check both sides just cause its newer don't rule it out shit happens to new stuff too! 3 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555680 Share on other sites More sharing options...
Joey Mack Posted July 22 Share Posted July 22 Yep, and see if the maxi lines are swapped by mistake Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555684 Share on other sites More sharing options...
seyser Posted July 22 Author Share Posted July 22 Thanks guys, Ill do that later this week and keep ya updated. Appreciate the help as always! 2 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555686 Share on other sites More sharing options...
Geoff Weeks Posted July 22 Share Posted July 22 On 7/18/2024 at 10:40 AM, Geoff Weeks said: Relay valves are similar to electric relays, in that they have a control that manipulates the output. They can fail in the same way. either the input can be faulty or the output is not following the input. The first is not the relay's fault it is what ever supplies the input. In short it could be, but it isn't 100% what is at fault you need more diagnoses. Your experience is why I posted this way back. I'm cheap and don't like to throw parts at a problem. Your eyes and ears are the only ones looking at the problem, we can give pointers but it is up to your to trace out what is happening when, and under what conditions. I have seen many brake chambers condemned and replaced that didn't fix the problem. There is an O ring to seal the push rod between the service and spring brake chambers, and while that can leak spring brake pressure into the service brake side, as others have said, it should vent from the QR valve or the QR section of the relay anytime the spring brakes are released. Some trucks have "anti compounding" or inversion valves in the tractors braking system, both do different things and are there for different reasons but the one thing they have in common is they have connections to both (service and spring brake) systems. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555688 Share on other sites More sharing options...
Freightrain Posted July 24 Share Posted July 24 The small lines are the control side(brake pedal) which opens a valve to apply air to the chambers. It is done this way for quicker reaction. The large lines are the main supply from air tank. I just replaced my relay(looks like yours). It was leaking severely suddenly. Likely O ring inside blew out. It was pretty old. If you are getting air from a large line, and replaced relay, then something is activating it. Remove the small control line. It should not have air pressure applied unless pedal is depressed. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-555816 Share on other sites More sharing options...
seyser Posted August 1 Author Share Posted August 1 Quick update - Took the truck to the local dealer and they looked it over. The tech found that my relay was mislabeled on the box and I didn't pay attention to the actual tag so he thinks it might be the incorrect relay. He found it has an extra port under the brass fitting on top. I'm going to swap my old top onto the new base or simply purchase another one and confirm its the correct one this time! The problem appears to be with the service brake and not the emergency brake like I was originally thinking. It only affects the front drive axle though when everything is hooked up. Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-556252 Share on other sites More sharing options...
Popular Post seyser Posted August 12 Author Popular Post Share Posted August 12 Well I finally rectified the issue. When the previous owner replaced the rotted out top of the relay he probably didn’t realize the new one had a check valve in the top plug. I didn’t catch that difference either. I went ahead and ordered another relay of the same model the previous owner had purchased which was actually the incorrect model. There was a divider in the bottom housing between two ports that isn’t suppose to be there for this application. Long story short I milled that divider out and removed the check valve in the top brass cap and everything functions as normal. 6 Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-556901 Share on other sites More sharing options...
mowerman Posted August 19 Share Posted August 19 The treadle valve looks brand new Quote Link to comment https://www.bigmacktrucks.com/topic/74353-replacing-air-relay/page/2/#findComment-557320 Share on other sites More sharing options...
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