rdauphinais Posted March 24, 2018 Share Posted March 24, 2018 So I bought a 89 midliner a couple weeks ago with a couple bad air brake fittings. Even though it had leak, it still built over 100psi. So I get new fittings, and replace the old ones with new ones, get it all together and go to test it. I can only build 10psi at half throttle, and as soon as I let off the gas it dropps to zero. I can't find any leaks or hear any. Nothing changed besides 4 new fittings. Any help is appreciated Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/ Share on other sites More sharing options...
Rob Posted March 24, 2018 Share Posted March 24, 2018 Those Renault compressors used on the engines can be troublesome in the valves. If you have an air dryer remove the inlet line from the compressor to it or the "wet" tank. You first need to ensure the air compressor is building airflow. Citing you are losing air very fast after limited build up of pressure, it may have exhaust valve(s) stuck open. In your wet tank if you have an open fitting that is plugged remove this and install a ball valve and air fitting. If not, remove the overpressure safety "pop off" valve and temporarily install an air fitting. Apply shop air to this and soap down the entire air system. With that massive of a leak you should hear air escaping with shop air connected. 1 Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395035 Share on other sites More sharing options...
other dog Posted March 25, 2018 Share Posted March 25, 2018 Or it could be just a bad air governor? Quote Producer of poorly photo-chopped pictures since 1999. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395060 Share on other sites More sharing options...
Rob Posted March 25, 2018 Share Posted March 25, 2018 1 hour ago, other dog said: Or it could be just a bad air governor? It could be and if a Bendix or Midland compressor, the first place to look. The Renault compressors were problematic, (IMO) and my reply is based upon past experience with them times about four trucks..... He has not responded with adequate information in which to offer effective t/s with yet, so staying generic. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395064 Share on other sites More sharing options...
rdauphinais Posted March 25, 2018 Author Share Posted March 25, 2018 Truck is a few miles away from me in a field so getting shop air there is almost out of the question. Just find it hard to believe that everything worked fine until I replaced 4 fittings and now it doesn't build hardly any pressure. I'll see what I can find later today, but I do t have hardly and experience with air brakes. Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395066 Share on other sites More sharing options...
Rob Posted March 25, 2018 Share Posted March 25, 2018 Post up some photos of what you are working with. If the truck is a CS-300 series the air compressor is buried behind the turbocharger mounted low on the right side and the compressor is next to it. It is very difficult to see with the exhaust in place. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395089 Share on other sites More sharing options...
rdauphinais Posted March 25, 2018 Author Share Posted March 25, 2018 I can easily see the air compressor right on the pass side of the motor in front of the turbo and behind the intake. I'll pull the exhaust line off and see if there is pressure coming out, I have a feeling there isn't. Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395103 Share on other sites More sharing options...
Rob Posted March 25, 2018 Share Posted March 25, 2018 1 hour ago, rdauphinais said: I can easily see the air compressor right on the pass side of the motor in front of the turbo and behind the intake. I'll pull the exhaust line off and see if there is pressure coming out, I have a feeling there isn't. You don't have the engine I was thinking you did. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395113 Share on other sites More sharing options...
rdauphinais Posted March 26, 2018 Author Share Posted March 26, 2018 If love to find out what motor I have rob Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395136 Share on other sites More sharing options...
Rob Posted March 26, 2018 Share Posted March 26, 2018 Single long valve cover, or six individual ones? Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395140 Share on other sites More sharing options...
rdauphinais Posted March 26, 2018 Author Share Posted March 26, 2018 Individual Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395186 Share on other sites More sharing options...
Rob Posted March 26, 2018 Share Posted March 26, 2018 You have a different arrangement than three 89's and one 1992 CS-300P trucks I had if you can see the turbocharger, or air compressor. I had underbody exhaust however as they were rollback car carriers. The engine should be an E-3 @ 210hp if original to the chassis. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-395187 Share on other sites More sharing options...
Neo Posted February 12, 2022 Share Posted February 12, 2022 I'm have air issue too... My pressure is not building up at all.... Replaced the compressor.... And it it pushing air hard.... I have no idea what to do... Someone said I should check the unloader valve ... Can you tell me where can I find it .... I have a 94 ms200 Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489216 Share on other sites More sharing options...
Onyx610 Posted February 12, 2022 Share Posted February 12, 2022 It’s in the head of the compressor. What kind of compressor do you have? What do you mean it’s pushing air hard? When’s the last time you changed the air dryer? Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489242 Share on other sites More sharing options...
Onyx610 Posted February 12, 2022 Share Posted February 12, 2022 Also when replacing a compressor it is good practice to replace the steel braided discharge line, air dryer cartridge, and governor. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489244 Share on other sites More sharing options...
Joey Mack Posted February 12, 2022 Share Posted February 12, 2022 I was wondering if youre Midliner has a steel pipe coming from the air compressor output/disscharge port.. Its been a while since I worked on one of those neat little cabovers.. if you have a metal pipe it may be clogged with carbon.. pics would be cool.... jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489270 Share on other sites More sharing options...
High Binder Posted February 12, 2022 Share Posted February 12, 2022 Hey Jojo, I made the same mistake you did. Only the last two or three replies are relevant. This thread is three years old and I'm sure he got his problem fixed. I was going to reply until I saw it was from 2018. Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489273 Share on other sites More sharing options...
Joey Mack Posted February 12, 2022 Share Posted February 12, 2022 I really thought NEO's post was current... ooop's... Dumb me.. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489275 Share on other sites More sharing options...
High Binder Posted February 13, 2022 Share Posted February 13, 2022 I'm sorry Neo's post is current. I didn't see that he posted the model of the truck. My mistake. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489277 Share on other sites More sharing options...
Joey Mack Posted February 13, 2022 Share Posted February 13, 2022 all good.. I have responded to a few old post's in the past, and probably will again... Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489278 Share on other sites More sharing options...
Popular Post theakerstwo Posted February 13, 2022 Popular Post Share Posted February 13, 2022 I have found when you cant get a air comp build air then remove the discharge line and connect shop air to it.A friend of mine put his cummins in a shop a few years ago for no air.He called me and said they want to sell him a compressor and i told him to have the guy working on it to air it up and check for leaks and i told him i would unload shorty and come down.When i got there they had put a compressor on it and no build air.I ask the mechanic if he tried to air the truck up and he say no because i dont got the fitting.Now the shop had to pay for the comp and when they did get around to making a fitting to air it up they find the braided discharge line full of leaks.So like i have said for years test dont guess. 4 Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489283 Share on other sites More sharing options...
Neo Posted February 13, 2022 Share Posted February 13, 2022 21 hours ago, Onyx610 said: It’s in the head of the compressor. What kind of compressor do you have? What do you mean it’s pushing air hard? When’s the last time you changed the air dryer? That's what I'm trying to do now .. to change the dryer and purge valve....I have no idea how this looks.... Or if other brands can be used because I'm not seeing it online Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489309 Share on other sites More sharing options...
Neo Posted February 13, 2022 Share Posted February 13, 2022 20 hours ago, Onyx610 said: Also when replacing a compressor it is good practice to replace the steel braided discharge line, air dryer cartridge, and governor. I'm hearing this truck does not use a governor....I already changed the discharge house Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489310 Share on other sites More sharing options...
Joey Mack Posted February 13, 2022 Share Posted February 13, 2022 Like Glenn said, Hook shop air to it, at the discharge hose off the compressor and try to find the leak, no need to run the engine and make noise. this way you can listen good to find the leak/s.. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489311 Share on other sites More sharing options...
Joey Mack Posted February 13, 2022 Share Posted February 13, 2022 I just went to my shop library.. My 2 midliner books do not have the info for youre issue. however, if you can find Mack book # ML526S, that may be the book you need.. good luck, jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52913-cant-find-this-air-leak/#findComment-489314 Share on other sites More sharing options...
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