M911 Building air slow

[TheTrainMagnifiq]

Firstly, pictures. Eventually I'll get it repainted but until then I don't mind the vintage look with a touch of Rustoleum.
https://photos.app.goo.gl/KnZ4xvD769N2EZ5T6

So it works well except there is a small air leak on the right rearmost brake chamber when the parking brakes are released. It will build air normally to around 120 then drop 10-15 psi when the brakes are released but the system stays steady around 105. But this thread is mainly for the following issue.

Not sure of the last time the air tanks were drained so last week I decided to drain them. Firstly I broke the knob on the line under the driver side of the cab leading to the center tank as it wouldn't budge so I had to get that one when I went under for the other two. The regular two tanks drained with normal condensation I suppose while the center tank (wet tank?) let out some water followed by some oil.

Now after draining the tanks, air pressure takes 2-4 times as long to build pressure. It can still build to 120 but takes a couple minutes longer to get there even with a little rev. Any reason why it was charging normal before but not anymore after draining?.......

I let it sit for a week and came back this morning to check on it. It builds air normally at first but after it got to 120 the first time, it was back to building slowly after pressing the brakes.

Thanks.

 

[US6x4]

Nice pictures! - that truck is pretty epic. Probably the first M911 I've seen a post about. I especially like the data plate about the applied rust treatment that's fastened to the rusty sheet metal

Sorry, I have no ideas on the pressure issues.

 

[Jbulach]

I would double check the drains and anything else you touched while repairing the one. Use a soap water mix in a spray bottle. How quickly does each tank bleed down after shutting the truck off with touching the brakes?

 

[Jbulach]

Also soap the air tanks checking for rust holes, especially in the bottoms.

 

[TheTrainMagnifiq]

Nice pictures! - that truck is pretty epic. Probably the first M911 I've seen a post about. I especially like the data plate about the applied rust treatment that's fastened to the rusty sheet metal

Sorry, I have no ideas on the pressure issues.

lol thanks

I would double check the drains and anything else you touched while repairing the one. Use a soap water mix in a spray bottle. How quickly does each tank bleed down after shutting the truck off with touching the brakes?

Also soap the air tanks checking for rust holes, especially in the bottoms.

It wasn't really a repair just a regular draining of the tanks. The knob under the driver side cab connecting to the one isn't directly attached to any air rather it is a cord that pulls a valve sideways against the tank. I think it only opens partially that way. But when you go under and physically push the valve on the tank in like a button it completely opens it. The other two are regular twist type valves.

The tanks themselves are leak free and seems to have only lost about 10-20 psi since this morning. One thing it might be as seen in some research last week is something about an unloader valve sticking but I don't know what I'd be looking for. Remember, it charged fine the first time after sitting but not so much after the initial charge.