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Hello Gentlemen, new to the site but I have to say it looks like I will feel right at home here.

Been driving trucks for 30 years and that is long enough to know that Mack is the absolute best truck out there as far as durability, dependability, and value. Especially for on/off road applications which is what I do for a living, hauling dirt, rock, asphalt, etc.

Just bought a 99 Mack RD690S tri-axle dump with a Mack E350 engine and Mack 7 speed transmission. The truck was fairly neglected by the previous owner and is fairly rough, but being a Mack is sufficiently sound and solid overall.

My problem is the air compressor overbuilds pressure to the point the gauge pegs out over 150psi and yet I don't hear any release valve spit out the excess air. With that much pressure wouldn't it blow out lines left and right, or is it possible the gauge is just defective? And on this model would the governor be located on the firewall or elsewhere? I'm sure I can trace it but just stumbled onto this site and thought I'd run it by you fellas first.

post-16177-0-20334400-1380744632.jpg

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you may want to check the air tanks for a blow off safety valve most should be set for 150/160. You could also take a pressure gage and stick it on the air tank

Welcome and what he said....or rotted closed.....

Lack of planning on your part does not constitute an emergency on my part....

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you may want to check the air tanks for a blow off safety valve most should be set for 150/160. You could also take a pressure gage and stick it on the air tank

Welcome and what he said....or rotted closed.....

Lack of planning on your part does not constitute an emergency on my part....

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Thanks everyone. Jay the air dryer does not make any noise at all, in fact id doesn't even spit wet air like it should. When I drain the air tank I get a lot of water every time also.

I don't hear any leaks, so that's good considering it is loading up so much pressure. The governor is on the firewall and after several adjustments it continues to peg out the gauge over 150psi.

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Before you do anything Check and Repair/Replace the air pressure safety blow off valve on the tanks, if it is building air like that and something is stuck it could blow a storage tank and someone will get hurt, or damage the air pressure system or compressor

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Robert

"I reject your reality and substitute my own."

 

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Thanks Thomas, that was the first thing I did.

Plan to pick up a new governor tomorrow for $17 and replace it. I'm thinking it should not be building that much pressure if it was functioning correctly. Also replacing the air dryer cartridge since it aint spitting air either. Like I said before, the previous owner neglected the truck and didn't seem to maintain or repair a whole lot of stuff. I nearly wept when I shook 2 cups of dust out of the air filter.

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I suspect the air compressor governor as well,relatively easy fix too,should be 100-120 Psi.max if functioning properly. Had a similar problem on my CX not too long ago (governor plus a stuck pop-off valve on the primary air tank) changed both and that cured the problem. Probly a good idea to service the air-dryer too,if the trucks been neglected as you stated........................................Welcome aboard BTW!...............Mark

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Mack Truck literate. Computer illiterate.

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I appreciate the suggestion and support, Mark. Yeah the governor is very easy access and replace, hopefully that and the air-dryer service will do the trick.

I look forward to reading and learning a lot from the different posts in all the forums here and benefiting from the many years of experience everyone here has to offer. Thanks again to all.

Bob

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Thanks for the welcome Marcel and Rob.

You guys know what to do if you're ever lost in the woods?

Just drive a grade stake in the ground. Within 10 minutes a dump truck will drive over it and you can follow him out.

An oldie but a goodie.

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