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Puff limiter


keg1

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The reversing valve( I guess that's what you call it) on the intake on mine has two lines coming out of it, one goes to pump, other to firewall to brake release. I also have a fitting something like a petcock which seems like a plug when I took it out. The valve on my parts truck had pipe plugs in every port so what I'm wondering is should I have another line going to the third port to make it work? At $250 for a new one I like to make sure mine is bad. It was unhooked when I got it but it smokes worse than I'd like.

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On the top picture the line from the brake release is just blowing air into the manifold, which is wrong and it will not work.  It should go into the supply port.  If I remember right on trucks with a mack transmission they had a 3rd line coming from the transmission tor put air on the valve to cut the power down when in lo lo gear.  Clean the other valve off and see if you can see if the ports are marked or move the line from the brake and move it into one of the end port and try it.

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7 hours ago, j hancock said:

Here is a 691GC218CP5X that came off a 1985 285. 

The yellow dot is the port for the manifold SIGNAL.  The red is OUT to the pump.  The lime green is the port at the end for air IN.

691GC218CP5X.JPG

Thanks for the picture. I didn't get a chance to switch the lines today but I'll get it tomorrow and see what happens.

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Theres a lot of info on here about puff limiters. The thread that helped me the most is this…...

http://www.bigmacktrucks.com/topic/44803-300-puff-limiter/#comment-332974

Swishy posted some shop manual pics in the very last post. They are very helpful.   Thanks Swishy !!

Another point that may be helpful , is in the pic that Jim posted you can see on the bottom there is a CP5X   . You will find a they are all stamped with a number that ends with X.

could be a 3X all the way to 9X (i think)  The lower the # the less smoke you get. I have a 3X on my 350 and a 5X on my 237 .  

The relay valve is just part of it though. The rack limiting cylinder (where the line is going to from the relay) has to be set and working properly. The info Swishy posted shows how to test .  

 

 

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Keith 

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I think I have it working now. I pulled it off and found someone had soldered the hole shut in the fitting that goes into the manifold and the end of the line going to the pump. So once I fixed that and hooked the line up right seems ok. Thanks for the help. I've never had one hooked up on any of my trucks so wasn't sure how it was supposed to go.

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40 minutes ago, 39 Baby Mack said:

A quick check to see if it's working.

Nail the accelerator with the spring brakes applied, exhaust should look like a house afire.

Release the brakes and try it again you should see a very noticeable difference!!!

Ron

Sent from my SM-G900V using Tapatalk

That's what I did. Definitely a difference. I don't mind the smoke but every time I started it I was blowing out a shovelful of soot.

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I checked mine today.  Last week when I would get into it more smoke would roll than normal and towards the end it would get a little gray.  I had the mini-me push and pull the parking brake knob and I could not feel it move.  I took mine of and shook it and nothing happened so I put air to the inlet side and it blew out the other so I stuck it in the vice and pulled it a part.  I figured it wasn't working to begin with so what to heck.  It has two buttons on the inside with a spring in between. A plastic lock ring and a diaphragm.  I suppose what happens is manifold pressure creates a vacuum and pulls/pushes the valve to allow compressor air in to reduce smoke.  

I cleaned it up and removed the lock ring and looked under the diaphragm and seen it had some oil so I sprayed it out with some can solvent and air then reassembled it and put on the truck.  With mini-me pushing and pulling the brake knob you could feel and here it click open and closed, which it wasn't before.  If It starts up again I will check the valve on the pump and probably replace them both.

What does the deal on the pump do when it gets air?  I was going to take it off but ran out of daylight for what I had on my agenda for the day.

20161002_132635.jpg

Robert

"I reject your reality and substitute my own."

 

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Is there any way to tell if it is working while it is on the truck?  I suppose it could have some oil  or dirt in it and resticts movement.   

How much are they maybe I will buy one and replace it andvsee v what happens.

Sent from my SM-G900V using Tapatalk

A quick check to see if it's working.

Nail the accelerator with the spring brakes applied, exhaust should look like a house afire.

Release the brakes and try it again you should see a very noticeable difference!!!

Ron

Sent from my SM-G900V using Tapatalk

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7 hours ago, thomastractorsvc said:

I checked mine today.  Last week when I would get into it more smoke would roll than normal and towards the end it would get a little gray.  I had the mini-me push and pull the parking brake knob and I could not feel it move.  I took mine of and shook it and nothing happened so I put air to the inlet side and it blew out the other so I stuck it in the vice and pulled it a part.  I figured it wasn't working to begin with so what to heck.  It has two buttons on the inside with a spring in between. A plastic lock ring and a diaphragm.  I suppose what happens is manifold pressure creates a vacuum and pulls/pushes the valve to allow compressor air in to reduce smoke.  

I cleaned it up and removed the lock ring and looked under the diaphragm and seen it had some oil so I sprayed it out with some can solvent and air then reassembled it and put on the truck.  With mini-me pushing and pulling the brake knob you could feel and here it click open and closed, which it wasn't before.  If It starts up again I will check the valve on the pump and probably replace them both.

What does the deal on the pump do when it gets air?  I was going to take it off but ran out of daylight for what I had on my agenda for the day.

20161002_132635.jpg

Yours looks a little different than mine. The way mine is made you can't take it apart.

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hey 39 baby mack could you tell this new guy why the difference with spring brake on/off?

The first emission system I saw was a steel line that went from the turbo down to the governor. It wouldn't allow the rack in the pump to open fully until there was sufficient boost to burn the fuel.(eliminating the initial heavy black smoke that the early Maxidynes were known for after an upshift in low RPMs)

It eliminated the "puff"!

This was fine except for trying to start one of these Maxidyne engines in cold weather. To get these started you needed to hold the accelerator to the floor to have the rack open fully. You couldn't get the rack to open fully with that set up.

With the reversing relay the puff limiter didn't work until the spring brakes were released and the truck was ready to go down the road. This allowed for a full rack in the pump to get the engine started when it was cold but set the puff limiter in operation once the truck was put in operation

Ron

Sent from my SM-G900V using Tapatalk

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I had forgot about line going to the governor.I have a freind that still has one.

Glenn,

Do you remember the first reversing relay, the one that was remotely mounted towards the front of the motor.

If memory serves me it was mounted off the thermostat housing. It was made by Fairchild.

How many complaints about an air leak did you hear about when somebody would shut one off in gear without setting the spring brakes?

Couldn't take your time adjusting the brakes with the truck shut off and in gear or the bleed on the reversing relay would pop the brakes back on!

Ron

Sent from my SM-G900V using Tapatalk

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Stopped by the Mack dealer and got some info, my truck has the AMBAC 300 pump.

Part# cyl Assy 31Qc212  (mounted on front of pump) $79.62   PAI#EAC-3964

Part# Relay Assy 691GC218CX (mounted on manifold) $234.25 PAI# EVA-2775-001

There are a lot of shims available to shim up the air cylinder on the pump so part # 505GC19P15 will get you there. $3.96 PAI# ESH-3849-010  (.010 inch thick)

Not sure on the PAI prices as I have not heard back from the parts guru.

Robert

"I reject your reality and substitute my own."

 

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