Air lines cut.....tranny shifts early

[Jonathan M]

Hello. I'm new to 5 tons and the forum. I never drove one until after I bought it. a couple weeks ago. So I'm trying to fix all those neglected things and am puzzled by something that was done to the truck long ago judging by the weathering. (1983 AM General M923) The air return lines attached to the front brake chambers (air line without the spring) were deliberately cut off but left attached to the frame and brake chamber on BOTH sides in exactly the same place. I'm wondering if I replace the lines I'll then find out why they where cut in the first place.

Also on an unrelated issue the automatic transmission seems to shift to early under load, 1400 rpm or so. Different on different gears. I don't have enough time behind the wheel to get a good handle on it. I'm thinking I should be locking out the shifting with the 5-1, 5-2, 5-3, 5-4 control when pulling a hill to force the engine into the power band and run it closer to the governor. I used to drive a 1964 White Constructioneer tractor with a 250 Cummings and a 10 speed Road Ranger grossing 92,000 lbs. It slowed down on the hills big time but it did it. The M923 is only 21,600 lbs with basically the same engine is a dog empty. I'm concerned if I throw 10 tons of coal in it it won't be able to get out of its own way.

Comments?

 

[simp5782]

Hello. I'm new to 5 tons and the forum. I never drove one until after I bought it. a couple weeks ago. So I'm trying to fix all those neglected things and am puzzled by something that was done to the truck long ago judging by the weathering. (1983 AM General M923) The air return lines attached to the front brake chambers (air line without the spring) were deliberately cut off but left attached to the frame and brake chamber on BOTH sides in exactly the same place. I'm wondering if I replace the lines I'll then find out why they where cut in the first place.

Also on an unrelated issue the automatic transmission seems to shift to early under load, 1400 rpm or so. Different on different gears. I don't have enough time behind the wheel to get a good handle on it. I'm thinking I should be locking out the shifting with the 5-1, 5-2, 5-3, 5-4 control when pulling a hill to force the engine into the power band and run it closer to the governor. I used to drive a 1964 White Constructioneer tractor with a 250 Cummings and a 10 speed Road Ranger grossing 92,000 lbs. It slowed down on the hills big time but it did it. The M923 is only 21,600 lbs with basically the same engine is a dog empty. I'm concerned if I throw 10 tons of coal in it it won't be able to get out of its own way.

Comments?

They are dogs unless you give them air. And then some extra fuel.

Air line being cut could mean a stuck brake wedge. Worn out shoes is unlikely. Q2 valve dumping air or a diaphram. Replace the lines and see what happens. Cutting the lines just means it will dump secondary air pressure.

You can adjust the modulator arm up on your injection pump for the trans to shift under a higher pressure at rpm

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[Floridianson]

On mine when the transmission is working correct if you give it part throttle it will shift early and if you put the peddle to the metal it should shift at close to 2000rpm for harder pulls. Think maybe you need to make sure the truck is road worthy then go out and drive it and see how she does before you adjust anything. Also sometimes if you don't get it rolling the second lock up makes it feel funny. They take awhile to get use too.

 

[74M35A2]

Welcome to the site, and congrats on your truck.

Sorry, glad to say I don't know anything about brakes.

Yes, adjust the trans modulator cable. It will be linked to the throttle lever at the engine injection pump as mentioned. You need it to pull more/further in order to hold each gear longer and downshift when needed to. Though I have an a2 (8.3L engine), mine will shift @ 2100rpm at wide open throttle, and will do forced downshifts just like a car if the accelerator is floored and RPM too low. Shoot some lubricant down this cable sleeve with spray can and straw while you are there, then pull the cable by hand and let it spring back. If all of this is setup and working correctly, you really should never need to manually select the gears, unless you want more engine braking assist.

 

[Floridianson]

Welcome to the site, and congrats on your truck.

Sorry, glad to say I don't know anything about brakes.

Yes, adjust the trans modulator cable. It will be linked to the throttle lever at the engine injection pump as mentioned. You need it to pull more/further in order to hold each gear longer and downshift when needed to. Though I have an a2 (8.3L engine), mine will shift @ 2100rpm at wide open throttle, and will do forced downshifts just like a car if the accelerator is floored and RPM too low. Shoot some lubricant down this cable sleeve with spray can and straw while you are there, then pull the cable by hand and let it spring back. If all of this is setup and working correctly, you really should never need to manually select the gears, unless you want more engine braking assist.

What is your rpm when soft pedal? 1400/1500 does not seem to low for saving fuel. Was reading where someone said 1850/1900 rpm but that to me is too high for soft pedal if 2100 rpm is the governor. I lock my gears as you said if I need more braking or in town light to light also off road to keep RPM high in fast changing terrain. Maybe OP should if not have someone else watch and record the soft and hard pedal shift points and report back.
As for the engine power that going to be needing tweaking.

 

[Jonathan M]

Thank you for the replies. I have driven it about a hundred miles so far, all on road but my 10 day temp expires today and I have other things I have to do today. Tops out at 60 mph according to the gps. Speedometer/odometer not working. Hour meter works. The brakes, power steering, tires, and wheel balance (the basics) a seem good. I put longer mud flaps on it. (Even that was a battle because of rust.) My wife complained I was pelting our car when she followed me home. Horn button awol. I need to add a fire extinguisher, city horn, and a cluster of three marker lights on the rear of the truck to get it registered. I have the replacements for the cut air lines on order. I might have to replace a bunch of air lines before I'm done. I need hinge pins for the rear tailgate......oh gosh the list keeps growing. I put brand new 7271 batteries in it. They must be a little taller than the originals it was designed for. I had to remove all the wood in the bottom of the battery box and replace it with 3/4" material fitted around the battery tie downs and ribs in the floor. I used a table saw to rip the boards the proper width to fit good. I replaced the headlights. I brought it home with only on working and I had to rap it with my knuckles to make it come on. I have broken 3 marker light fixtures. The screws just break off when I try to remove them. Those that came apart got grease on the threads when I reassembled them. 3 out of five screws broke on my tail light fixture. Two screws will hold the lense in but it won't be waterproof. I have tried penetrating oil where I can and hammering on the screwdriver before turning the screws but it didn't seem to help. What's done is done. $107 worth of new marker light should arrive today. Rust is my enemy on this project. I drilled out all the bolts on the red reflectors yesterday. They were all shot. I was to wet to prime and paint yesterday, to cold today so the replacement reflectors have to wait. The little bolt holding the windshield wiper blade kicked my butt yesterday. I'm going to try and hack saw it off this morning when I get done with the honey do list. Pintle hook rusted solid. My neighbor complained to me a couple days ago. He said I was stinking out his whole house. It pushed out a lot of smoke on a cold start and I let it idle a while. The wind was just right to drift it his way. His house must be drafty to get the diesel smoke stink inside. I apologized and shut it right down. Now I look if their cars are in their driveway before I start it up. Buyer's remorse setting in. Maybe I'll get over that when the thing is properly registered and and running right.

 

[Jonathan M]

What is your rpm when soft pedal? 1400/1500 does not seem to low for saving fuel. Was reading where someone said 1850/1900 rpm but that to me is too high for soft pedal if 2100 rpm is the governor. I lock my gears as you said if I need more braking or in town light to light also off road to keep RPM high in fast changing terrain. Maybe OP should if not have someone else watch and record the soft and hard pedal shift points and report back.
As for the engine power that going to be needing tweaking.

I might be days before I can get to messing with it. Thank you for pointing me in the right direction.

 

[Jonathan M]

Yep Yep, a place to start. I didn't have a clue where to begin. Thank you.

Welcome to the site, and congrats on your truck.

Sorry, glad to say I don't know anything about brakes.

Yes, adjust the trans modulator cable. It will be linked to the throttle lever at the engine injection pump as mentioned. You need it to pull more/further in order to hold each gear longer and downshift when needed to. Though I have an a2 (8.3L engine), mine will shift @ 2100rpm at wide open throttle, and will do forced downshifts just like a car if the accelerator is floored and RPM too low. Shoot some lubricant down this cable sleeve with spray can and straw while you are there, then pull the cable by hand and let it spring back. If all of this is setup and working correctly, you really should never need to manually select the gears, unless you want more engine braking assist.

 

[Jonathan M]

Y am I so Upset?.....Y am I so UPSET? the sock puppet asks......Because I bought 21,600 lbs of rolling rust and now I have to deal with it. I did it to myself. But it was such a good deal. Oh did I mention having to track down air leaks......I think I left that out of my tail of woe.

 

[Jonathan M]

Also I drilled out the bolts for the dimmer switch. Rusted solid. When I put things back together they get stainless bolts, nuts and grease or never seize.

 

[porkysplace]

Y am I so Upset?.....Y am I so UPSET? the sock puppet asks......Because I bought 21,600 lbs of rolling rust and now I have to deal with it. I did it to myself. But it was such a good deal. Oh did I mention having to track down air leaks......I think I left that out of my tail of woe.

It's usually cheaper in the long run to buy a more expensive better truck to start with . Even one with mechanical problems , rust is a on going problem that just gets worse.

 

[rbrown225]

Something that might help with the rust is White Vinegar ( ie grocery store). We put a lot of our rusted parts into soak for 24 - 48 hours. It eats the rust. Had a couple of large 1" sheaves that were rusted solid. After 4 days they were freed up and running smooth. it lasts for quite a while, we go until it turns black.

 

[Jbulach]

I wonder how many gallons it would take to soak a truck? I always wanted a black truck...


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[MyothersanM1]

Those cut air lines lead from the non-service side of the of diaphragm in the brake chamber. They are there to equalize pressure, if any, on that side and it does not really effect the service pressure. All those vent lines lead to your air intake stack. When I installed M939-series front wedge brakes on my M818 I vented them to the atmosphere via 3/8" NPT breather vents in the chamber vent ports.

 

[Floridianson]

Looks like the vents would work as long as your not fording but one would think you should have run vent lines.

 

[Jonathan M]

Something that might help with the rust is White Vinegar ( ie grocery store). We put a lot of our rusted parts into soak for 24 - 48 hours. It eats the rust. Had a couple of large 1" sheaves that were rusted solid. After 4 days they were freed up and running smooth. it lasts for quite a while, we go until it turns black.

In the past I used citric acid from the canning goods section of the hardware store to clean up old yard sale cast iron pans. I never thought of using vinegar. I think vinegar would be more economical. Thanks.

 

[Jonathan M]

The breather vents look like an alternative for on road use. I kind of doubt I'll be running the truck in deep water but you never know what curve ball life might through my way. Understanding what I'll looking at helps a lot. I already ordered the correct replacement hoses. Got to thinking with those hoses cut it could allow water into the air intake as well as back feed into the air chambers. As a rule of thumb I think I will try to keep the original systems in tack whenever economically feasible.

I did find time to take the truck on the road before my temp expired. I controlled the shifting with the gear selector (1-2, 1-3, 1-4, 1-5). I was much happier with the way the engine/tranny performed when I forced it to hold the gears to higher engine rps. I studied the linkage by the fuel pump with the "slide link" to the tranny. I didn't mess with it and probably won't until I have another temp plate. There will be some trial and error involved to get it the way I want it. The cable to the tranny seems well lubed. It has rubber boots on the ends to keep the grim out. I'm thinking I need to shorten the linkage to make it shift at higher rpms normally. It doesn't look like there is a lot of adjustment at the fuel pump end. I haven't tried to look at the tranny end yet. ......One step at a time.

Sorry for the delayed response. I did't realize the thread went to page two.

 

[Floridianson]

I took my Allison governor controlled out to fuel her up. The first to second shift was at 1600rpm doing a soft touch pedal and my hard pedal is 2100. I was playing around after I got fuel and was just soft pedaling and there was a small down hill. The last shift came in at 1000rpm because of the hill increasing my drive line rpm. When all is correct with the Allison you have to get to know how the governor is feeling. By that I mean when the second gear lock up comes in if you don't keep pushing the pedal and the tail shaft / drive line slows down just a little then the governor sees that and will down shift. There is a lot of weight you have to keep rolling and they don't act like a pickup truck.

 

[Jonathan M]

Looks like I'm going to have to do my Vulcan mind meld on the governor and use my Jedi mind tricks to get the governor to do my bidding. I think I understand the difference between a hard and soft pedal and how that effects how the tranny shifts. I don't see the early shifting to be a problem with a soft pedal. My problem seems to be it shifts early even when I have the fuel pedal mashed to the floor. Looking at this from another angle, I wonder if when my fuel pedal is mashed to the floor I might not be getting full throttle. Up to this moment I have just assumed I was getting full power because of normalcy bias. I'm just thinking out loud so to type. I was told the mechanic that took care of this machine for three years was a hack and they only did the bare minimums to keep it running so I shouldn't assume anything.

 

[rbrown225]

To clarify the vinegar will turn black after several parts have gone thru. The part will come out brownish but the rust will have dissolved.