JoeH

Looking at E7 tags found on used engines online I've seen 7-18.

All due respect and to keep things straight for reference, but the industry refers to those as Synchronized Transmissions, not Constant Mesh. The transmission in this DM is a Constant Mesh, and using that terminology to search for shifting advice will yield different shifting explanations than searching for Synchronized Transmission.

The oil fill tube on this does look like an E6 though. Doesnt match my e7's fill tube. More pictures would help.

Looks like an e7 to me. An E6 would have two removable plates on the side of the engine block next to the fuel pump. These plates provide access to where the pushrods set into the lifters.

If you go to your local Mack dealer they should be able to look up book # 5-672 and order it for you. It's an engine overhaul book for 1981. Pretty much identical engine to what you have, just 2 years newer should cover multiple HP ratings. Not sure what transmission you have, but that book will likely be available as well. Same on rears. Other than that you're largely on your own to figure things out by asking around here.

Not sure what book you're looking at. There's a whole slew of individual component books. Book for pretty much every engine, trans, chassis, suspension, fuel, etc. Usually each book is $40 or $50 at the dealer, but you gotta know which ones you want. They're numbered.

My 95 e7-350 mechanical had a bit of a stumble at one point. Almost sounded like the name brake was trying to come on under acceleration. I changed the fuel filters and it went away. Been 3 years now? Could be a lift pump at the borderline of spec, the truck does have 24,000 hours.

There's 2 brake light switches. One comes on when air pressure is sensed in the brake lines. The other is set to kick on below a certain pressure, when air in the parking brake circuit is dumped. If I recall, the service brake sensor should be attached to an airline on the interior firewall above the brake pedal. The parking brake one is probably on the parking brake knob in the dash. It might also run the low air pressure buzzer and light.

TLDR. Spokes vs Budds comes down to brake jobs for me. We've always had spokes til our MR688 we bought 2 years ago. Brake jobs were always a 2 person job on spokes. One to run the car jack, the other to steady the hub on the way off the truck. On Budds, you grab your big 1.5 inch gun, spin the nuts off, pull the wheels,and boom you're at the brakes. No need to pull the axle and hub. First. Also, we've had spoke rims spin the valve stems behind the spokes. Not fun. We've also had the tips of the spokes that hold the rims on snap off. Budd brakes are a one man job. And if you do need to pull the hub... It's still a one man job as the hubs are so much lighter. We also run a 15 mile radius, so on a flat tire you just drive slower on the way back to the yard. Seldom have flats, even less common to have to change them on the side of the road.

This truck is from an era where the VIN actually told you something about the truck.

Once you understand all that, then you have to learn to do it, lol! There's lots of factors that play into making it harder. Rolling resistances working to change your vehicle speed, whether it's soggy ground or going up a hill, or going down a hill, all throw off your timing and you'll have to learn to adapt to the miriad of scenarios you may find yourself in. Because you said your truck is a 5 speed single stick, I'm gonna guess the VIN starts DM685SX where the 5 indicates is an ENDT675 engine, which is a 237hp Maxidyne. It's an 11 liter 2valve per cylinder engine. It's pretty much the same as a 2 valve E6 mack engine. I have one in a yard crane here, and a spare as well. I've also got 2 of the 283hp variant "ENDT676" in running trucks as well as a spare parts engine from my grandpa's truck. The SX is an extreme duty suspension, the rear tandem would be rated for at least 55,000 lbs on an SX. Sometimes rates higher. If it's just an S in the VIN then it's typically be a 44,000 lb rear tandem. ST is typically 38,000 lbs, though sometimes 34,000 lbs a T with no S would be a single rear axle truck.

Rear Trans(S)Forward Trans(C)Engine (S) is the shifter (C) is the clutch. You have three different spinning sections going down the road, which can be separated from each other at by either S or C, or both. Rear Trans is fixed to the driveshaft, and all gear sets are always spinning, hence "Constant Mesh". Engine is always spinning at whatever speed the RPM gauge says. In a synchronized transmission (not what you have) unused gear sets are not spinning until you try pushing it into a gear. Synchronizers match the gear speeds together for you. Looking at my above diagram: when you're going down the road and you go to shift you break the connection between the wheels("Rear Trans") and the engine by putting (S) in neutral. Now you have to use "Engine" to spin "Forward Trans" at the right speed for the gear set you want to be in. "Double clutching" you tap the clutch to facilitate getting into neutral, then you match engine speed to the gear you want, then you tap the clutch as you slide into the gear you want. Basically all the "double clutch" action does is take the tension off the gear teeth so that the shifting mechanisms can function without being under load.

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Unsure how familiar you are with trucks but I'm gonna guess not. You don't shift it like a car/pickup, this is a Constant Mesh transmission. You "double clutch" or dont use the clutch at all for shifting. There's no Synchronizers to match gears for you, you have to do that yourself with the accelerator pedal with foot off the clutch while coasting between gears. Also there is a "clutch brake" that stops the trans from spinning when you push the clutch pedal ALL the way to the floor. These break, get abused and worn out, and are easy to replace once you're familiar with them. There's a step by step process to adjust the clutch and clutch brake, so while what you did got you home, it wasn't the right way to adjust the clutch. The clutch itself gets adjusted by a bolt head on the clutch itself that's accessed through the window on the underside of the bell housing. Clutch brake gets adjusted through clutch linkage. One has to be done before the other, I forget which. Done properly your clutch pedal should have 2 inches of Freeplay before you feel the clutch springs start to resist pedal travel, and the clutch brake should engage on the last half inch of pedal travel before the it bottoms out to the floor. Take note, the clutch pedal should only ever be pushed to engage the clutch brake when the truck is stopped and at an idle. When "double clutching " you are only punching the clutch to about an inch or two into the clutch spring resistance zone. You are not punching it all the way to the floor.

Ant really speak about that particular machine, but I bought a used backhoe this year and it's kinda jerky when the boom is most of the way up. Basically comes down to "how many inches of piston travel" = "how many degrees of boom angle change". The higher up the boom goes the more the boom moves per inch of piston travel. Mine tends to work pretty smooth when I'm using 2 functions at the same time. Helps to split the hydraulic GPM flow to slow down the sensitivity. I also run it at maybe 30% throttle?

No pictures no help! (Kidding... but seriously...)

Start with checking the engine software level at the dealer, the "12b" update should correct much of your issues. If not then give this a thorough read.... https://www.bigmacktrucks.com/topic/50251-mack-ai460-ai427-ami-low-torque-low-horsepower-poor-fuel-mileage-granite-dead-dog-remediation/

The E7 was made with a 460hp option, so there's no reason you shouldn't be able to hit 400+, just need the pros to chime in with what your 350 needs to turn it up.

Wow that's some carnage. I'd say you need a head. Here's a piston from my '79 R686 that dropped a valve seat. Bits of the seat are embedded in the piston.

How many hours are on the motor? Any clue? I think you're headed in the right direction trying to take care of the leaky injector lines. I'd start there before pulling injectors, but my maintenance history relies heavily on how durable Mack trucks are.

Simple til you have to change driveshaft length etc.

My napkin math says you need to be around 3.84:1 rear to hit 60mph. That would be your easiest way to get highway speed.

If you can't get exhaust manifold nuts off, just split them with a hammer and sharp chisel. The water & intake manifold bolts require some tight access to get into, and I believe the intercooler box lid has to come off to get to some bolts on the inside.

My first "tear in" on an engine was the same motor you have there, same year and all. Our '79 broke a valve seat and it dropped into the top of the piston, ruining the head and piston. Similar business size, it's just my dad and I plus my cousin seasonally, so I can relate. Get the head off and see what's really broke. Many of us have the books with torque sequences and settings, so we'll post info for you as needed. Remember though, DONT SET THE HEAD DOWN ON THE INJECTOR NOZZLES!

My strategy is typically remove valve covers and oil pan to get eyes on all the internals. There is a fair amount of manifold work on this particular engine to get the head ready to come off, but it's gotta be done, whether he needs a valve or a head. I'd have that head off right away too, but I think RS is working through a mechanic, so there may be a DIY factor missing.