JoeH

Does it have Jake brake? If so, inspect the top of every exhaust valve for the disc spacer that rests on top for the Jake pistons to push down on. Our '79 endt676 has a weak valve spring on one valve, that disc kept popping out. We deleted the Jake brake after the second time it did it. I'd walk the engine round again slowly and feel for excessive valve lash. Carbide face may be missing off one lifter tappet, starting to wipe a lobe off the cam.

Did you lubricate the fuel filter o rings on assembly? Dry filter o rings could have bunched up, allowing it to suck air.

1979 R686ST This guy is likely getting retired in June while there's still something left to restore. Where do we get cab repair panels for it? Roof, sections around rear window, gutters.... Undecided if it'll get a 5th wheel or a coat of paint inside & out on the mixer body. My dad bought the mixer in 1976 on a different horse, and the truck in 1987 when the old horse died. Both truck and mixer are good talking pieces, & you'll be hard pressed to find an older volumetric mixer than this one. (It's a 1968 Daffin. Volumetric Mixers were invented around 1962)

If it does it again, wiggle the fuse for the EECU. My 2003 ETech had that problem, yielded a code 9-1? Or 9-4. I forget which code number. It's "engine power loss without key"

Serial number will matter too, different years have different modifications. Could be different gear ratios used in same model trans.

Any shop you hire will need tranny model and serial # so they can order the right stuff. "5 speed maxitorque" is like saying "I have a car, what oil filter do I need?"

I wonder if you're going to run into issues with the front spring brackets. The crossmember bolts to the inside of it, may be different. Your picture looks like the crossmember is between the damper and timing cover, whereas my '95's crossmember is in front of the damper. The engine rests on a shelf welded to the backside of my crossmember. This swap might require different front spring brackets.

We had to delete the engine brake on our 283 however, because one cylinder has a weak valve spring and the spacer that rests on top of the exhaust valve kept popping loose. After the second time we pulled the Jake off. If you have 50-80,000 hours on your engine like we suspect our has, then you may want to replace valve springs if you add a Jake brake.

Having driven a tandem axle with the same setup for some years, I would steer you away from a trans swap and into a Jake brake for faster shifts. Your engine makes 90%+ torque across an 800+ rpm powerband. Extra gears are wasted on this engine. The 8LL is designed for engines with a 4-500 rpm powerband. Faster shifts, however, help you catch the next gear while you're still in your 90%+ powerband. You'll also be giving up your multi speed reverse, which let's you crawl up a mountain or fly across soggy ground. But at the end of the day, you know your workload conditions and needs better than me. It should be a doable conversion if you have access to a good Mack junk yard.

You have to stick to an E7, you cannot use an ETech "E7". However if you had all the right components plus the know how, there's no reason you couldn't transplant a running ETech engine into the truck... But I wouldn't. What failed, the head gasket? If that's all, then I'd just be pulling that head and replacing gasket. Better to stick with an engine you know is good (albeit with a lot of use) than trade for one you don't know...

@Keith SS report to the managers office...

Change the bulb in your lightning bolt.... You could have engine codes that we can diagnose through that light if you can get it to work.... Key on, if the lightning bolt is in, you press and hold the cruise set/decel button until it goes out. Then count the flashes to get a 2 digit blink code. Press the set/decel again, if there's another code it'll spit it out too. Keep doing that til it starts repeating itself. Note that you perform this procedure with the cruise control "off". Engine can be running, or not. Tell us the blink code and we can stop guessing.

You probably have a fuel return line leak. The plastic lines on top of the head that go from injector to injector are prone to leaking. Any dampness up at the injectors is likely caused by the plastic lines failing. Also if any of the hard metal fuel injector lines have dampness at the ends then you can lose prime and have hard starting.

State trucks (In northeast USA) are all overpriced junk with so much rust from salt work. Not worth looking at. Truck Paper is a great app to scout what you're looking for. R(D)6xx"P" would be a single axle, R(or RD)6xxS(or ST) will be tandem axle from factory, but may have a liftaxle as well. xx is in place of either 85, 86, 88 or 90, which tells what engine/fuel characteristics the truck has.

Look for a truck with a good cab and good frame. Everything else can be rebuilt.

Truck is working well; concrete season is over, now we have to keep our heads low to pay off the mixer over the next 4 years. This is our current project we've been working on. Hopefully we can get this mixer rebuild completed sometime in the first half of 2023. Less Mack related stuff on this build, so it probably won't find it's way onto the forum. The horse is a 1988 RD690S with an EM6-300L.

Probably torque rating.

Pretty sure they "crush" a little to seal. So you get one "crush" out of them.

The deterioration also happens slowly, so you adjust over a long period of time. Abnormal becomes normal, and it becomes normal to keep driving as your body becomes less capable.

I heard a study on the radio a couple years ago. Babies' eyes/brains process a ton of images per second. The older you get: the less images per second your eye/brain process. Reality is, as you get older your body becomes less capable. Some people's bodies deteriorate earlier than others, so I think it's foolish to stamp an age restriction. If you can pass an honest Medical Card Exam (USA requirement, don't know what you Aussies have) then you're good to go. That being said, you have to be an honest critic of yourself. I had a little old lady pull out in front of me from a side street once, almost T boned her in my empty triaxle. I slammed on the brakes and left tire skids. That's a lady that obviously couldn't pass a vision test but the bloke in the DMV last time she had to renew her license didn't have the heart to tell her. We've all been there, driving behind an elderly person driving 15 mph under the speed limit because they have cataracts and have to use peripheral vision to see straight ahead. As a "young bloke" trucker whose been driving with his almost 70 yr old dad for 15 years I can tell you vision aside: muscle memory is huge. My dad has been in his same 1979 R686ST since 1986 with a few other trucks coming and going in our fleet. The body knows what it knows. He'll take the old truck and work it right to it's limits. We're trying to finish rebuilding a mixer for a 1988 RD690S so we can retire his truck while there's still something left of it worth restoring for shows. Also, regarding texting & driving: I see just as many middle age and elderly looking at their phones in the car as young people.

Slow down on a CalAmp delete, that's your ELD compliance right there. If you're operating locally and don't need it then great, delete it. Don't assume it's the problem til you've done your homework. What blink codes do you get from the Engine Malfunction Light? Fire up the truck. When the lightning bolt comes on: press/hold the set/decel button til the lightning bolt goes off. It will then blink a 2 digit code at you. Write it down, press it again. Keep doing that until it starts repeating codes. Post the blink codes here, we can provide you with the data on the codes.

Vital info! Thanks for including it! Joey and fjh are going to steer you right.

Queers just became the hot kidnap targets of our enemy nations.

Those relays are junk. The ones from Mack last... 2 years at best on my '95 R model...

2001 saw the changeover to the left side ecm I believe. With info provided initially I'm thinking this is a simple power issue. He said engine dies, as well as battery voltage. This tells me there's a power supply fault. Do these use the relay under the ash tray for power like the pre-Etech R models? Check your ignition switch circuitry.