JoeH

Carrier bearing.

Good fleet; I'm partial to the green Mack's hood.

I have a 1988 RD690S with an em6-300L

Maxi brake Chambers have 2 sides, each side can act on the brake rod. If you are flooring the brakes and you pop the park knob, you're trying to use both sides of the brake chamber to hold the truck. You may not hear a hissy from the park brake engaging because of this. Have you had situations when trying to set the brakes where they didn't actually set and the truck started rolling?

My 79 does it, we figure it's just a driveline balance thing or just how the truck is loaded. Started life with a 5tg wheel, but we have a concrete mixer on it with most of the weight sitting on the Camelback. On a full load I probably have 12.5k on the steer (rated at 11k) and 40k on the Camelback (rated at 38k). My guess if it's not a driveline balance issue is just soft springs on the front with a top heavy load. Come to think of it, there's a 100 yard section of road near me that would make my 95 rd688s triaxle do it at like 42mph itd get that same hop going. If I went through slower or faster it wouldn't do it. But they repaved the road last year so it doesn't do it any more.

Not sure what you mean by bounce the throttle; my 79 gets a hop in the chassis around 45 mph or so, it has the shackle style steering springs. Gotta plant your heel.

With that motor in that truck I doubt it could handle a 7.5 foot plow. But it's possible, no holes for plow lights on the fenders because the engine can't handle anything bigger than a pickup truck plow which would ride below the factory headlights anyways, or would have its own light bar. That'd make a decent yard truck for someone that just needs to putt putt around moving dirt on their acreage. That's what we use our U685T for. Run it like once every 5 years for projects on our property. It's days plowing snow are long gone unless I replace the whole cab and redo all the airlines brakes and tires and hydraulics.

Yes the engine is factory, no idea about the bumper.

That hood cracks me up. It's fiberglass, but is set up with the foldup sides you see on steel hoods. You flip those sides up and the motor is 4 feet down below the hood! Lol that hood is useless like that.

Probably also around the time they added 3 inches to the back of the R cab too.

My 1980 DM is a slipper style rated at 20k, 12 leaf.

Nice toys by the way! We never get pictures from new members.

Go to a yard near you, snap tons of photos of a set forward axle truck, and note every difference you see, make your list off that. Make sure you take a peak at the oil pan to make sure yours doesn't have the sump in the front whereas a set forward might have it in the back.

That's a more accurate phrasing of what you're trying to find out. My 79 is shackled. I have an old U model and a steel dash R Ill look at today and see how they're set up.

If I had the money I'd just buy a mid 90s Rd, drop a new frame in, rebuild engine trans and rears and call it a day. Would still be cheaper than new, and would spend a lot less time at the dealer. But if you're bent on new, I'd agree the dealer makes or breaks the brand.

Engine looks like an ENDT676, rated at about 283 hp. Engine tag should be on the valve cover or near the fuel pump... Likely has a 2 stick transmission: left stick is 1-5, right stuck is reverse, lo, direct.

We had a Jake on our '79 endt676 up until last year when we had to delete it. Weak valve spring on one cylinder wasn't closing fast enough so the disk sitting on top of the valve kept popping out, resulting in that exhaust valve suddenly having way too much valve lash. I ran the truck pretty much every day for 6 years here in southeast PA. The truck shifts gears twice as fast using the Jake. Which means climbing a hill you wind it up to 2100+ and when you shift you're still in your powerband with the perk of still having your turbo spooled up. I've driven the truck over blue mountain a couple times, that's a nice hill. Don't let anyone here dissuade you from a Jake on your Mack. Its completely worth it just for climbing hills alone. And a properly adjusted Jake brake works well on these motors, you just need to ride it around 2100 rpms. When I retire my '79 I'll likely restore it and replace the valve springs and put the Jake back on.

And to add, I have a retired 1980 DM686SX with a 20k steer axle, I would guess 12-16 leaves but I never counted that truck.

My 79 has 3 leaves on an 11k steer axle, just bought an '88 with 4? Leaves on a 20k steer axle, and I have a 95 with a 16 leaf 18k steer axle. The 79 is an R686st 88 is an RD690S 95 is an RD688S It's not really a year thing, it's more of a weight rating thing....

Up until the early 80s the VIN number would be something like my 79's: R686ST30072. This would tell you which engine and typically suspension. ST was a six wheel tractor typically with 38k Camelback, though sometimes 44k S would typically be 44k Camelback SX would indicate extreme cameback ratings of 55k+. Make made 80k rears too, which I think just used a Ridgid beam instead of springs on the Camelback. I wouldn't want to ride that truck....

The 2 valve ENDT676 went away in the early 80s I believe, as the 4 valve heads were phased in. Honestly not sure about the 87 "Econodyne 350hp 686" with 6 gears. To have a 6 speed it must have a hell of a powerband, much like the maxidyne. I know there were Econodyne versions of the 2 valves, I always assumed they had the same big powerband the maxidynes had, just with a few fuel saving tweaks. My numbers are correct on the 685 and 686 up until at least the early 80s; they may have modified their numbering system when they introduced 690 to indicate maxidyne. That would leave the R686 meaningless, perhaps they repurposed the number. This is also around the time when the R became RD I'd guess...

Perhaps; clean your wire connectors and put dielectric grease on the connector?

Your 87 is a maxidyne rated at 300 hp, whereas your 89 was a 350 hp econodyne. Same engine, different fuel pump. The Maxidyne makes 90%+ torque from 1020 rpms to the governor, whereas your Econodyne didn't. The Maxidyne's powerband can't be compared to any other brand's 300hp because no one else has one that has that big of a powerband. You don't need many gears because you're always making peak torque.

68"5" was the 237hp variant of the 672 cu inch 2 valve diesel, 68"6" was the 283 hp variant of the 672 cu inch 2 valve diesel, 68"8" is a non maxidyne engine, commonly rated at 350 hp, designation used both on E6 motors and E7 motors 6"90" was the maxidyne version of the E6 and E7 motors. The E6 uses the same 672 cu inch block as the old endt676 motors of the R685 and R686. Probably minor internal block changes typical over years of running the same engine. The E6 used 4 valves per cylinders, whereas the ENDT675&6 used 2 valves per cylinder. So they have different heads.

Is that ready to go as in you're selling? Or ready to go as in still runs and you use it on your property for fun?