JoeH

I have 2001 in my head as the ideal year for a Mack motor.  Rebuilt engine in the last three years? If the frame is clean I'd take it if the wiring harnesses look clean.  2001 is the first year they moved the engine computer to the left side, away from heat and possible pinch against frame rail.  Emissions BS with the ASET engines started sneaking into the trucks in 2003 and was in all 2004 trucks.

I'd talk to someone in your state about axle weight configurations.  In PA we get away with 73,280 on steer, lift, and tandem.  Other states require 4 or 5 rear axles to hit that much weight.  Don't know what Arkansas allows.  Pull up and ask a state trooper next time you see one!   As far as being caught overweight on one axle, DOT enforcement has portable scales they'll use to weigh each wheel.  If you're moving dirt on site you don't have to worry about "legal" weights, Mack rates their 44k rears for more if kept below a certain speed.  If you're going down the road it's another story.

Lift axle bolted on.  Have the trans power sorted out, but now we have a blink code 6-4, cranks but won't start.  Mobile diagnostic guy comes out on Wednesday to try and figure it out. Yea, we're planning on driving this sucker out to Iowa (from Philadelphia area) by the end of this month... Call us crazy.  I'm not looking forward to a probable breakdown on the 20 hour drive...

If I had a 1908 I don't think I'd be driving at night, I'd be too afraid of hitting a deer!

Axle Ratio is 5.55, so that will be nice with that trans/engine.  Frame and underside of the bed look immaculate short of being new (bear in mind a halfway decent used truck up in the northeast has the frame rails spreading up to 1/2 inch from rust...) Hard to really tell frame rust from the pictures, but it looks good.  Just needs a lift axle to take it to PA's 73,280 maximum legal weight for triaxles and it'd sell quick up here!

Not sure how familiar you are with Mack model numbers, but a 688 is a 350 hp standard fuel setup with about a 400rpm powerband.  A 690 is a 300 hp Maxidyne that makes 90%+ of it's peak torque from about 900-1100 rpms all the way to the governor.  Hence the 690 gets away with a 5 to 7 speed trans.  You simply don't need in between gears because you're engine pulls so far down.  An engine brake is perfect on the 690 for shifting up hills, cuts the shift time down to 1/3. 

It's never cost prohibitive due to rears and trans.  You can have a cutoff from a junk yard for 2k with good differentials.  Rebuilt 8LL is 3-5k I think plus install. What you save on truck cost will far outweigh those "incidental" costs you might incur in 5 years.  If you can pick up a mid 90's mechanical e7 then you are into about the best Mack possible.  No aging computer and related wiring harness.  I have a 1995 RD688S with 272k miles and 22,000 hours. In the 7-8k hours we've owned it we had the valve covers off once just to check adjustment.  And replaced the oil pan as the old one had fatigue cracks.  And the truck got a clutch.  Engine brake is a joke but I wouldnt trade the truck for anything.

Fuse wires at the battery box never got hooked up after frame reinstall.  Now I have a Crank No Start with blink code 6-4.  Need to delve into voltage fluctuations under start conditions for the EECU and VECU... Apparently it's an issue, and there's a service procedure to add supplemental power from the starter relay to the 3 EECU 12volt inputs.

On 12/8/2021 at 5:35 PM, Joey Mack said:

Just in case you chase wires in the cab.  They will say VJ1-2or3, then wire # then a letter, (a,b,c) for example.. those represent intersections in the wires, and then the wire size will be the last #.. The V stands for V.E.C.U.   jojo

Great info right here; I'm chasing a crank/no start code 6-4 problem on a new to us truck.  Can you explain what the intersection letters mean exactly?

As with all things mechanical, parts can fail.  If you have a noise coming from the rear you could have a bearing failing. We had one go about 10 years ago.  Ate a few teeth off the ring gear so we dropped a pair of differentials that gave us about 10mph more speed. (Previous top speed was 48mph floored. You could slide into first gear from a stop with no clutch.)

Clogged fuel filter? New problem? Symptoms surrounding the problem's start?

Truck should have 3 Torque Arms, one from the top of each axle tying to the trunnion stand cross member, and the third Torque Arm goes from the rear drive axle to the right frame rail.  The joints of the torque arms wear out, expect to replace one or two of them.

Camelback suspension is about the best you can have for offroading. Provides perfect weight distribution to all 4 wheels at all points of articulation, regardless of how fast you're going over rough terrain.

Air suspension articulation requires time for air to vent from one bag and the truck to fill the other bags. By the time it's done that you're three bumps ahead of where you were or you're stuck.

I'll have to sift through all the wiring to find it... Currently I'm looking for the "VIM" as Allison calls it: "Vehicle Interface Module", a series of ~6 relays, a couple 10a fuses, and a couple other odds and ends.  Probably need to just grab a 10a fuse and start swapping it for 10a circuit breakers to see if I get a positive result....

After a day of beating my head against the wall, I have determined that Pins 1 and 16 on the "grey" "V" plug on the Allison ECU don't have power, when they are supposed to. Allison wiring schematic shows a 10a fuse, but it's on the Vehicle side and I don't have a diagram showing me where this fuse is located....

I'd love a fuse location diagram for a 2003 MR688S if anyone has access to one... Or could provide any insight as to where fuses/breakers are for the auto trans...

Thumb is pointing at cab gauge oil signal.

Index finger is pointing at computer oil pressure sensor.

So yes, 2 separate oil signals.

(This is a 2003 ai350. Forget what yours is.)

2003 MR688S AI350 w/ Allison HD4560 trans. (see post in Modern Truck section to see what we've done) got frame rails back in, everything (I thought) is hooked up.  No power to the trans controller, thus not allowing us to crank the engine.  (Got it to fire up by jumping a solenoid). Runs but won't go into gear as there's no power to the gear selector! Truck has a ton of hours on it, so needless to say wiring has been "repaired" by former owners a time or two.  

There's a makeshift power wire coming off ignition terminal in dash, T's into a wire in the gear selector harness.  This wire has power when key is on. (According to my dad, I haven't verified. Will do so tomorrow.)

Assuming it's getting power, where does it ground? This tiny power wire seems hardly sufficient to power "everything" so what else should I be looking for?

Also note it has Blink Code 6-8, which indicates a failure in the J1939 serial data link, which is 2 wires twisted together (to obscure any potential interference,) running from the VECU to the Transmission.  Would a break in this link cause the above No Power fault? 

Plan on doing a full delete next time the truck gets a clutch.

Oil lubrication ports may be left wide open thus bleeding oil pressure, the idler gear is still in there slapping around waiting to grenade... And it still may not solve your noise complaint as the idler gear could be a large part of the noise.

Last one we did was a dry liner in our 1979 endt676 12 years ago.  Dropped a valve seat so it got one piston/liner kit and a rebuilt cylinder head.  I remember my dad welding the inside bore of the old liner to get it out, and I don't remember doing anything special to drive the new one in. Probably scuff sanded the block bore and drove the new liner in with a wheel seal driver and/or a block of wood.  We aren't technical enough to measure bore interference.

Cylinder liner kits aren't too bad to do.  You already have the head off, that's the hardest part.  Drain the oil, drop the oil pan, pull the connecting rod off the crank and send the piston and rod out the top. A vertical weld up the old piston liner is all you need to loosen it.  Forget how we drive the new liner in, probably a block of wood and a hammer... Might be a brass punch involved at the end.

Yes, it has the disconnect switch. Batteries have been out of the truck for a couple weeks now for the frame work, so I can't look into this light thing til tomorrow when I go over everything with a fine tooth comb to make sure I have everything hooked up properly.  I'm a bit nervous of the wiring.  It's only 19 years old, but.... 26,000 hours on it....

So is this a programming thing? A parameter that can be switched off?

Diesel gels over at 13 degrees, and thaws back out around 35 degrees. (Fahrenheit) additives reduce the gel temperature some, but -20-40 is pretty cold.  Fuel is probably gelled over.