JoeH

@Joey Mack

Go to your dealer and order book # 8-211!

3-4 is engine position sensor, located on the timing cover. Camshaft.

Appears your VECU power is dropping out. This is likely the trigger for the 6-3 code, as the VECU dropping out will obviously disrupt data communication.

So some Mack camelback trucks have a torque arm on the rear differential going to the right frame rail. It prevents the axles from walking. Check to see if you have one, check condition of the joints at either end. Replace if worn. Also, elephant pads aren't a terrible job, doable in a day, but they do take some serious torque to tighten down. Expect to replace all bolts, you will likely be torching some off. Few different styles of pads I believe. Some use a metal side insert some don't.

Remove one side, separate, sandblast/paint, bolt back together, install, shift cribbing to other side, & repeat.

This is the second truck I've done this to. Leave one side in to hold alignment of everything. Put jackstands/cribbing under everything on the other side, and pull the supported side out. Separate by driving a long 2x6 (cut the one end into a wedge) into one end. Lots of hard work involved, be careful you can kink the rails if you try separating them like a wish bone. If it's a dump truck you will have to pull the dump body off. First truck we did was an RD model, the cab had to get jacked up pretty high to let the frame clear. This one I linked is an MR, the cab tilts forward giving tons of room to work.

Also that motor/trans has a lot to be desired for on hp/gears for 99k.

If you want to haul heavier then hold out for 55/58k rears.

You want 44k rears. Simply not worth investing in an underrated truck. The 38's will hold up for a while, it'd do the work ok, but potholes will beat the truck up. And you will be getting redflagged by DOT for being over the rated capacities of the truck.

Where are you located? You might have an expert on here not too far away....

Does it make a difference what gear you are in? Hi range? Low range? If you put your foot on the clutch pedal and apply gentle pressure to the throw out bearing (without disengaging clutch) does the noise change?

A screwdriver is what I learned to use! Put the tip of the screwdriver on the engine or trans and cup the end of the handle to your ear and it's like a whole symphony suddenly comes to life.

Call your dealer and get the part number from the heads for your truck. Use VIN from other years/models to check compatibility. Chances are your head # supersedes to another number, so make note of that number to see what else might have it. VIN #'s can be had easily from online auction/sales sites.

Door lettering. Since we're buying our first brand new volumetric concrete mixer since 1967 from a company we have never used, I couldn't help myself. Had to add when we started into the business. These mixers were invented in the early '60s, so there can't be very many companies with as many years in "the business" as us. We're tiny, don't get me wrong, it's just my dad and I. Tons of businesses much bigger than us, but we love what we do and are quite happy being small and paying our bills.

Yea I completely brainfarted. I've been 100% focused on getting our mr688 ready for Iowa. Stress is through the roof, we function quite happily in a 15-20 mile radius. 1,500 mile trip on a truck we have put about 25 miles on test driving since Monday! Fingers crossed no more hiccups! This truck leaves tomorrow morning!

Coopersburgs Kenworth had a rare? used heavy single frame MR, 2 customers got into a bidding war over it. Heavy single is such a bonus.

Interesting. That's the one thing that eluded me. I think the technicality I'm combatting is that I'm marked Intrastate on my DOT #. JJ Keller implies most states are just happy to get the trip permit $$$, despite the minor DOT intrastate technicality, but Illinois is very strict and wouldn't dismiss it as trivial. Regardless, my parents want nothing to do with Chicago/Illinois, so they're set on cruising Ohio to Kentucky to Tennessee to Missouri to Iowa. There's a ferry from Kentucky to Missouri but the ferry seems to have been broken down for a few weeks so the only other Mississippi River crossing (without going through Illinois) is to drop down to Tennessee.

Or the engine or valve cover is a transplant.... Or not. Looks like the engine # is labeled in the cab too...

Gauge worked fine up until the other day when I replaced the sending unit gasket. Now the gauge is pegged down to about a 5 o'clock position... I read 4.3 volts from positive to negative wires on the sending unit, and 4.3 volts to a known good ground. I did reroute the sending unit wires as I didn't like them laying loosely on the top of the transmission. Damaged wire strands? It had been folded back and forth about 5 times and zip tied to the fuel tank lines. I straightened it out so I could run it along the crossmember.

https://www.emanualonline.com/material-handling/industrial-equipment-tools/vehicle-parts-accessories/transmissions-gearboxes/allison/4000-series/allison-transmission-4000-series-full-service-repair-manual-emo-171892.html?currency=USD&product_country=US&product_id=171892&placement=&adtype=&keyword=&gclid=CjwKCAiAl-6PBhBCEiwAc2GOVLpvhBeptBaObblZHzI6nRoPzRU1hylOl8ZohDFiQfdTkXVURgzllxoCMOYQAvD_BwE I believe this is the transmission manual I bought. Worth every penny. There's about 10 or 15 pdf files that it comes with for different books, but the information is very good, and has the DTC codes in it.

2-3 intake air sensor 4-1 vehicle speed sensor (you have trans codes, so this will likely be linked to whatever is going on there) 1-4 ambient air temp sensor To verify EECU power, there's a bolt holding the wiring harness to the engine lock below the EECU. Takes a 10mm socket. Remove that to create enough slack to undo the 2 plugs into the EECU. They're pretty odd how they unlatch, the end the wires come into needs to lift waaay out once you undo the retainer lever. On the bottom plug, pins 10, 22, and 41 should have 12v power sourced from one of the 4 big relays hanging next to the VECU in the dash. You are probably fine on power to those terminals, I see you have a CB in the #40 slot now.