2. Also, that's good to know on rolling back when starting on a hill. Obviously I try not to, but I'm also not perfect. As a side note, I don't have my CDL and am hoping to get away with not needing it, but I still need to call the DOT or find a trooper to talk to and make sure my understanding of the law is correct.
3. I bet that feeling the front engage and disengage as you describe is an interesting feeling.
I'm not sure how I'd know that the transfer case was engaging properly until it snows or maybe I find a mud puddle
9. One thing I like hearing about the Mack is it sounds like it does a lot better at low rpm than the Cummins does. Parts availability and price sounds like a major plus for the Cummins. I'm pretty sure I don't want a multifuel in a 5-ton though, which seems like what's in most of the M39 trucks I've seen
DougB
2: that's one of the things the hand brake is handy for .
26001# and up is the magic number regardless whether a vehicle has air brakes or not . The M39-series and M809-series are considered hydraulic brakes
although federalization was supposed to make all the rules standard in all states , they are not .. Some states are written "registered GVW", others go by the tag GVW , and as you have found, exceptions vary by state . a state's definition/interpretation of "commercial" is key
3: it is an odd feeling, it has everything to do with change of momentum... for example, at road speeds the slipping truck will all of a sudden enter supersonic forward pull as the G-force sinks you into the back of the seat
.. but BS aside, OTR you can feel (barely) an increase in momentum as long as the front wheels have a good bite
for lack of a mud puddle or steep bank or gravel pile to test the sprag and transfer case, the difficult option would be to pull the driveshaft behind the transfer case and see if truck moves fwd/back ..
there is a compromise though, i will call it the Snap-On ratchet test. On level ground, set hand brake and chock rear tires fore & aft. Jack up one front tire just enough to clear the ground. Be careful, the tire might spin if residual driveshaft torque is present .. Test is done with truck engine off and air at full pressure
Step 1, rotate tire
forward with tranny in reverse , it should lock up but should also spin freely in opposite direction ..
Step 2, rotate tire
backwards with tranny in neutral or a fwd gear, it should lock up but spin freely in opposite direction
If the tire locks for both tests, the sprag is working ..
Now Dump the air and repeat the 2 steps.. The tire should rotate freely in both directions.
If tire locks up in either direction with no air present, the sprag cylinder is sticking ..
Also keep in mind sometimes poppets get worn and air gets put to an inappropriate side of the sprag cylinder, but sprag & poppet issues are simple issues. It's just that they are a PITA if you are short of time to deal with it
9: the 673 mack's have their highest torque at 1400-1600rpm, they are proven exceptional luggers, they will pull down to that rpm and just sit there most of the time ..
the cummins 855's however, do not like to be lugged .. i've literally heard rod knock develop after certain drivers constantly lugged loads up hills at under 1700rpm .. Myself, i've always tried to not let any-sized 855 cummins lug below 1800.. A wise man somewhere once said something like this; "lugging a cummins hurts it far faster than over-speeding it"
i have never been a fan of multifuel 5-tons .. Many of us in heavy transport ran to the gassers or the macks or the (not in winter) cummins' instead.. As mentioned, my armor BN had A2's that got stuffed with macks and got the OD tranny. The multifuels are a great match for a deuce , but the LDS in 5-tons lack for OTR performance .. There's an old railroad formula, "HP is proportionate to speed" .. At the time, the multifuel 5-tons had their reason to exist and they did the job they were expected to do . They just couldn't be expected to pull heavy uphill without holding up the rest of the show
