Geoff Weeks

No matter what suspension, how the load is distributed on the trailer make a much larger impact on ride than what the suspension type is. For best ride, if a concentrated (dense) load, split in 1/2 and place 1/2 over front and rear. For less dense, you'll need to place the load through out the trailer in order to get it all in. Worse thing you can do is "belly load" a dense product, placing the load in the center of the trailer, it will ride like hell and that sound like what you have. Doesn't matter what the product is, rock or iron, how load will make a big difference. The problem comes with a rear dump, where you wouldn't want to have the weight concentrated at the front and rear and try and dump it. In that case safety of unloading trumps ride comfort unfortunately. try to avoid mounding it in the center of the trailer. In short it sounds more like the product being hauled, not the truck or trailer suspension.

Here is a chart (may be the one you looked at) 2070-2080 that shows the ratio, in both cases 1st in direct is 5.24:1 which would be fairly high starting gear. Somewhere between 3rd and 4th (if you count the lowest gear as 1) on an Eaton. I think you'd still want the compound for starting.

I do not remember. I was looking for a parts breakdown of the BM9 and found some chart that showed it obsolete and the new 150BMP that replaced it.

Yes, I wasn't saying your had a snap ring just the the two models used differing retaining methods. Since air starters are made in right and left rotation (noted in your model number) having a left thread on RH rotation, means they had to make another part with a right thread for LH rotation, explains why newer models went with a snap ring retainer, works for both rotations.

Cats of that vintage and 400 hp could be water aftercooled, that is one place it could be leaking. Coolant doesn't just disappear, so I would put some time into finding where it is going. head/spacer plate gasket is another. .6 OD puts a lot of heat (and power) into the transmission oil. You have a large OD and can drop the rear ratio quite a bit to move "in the mud", and still get down the highway at decent speed. My Marmon will top out at 80 with 4.11's and .78 OD, how much more do you need? If you have gears you can not use most of the time, but are paying a penalty for not having low enough gears at the same time, you are not making the most of what you have. Flying when empty, is a poor tradeoff for working well when loaded. Look at the total ratio, not the individual boxes, make the best compromise over the total ratio, so you are likely better off with a ratio that tops out at 80 mph but gives you a lower starting overall ratio.

Eaton ratio chart I often though of doing what you did, but installed 13's instead. B ratio is OD main, but I was going to go with U/D back. with .6 OD and 3.54's you are way over geared. With a 425 Cat and 4.11 gears with .78 od was about right.

the 150BMP uses a snap-ring in that location I believe.

I have not had the BM series apart, they sound like they are different then the 150 series.

BTW a place Cats like to loose coolant is the gear driven water pump weep hole, if that is were it is leaking, or if the weep hole is plugged up, it can force the coolant into the pan. Where is yours losing it from?

TBH, I did regular and heavy haul with Eaton trans. I drove a Mack 5 spd for a short while but never owned one. I would suggest going to Eatons site and downloading a ratio chart for what you have now, plot it out on a spread sheet for MPH at 1000, 1600 or 1700 and 2100 rpm for each gear to give you an idea what you are looking for. You already have the rear ratio for the math and Lo-pro 24.5 tires are about the same rev/mile as 11 22.5, 498-501 revs per mile. Do the same for any truck you are looking at or considering.

Eaton and Spicer (TTC) are twin countershaft transmission not triple. IFAIK Mack was the only one to use triple. You're unlikely to find a 2 spd in a used truck now, but any Eaton 402 equipped truck housings can accept a Eaton 2 spd center section. Eaton or Spicer/TTC 18's have lower ratios in the bottom end while still having O/D's on the top. Problem is with the deep reduction on the bottom, the driveline has to take all that torque.

The fact that it charges when connected is a good clue, how did you connect? to which terminal? I think you are going to need someone who knows the wiring on that model, but I would trace the output wire back to where it connects to the battery (often at the starter motor) and look for a fuseable link in the wire. It will likely be in the first few inches at the starter end (battery supply end) if it has one.

Alternator output is not generally fused, as the voltage spike of dumping the load can damage anything still connected. I have seen fuseable links used between the battery and alternator, but not between it and the rest of the electrical system. I don't know about the truck in question exactly, but I would tend to doubt more than a fuseable link. Is the 12 volts present at the output stud with the engine off? What are the problems?

If you get jammed up real bad, here is one, may or may not need your drive on it.Air Starter.

Which bolt has a reverse thread? I can't think of one off the top of my head? Yours is slightly different then the 150's but I don't know of any LH threads on them.