Geoff Weeks

Single counter-shaft transmission are not built the same way, and this is not a "theory". Single countershaft have no opposing force so the main shaft carries the side thrust. The gears on those run bushing in the gears that ride on the main shaft

Joey, that sounds just like Spicer and Fuller, The spacers and lock rings just keep the gear located fore and aft, the countershaft gears keep the gear centered but not riding on the main shaft.

Not if you look at the 1st picture I posted from the manual, that gear is going over the splines at quite and angle. Also there is no listing for the clearance of the gears on the shaft. The only listed clearance is for fore and aft float which is .005-.012 adjusted with spacer thickness. If Glenn Akers was still with us he could settle this quickly. The main is held by a bearing at one end and bushing in the input shaft pocket. the gears are held located by the countershaft gears they mate with. They don't ride on the main shaft when the trans is assembled.

Better picture of the main shaft, showing splines and grooves for spacers and lock ring to locate the gear fore and aft. this is from a different manual that better shows the shaft.

Not the main shaft itself, but the gears that are on it are floating, the countershaft keeps them centered over the shaft. Being "pretty sure" doesn't cut it. That is why I posted a picture from the Fuller Roadranger manual. I have no idea on a Mack triple counter shaft trans, how they do it, Jo-Jo could chime in on that. The main shaft except the nose (where there is a bushing between it and the input shaft, is splined the whole length with grooves tangentially for snap rings to hold the fore and aft position of the gears, The clearance between the gears and main shaft are maintained by the gears on the two countershafts. If the counter shaft or its key gets a twist, the gear on the main shaft gets out of line and it can be difficult or impossible to get into that gear. It is one of the 1st things to check on overhaul. A bushing riding on a splined shaft would have an extremely short life.

I count 4 air filled tires!

The main shaft is supported front and rear on bearings, the GEARS loaded on the main shaft aren't bushed to the shaft, and are floating, When a dog clutch is moved into the inner spline on the gear and the outer spline on the main shaft then it is locked on the main and power is transmitted. There is no smooth bushing between the main shaft gears and the main shaft on a Eaton or Spicer. There are no places for a bushing on the main shaft nor the gears, they are held in position by the timing of the countershafts, There are snap ring to keep the gear from moving fore and aft on the shaft but no bushing or bearing because they do not bear on the shaft. When that ratio is selected the dog clutch engages with the internal spline on the gear and the clutch is splined to the main shaft. When not selected the gear floats off the shaft being held in position by the counter rotation of the countershaft gears. show me the bushing in this picture! correction, there is one bushing in the input shaft that "supports" the main shaft, but that shouldn't be seeing any load to speak of, unlike a single counter shaft trans, that normally use a bearing in that location of some kind, but still no bushing or bearing between the main shaft and its gears.

Also, close ration main boxes with wide ratio range boxes make the difference in gear sizes on the shaft less dramatic, wide ratio main boxes there is a larger difference in gear sizes from lowest to highest. Spicer box is a wide ratio main with closer ratio range and splitter. The more torque and side load a gear will see the larger it has to be, keeping ratio between mated gears close the smaller they need to be, splitting the torque between 2 or more countershafts also allows for some reduction is size of gears (width), for a given overall capacity of the transmission. Multi countershaft transmissions are a mathmatical nightmare to design so all gears required can mesh and operate at one shaft spacing between main and countershaft and still keep the mainshaft gear centered at all times. That only happens when the two countershaft gear sets are timed to each other and the main.

Larry, Eaton staggers the countershafts ,one below and to the side of the main and one above and to the side. Spicer they are straight across, which does make the Spicer wider. Meritor is more like the Eaton IIRC. In all cases the two countershafts are in a 180 deg angle from each other. This means the main shaft only sees rotational forces and the countershafts only see 1/2 the force that pushes them away from each other. Never been inside or paid much attention to Macks other than pictures, but I believe on the triple countershaft units the countershafts are in a 120 angle to each other or more or less a Y with the mainshaft at the center. Again this places only rotational forces on the main shaft and the forces trying to push the countershafts away from the main is carried by all three so any one only sees 1/3rd of the total. If you remove any one of the three the main shaft now has to counteract the force normally carried by the missing third countershaft. If one was removed, and the remaining two were relocated 180deg from eachother than the main would continue to "float" between them, if not it has to carry 1/3 rd the side load. In a Eaton or Spicer (now TTC) the gears on the main shaft "float" without bearing or bushings riding on the shaft, they are held in position by the two counter shafts which also keeps them from contacting the main shaft, which is why timing of the countershafts is critical on rebuild. I assume Mack triple countershaft transmission are the same way. Leaving the triple shaft design as it is, and removing one shaft would cut weight and make a light duty transmission, but hardly seam worth the savings for the other "costs" such a design would entail. now the gears on the main shaft would be pushed in the direction of the "missing countershaft" and must be bushed and the main shaft carry that load. Macks triple countershaft design allows for a narrower overall transmission with high torque potential but more gears and their weight which can be off-set with an aluminum case because the side loads are now split to 3 sets of bearings.

A main shaft on a 2 or 3 countershaft transmission only sees rotational forces, the two or three counter shafts share the lateral forces pushing them away from the main shaft.

Well, Mack's 3 counter shaft design is strong, because all three shaft push against the main shaft and all forces counter act each other, Kind of like a 3 planet, planetary gearset. Fuller, Spicer and Meritor two countershaft design the counter shafts are 180 deg apart, so the forces counter act eachother. With three counter shafts 120 deg apart the forces counter act eachother, but when you remove one, the mainshaft is side loaded toward the missing shaft. Having the forces counter-act allow the gears on the main shaft "float" without bushing or bearing supporting the gears on the main shaft. You could use bushing and remove one countershaft but that make the transmission much weaker than a 3 countershaft or a two countershaft that are 180 deg apart. It would still be stronger than a single countershaft design of the same shaft sizes, as that one suffers from no counteracting forces on the shafts at all, they are always trying to push each other apart. The counter shafts always are being pushed out from the main shaft but with a 2 or three countershaft transmission those forces are divided equally between all the countershafts, so each would carry 1/2 or 1/3 of the force. When a three counter shaft case has one removed, the main shaft must counteract the forces normally carried by the (missing) 3rd shaft.

Yes, but the countershafts are 180 deg apart on the fuller and spicer, the Mack case has two on top and one under, each force plays against the other two.

This thread seams to confirm 2 counter shafts, I wonder why/how that works? Learn something new every day.

Re-reading this, what I see is it cooled when the mechanic "jumpered" the compressor. Now it doesn't without the jumper. Either wrong switches (if switch type is used) or an APADS problem if that is used. In short, you have an electrical problem not a refrigerant system problem.

Multiple counter shafts are arranged so all the forces on the main shaft are equal, so a twin would be 180 deg apart on the countershafts. I can't see a triple with one shaft removed even working, it would continually be trying to push the main out of alignment?