Buying Another R Model For The Farm

[snowcombine]

I am looking for another R Model tractor for pulling our grain trailer and equipment trailer. Would a 350 & 12 speed handle 140,000 pounds or should I be looking for an E9? We don't have much for hills ( don't have to shift down ever with a 435 cat 18 speed) Our 237 six speed will almost handle the load but it is pretty hard on the truck. Any thoughts?

[vanscottbuilders]

It's all in the gearing and how fast you want to go!

The 350 is plenty of power - and not as expensive to

maintain or overhaul as the V-8.

140,000# is a pretty healthy load for any power train,

but I would think with 4.11 or so rears, and an overdrive

for running when you're not that heavy, the 350 should handle

the loads very well, hills or not.

Think about the rear ends, too. Minimum 40,000#, and it sounds

like 44,000# or heavier might be better. And springs rather than air,

if you're off the road very much.

Nothing like a good R Mack!

Paul Van Scott

[snowcombine]

Our 237 has a 4.17 ratio and in deep reduction it has no trouble starting the load. So I was thinking that since the 12 speed has a similar deep reduction ratio the 350 would probably do just fine. It would be nice to have the rpm a 100km (62.5 mph) a little lower but I guess that is the trade off. Also I was told that the only difference in mack 38 and 44 rears was the housing, and the internals are the same. any truth to that?

[David]

The carriers are the same. The housings, axles, hubs, and springs are different.

[snowcombine]

Thanks I thought the rears would be more than just housings. I am finding it hard to find a 350 powered truck and am thinking about a swap as the local wrecker has a couple including a 12 speed to go with it. My old mack operators manual lists both a 2valve head and a 4valve head engine with different torque and hp specs. The 2 valve peak tq is at 1400rpm and power at 1950rpm.The 4 valve is torque at 1250 rpm and power at 1800 rpm . It doesn't say what the Torque actually is, but I am assuming the 4valve engine is the one to go for with my loads? With 11-24.5 rubber, 4.17 axle ratio, and the 12 speed OD at .78 it works out to 1650 rpm at 60 mph. would this be a good cruise rpm? the book says best fuel economy at a rpm less than that or should I care?

[Lmackattack]

2 valve engiens are very strong and good runners parts getting a little hit an miss lately.

4 valve engine just as good as the 2V and parts can be found easy

Standard mack engines ran up to 2100RPM there were also "low rpm" engines that were set up to tach out at 1800 (governed RPM speed) some old macks (and many other older diesels)had a power curve that would allow the engine to spin faster yet use less fuel. if you were to be running at 1650 and it felt like it was a dog just split it into direct and it will be back up aroun 1800 and may pull better. I have found with maxidynes that they like higher RPM with a heavy load but will do just fine at 1650 on the flats

12 speed is a great transmission. you have every gear you will ever need. the od trans will give you that get home gear and still have a low low ratio to get started

4.17 rears are very good for the offroad. if you can snap one you likely did something wrong or they were just way over worn.

thats my .02

[RowdyRebel]

Thanks I thought the rears would be more than just housings. I am finding it hard to find a 350 powered truck and am thinking about a swap as the local wrecker has a couple including a 12 speed to go with it. My old mack operators manual lists both a 2valve head and a 4valve head engine with different torque and hp specs. The 2 valve peak tq is at 1400rpm and power at 1950rpm.The 4 valve is torque at 1250 rpm and power at 1800 rpm . It doesn't say what the Torque actually is, but I am assuming the 4valve engine is the one to go for with my loads? With 11-24.5 rubber, 4.17 axle ratio, and the 12 speed OD at .78 it works out to 1650 rpm at 60 mph. would this be a good cruise rpm? the book says best fuel economy at a rpm less than that or should I care?

I've got 11R24.5 rubber with 4.17 gears in the rears...works great for what I do. I'm pretty sure the OD in my 2180B is a .71. Sometimes I wish I had 4.35 rears (when I'm running local/short-haul, in the hills, or off road)...while others I wish I had 3.94 rears (to run less than 1900 rpm's down the big road)

Overall, though, it seems to be a good compromise gear.

[B61TENDT711]

Hmmm i was told the 237 300 n 350 would spin right out 2300-2400rpm's and started pulling around 1,100-1,300rpms.

I also got the 237-350 Mack engines would withstand running 2200rpm down the road if loaded heavy on short trips then other say they'll hold 2250rpm all day long loaded or empty. . .

Mike