67RModel

I am running a fully mechanical EM7 in a 1994 RD690 dump truck. It is a bone stock, one owner (before me), all original unit with 335,000 miles and 11,500 hours on the clock. It has some type of miss while under light throttle input from 1100 - 1300 rpm. For instance, if you are slowing down to make a turn, downshift, and your rpms fall within that range and you apply light throttle to maintain that speed/rpm it will make and audible missing sound. If you lift completely out of the throttle and let the trucks momentum carry itself it will go away. If you apply more throttle (say half or more) it will accelerate and go away around 1300 rpm. If the truck is on a downgrade or coasting in that rpm range under its own momentum with no throttle input at all it will not happen. It only happens when the throttle is lightly depressed in that certain rpm range. Any idea what it could be or tips on how to troubleshoot it. It appears the pump has never been apart as it and the timing gear cover still have the security wires and pressed lead fasteners still intact. Its drivable as is but annoying and obviously not right. For reference this is an EM7, 250 horsepower, governed at 1750rpm. Thanks in advance.

I would get the engine serial number and CPL (critical parts list) number and call a Cummins distributor. They probably have one on their shelf. The Cummins distributor by me is Bridgeway Cummins. If you have those two numbers off your engine they can get you anything for it. Very similar to Caterpillar's parts network.

I always thought this was the case. I think the trucks with maxidynes that have the econodyne badge on the hood are governed at 1750 rpm. From the beginning the maxidynes were 2100 rpm engines. Somewhere along the line some of them were governed at 1750rpm to save fuel and reduce driver fatigue by cruising at 1750 instead of 2100. My 1994 RD690 has a fully mechanical EM7-250 under the hood but it is governed at 1750rpm. It has a silver bulldog on the hood and no econodyne badging though.

I have always wondered about this. I feel like if I were to go to Australia I would not be able to drive a manual transmission. It seems so ridiculously nuts to have to shift with my left hand since I am right handed. I don't know if I have that coordination. I guess it would be the same concept for leftys pretty much everywhere else that drive manual transmissions. I guess you just get used to it?

No I jacked the pinion up with a floor jack and just rolled the whole assembly forward by hand. I had to cage the spring chambers to release the emergency brakes but once released the whole axle assembly will roll very easily on a level concrete floor. Yes air lines can easily be shortened. If they are the new style plastic material you can simply cut them, install an new ferrule, and reinstall them into the fitting and tighten. Mine were still the original flared copper tubing. I just ended up replacing mine with all new materials and fittings since the copper was covered in hardened grease and 3 different colors of paint.

Shortening the wheelbase and driveline is a generally fairly simple project. Especially something with leaf spring rear suspension. I shortened my R model from 207" to 165" wheelbase with just basic tools last spring when I was forced to stay home for covid19 lockdown. Took about three days of work to complete but I took my time and was methodical about it. Pretty much all I needed was a 1/2" breaker bar with a 15/16" socket, 15/16" wrench, 1/2" drill, 5/8" drill bit, a tape measure, sledge hammer, and a lot of muscle. The driveshaft can be shortened by a driveline shop fairly easily and quickly once you get the rear axle bolted back in to its new location, and a final measurement. I think the shop charged me somewhere around $150 to shorten and rebalance my driveshaft. I wouldn't hesitate for a minute if all a truck needed was some wheelbase removed to be what you wanted....Attached are some of the pictures of when I shortened mine. Very doable project.

Here is another single axle diesel B model that is not rusty for sale on Ebay. https://www.ebay.com/itm/203543149764?hash=item2f641dfcc4:g:9i8AAOSwWo1hBgw8

Yes. You can buy remanufactured compressors so they can obviously be rebuilt, however I'm not certain if you can buy a parts kit to do it yourself. I'm guessing most likely but someone else on here will know for sure.

Yes the air compressors are pressure lubricated by engine oil. They also generally have a coolant line going to them too for cooling.

Here is another fairly close to me. Near Youngstown, OH. They are literally all over if you look....

4 in Scranton PA.......

I always see at least 2 or 3 for sale on Facebook Marketplace whenever I look. Granted they are not always close to me but they are definitely out there. Look on the ATHS backlot classified listings as well. Always at least one for sale on there as well. Below is a very nice one in Uniontown Ohio.....There are 2 or three very close to me on Marketplace but they are project trucks requiring considerable investment..

Yes. When you pull the pump away that machined/keyed coupler will fall out. Once you see it you will understand. It only goes back together one way. Just don't spin the engine while the pump is off.

That looks like an American Bosch pump. Removal is very strait forward. Disconnect all linkages and lines then just unbolt it from the front cover / timing gears. There should be a support underneath pump that supports the back end of it. The two bolts a real bear to access. In my opinion that is the hardest part of the job...removing and reinstalling these support bolts. Once it is unbolted it just slides out of the timing gears and lifts out. A real back breaker. It is a lot harder when it is the engine is in the truck and you are leaning over a frame rail to get to everything. It can only be installed the correct way or 180 degrees from the correct way so as long as you dont move the truck (or rotate the engine in this case) while the pump is out you will not loose the timing. There is machined metal puck that couples the pump to the timing gears much like the rubber part of a lovejoy coupler. It will fall out when you take remove the pump so be ready to catch it. The gasket to reseal the pump to the engine is still readily available from the Mack parts counter for about $12. I will look in my records to see if I can find a part number.

I don't even know where to start with this one. Running on 11R22.5 rubber with a 2.28 rear end and a T2070 you would be turning 678 rpms at 60mph and 791 rpm at 70 mph in 7th gear😂. A 4700 or 4900 series poop spreader chassis is not designed to fit a 12 or 15 liter engine under the hood so serious modifications would have to be done plus the front suspension would need beefed up....A DT 466 is only 7.6 liter by comparison. Plus I doubt either of the two larger engines' radiators would fit under the hood. I don't know you so I would never pass judgement, but in this case I will say it is just another stupid idea of yours 😅. Just change the rear end gear in the truck you buy.

This truck is on Ebay for sale. Looks like it got damaged in some type of accident.... https://www.ebay.com/itm/194216557302?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D5794447c5c4d480680f156e7047d40cf%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D194216557302%26itm%3D194216557302%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ae1afbddc-d8f5-11eb-9b10-d6abf6455abd|parentrq%3A58922e0717a0a44e6ab6a657ffec1818|iid%3A1

Why do so many LTL freight trucks from the 60s, 70s, and 80s have the front bumper cut off on the ends? You only really see it on the fleet trucks from that time. Was it a weight and/or cost saving measure? It always jumps out at me and I don't know why companies did it.

Yes. And this combination is easily worth $32,000 to somebody who wants a nice B model and realizes its going to take $30k - $40k and a year or two of their lives to build one from a $2500 pile of would be scrap metal they bought off Craigslist or Marketplace....assuming they even had the means to do a restoration. Plus you get a trailer with this one.

Generally how large is the annual White bash? Is there a large turnout?

Figure $3,000 or $4,000 dollars for the trailer alone since it is operational and assuming it has a title. The truck has $2500 worth of tires on it plus new rims. It says new drums and brake linings. Drums for dayton hubs are outrageous these days compared to a regular budd wheel or hub pilot drums. An engine overhaul could range from a few thousand dollars for new rod and main bearings to 15 or 20 thousand dollars for a complete overhaul, and new head / machine work. I imagine overhaul parts for a thermodyne are crazy expensive if you can even find them. The bodywork and details look pretty darn nice too. Plus I just reread the ebay listing.....trailer has 8 new tires and brakes and oak deck....somebody has a good $7000 wrapped up in just the trailer alone. Not enough information on the engine overhaul to figure a price on that plus it depends on the condition of the truck before they started the restoration. Somebody has an easy 25,000 to 35,000 in todays dollars to get to what you see there (truck and trailer). When you start down this road the dollars add up exponentially....🤑

This is not 100% accurate. In Pennsylvania there are Class A, B, (maybe C), and D licenses. There are also Class A CDL, class B CDL, class C CDL licenses. There is a distinction, however it is not well known. You technically need a class B license to drive a motorhome with a GVW/GVCW of greater than 26,000, however most people I would suspect do not obtain one. They just roll with their class D passenger car license. You need a CDL when you are operating any of the above classes of vehicle for ANY type of commerce including farming. The class A/B CDL license exam vs the class A/B license exam is very different and also very lenient for the regular class A/B license type. Basically you need a CDL if you are making money with the vehicle. You need a class A or B license if your vehicle / combination meets the above requirements but you are hobbyist / using for recreation. Another example of this is all the large gooseneck horse trailers you see going down the road. They all generally have a GVW of grater than 10,000 pounds so technically the people pulling them need a class A license (not class A CDL), but most do not have one. Also in Pennsylvania any tow vehicle pulling a trailer with a GVW of 10,000 or more needs to be registered in combination whether its for recreation or commerce, but most people pulling large recreation trailers never do this and the penalty for not doing so is usually a slap on the wrist.

Just about every R model you will find will have air brakes. There may be some R400s floating around that have hydraulic brakes but they would have to be extremely rare.

It is a tandem axle spring type suspension that was designed and patented by Mack a very long time ago. It is still very common on vocational specd trucks and is exclusive to the Mack brand. It provides tremendous articulation and off road traction. Not the smoothest riding but certainly not the worst either. If maintained properly it is bulletproof. It has been offered in capacities from 38,000 lbs to 64,000 lbs (maybe more). It is probably the finest all around vocational suspension ever developed, which is why it is still so common after probably 75+ years. The principle has been copied or used as the basis for other similar spring suspensions such as the Volvo T Ride and Freightliner Tuff Trac suspensions.

An R300 does not exist and never did. Based on the VIN provided it would be an R600 series single axle that originally left the factory as a road tractor configuration. It would have originally had a 237hp Maxidyne given the "85" after the 6. The 6 represents the chassis class. 600 in this case. The T represents factory tractor and the 40764 indicates the number this R685 is in the production run. Given that Mack serial numbers started at 1000 (I think) this would have been the 39,764th built. If you are getting the VIN off the tag inside the drivers door you need to be careful that the door has not been changed over the years. A safer place to look is the passenger side frame rail just behind the front shock mount. The VIN number should be stamped there.

Back in 2017 - 2109 I set up a 1995 Volvo (White GMC) to pull pneumatic trailers to haul frac sand to the Marcellus wells. It had a 365hp 12.7 Detroit and a Eaton super 10 transmission with 3.90 rears. I always ran at 80,000 pounds or heavier since I ran at night. Most of the guys I ran with had big horsepower and 18 speeds. A few were running gliders with 550 and 600 hp caterpillars. Every shift we worked together I always managed to get the same number of loads hauled. Plus I had a tare weight of at least 3500 pounds less than them and burned a lot less fuel. For legal weight or less I'm not sure what the purpose of more than 9 or 10 gears is and more horsepower is just wasted fuel in my opinion.