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Would the original maxidyne have been better with another gear/ gears between fourth and fifth. I think the cummins high torque copy had seven gears. The original maxidyne died on the hills.

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I've always kinda thought Mack dropped the ball on that one when in the design stage. The Maxidyne concept was more for the flat and off road scenario's I've always felt but why wouldn't human nature push it into other arenas? With the early ENDT-675 engines barely breaking into the 900 foot pounds of torque, the gearing step from forth to fifth gear, (direct) was far too coarse. Running into the bottom of a hill flat out and waiting so long to downshift really put the engine at a disadvantage in my opinion. Now city traffic, or vocational use they were great and performed well. Driver's liked dump trucking and P&D operations in cities as there was a lot less shifting involved but as stated into the hills, they lost favor fairly quickly.

I like a triplex myself if not a Fuller due to the percentage ratio between the gearing. Quadraplex is nice for slow speed and probably the best for dump truck type work. Hard to beat an 18 speed Fuller nowadays however. 

JMO

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For the late 60s 900 lbs./foot was a lot, and by the early 70s Mack upped the ante with the 285 hp. "676" and 325 hp. V8 Maxidynes. As far as gear ratios, IIRC Mack offered a 5 speed with a closer 4th to 5th split, but it didn't sell well. After cabover sales dropped off and the shift gate no longer had to fit in the couple inches between the drivers seat and doghouse Mack solved this problem with the 300 series Maxitorque, featuring a closer .71 ratio split between top and the next gear down.

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The ENDT-676 came out in 1976 IIRC for either the 1976 model year, or 1977 model year. Mack dealer brought a new one out to where I was working and I asked him if it ran hotter than the 237 engine as I thought it had an additional radiator. Nobody laughed as they thought the same thing till it was explained to us. The original ENDT-675 engines were 906 foot pounds torque and the ENDT-676 was a whopping 1080 foot pounds!! Both produced maximum torque right at 1200 rpm. Both engines were a significant step up in power from the T673C, and 673E series. It seems the END673E series engine was about 540 foot pounds at 1400rpm, and the T673C engine was 700 foot pounds at 1500rpm.

Used to put a lot of duplex, and quadraplex transmissions replacing the TR-107 five speeds and recalibrate the governors as the driver's just didn't like the Maxidyne power layout. Was expensive on transmission maintenance behind those engines but I wasn't involved with the actual rebuilding, just replacing. I'd swap a trans and tack together the driveshaft, then pull it sending it into the driveline shop for finish work and balancing.

The 200, and 300 series transmissions are after I finished working on trucks so have known hardly anything about them.

Completely forgot the other conversion that was popular was a Fuller RT, or RTO-9509B with the "F" style top cover dependent upon axle ratio and tire size. This allowed placement of the shift handle further forward in the case. A small nine speed nowadays, but worked well in that application.

Edited by Rob

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Yup, for a lot of drivers it just got too quiet down around 1200 RPM, so they swapped to a gearbox with more and closer gears so they could enjoy the higher RPM noise they were accustomed to. Didn't make the trucks go any faster, though...

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For loads grossing 80,000, as long as the puffer valve was adjusted correctly, 237's and 300's would pick it up at 1200rpm and go...

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1 hour ago, dockmen027 said:

For loads grossing 80,000, as long as the puffer valve was adjusted correctly, 237's and 300's would pick it up at 1200rpm and go...

By correctly, do you mean set to make the truck run good? 😉 I remember setting some AFRs on Cats and aneroid valves on Cummins.

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6 hours ago, james j neiweem said:

Would the original maxidyne have been better with another gear/ gears between fourth and fifth. I think the cummins high torque copy had seven gears. The original maxidyne died on the hills.

Jim, we offered just such a Maxitorque transmission for those who wanted it with the Maxidyne high-torque rise powertrain.....the 7-speed TRDLG1070.

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I have books with that transmission listed but have never seen one in person. It is basically a TRDL-107 with something slightly different giving only seven forward speeds. Looking in the parts breakdown for that trans, there is nothing listed that differs from the TRDL-107, or TRDL-1070. It appears all parts are interchangeable from the diagrams I have. It is possible something is not used in the seven speed variant however or the gearsets are arranged different on the shafts?

Edited by Rob

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I like my Triplex, even though I heard many stories of how it won't work well, blah, blah, blah.   I like my ability to split the top gears.  Pulls hills without issue, though I'm not 80K lbs.  If I get my mits on a RTO or such, I'm going to work on getting it installed.    Only because my Triplex is whipped hard and put away wet.

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15 hours ago, Rob said:

The ENDT-676 came out in 1976 IIRC for either the 1976 model year, or 1977 model year. Mack dealer brought a new one out to where I was working and I asked him if it ran hotter than the 237 engine as I thought it had an additional radiator. Nobody laughed as they thought the same thing till it was explained to us. The original ENDT-675 engines were 906 foot pounds torque and the ENDT-676 was a whopping 1080 foot pounds!! Both produced maximum torque right at 1200 rpm. Both engines were a significant step up in power from the T673C, and 673E series. It seems the END673E series engine was about 540 foot pounds at 1400rpm, and the T673C engine was 700 foot pounds at 1500rpm.

Used to put a lot of duplex, and quadraplex transmissions replacing the TR-107 five speeds and recalibrate the governors as the driver's just didn't like the Maxidyne power layout. Was expensive on transmission maintenance behind those engines but I wasn't involved with the actual rebuilding, just replacing. I'd swap a trans and tack together the driveshaft, then pull it sending it into the driveline shop for finish work and balancing.

The 200, and 300 series transmissions are after I finished working on trucks so have known hardly anything about them.

Completely forgot the other conversion that was popular was a Fuller RT, or RTO-9509B with the "F" style top cover dependent upon axle ratio and tire size. This allowed placement of the shift handle further forward in the case. A small nine speed nowadays, but worked well in that application.

I have a running low rpm ENDT676 stamped 1976, not sure if that makes it a 76 or a 77 model year. It's in a 1980 DM chassis we just retired.

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Hard to say Joe. Back in those days "just in time" inventory wasn't the way everything was done with no stocking of parts so the engine could have been built and stored till a larger bulk shipment was sent to Mack Trucks for assembly, or the series truck was in line to be built? I've seen lot's of engines with casting dates one or two years prior to the actual installation into a chassis knowing the chassis from new. It was also fairly common to have a truck built in one year and titled as the following year much the same as they've done cars. They "used" to title trucks according to the year in which they sold, not built, as we've seen this in several iterations over the years. 

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On 2/10/2019 at 4:21 PM, Rob said:

The ENDT-676 came out in 1976 IIRC for either the 1976 model year, or 1977 model year. Mack dealer brought a new one out to where I was working and I asked him if it ran hotter than the 237 engine as I thought it had an additional radiator. Nobody laughed as they thought the same thing till it was explained to us. The original ENDT-675 engines were 906 foot pounds torque and the ENDT-676 was a whopping 1080 foot pounds!! Both produced maximum torque right at 1200 rpm. Both engines were a significant step up in power from the T673C, and 673E series. It seems the END673E series engine was about 540 foot pounds at 1400rpm, and the T673C engine was 700 foot pounds at 1500rpm.

Used to put a lot of duplex, and quadraplex transmissions replacing the TR-107 five speeds and recalibrate the governors as the driver's just didn't like the Maxidyne power layout. Was expensive on transmission maintenance behind those engines but I wasn't involved with the actual rebuilding, just replacing. I'd swap a trans and tack together the driveshaft, then pull it sending it into the driveline shop for finish work and balancing.

The 200, and 300 series transmissions are after I finished working on trucks so have known hardly anything about them.

Completely forgot the other conversion that was popular was a Fuller RT, or RTO-9509B with the "F" style top cover dependent upon axle ratio and tire size. This allowed placement of the shift handle further forward in the case. A small nine speed nowadays, but worked well in that application.

ENDT676 came out in '73,followed by the ETAZ673A "300 +" in 1975

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Not very common then in the early years. My 1976 TS-442 manual does not make mention of the ETAZ673A, or/nor B series, but I do have a supplement for the engine dated 1979 given to me by the St. Louis Mack dealer whom alluded the engine was new for that time? The same manual makes mention of the ENDT-676, but the same series from 1975 does not? 

My 300+, (ETAZ673A) is a 1980 model and original to the chassis.

Edited by Rob

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