Triplex Question

[vanscottbuilders]

Does anyone know where I might find the percentage of overdrive of the double overdrive triplex transmission that was available in the B model?

And - would anyone have one of these transmissions that they would like to part with?

Or - is it possible to purchase the gearset necessary to convert my single (.86) over triplex to a double over unit?

A .70 or so overdrive would let me use the good original 5.46 single reduction rear I have for a 65 mph or so top speed.

I am trying to avoid buying another rear end for my B67 project, and yet still have enough road speed to at least stay out of the way. And, I would really like to use the original housing with the Mack logo machined in the back.

Another reasonable alternative might be to find a good 4.17 ratio rear end from an R model - can anyone help me with one of these?

I will be at Macungie - I just need to know if I should bring a trailer - if someone has the parts available.

Or I can use our new BMT transportation assistance forum to get the parts from anywhere in the country to upstate NY.

Thanks,

Paul Van Scott

[Doug Maney]

The easiest way to find the ratio for the Triplex would be to check here (which you already have) or call the Trucks Museum. They can look the model up and get you an answer pretty quick.

I looked through my spec sheets for B, H, G, N and found only single over aluminum case Triplex (TRTL 72) listed, one of my G's have one of these, It has a .85 overdrive. It may be easier to change your rear to get where you want to be instead of tracking one of these down.

All of the info that I looked through does not mention a double over Triplex, I can't say that I have diriven any or if any were built.

Check with the Museum, they'll have the info that you need! Doug

[Rob]

Does anyone know where I might find the percentage of overdrive of the double overdrive triplex transmission that was available in the B model?

And - would anyone have one of these transmissions that they would like to part with?

Or - is it possible to purchase the gearset necessary to convert my single (.86) over triplex to a double over unit?

A .70 or so overdrive would let me use the good original 5.46 single reduction rear I have for a 65 mph or so top speed.

I am trying to avoid buying another rear end for my B67 project, and yet still have enough road speed to at least stay out of the way. And, I would really like to use the original housing with the Mack logo machined in the back.

Another reasonable alternative might be to find a good 4.17 ratio rear end from an R model - can anyone help me with one of these?

I will be at Macungie - I just need to know if I should bring a trailer - if someone has the parts available.

Or I can use our new BMT transportation assistance forum to get the parts from anywhere in the country to upstate NY.

Thanks,

Paul Van Scott

When I had my double over triplex on the floor, my daughter counted almost 70 complete revolutions of the input shaft when I twisted the output shaft 100 times. The transmission is a 1958 model according to the build date. Don't know much else about it other than works well.

Rob

[mattb73lt]

When I had my double over triplex on the floor, my daughter counted almost 70 complete revolutions of the input shaft when I twisted the output shaft 100 times. The transmission is a 1958 model according to the build date. Don't know much else about it other than works well.

Rob

I Have converted my B42 to a "B43" by adding a END-673 and a tri-plex. The give-away on the tri-plex is on the stamped info on the Left side. There's a TRTL and a TRT. The first one is a Light or aluminum case, the second is the heavier cast iron case. Then theres the numbers, 72 means you have a single overdrive, 720 is double overdrive. First overdrive is in the auxillary box, the second overdrive is in the main box. Single over, I believe, is 1to0.86. Doubleover is 1to0.68. It's been a couple of years since I ran all the numbers, so someone correct me if I slipped up! As for coversion by changing the internal gears, due to the scarcity of parts and expense it may be more practical to find one with the gears or to change the rear ratio. When I did my conversion I needed to also change the rear gear set as it was a single reduction with a 6.00 or so ratio. I was able to find a 4.62 CRD-117 chuck from a salvage yard for $500. Due your math on all components to include tire height to due it right. I chose that ratio for the rear for what I due with the truck. Top end for me is about 80MPH with 20" rubber and empty with the engine around 2000RPM. Now, that's way too fast for normal cruise, ie:tickets and being able to stop!!. But, I chose all the parts to allow me to run at about 65MPH and the engine only turns about 1600 to 1700 which is great for economy. I like this set up so well I'm building up my next project, A 1960 B-73LT(L-cab) with the same transmission, Cummins NH-220and a CRD-78 with a 4.68 ratio

[Packer]

Check in Tom G's (Fuzzy Buzzard) 'oldmacksrus'. He has listed all the gear ratios of all transmissions. Good info can be found in that web page, including parts for sale.

I have a double overdrive '18 speed' Quad box that, if I remember right is .65:1.

Forth-over is .85 and the next shift is to fifth-over at .85:1. Combined overdrive is .65. Under and direct are skipped.

Packer

[vanscottbuilders]

Thanks everybody !!

What I was hoping for, in part, was to keep all of the pulling power of the original 5.46 rear end, and get some top end speed with the double over transmission. Sort of have my cake and eat it too.

I have a single over triplex with the light aluminum case all ready to go in the truck, and I own an older Rockwell rear of about 4.11 that is in used condition and largely unknown (It isn't too pretty). With a higher ratio rear, I can definitely get more road speed - but with a 711 motor, I don't really have any extra grunt for the low end.

I'm curious Packer; does the double over quadruplex transmission have a larger case than the triplex - and would fitting be any issue? That transmission might be the best answer, if any were available. And does the "720" designator apply to the quadruplex as well as the triplex?

The idea of getting a 70 or 75 mph top end at redline is what I was thinking, too. That way an easy cruise of around 60 or 62 is comfortable for everyone involved - noise and fuel consumption are minimized, driver fear is reduced, and tickets are less of a concern. (Until now, I didn't think it was possible to get a speeding ticket in a B model !!)

To achieve the 75 mph top end - I calculated a need for a 3.59 final drive ratio, including the overdrive reduction and 22.5 rubber. To get there, I need a rear axle ratio of 4.10, using the single over triplex with the .86 over gear. With a double over transmission gear of .68, I get real close (3.71) with my original 5.46 rear end.

For "fine tuning", I still have the option of 24.5" wheels and tires.

Thanks again,

Paul VS

Matt,

Are you using a double over (#720) triplex with the 4.62 rear axle to get an 80 mph top end speed?

If it is a single overdrive (.86 gear) - then my math is seriously flawed - and that happens a lot !!

Let me know, before I do something stupid - Again. Just ask my wife.

Thanks,

Paul VS

[Packer]

Paul,

Wish I had my info in front of me but I don't!

go to:

http://www.oldmacksrus.com

and look up all the transmissions.

TRQ-720 TRQ-7210

These are the two transmissions with double overdrive.

They are big! But what the hell?!?

I didn't look at tri-plexes, just quads.

Packer

[vanscottbuilders]

Packer,

I went to the oldmacksrus site - I had forgotten what a great reference tool that is.

Those guys should get medals for all of their work. Tom Gannaway actually convinced me to go forward with the B67 project, and not to be afraid of tailoring the truck to my own use rather than being strict about a perfectly original restoration. I guess I can blame him for all of this confusion.

As it happens, there is a B83 close by here with a double overdrive quadruplex that I can probably acquire. So I am going to look at the physical size of the case and the transmission model number. Once again however - I will probably not accomplish my original mission - rather I will bring home the whole truck for another one of those "future" projects. Ah well. I guess it's good to have spares.

Say - I'm curious, are you anywhere near Afton, Wy.? The Aviat Aircraft company in Afton built an airplane for me a few years ago - they are really good guys.

Thanks,

Paul VS

[HK Trucking]

TRQ-720 TRQ-7210

These are the two transmissions with double overdrive.

Lets not forget the TRQ7220.

I have a double overdrive '18 speed' Quad box that, if I remember right is .65:1.

Forth-over is .85 and the next shift is to fifth-over at .85:1. Combined overdrive is .65. Under and direct are skipped.

.84 and .70

According to my reference materials.

[Freightrain]

The only size difference between tri and quad would be the rear box. The quad would be a shade bit longer with the extra gear ratio. The front boxes should be the same size. I was looking at a quad box to put in mine and I seem to recall measuring the differences between my triplex and the quad. It's been a couple years and I can't say I recall the actual numbers. I have an extra driveshaft, so I was going to have it shortened so that I still have the triplex shaft if I ever needed it.

I've wanted to add some road speed to mine, but just haven't got around to it. I have 4.62 with single over. Gets me around 64 mph on the gov. Double over gets me about 8 mph, so I can cruise at 60-65 about 1700 rpm or so. Pulling my trailer might be a bit much, but I can always just keep it outta double over on hilly terrain.

[vanscottbuilders]

Freightrain,

The 4.62 with a single over triplex makes sense for about 64 mph, Thanks.

Sounds like you can cruise comfortably at around 60 mph, which is pretty good.

Do you have sufficient pulling power for the loaded race car trailer with this combination and the 673?

This has been an interesting forum for me, as the conditions under which we drive today are so much different from the driving conditions in the fifties - when these trucks were really the state of the industry with their use of super dependable low horsepower diesels, low rear end ratios and plenty of transmission choices.

Thanks,

Paul VS

[Packer]

HK,

I was looking for a double overdrive to get max speed without changing the rear ends. that's why I only listed the two Quad boxes. Never thought to look at any tri-plex ratios.

Paul,

I'm on the same side of the state as Afton, but I'm on the South end and Afton is on the North end of Wyoming. My-son-the-lawyer has a lot for a summer cabin up there.

Packer

[Brian]

The information that I have lists the ratios on the double overdrive transmissions as follows the trt(l) 720 has overdrive ratios as follows 5 direct is 0.84 and 5 over is 0.69. The ratios on the trt(l) 7220 are 5 direct is 0.84 and 5 over is 0.70 hope this helps Block

[Freightrain]

The only real difference between Triplex Double over and Quad Double over is the fact you lose some of the first gear ratio in a triplex d/o. If you plan on pulling heavy, getting started will be a bit harder since first is not as deep. Not a problem for a hobby truck.

Paul, I'm around 26K lbs fulling loaded. I can run about 62 or so flat out. It's pretty hilly around here and not many places I'm not just holding it on the floor to keep it up to speed. I think I have enough HP to pull it with more O/D, but maybe only on level ground? Like I mentioned, if I can't use D/O all the time it will make it a bit nicer when I can.

Somehow I'd like to get a ENDT673C someday to up the juice a bit. Someday.

[vanscottbuilders]

It appears that, after some analysis of my wallet, the best choice for me is to find a good used 4.17 Mack rear end and use it with my TRTL-72 (.86 overdrive) transmission bolted to the 711 engine for a final drive ratio of 3.59, and a little more grunt than the original 673P. Putting the truck on the tallest 22.5 rubber I can find should give me about 72 mph at the redline in overdrive without having to convert to 24.5 hubs. Yet I should still have sufficient pulling power down low.

At last - all those wasted nights at the drag strip figuring this stuff out is starting to pay off.

And my mother said I would never amount to anything!! Who would have guessed.

Now - does anyone have a good used 4.17 axle assembly - either on Dayton or Budd hubs?

Springs are not necessary - I'm using an air ride set-up.

Thanks,

Paul Van Scott

[mattb73lt]

Thanks everybody !!

What I was hoping for, in part, was to keep all of the pulling power of the original 5.46 rear end, and get some top end speed with the double over transmission. Sort of have my cake and eat it too.

I have a single over triplex with the light aluminum case all ready to go in the truck, and I own an older Rockwell rear of about 4.11 that is in used condition and largely unknown (It isn't too pretty). With a higher ratio rear, I can definitely get more road speed - but with a 711 motor, I don't really have any extra grunt for the low end.

I'm curious Packer; does the double over quadruplex transmission have a larger case than the triplex - and would fitting be any issue? That transmission might be the best answer, if any were available. And does the "720" designator apply to the quadruplex as well as the triplex?

The idea of getting a 70 or 75 mph top end at redline is what I was thinking, too. That way an easy cruise of around 60 or 62 is comfortable for everyone involved - noise and fuel consumption are minimized, driver fear is reduced, and tickets are less of a concern. (Until now, I didn't think it was possible to get a speeding ticket in a B model !!)

To achieve the 75 mph top end - I calculated a need for a 3.59 final drive ratio, including the overdrive reduction and 22.5 rubber. To get there, I need a rear axle ratio of 4.10, using the single over triplex with the .86 over gear. With a double over transmission gear of .68, I get real close (3.71) with my original 5.46 rear end.

For "fine tuning", I still have the option of 24.5" wheels and tires.

Thanks again,

Paul VS

Matt,

Are you using a double over (#720) triplex with the 4.62 rear axle to get an 80 mph top end speed?

If it is a single overdrive (.86 gear) - then my math is seriously flawed - and that happens a lot !!

Let me know, before I do something stupid - Again. Just ask my wife.

Thanks,

Paul VS

Paul,

Yes, I'm running a double overdrive. My set-up is a END-673(N/A) backed by a TRTL-720 through a final drive of 4.62 with 20" rubber about 43" in diameter. The Triplex has fifteen speeds but you only use thirteen as you don't split Fifth. It's a pleasure to shift as you can skip some of the splits depending on loading. Most of the ratios have about a 300 RPM drop and it shifts very easily without the clutch. The upper gears are great for hill climbing and I can't recall having to go below 4th Lo-split on the highways around CT with the loads I carry(antique cars and pickups). When I was collecting up the parts to do the project I bought a book about auto math to get the math equations for gear ratios, very helpful!! Then I started to play with them to determine the final drive ratio, then found one to with the right ratio complete the set-up. I ran the equation for each ratio to confirm the shift points to make sure I was in the power range of the engine.

It seems as if everyone here has been very helpful and in the same ballpark with answers for you so you shouldn't be off when you set yours up. By the way, if anyone needs a TRDX-720 Duplex with a deep reduction and a single overdrive(.86) out of a B-61SX or a TRD-67 Baby Duplex, direct, I have one of each.

Let me know if you need any thing else. Matt Let me

[b61fred]

Hi Paul,

I think I would hunt for the 4.17 rear axle, When I drive my truck with the overdrive duplex(overdrive in the front box) with 5.13 rears, 20 inch rubber, I can get up to 75 mph at 2300 rpm. I hardly ever split the 5 speed until 3rd gear, so low end grunt is still there if I need it. Or I can split the gears if I want to sound cool or impress someone by shifting with both hands. I believe the trans you got from me would work very nice. I do have some 12.00X22.5 tires (goodyear recaps) in very nice shape. they are the same hight as a 11.00x24.5, might help some.

Fred