mattb73lt

Yeah, that's what I had in mind. Much longer wheelbase,though, due to the body length. I was going to demount the body, blast,prime and trim/repair the donor frame. Repair the B-73 frame, as it had tandems installed at one time, then mate the whole thing together as you did and remount the body to complete it.

About six feet of overlap. I was planning to bring the Ford frame as far up to the cab as possible. Trimming as neccessary to avoid interferance and remounting issues with fuel tanks. Geometry is a concern to keep it as square as possible.

I was looking for some imput on how to best do a frame stretch.

I have a fairly short wheel base 1960 B-73LT(L cab) and am going to stretch it into a car carrier for my antique cars. What I have for a body is a late 70's Jerr Dan roll back that was mounted to a Ford truck. I saved everything from the Ford from the cab back and it's all still mounted to the frame.

The Mack frame is about an inch shallower than the Ford frame and the outside measurements are about 1/4" less than the inside measurements on Ford frame. This would allow the two frames to slide together and by placing two 1/8" shims down the length of the joined areas, take up the difference.

I was thinking about doing the stretch in this manner, then using body bound bolts, bolt the whole thing together using the cross member patterns and a logical bolt pattern in-between for maximum strength.

The reasons for method were to simplify and speed up the mounting of the body, since it's already mounted to the frame and to create a double frame for more strength due to the increased wheelbase.

The dimensions of the two frames are so close to allow this. Once alligned,squared and joined, I would use all Mack components for the drive line.

In theory, it would seem the best way to proceed, but I'm also thinking safety and not creating something dangerous. Also, if I ever sold it, it would be very easy to separate and return to it's original configuration if so desired by the new owner, leaving the frame very unmolested.

Looking for some thoughts and possible alternate methods?

Thanks, Matt

I recall when I added the CRD-117 that there were four "pads" on the bearing caps that married up into the rear of the housing that seemed pretty significant. I've hauled some pretty good loads with the truck and never seen any signs of stress or flex on the RAS housing. It is a hobby truck and I don't max it out or use it like a work truck. I've seen a few of those torque arm rears and they are VERY heavily built. I was thinking that you might find something to fit that rear that was more modern and provide a better ratio for the highway, while retaining the original set-up.

What kind of rear arrangement do you have? You should be able to replace the carrier with one from an R-model. I was able to upgrade my stock RAS axle in my B-42 with a CRD-117 in 4.62 ratio. Many more efficient ratios are available in that carrier. I was told that a single reduction axle would not accept a double reduction carrier, but there were no issues at all. It's been that set up for years and thousands of miles. Ahead of that I have a TRTL-720 and a 237. I can cruise all day at 65 MPH, turning around 16-1700. Top end is around 80 MPH @ 2150 RPM.

IT was a 1963 B-42P, I made it a "B-43P" but it really is a B-61 due to all the swapping.

I did this swap about 13 years ago with a 1963 B-43P. Found a doner, 1965 B-61SX. It was very easy as the frame was predrilled to accept both gas and diesel mounts. Stripped out a EN-402 and a TR-67 Duplex along with the mounts and bolted in a END-673 and a TRTL-720. It was also a single axle, single reduction rear and swapped in a double reduction third member from a R model for better highway speed (cruises at 1700 RPM at 70 MPH). I recently upgraded the engine to a ENDT-675(237 HP) after the 673 failed after all that time without issue. It was great to have the doner for all the bits and pieces you'll need to do the swap right. The B-42 I started with was a very low mileage local truck (69K mileage) and made all the difference.

The 20 speed may give you some issues as to allignment if it's single or double disc clutch and it will need a third support on the tail end due to weight.

I converted a B-42 to diesel power and used the original RAS 508 axle. I replaced the original CRS 84 carrier with a CRD 117 (4.64 ratio) out of an R model. I was worried about going from from a single reduction carrier to a double carrier with the single reduction axle. I had no issues at all with installation or operation. The CRD 117 will probably be easier (more plentiful) then the B model and give you more ratio options. Plus parts will be easier. Matt

Gentlemen --

I have a B-42S that I am looking to swap out the gasser and put in a diesel. I have a Detroit 671, which is simply to big, over 54 inches long. And while I could make it fit but cutting into the cab, the cab is small enough on it town without putting a doghouse in it. I now have a lead on trading my 671 for a Cummins 6BT. While the 6BT is right about the same size as the original gasser in terms of over all physical size, I just am going back and forth on if it will be powerful enough.

I am looking for some over all suggestions to help get me pointed in the right direction. I will say that I am very new to dealing with Mack trucks and big diesels. I know that what I will be doing with the truck will determine the over all horsepower I'll need and such. The truck will be doing medium to light duty tasks. I will be putting a 20 foot flat bed on this truck, to haul some of my older vehicles, and towing from time to time a 24 foot enclosed trailer.

I also know a lot will also depend on the transmissions and the gearing... A ton of "ifs"... But the cummins is a great deal for me, and from my research they used it in light duty and buses so it might be just what I need. But I thought I would come to the experts and find out what you think.

Thank you for your time and help!

--Josh

I did the same swap on a '63 B42P. What saved me a lot of pain and aggravation was buying the front half of a donor truck, a'65 B61SX. The Mack frames are pre-drilled to accept gas and diesels. You'll need to swap the front cross member and the transmission mounts. As for an engine, I used a END-673. A 237 should bolt right in with some bolt on mods,possibly the bellhousing to position the starter and avoid interference. I also put in a TRTL-720 Triplex. I kept the original rear axle but swapped out the carrier from single reduction to double reduction with a 4.62 final drive. Over all, a very easy swap if you use Mack components. The donor truck was invaluable for all the small bits you'll need, radiator shutters, brackets plumbing. That cut down significantly on parts hunting and fabrication. You can use any engine you really want, if you have the time, patience and resources to expend. I would recommend swapping the transmission as well, the small one won't stand up to long with a bigger diesel. I ended up with a really fun truck that has enough power for what I need, hauling antique cars on a roll back body I added and speed, I can do 65 MPH all day turning about 1700 RPM's. Top end is about 80+ MPH, but don't forget you have to stop all that weight. Good luck, Matt

I have a TRD-67 tenspeed direct duplex out of my B42P sitting on my floor. No known mechanical issues with it. The previous owner welded a broken portion of the bellhousing back on, but it never gave me any problems. It's located in Berlin, CT. Let me know if your interested. Matt

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

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

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