LTL Trunnion cracked

[Macman]

The trunnion mounts are cracked on my LTL, as well as the cross member under the cab.  What have you guys done in this situation?

[mechohaulic]

years back one of my customer/ part-time jobs had a B61SX which had cracked trunnions, they had a professional  welder come in and make repair the right way. he cut  a  massive gouge in  trunnion  and with stick rod  rewelded  back to new condition. todays world everything wire feed welders . the prep is the important part. if BOTH sides are cracked ,you are in different position. $$$ and time wise a set of cut off replacements might be the way to go. with all the cracks , has this unit been over worked? or abused ! 

[Macman]

I am sure the truck was over  worked, I don’t know.  Where does one find parts for these trucks?

[Brocky]

Start with Barry at Watts Mack, the sponsor of this website!!!

[blackdog2]

There are a lot of after market made with 1"-plate ?

[mackaholic]

I am guessing both the trunnion mounts and crossmember are aluminum? I took my trunnion mounts to an old school welding shop and had them welded up. They were not impressed with the quality(or lack of) in Mack's castings. I'm hoping they will hold up for truck show type use but I wouldn't want to use them for hauling any weight.

 As for the cab crossmember, If it's not too badly broken it can also be welded. About 5 years ago I had a couple of new aluminum crossmembers cast. All spoken for now but if you needed one I can check into what it would cost in todays dollars. Was about $1100/copy the last time. I didn't have an aluminum crossmember for my LTL so repair wasn't an option.

[mattb73lt]

I'm sure the quality of that new casting is way above the original. when I had my frame completely apart all of my aluminum castings were of pretty poor quality, never mind the years of use and corrosion damage. A lot of them needed repair and re-machining.

[Macman]

Wow this is amazing thank you for sharing your experience.  I was not aware that a new casting could be done.  My cab crossmember is broken in half so a new one might be a option….  If I can afford it.  If you can share information about obtaining a new casting that would be great.

[mackaholic]

On 9/26/2023 at 7:34 PM, Macman said:

Wow this is amazing thank you for sharing your experience.  I was not aware that a new casting could be done.  My cab crossmember is broken in half so a new one might be a option….  If I can afford it.  If you can share information about obtaining a new casting that would be great.

Its a pretty detailed process. I managed to borrow a very good original cab crossmember from a friend who agreed to take one of the replicas in exchange. The original then went to a pattern maker familiar with aluminum casting. Aluminum shrinks about 5% when it cools after pouring so the original had to be built up in most areas so the final dimensions would be close to original. After that was finished, a follow block was built that the crossmember fit into. It defines where the parting line is(roughly the mid point of the crossmember side to side and vertically when it's in the truck). These two pieces allow the sand mold to be created. The original and the follow block then go to the foundry where the sand mold is made. The follow block and the crossmember are place in a metal frame and casting sand is packed tightly inside the frame around the parts.  The metal frame gets flipped over and the follow block gets removed. Another frame goes on top of the first and it gets packed with sand. If everything goes well, the two halves are taken apart and the original crossmember is removed. When the two halves are reassembled the void is where the new piece is formed when the molten aluminum is poured in. If your familiar with sand casting this might make sense. If not it probably doesn't. (KInd of a sad side note, when I was in high school, I was taught this process. I doubt it's taught anywhere anymore) The picture above is of the newly cast crossmember after it's been cleaned up. The final width still needs to be machined and the mounting holes drilled in the correct places. This is what I got back from the foundry.

I'll get a picture of the original and the follow block posted when I get home. Maybe that will help explain it better. 

I still have the original crossmember and the follow block. I could be taken to a foundry and another cast fairly easily. If your original isn't too badly broken it might be easier to weld it up. If you're interested in casting one, message me your number and we can talk in person.

Good Luck, Brad

[1961H67]

That’s very interesting, I don’t think I have ever heard of a foundry near me. I doubt they teach that in high schools anymore. Thanks for the info 

[mackaholic]

Here's a couple of pictures of the original crossmember in the follow block. 

[1961H67]

That definitely is a dying trade! One reason they couldn’t teach that in High School is they couldn’t find anyone to teach the class! And the kids today wouldn’t know what it was if they cast it . Thanks for the pictures, The Towing Museum in Chattanooga has a lot of the gear wooden blocks and molds for the older winch gear,, I always found that interesting but was never able to see it done. 

 

[mattb73lt]

It is sad that a lot of the skills and knowledge to manufacture parts like that are disappearing. When I see a raw casting like that, my mind immediately goes to how I need to set it up to machine it into a useful part. That comes from my technical education in high school taking a Machine, Tool & Die course. At the state technical school I went to we had a huge machine shop and a large class. The classes behind us were smaller each year. The overall school population declined through the years and the state closed it for several years. When it reopened a few years ago one of the shops that was cut was the machine shop. One of the largest spaces in the school is now occupied by a Nursing course. I went there nearly 40 years ago and still call upon what I learned there all the time. The younger generation doesn't seem to have much interest in learning hands on skills anymore. It gets harder every year to find places to do work like what you've shown.