hey this is a question for the 6 door or the 87...looking at a internatioal dump truck (getting junked) any way it has 2 trannys the truck is a 70's model would say 76? the 2cnd trany has ud od and d so it has a underdrive overdrive and drive would be 1to 1 but will it be sycronized where i could put it behind a automatic ? would i be able to start in ud and when i wanted to shift the ud to d put the truck in n and shift the aux tranny or do they only work with stick shifts
I don't know the answers to your questions, but...
There was a guy in my 4x4 club that has a 60s era f-750 4x4 that had the manual tranny, I assume it's like you're talking about, mounted behind an automatic tranny.
I think the club has a website. www.ozarkmountain4x4club.com there maybe some pictures, or at least you can message them and ask about the truck.
You're not the first person to do that. I know of guys that stacked manual transmissions, but I never heard of an under/over unit hooked to an automatic. I guess anything is possible with enough time and money.
I drove a Mack ONE TIME that had that setup (UD, D, & OD). My memeory tells me it was NOT synchronized, but that was OVER 30 years ago & my memory lies to me about what I had for lunch, so I wouldn't trust it too far.
my dad drove an old white that had 3 trannys in it. he hated that truck because it had three shifters. man thats been 35 years that i know of. and it had a v-8 detroit in it. no power steering either. i think it was a 18 gear.
Those old twin stick Macks are a whole 'nother animal. The second stick is a range selector. (now-a-days it's an air operated toggle on the shifter.) It was the old Mack straight cut tooth five speed. You shift one through five in low range, then you shift up to high range and shift back to first gear. (which requires two hands to do this. Which hand do you leave on the steering wheel?) By the way, the transmissions are NOT synchronized.
Mack's are finicky trucks, if it didn't like how you put it in gear, it would throw it back at you and try to break your wrist in the process. The plus side is, you could do NOTHING to hurt that trans. I think it was literally bullet proof.