Little Trucks, Big World

What are the chances? Here I am with this almost 33 year old Nissan/Datsun 720 truck and I am in need of some parts. When I got my Texas truck back in 1999 it came with an extra engine and I was fool back then I scrapped it. It had the old transmission in the back, apparently it was worn out so I scrapped that one too. So the truck was on its second transmission, a donor from another truck. That one went for a good long time as it had been rebuilt with new bearings. When I moved back to Quebec I used this truck to move all my stuff, back and forth we went, and one day I noticed the transmission bearings where getting noisy. So I had it rebuilt in Quebec. But I made one big mistake, they suggested I use ATF and I argued about this and wanted them to put in the GL4 which is 75/90 gear oil, great for warm regions. So one winter later whilst traveling through the mountains of Vermont, on I-89, and it was very windy, temps probably about -50 F with the wind chill, suddenly that way too thick gear oil, did not work properly and I lost gear number 5, my overdrive, and there was a very loud clanking noise. It is now about 5 pm on New Years day, and I limped it in to the next exit only to find everybody was closed, and soon it will be dark, and I’m still 2 hours from home in Montreal. What to do? ... with the engine running, I listened to the transmission in neutral, and it only made a small noise, not too loud. So I tried it in 1st, then 2nd, then 3rd, and then 4th, all of them where just fine with a faint small noise. Forget 5th, sounded like a hammer in there. So I drove home with 4 gears, no problems. I then ordered a new rebuilt transmission from Midwest transmissions and it came with a warranty of 1 year unlimited miles. I used the recommended oil, and now 2 years later with only 25K on the transmission I am hearing a little whirring noise from 1st, 2nd, and 3rd, but its not loud, just I know a bearing is wearing out. So my dilemma is I need to get another transmission and this time will keep the one I have and rebuild it with good quality parts so in this way I’ll have a spare. But it will cost me about 1,600.00 CAD buy the time I pay for all the costs and currency exchange of 25%. Could there be another solution? At my job we closed building one, and I went to work at building 5. I have a new foreman, and he noticed my 1984 Datsun because his Uncle who is now 85 years old has one just like it in his yard, (he’s had it for 31 years) and the engine has problems so it has been sitting for 2 years with the engine partially taken apart. At first he wanted to buy some parts from me, because he wanted to give his truck to his nephew (a student) and he would fix it. But I brought them up to date with the fact that it will take at least 2500 to get this old truck back on the road and parts are literally not available from Nissan. So I suggested I would come look at it and make an offer to buy it. My foreman Claude said he would have a talk with his Uncle to confirm. The next day I’m invited to come have a look, meet his Uncle and make an offer since it is too much work for him. I get there to find a 1984 Datsun 720 4WD King Cab truck made in Japan, in the month of December,,, 1983. My truck was built in Smyrna Tennessee at the USA Nissan factory, in the month of December, 1983. They are literally the same truck. His truck has 94,000 km, that is about 58,000 miles. The transmission is excellent I am sure of it, the stick has a very tight feel which is good. The engine I know has a blown head gasket because it was a common problem especially if he let it overheat and may have towed too much with it. He tells me he wants 500 cash, I agreed. Now I have a complete truck just like mine, and I have all the parts I could ever need for a great price and since he undercoated the truck with oil, it is not even rusted. What are the chances? That I could be led to meet someone who would supply me with exactly what I need? Only 30 minutes from my house ! There’s more... I estimated I would need to pay about 100-200 dollars to have it towed to our home. The day before I get a call from someone I know and they have an emergency... they need me to help an elderly person move about 50 big boxes from her Condo on the 6th floor, to a storage area, and it must be done this Saturday ! ... I am told I will be paid 200 cash for the job. I then search and find a towing guy who agreed to tow the truck for 100. So all said and done I really got the truck for 400 and still have 100 in my pocket! 


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Great 720 story! GL-4 is the correct oil but thick for below  -20C.... But only for cold starting. Once the truck warms up the transmission oil will too and thin out.  Check level and for leaks (wetness) yearly or when ever the truck is up in the air and replace the oil every 3 years or 50,000 K. It doesn't last forever and must be changed. I'm on the left coast where it barely gets to 0 C. I have an old 710 car and run GM Synchromesh  Transmission oil in it. It's a synthetic oil about the 'thickness' of 10w30 engine oil. It has vastly improved the shifting of the transmission. It's like GL-4 and safe for copper alloy synchro rings.  Much better than ATF and thin for cold weather use.

Datzenmike, Thank you for your reply. I've looked a bit today online but can't seem to locate any GM Synchromesh but I'm sure it's for sale somewhere around here. What do you think about Royal Purple Synchromax? They have it in stock at Canadian tire so its an easy find. I'll have to ask and see if they have the GM Synchromesh. .... I like what Channing had to say in his reply. I would definitely agree that in a car the B series with small counter-shaft bearings will survive longer. But I am up for either machining the main plate and installing larger bearings myself, and / or getting a 571C as he stated. What are your thoughts on this? 

Do you think I have enough room to up-size my countershaft bearings? 

Royal will work the other is at Lordco and caller GM Delco Synchromsch Transmission oil. About $17 a liter.

It's also called friction modified. There may be a US and Canadian part number difference. I tried at a GM dealer but the parts guy wasn't helpful and kept asking what GM car it was for? Kept telling him the part number and it didn't matter just I want it. Eventually he wouldn't go any farther so I said a '76 710 Datsun and he look all pissed off like I tricked him or something. Said he could order it in... I had had enough and went to Lordco.

Royal purple is probably the same thing with dye in it. Chrysler and Mazda also use a similar product probably all made my Mobil and repackaged.

The '85 and up 720 use a 62mm counter increased form the previous 56mm. The front case would need milling to upgrade. The 71C from the '86.5 and up D21 Hardbody is an excellent 5 speed and very rugged.... it's just not the same length and the 71B.

Al Mike is correct. Engine will bolt up fine. The primary shaft needs to be shortened, the shift hole moved and a simple plate made for the trans. I also made two spacers to drop the cross member to keep the driveshaft at the original hight. I wrote this up here a long time not sure if it is searchable. I am traveling so no computer for a few days and typing on the phone sucks nuts. Good luck.
Datsun Al. You will keep swapping transmissions as long as you keep putting B series back in. I killed 4 before swapping to a 571 C and no more issues for over 10 years. B are garbage for trucks, undersized countershaft bearings fail routinely as you have discovered. Good luck.

Channing, thanks for your reply. Its the kind of reply I was hoping to hear about. I'm definitely up for putting in a better transmission. Can you give me more details about the 571C ? Im very interested to hear about it. 

Datsun Al, 

D-21 Hardbody 2wd would be the closest for length. They are around 30"?? Definitely a good 5 speed. Used in the non turbo 300zx. The KA and the Z series used the exact same bolt pattern.





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