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Minitruckmarauder

720 Diesel Transmission Meltdown S.O.S.

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I was cruising along the other day when all of a sudden 5th gear just disintegrated.  It was like I was in neutral. Shortly after fourth started grinding, which is when I called CAA. I got a tow to a 'mechanic' who said after driving the truck that he didnt even want to open up the transmission for a proper diagnosis because of the difficulty in finding parts.

Anyone know where to find a transmission for a Diesel 1981 720 kingcab?

Limited mechanical expertise here, just boundless love for this truck.

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If no Diesel transmissions any L or Z series 5 speed will work if you swap your diesel front case onto it. It's the front case that really make this transmission usable by no less than 5 different engine types. Any problem I see is getting the wide ratio gear set that the diesel used. It has a 3.592 first gear which makes taking off, specially with a load on or up hill, easier for the somewhat under powered SD22 engine.

 

The most common ratio is the 3.321 mid ratio box found on...

 

'77-'78 280z

'79 280zx

'78-'80 810

'77-'78 620 truck the '79 has the wide ratio

'81-'84 Maxima

'80-'84 720'.

'80-'81 S110 200sx.... the '82-'83 has the wide ratio

'84-86.5 S12 200sx

 

Any transmission after '84 you will have to swap your smaller counter bearing onto.

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Mike pretty much covered it. But if you find another trans to replace it, i would possibly interested in buying the front case from your busted one.

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 I know what you're up to.

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Yup 5speed for the roadster. Its trashed and frightening but it runs! Its the only Datsun I've ever owned with a functional reverse light switch. :rofl:

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First you have to pull the transmission and take a look at the damage to the front case, if it is good then you can use any of the gasser transmissions Mike mentioned above like yours(longshaft), all you do is put your front case onto the doner transmission.

When 5th went away I would imagine the whole truck shook/jerked/made a loud noise, that was likely the cluster gear/counter shaft self destructing, it should have been making a whining noise or some other kind of noise before that except in 4th gear, if it makes a noise at an idle in neutral it is time to fix it.

You need to check your front case first, if it is not busted between the bearings or the hole wasted, you are good to go with the case, the front cover might be an issue if yours is broke unless you find a transmission(pre 1983) with the small bearing, you can then use that bearing cover.

If the hole is buggered up but not broken between the bearings you can likely have the lower hole turned out to the large 63mm bearing to save your front case.

These diesel transmissions are getting very hard to find, everyone wants them to fix their diesel or they use them to put a Zcar transmission in there Roadster.

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4G8ZnN5.jpg

 

'85 diesel front case. Note the 62mm counter bearing used after '84.

 

 

IgazraN.jpg

 

Roadster front case (trimmed) Note all Roadster bolt holes line up with matching holes in the 720. Sizes may vary but they are there.

.

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I always thought it was a 63mm bearing, but it measures out to 62mm as you mentioned, I don't know where I came up with 63mm.

I sold a Datsun 4 speed Roadster transmission that was going to get trimmed for mock up purposes on an SD33 marine engine, I expect it was going to be used to start the engine, the guy also bought a bunch of other stuff from me, the SD33 is a lot like the SD22, they share parts.

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ha ha I wrote down 63 in the last post just copying you. Then when re reading it looked strange so I looked it up. Not used in '84 but was used for '85 transmissions. Not all front covers are the same either. This one receives oil from the main case at the top and this groove between the bearing for drain back? Might not hurt to modify all covers if you remove them for anything.

 

HqA1JAC.jpg

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