Driveshaft question? Auto to Manual swap

[FNLO620]

I will be picking up a 72 datsun 620 single cab here in the next few days. I have actually owned the truck before and traded it to a buddy and am trading him back for it. It is almost 100 percent rust free and in awesome shape.

From what I understand it is somewhat of a rare options truck because it is an automatic and has the under dash a/c.

 

The automatic is where the main problem with the truck lies. The flexplate is worn out and the starter doesnt catch all of the time. I have looked for a new flexplae but I have been told that they are no longer available. I have acces to a parts truck with a good 5 spd manual in it and was wanting to make the swap because I plan on driving the datsun alot. I know that I am going to have to swap the pedals and put in the clutch master cylinder.

 

My biggest question is does anyone know if the driveshaft from the auto will work with the standard?

The parts truck I have access to is a kingcab so I know that it wont work.

 

Hope that you guys can help

[datzenmike]

EDITED

 

Early 620s use a short  26" 4 speed and 'long' 31.5" automatic... thus the front or forward half of the 2 piece driveshaft is shorter on the automatic than the 4 speed. The later, '74 and after 4 or 5 speed transmission is a 'long' 31.5" and the same length as a later 4 or 5 speed... thus so the driveshaft is almost identical in length.

 

A later 4 or 5 speed should fit right on your '72 automatic truck

 

 

Might be a good idea to use the five speed transmission rear mount X member too. I don't know if thew early will work... perhaps you just need to rotate it 180 to move the mounting bolts back.......

[athoose]

 

Just thought I'd add this here for reference. I have a stock 620 dated 6/73 with a long tail auto transmission. 

[tr8er]

I bet you can find a flex plate. Unless you wanted a standard anyway.

[datzenmike]

Always assumed the 620 used the short 26" automatic just like the 510. This is interesting. I have to confirm the automatics on all 620s were the long 31.5". The mainshaft length is the same as any other '70s to mid '80s car or truck, including the 280zx/ Maxima/S110 etc.

 

For a flex plate it has to be from a 3N71B automatic, any 510 auto flexplate made after 'April '71   will fit. Above that any L16 or L18 610/710/620 will fit.

[red13]

Had a buddy with a 73 auto that did a 5 spd swap and it was the same length shaft needed

[athoose]

Just came across this in the 1973 620 FSM 

 

Propeller shaft/ drive shaft dimensions. I wonder if the long wheelbase models are the same size as King Cabs.

 

[datzenmike]

The '73 were only short WB.

 

The '75 and up long and the '76 1/2 and up KC are the same drive shaft, 37000-B8900, for 4 or 5 speeds and automatics.

[Charlie69]

If the ring gear on the flex plate is all that is wrong with the automatic you can take the flex plate to a machinist and have him remove the ring gear from the flex plate and flip the ring gear and weld it back up.

 

I am old but I would keep that 620 stock.

[datzenmike]

All ring gears are the same, manual and automatics. Manual flywheels are frozen and the ring gears heated to expand them and slipped on into place. Just find any L series flywheel with a good ring gear and tap in a circle around it's edge to dislodge it. Grind away the flexplate wends and remove the old one and have the 'new' one welded on.

[athoose]

The '73 were only short WB.

 

The '75 and up long and the '76 1/2 and up KC are the same drive shaft, 37000-B8900, for 4 or 5 speeds and automatics.

What does the "for long wheelbase models" refer to, in the diagram? It's a 73 service manual?

 

If the ring gear on the flex plate is all that is wrong with the automatic you can take the flex plate to a machinist and have him remove the ring gear from the flex plate and flip the ring gear and weld it back up.

 

I am old but I would keep that 620 stock.

I'm not the original poster but I do have a 73 auto. I am leaning towards keeping mine an auto but it's not very interstate friendly. 

[datzenmike]

I have that manual and can't explain why they have that. There were no long wheelbase '73 trucks. All were regular cab and having a 100.2" wheelbase through '74. Sept '74 (start of the '75 model year) was the first Long Bed on a longer wheelbase of 109.6"

 

The 521 and the 620 came in a 'Double Cab option. Here's the 620 version (not sold here)...

 

 

 

Also a U620 mash up of car and truck. (also not sold here)

[Charlie69]

I'm not the original poster but I do have a 73 auto. I am leaning towards keeping mine an auto but it's not very interstate friendly. 

 

 

You can always change the rear end pumpkin to a 3.899 gear ratio out of an early 720. 

[datzenmike]

Charlie the automatic through '73 (with the L16) used a 4.625 ratio differential. I don't doubt it screams.

[athoose]

You can always change the rear end pumpkin to a 3.899 gear ratio out of an early 720. 

 

Or get another 620 with a 5 speed.  :rofl:

[datzenmike]

A 3.889 from a 4.625 is a 18.9 % difference and a bit much for an L16 to pull. Not at all impossible, just 'sluggish' as it affects the acceleration of all gears. There's a reason Nissan chose a 4.625 with the automatic. It has to haul 500Kg at highway speeds. If you are not using it as a truck, you could reduce the gearing. A 4.11 would be 12% drop. Swapping the differential is cheap and very easy.

 

A mid or wide ratio five speed would give about the same acceleration 1st through 4th but 5th would be 12-14% over drive. Like keeping your cake and eating it too. More expensive, more work.

[athoose]

I could also put some taller tires on, they are due.

 

But I did just buy this.

 

 

[datzenmike]

Almost certainly a 200mm flywheel.