1980 720 transmission upgrade

[Datsdat]

Do any members have info regarding which transmission would be the strongest and latest model Nissan trannny that would back my turbocharged L-20B and which vehicles could be used as donors? My F5W71B just went tits up. Can't find any donor Nissans close to my model year here in Dallas. Don't mind swapping front case if necessary as long as no major modifications are needed.

[datzenmike]

 Unfortunately you have the wide ratio with the lower first gear. Good for faster revving with a turbo. Most other 71Bs are mid or close ratio and will spool slower, well slightly slower. The '79 620 used these and the Diesel 720s. You may have to settle for a mid ratio.... but you can always put a 4.11 or 4.375 differential in it.

 

Generally the later made 71Bs wer the most up-graded. The '85 had the 62mm counter bearing to replace the 56mm one from earlier years. This is the same bearing used in the later 71C transmissions.

 

I myself would get a later 71C 2wd KA 5 speed from the D21 Hardbody and modify the driveshaft to fit the length.  You'll never break the 71C. Use your release bearing and collar that holds it.

[datzenmike]

All these will fit, some will need an L series front case put on to convert it.

 

There are 3 gear ratio sets for the 71B. For lack of a better terminology and strictly in relation to each other they are wide, mid and close ratio. A wide ratio has a lower (higher numerical number) gearing for first with the other gears more spread out with forth always being 1 to 1. For example for the 'wide ratio' the engine turns 3.592 times for one output turn while the close ratio only turns 3.062 times  for one output turn. A wide ratio helps if you are a heavy loaded truck or a turbo engine that needs the engine to rev faster to spin the turbo up.

 

 

WIDE Ratio vehicles

'79 620

'80 720

'84-'86.5 200sx (CA18ET and CA20E)

'80-'86.5 720 ( all SD22/25 diesels)

*80-'86.5 720 4X4 but no way to run a speedometer drive off of them*

 

 

MID Ratio vehicles

'77-'78 280z

'77-'78 620

'78-'80 810

'79 280zx (one year only)

'81-'84810/Maxima

'81-'86 720 2wd Z20/22 or 24 engines

 

CLOSE Ratio

'80-'83 280zx non turbo. These have about a 25% overdrive and would be a tall order to turn effectively in a heavy 720 truck and a small L20B engine.

 

 

The Cab/Chassis 720 with Z22 engines were 4 or 5 speed wide ratio. The '82 with Z22 were mid ratio. All Z24 engine Cab/Chassis were mid ratio.

 

* the transmission rear case is not machined to take a speedometer drive pinion sleeve nor is there a worm gear on the mainshaft inside to drive it. Probably your old 5 speed tail and worm gear could be fitted on, I don't see why not. It's held on with snap rings.

 

There is nothing on the body or engine bay tags to indicate what ratio the transmissions had in them other than to say F4W71B or FS5W71B for the 5 speed.

 

If you have a transmission and are curious as to what ratios you have inside... mark the clutch input spline (I slip an old clutch disc on and mark it and it's easier to turn) and mark the output spline. Get help to watch. Turn the input 20 times while counting the output turns...

 

Wide Ratio........... 5.5 turns

Mid Ratio............. 6.0 turns

Close Ratio.......... 6.5 turns. There''s no way to fuck this up with half a turn difference between each one.