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What transmission should I use for my 620

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I have a '73 620, it still has the original L16 with the 4 speed transmission. I want to to swap a 5 speed into it what would be the best one to look for?

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There are two.

Keep in mind that a vehicle driven primarily in town doesn't use 5th that much. A fifth gear does not make it go faster. Over drive is simply to lower highway revs and may increase mileage very slightly.

 

 

The FS4W63A from a '77-'79 S10 200sx. Rare to find one, rarer to find one not worn out or rebuilt. Same length as your 4 speed so the drive shaft does not need shortening. It's an adequate transmission with a unique shift pattern of reverse above first, speedometer in the same location, and was never used in the 620. You will need to modify the transmission mount.

R,,2..4

1..3..5

 

The FS5W71B from a later 620, 280z or zx non turbo, 810 and Maxima. As you can see this is a much stronger six cylinder transmission used in many more vehicles and more plentiful to find. There are wide, mid and close ratio gear choices and mild to wild over drives. The 71B is longer than your 4 speed so shorten your front driveshaft or get one from a '74 or newer 620 that is already the correct length for this transmission. Has regular H pattern shift.

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If u swap from the short tail to the long tail trans, you will need the front drive shaft from a later truck, trans crossmember, the trand tunnle cover plate. If you have the stock bench seat with no notch, it makes it difficult to shift it Wil hit the seat when shiftinf

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What about a 5 speed off of another 620? Which one would be best and what needs to be done to make it work for my 73?

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You will need the front driveshaft from a '74 or newer 620 (it's shorter) and the cross member and rubber mount for the transmission..

 

For the transmission '77-'78 from a 620 is the mid ratio and the '79 is a wide ratio gearing. Either is fine, the '79 would be marginally better if this is a working truck carrying loads.

 

 

The following are all L series 5 speeds that are the same design 5 speed as the 620 and may be available. They are no stronger or weaker...

 

The '77-'78 280z and the '79 280zx as well as the 810 and Maxima 5 speeds are also mid ratio and identical to the 620 5 speed.

The '80 720 2wd is a wide ratio and will work also. This is a one year only 720 L series transmission.

The '80-'83 280zx non turbo 5 speed is another L series transmission that will fit and work but I think the close ratio a bit tall for the L16.

 

 

KEEP the clutch release bearing collar you are using now. Get a new bearing for it and put it on the 5 speed's clutch arm. The release collar is matched to YOUR L16's clutch. Do NOT use any collar that may come with any 5 speed.

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rule of thumb i have found was when swaping the trans forget where it came from for parts. get the parts for what it is going to , like in your case for l16

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It's about 29" from front to spline and 40" including the shifter. Worse, it does not in any way bolt to an L series engine, is massively over size and overkill for a 70 hp engine.

 

A better choice would be a JDM SR20 6 speeds but again overkill. This is a small L16 engine in a truck.

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If you have a '74 or later 620 these 5 speeds will drop right in...

 

'77-79 620

'80 720 2wd

77-'78 280z

'79-'83 280zx non turbo

'78-'80 810

'81-'84 Maxima

 

By drop in I mean all are L series and will bolt up, all are the correct length. Transmission speedometer pinions may not match your intended use. The '80-'83 280zx 5 speeds have an insane overdrive ratio making them only usable out on the highway. There are three ratio sets of gears wide, mid and close, all will work but may not be suitable for your use.  

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Thanks Mike I screwed up and put a 280zx 5 speed in .and it's just geared way too high for me. I found one out of a 84 Maxima hoping it works out better

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Geared too high?  That's the good one, unless your engine is not in very good tune.  1.8L MGBs work great with that transmission.  

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Maybe they are lighter. The 4 cylinder truck is a little too heavy at 2,700+lbs for 25.5% OD. Sell it for $$. 

 

 

I really like the closer gears but the OD is a bit much making is only useful on the highway with down shift for passing climbing inclines or head winds.

 

81-83zx. % RPM drop per shift...  39, 29.6, 23.5 and 25.5%. You really need a six or a light 510 (2150 lbs)

 

Mine is.......................................... 37.5, 37, 23.5, and 13.6% or perfect for a 4 cylinder

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Hi folks, I'm a retired mechanic in Maine and I used to have a 510 sedan that I built up and autocrossed in my twenties. I now have a 1978 Datsun 620 Sunrader fiberglass camper that I want to do the 5-speed swap on. I just love it and we want to go on a road trip but I'd like to quiet it down on the highway. It's very short at 16ft overall and is on the standard wheelbase chassis with dual wheels added by Sunrader. I've located a 5-speed from a 78 620 in Texas and it's still in the truck so they are going to test it for me this week. I've read over this discussion but I need further clarification. Am I going to need the front drive shaft and transmission crossmember for the swap? You guys are a great resource , I'm so glad I found you.

Thanks,

Ross

207-447-2302

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The 620 camper and Cab/Chassis option was never offered with a 5 speed option. There's a reason for this. Fifth gear is for light throttle cruising on the highway. Hauling a load like a camper, passing, hill climbing or driving into the wind puts excessive side loads on the front counter bearing wearing it out. The 5 speed is not made for hauling a camper. Stick with the 4 speed. Four speeds transmit power directly through the transmission on the main shaft and does not use the counter shaft. 

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Hi Mike, I understand what you're saying and I get it. If I'm willing to take that chance especially if I run synthetic gear oil can you clarify for me my original question about needing the front drive shaft and cross number please?

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As described it will totally swap in. Keep and compare your 4 speed speedometer drive. If the 5 speed is different color or number of teeth use your 4 speed sleeve to keep your speedometer accurate.

 

If the 5 speed has a new output seal in the end it will probably hold synthetic. I use GM Delco Friction Modified Synchromesh Transmission oil. Lordco has it cheaper than the dealer. Ain't cheap but works very well. Two liters will be enough for the 71B 4 or 5 speed.

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Thanks so much for your advice Mike, my way of thinking and why I'm willing to take this risk is even if it reduced the life of a freshly rebuilt transmission by 50% so that it only lasted 80000 miles on synthetic oil, that would be 20 years of use at 4000 miles a year which would outlast me!

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If you rebuild the 5 speed but if it's just a used one watch out. Better get some guarantees.

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 Depends mostly on the length of the 720 5 speed. If 26" long it will fit other than maybe needing some mods to the transmission mount. If 31.5" long add shortening the driveshaft.

 

In both cases keep and use the release bearing collar that is on the '73 clutch arm.

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