nicksabeast Posted June 6, 2016 Report Share Posted June 6, 2016 I have a 1978 Datsun 620 with an that I want to take on a road trip, but highway driving is a killer with its F4W71 4 speed trans (4500+ RPM at highway speeds). One of my friends has a 1986 Nissan Z31 300zx VG30 with a FS5W71C 5 speed transmission that I want to swap into my 620, since I can't easily find a FS5W71B 5 speed that was available as an option for the 620. From what I've been able to find, it should be a direct fit except for a different output spline and needing to shorten the driveshaft? I'm not sure what needs to be kept from each transmission or what work would need to be done to make this work. Does anyone have experience with this kind of swap and know if this particular 71C would work behind a 78 L20b with the front housing from my stock transmission? Quote Link to comment
datzenmike Posted June 6, 2016 Report Share Posted June 6, 2016 4,800 is almost 80 MPH so not really highway speed. Something to think about is that at 40 MPH it takes 4 times as much power to only double your speed, and this is just the wind resistance. Your L20B is making power enough to go 80 but reducing the RPMs by 0.79 (the over drive ratio) or down to 3,643 RPMs... is it going to be making enough power now??? You may end up slowing down or having to step even harder on the gas. There are practical limits to gearing, engine power and wind resistance, and why your truck can't go 200 MPH simply by changing gears. Just something to think about. FS5W71C. The 620 4 speed front case will swap to the 300zx FS5W71C if you... Remove the 62mm counter gear bearing and put your 620 bearing on. Drill out the 1st/2nd shift rod hole in the 620 case to 16mm from 14mm. Have a machine shop remove metal from the case around the counter gear bearing for clearance. At the same time you could have the 5mm bearing hole enlarged to 62mm to use the 300zx counter bearing? This is what you have now This is what's needed to modify your 620 case to fit an FS5W71C... Use the 300zx front cover... (has the larger counter bearing (right)) Differential... Another, is why not just change the differential gears? Much easier, cheaper. A 4.11 would drop the RPMs to 4,540. 3.90 to 4,308. A 3.70 to 4,087. The 720 used these diff ratios... 3.364 3.545 3.70 3.889 4.11............ if you don't like one, try another. You should be able to get one for under $100??? 1 Quote Link to comment
Stoffregen Motorsports Posted June 6, 2016 Report Share Posted June 6, 2016 Be careful drilling the shift rod support bores. If they get sloppy, the shift rods will wear prematurely. I would drill them out small and then ream them to size. You can buy reamers in all sizes at places like MSC or McMaster Carr. 2 Quote Link to comment
scooter Posted June 13, 2016 Report Share Posted June 13, 2016 Stroff is right. A reamer is best. If you have to ratsun it a good 5/8 drill bit and a flapwheel works well. A straight drill and patience is needed here. Quote Link to comment
]2eDeYe Posted June 13, 2016 Report Share Posted June 13, 2016 still 2500 rpm from redline....I don't see the problem :) Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.