converted_to_datsun Posted March 11, 2012 Report Share Posted March 11, 2012 Hey, I'm brand new to datsun. I've always been a toyota guy but I just traded my 1988 celica gts for a 1979 620. I've always liked these trucks and I wanted a truck for work and play haha. I'm impressed with how much power it puts down for the year but top speed needs work. There's no tack and 4th seems to go forever, 40-70? Top speed is suppost to be 87 but I'm too chicken to push it right now. I have a good amound of body andpaint ahead of me whick i can handle. and the motor only has 125k and seems extremely healthy. It came with an extra 4 speed.... but I want a better highway gear... soo what 5 speeds could I put in without having to change my driveshaft and with little modification? Quote Link to comment
flatcat19 Posted March 11, 2012 Report Share Posted March 11, 2012 Your 79 620 came stock with a 5 speed. Where did that go? And if you don't have a 5 speed-what motor do you have? There are 2 main lengths between the L-series trannys. 26.5" and 31". Knowing what you really have will help produce positive answers for you. Pics would be great. Welcome to Ratsun! Quote Link to comment
converted_to_datsun Posted March 11, 2012 Author Report Share Posted March 11, 2012 Your 79 620 came stock with a 5 speed. Where did that go? And if you don't have a 5 speed-what motor do you have? There are 2 main lengths between the L-series trannys. 26.5" and 31". Knowing what you really have will help produce positive answers for you. Pics would be great. Welcome to Ratsun! I'll get picks up later today. It has the stock l20b in it. Not sure why there's a 4 speed in it but I also have a second 4 speed. I thought 5 speed was just an option. I'm really new to datsun as you can tell. I just measured the tranny in my garage and ti's the 31" and I don't see a pan on it like I read about in another thread.... So maybe that was the original 5 speed? Quote Link to comment
flatcat19 Posted March 11, 2012 Report Share Posted March 11, 2012 31" 4 speed? Wonder if it is for a Z series? Take some pics. DatzenMike, and others are better with that stuff than I. If your truck has a 31" trans in it...take a 31" 5 speed from a Z car with an L, non-turbo or a 78-79 620. As far as I know...they all came equipped with 5 speeds stock. Quote Link to comment
datzenmike Posted March 11, 2012 Report Share Posted March 11, 2012 The 5 speed was only an option on the '77-'79 620 truck so it's normal to not have one. First I wouldn't worry about a 5 speed as the '79 also came with a much lower 4.11 rear end compared to all other years. A 5 speed should never be used for increasing the top speed that's not what it's for. Very likely it will go faster in 4th than 5th anyway, even more so with a 4.11 in it. The limiting factor in getting to top speed is wind resistance. Fourth gear will be revving higher and making more power to push through the air than in 5th gear. Fifth gear is intended for reducing RPMs slightly at cruise speeds to boost mileage. It shouldn't be used for accelerating for passing, climbing steep hills or towing a load. If looking for a 5 speed try to get one from a '79 as it is geared differently to compensate for the 4.11 differential. If you don't plan to ever carry loads in it then the '77-'78 truck and '77-'78 280z and first year '79 280zx 5 speed would be just fine. The '80-'83 280zx 5 speed is geared even lower and with 4.11s in the back may have difficulty taking off in first. Quote Link to comment
converted_to_datsun Posted March 12, 2012 Author Report Share Posted March 12, 2012 The 5 speed was only an option on the '77-'79 620 truck so it's normal to not have one. First I wouldn't worry about a 5 speed as the '79 also came with a much lower 4.11 rear end compared to all other years. A 5 speed should never be used for increasing the top speed that's not what it's for. Very likely it will go faster in 4th than 5th anyway, even more so with a 4.11 in it. The limiting factor in getting to top speed is wind resistance. Fourth gear will be revving higher and making more power to push through the air than in 5th gear. Fifth gear is intended for reducing RPMs slightly at cruise speeds to boost mileage. It shouldn't be used for accelerating for passing, climbing steep hills or towing a load. If looking for a 5 speed try to get one from a '79 as it is geared differently to compensate for the 4.11 differential. If you don't plan to ever carry loads in it then the '77-'78 truck and '77-'78 280z and first year '79 280zx 5 speed would be just fine. The '80-'83 280zx 5 speed is geared even lower and with 4.11s in the back may have difficulty taking off in first. Oh good stuff to know for sure. I do plan on hauling some loads because I work construction. I basically just want a better cruising gear for the highway cause it's now my daily driver for a 50 mile roud trip comute to work. I'll get some pics up but be warned it is in the middle of body work so it might not be so pretty. Quote Link to comment
datzenmike Posted March 12, 2012 Report Share Posted March 12, 2012 The '79 4 or 5 speed has a much lower 1st gear to make starts easier with the 4.11 gears. If it helps the first year 2wd 720 also uses this same lower geared 'wide ratio' 5 speed. Not saying the earlier 5 speeds won't work. It's just slightly more clutch slipping to get going if heavily loaded. Quote Link to comment
dscottdatsun Posted March 12, 2012 Report Share Posted March 12, 2012 I have to say that my 79 620 came with a 4 speed and 4.375 gears. It has what should be, by all appearances, the original rear end. I recently swapped the third member to an aluminium housed 3.88 set of gears from a 69 510 wagon. I love it for cruising on the freeway to work. I added a weber and lost the smog pump & etc. which made it even better. It will probably get even better yet with the soon to be rebuilt motor. Glad to see you have made switch, hope you enjoy your truck as much as I do. Scott Quote Link to comment
datzenmike Posted March 12, 2012 Report Share Posted March 12, 2012 The '79 automatic and cab chassis models came with 4.375 gears and after well over 30 years the whole axle could have been swapped. Possibly it was auto converted to standard. You must have swapped the truck side gears into the 510 diff to use the truck axles. Quote Link to comment
converted_to_datsun Posted March 12, 2012 Author Report Share Posted March 12, 2012 720 is helpful, a little easier to find in my area. Thanks for all the advice, I went from a 130mph+ car to a little 620 and even though it's not as fast it's soo much more fun to drive. working on pics now. Quote Link to comment
datzenmike Posted March 12, 2012 Report Share Posted March 12, 2012 I agree fast is cool. But drive a go-cart sometime. It's all relative. Quote Link to comment
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converted_to_datsun Posted March 12, 2012 Author Report Share Posted March 12, 2012 needles to say it needs body and paint... and floor repair badly. but it runs amazing, drives goos and I'm happy Quote Link to comment
converted_to_datsun Posted March 12, 2012 Author Report Share Posted March 12, 2012 I'm thinking electric blue for sure Quote Link to comment
]2eDeYe Posted March 12, 2012 Report Share Posted March 12, 2012 Hey, I'm brand new to datsun. I've always been a toyota guy but I just traded my 1988 celica gts for a 1979 620. I'm impressed with how much power it puts down for the year but top speed needs work. There's no tack and 4th seems to go forever, 40-70? Just an FYI, the L motors redline at 7000 rpm which is a good deal higher than the toyotas your used to. 90 mph is no problem with a 4-speed, just seems weird cause of the rpm difference. Get a tach, it will help get your mind around the issue. :) Quote Link to comment
datzenmike Posted March 12, 2012 Report Share Posted March 12, 2012 A stock tire for a 620 is 23.65" tall and at 6,000 RPMs you would be going almost 95 MPH. Naturally I doubt you have a stock tire but by tire diameter... 24"............. 106 MPH speedo will still read 95 MPH 25"............. 110 MPH 26"............. 114 MPH 27"............. 119 MPH The L20B might make enough hp at 6K to go over 90 MPH but not at a corrected 120 MPH. Quote Link to comment
Zfighter76 Posted March 13, 2012 Report Share Posted March 13, 2012 Using a gps speedo with the stock 4 speed and rear end on my truck but a z20 with sidedrafts I got to 87 mph @ ?? rpms. I had stock 14s with 195 60 14s. Not sure what the calculations say about that but I keep hearing that z heads flow to 4500 only so is that true? I know the gpa speedo is correct and I think I have 4.11 gears (the numbers stamped are very shallow and I can't completely make them out) Quote Link to comment
datzenmike Posted March 13, 2012 Report Share Posted March 13, 2012 I get 5,175 RPMs with 4.11s which is what is supposed to be in the '79s. Quote Link to comment
converted_to_datsun Posted March 14, 2012 Author Report Share Posted March 14, 2012 sounds like I need to put a tac in my truck. From what I hear those stock tacs are hard to find? I have an old sun tac that would fit but it kinda seems wrong to put that in there. Quote Link to comment
flatcat19 Posted March 14, 2012 Report Share Posted March 14, 2012 sounds like I need to put a tac in my truck. From what I hear those stock tacs are hard to find? I have an old sun tac that would fit but it kinda seems wrong to put that in there. Ain't nothing wrong with that. Besides-it's not like it's permanent. At least for informational purposes, it would be good as a temp. Quote Link to comment
converted_to_datsun Posted March 16, 2012 Author Report Share Posted March 16, 2012 Good point. As soon as i get payed I'm headed to the local parts yard where there is 6 620's so we'll see what i find haha. On my shopping list are the two front turn signals, drivers side fender, a tac, and whatever i see that i like Quote Link to comment
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