allen dodson Posted May 6, 2008 Report Share Posted May 6, 2008 Is there any way to change the differential gears in these pickups? I know i need to get a five speed but still there has to be a way to lower the gear ratios in the rearend? Help! 1 Quote Link to comment
datzenmike Posted May 6, 2008 Report Share Posted May 6, 2008 You mean lower the ratio, like from 4.375 to 4.11 or 3.889? I think the rear end from most 620 and 720 trucks will fit your H-190. But not the Z24 4X4 rear. Basically unbolt the four 17mm nuts behind the rear backing plate and slide both axles out. Disconnect the drive shaft. Unbolt the 12 fasteners around the differential and lift out. You will have to disconnect the brake lines unless you can pull the axles out 3"-4" to disengage the side gear splines. One of the axles will have shims... don't loose them. Support the axles so they dont damage the grease seals in the axle tube if you don't take them out. The '79 standard 620 had 4.11 as did the '80-'86 2wd 720 automatic. '81-'86 2wd 720 standards had 3.875 and if you can find one, and if the tiny L will turn it, the '84-'86 720 Mileage Option w/ Z20 motor had a 3.364 in it. 1 Quote Link to comment
qship510 Posted May 7, 2008 Report Share Posted May 7, 2008 ALSO, 2000 Roadsters had 3.70's, and 510 Wagons and 1600 Roadsters had 3.90's, all you have to do is change the side gears in the pumpkin. Or install a 521 Detroit Locker in a wagon diff..... 1 Quote Link to comment
superc_1 Posted May 7, 2008 Report Share Posted May 7, 2008 Datzenmike Will a rear end out of a 720 Fit under a '77 620 or is the widths different? Whats the gear ratio on the 620? Mine has an automatic trans but it really wines at 75 mph? 1 Quote Link to comment
datzenmike Posted May 7, 2008 Report Share Posted May 7, 2008 '77 auto is the same as standard ... 4.375 I believe. If the 720 has good brakes (no leaky cylinders) and wheel bearings, I guess you could just swap the whole thing. 2wd only though. Only the carrier in the middle really needs to be changed to switch gears. 620/720 are same width I think but will check tonight. 1 Quote Link to comment
fryanbacon Posted May 7, 2008 Report Share Posted May 7, 2008 The '79 standard 620 had 4.11 as did the '80-'86 2wd 720 automatic. '81-'86 2wd 720 standards had 3.875 and if you can find one, and if the tiny L will turn it, the '84-'86 720 Mileage Option w/ Z20 motor had a 3.364 in it. so you don't think the stock l16 is powerful enough to push the 720 diff? 1 Quote Link to comment
datzenmike Posted May 7, 2008 Report Share Posted May 7, 2008 Oh it will turn it, but if carrying a load, climbing hills and driving into the wind you may be constantly down shifting. I'm just advising caution as once in, and you find you don't like the performance, well you are sort of stuck with it. I think a 4.11 would be a good compromise for a 2wd light truck with L16. 1 Quote Link to comment
fryanbacon Posted May 7, 2008 Report Share Posted May 7, 2008 haha. well I guess I just need a 5 speed. with my built L18 on my stock 4, my 521 is getting me 18mpg at best.:mad: 1 Quote Link to comment
banzai510(hainz) Posted May 7, 2008 Report Share Posted May 7, 2008 the 510 went ok with a stock L16 and 3.9 gears 1 Quote Link to comment
datzenmike Posted May 8, 2008 Report Share Posted May 8, 2008 haha.well I guess I just need a 5 speed. with my built L18 on my stock 4, my 521 is getting me 18mpg at best.:mad: I would expect WAY better mileage than that. My 3,600 lb 620 gets 20-25 MPG on the highway. You are almost 1,000 lbs lighter than me. 1 Quote Link to comment
datsunfish Posted May 8, 2008 Report Share Posted May 8, 2008 4.11 is great with a l16.Mine went out in my 521 and I ended up with a 4.88.It really kinda sucks.I dont mind the high rpms on the highway since it is built up a bit.I can always take right off at any speed.I hate that I have to shift so soon at such low actual speed when the motor is screaming. I have many plans for the future of my dattos.I would like to do the LZ 24 with a lower than 4.11 rear end and a long 4 speed in the 521 but for now this works with the l16. 1 Quote Link to comment
datsunaholic Posted May 8, 2008 Report Share Posted May 8, 2008 the 510 went ok with a stock L16 and 3.9 gears The 510 was also pushing much smaller tires. Makes a big difference. 1 Quote Link to comment
J.C_620 Posted May 8, 2008 Report Share Posted May 8, 2008 how do you find out what rear gear you have? i have changed the whole rearend and have no clue what year it came out of but i do know it was a 620 1 Quote Link to comment
Bleach Posted May 8, 2008 Report Share Posted May 8, 2008 i have changed the whole rearend and have no clue what year it came out of that's not good :mellow: 1 Quote Link to comment
socaldatsun Posted April 10, 2012 Report Share Posted April 10, 2012 Im kinda confused on these rear dif. The lower the number the better? like a 3.90 better then the 4.11? I have a L20 that was built up a little with a dog leg but noticed that i'm running out of 5th on the freeway. I know that the dog leg isnt exactly the best trans but what can I do to get the most out of it? 1 Quote Link to comment
Turd Ferguson Posted June 8, 2012 Report Share Posted June 8, 2012 ive got 3.875's in mine. original tired l16, with a 4 speed. on the freeway it scooted right along, honestly i have no clue how fast though lol. the speedo is off and not sure how far, but the other trucks in my group didnt catch up to me and they said they had cruise set at 70 to 75 so i was happy with that. i drove a load of yard debris( 1st load 420 pounds 2nd load i forgot to look but it was moar) from river road, took theisen, to mcfarlens bark had enough power to make it over all of those hills. i did run into an issue on concord though. they put in a speed bump and its not painted yet, so everyone i know that drives the road has shat their pants when all of a sudden they hit a big bump. none however have flown off of it in a 70 521 with 500 pounds of yard debris in the back. i was going 40 and its a big ol speed bump. a group of like 10 people saw a datsun fly. it blew out my tire from impact and destroyed my passenger side shock. im taking this up with the county. schwab was cool and swapped my tire for free, i showed up 5 min till they closed too. 2 Quote Link to comment
Jayden71 Posted July 8, 2012 Report Share Posted July 8, 2012 I'm thinkin of 411s in my truck with dogleg tranny. I think it will do fine 1 Quote Link to comment
oldskoolvws Posted July 12, 2012 Report Share Posted July 12, 2012 What were the 521 options? 1 Quote Link to comment
wayno Posted July 12, 2012 Report Share Posted July 12, 2012 What were the 521 options? Any rearend pumpkin from a 520, 521, 620, and early 720 will interchange amongst each other, they all have the same axle size/ tooth count. 1 Quote Link to comment
ggzilla Posted July 12, 2012 Report Share Posted July 12, 2012 The lower the number the better? No. Yes. Lower number/higher gear = more relaxed RPMs at 60 mph (less noise), better fuel economy. But accelerates slower Higher number/lower gear=Accelerates faster, takes more RPM to do 60 mph, less fuel economy The dogleg is a great transmission for an L16. The main complaints are it wearing out behind larger engine/carrying heavy loads. Quote Link to comment
ggzilla Posted July 12, 2012 Report Share Posted July 12, 2012 i'm running out of 5th on the freewayWhat do you mean by that? Yes, you will be in 5th on the freeway. That's good. Quote Link to comment
datzenmike Posted July 12, 2012 Report Share Posted July 12, 2012 The L16/18 can rev and rev and live to talk about it. There's virtually no upper limit to how high you can rev them. If you are in 5th there's no way your running out of revs. 5th is a 14.6% decrease in revs from 4th gear. Maybe you mean it simply won't go any faster? This is believable as it takes 4 times the power to double your speed. So going faster eats power very fast. It's possible too that you are making less power in 5th because the revs drop the motor from it's peak torque range. Quote Link to comment
Idaho Hillbilly Posted July 12, 2012 Report Share Posted July 12, 2012 how do you find out what rear gear you have? i have changed the whole rearend and have no clue what year it came out of but i do know it was a 620 The only way to REALLY know is to pull the gear set out. You count the # of teeth on the ring gear and then the " of teeth on the pinion gear. Simple math... ring/pinion=gear ratio Quote Link to comment
ggzilla Posted July 12, 2012 Report Share Posted July 12, 2012 You can also *really* find out by careful counting, say 10 turns of input with one wheel jacked and count the output. But I can never remember if you half the count or what. Datsun gears came in certain ratios, so it can be definitive, depending on how carefully you count. The most definitive way is to not count. Just read the numbers stamped on the side of the ring gear. It will be like '37:10' or similar. Divide to find gear ratio. Quote Link to comment
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