L18: 5-speed swap: 80-83 280Z Close Ratio 3.062 1st / 0.745 5th: Thoughts?

[DanielC]

This is the reason for the close ratio, with a big overdrive.  If you are driving the car in a "sporty" manner, you would never use fifth gear.  The big overdrive allows a lower (higher engine RPM) rear axle, but the big overdrive then is used on the freeway, to keep engine RPM in a more economical range.  

This philosophy does not work as well in a truck, because two less cylinders, and a less aerodynamic shape.

[datzenmike]

This (71B) is a six cylinder 150+ HP transmission used in a truck because of it's strength. Remember it takes 8 times the power to go only twice as fast. The 280zx has tons of torque at highway speeds, enough to easily drop 1,000 RPMs below forth gear and cruise. Your L18 will be working hard to hold 80MPH. I would hazard a guess that it can't maintain 80 MPH in 5th without being floored. You will always be able to go faster in 4th than in 5th.

 

The close ratio zx 5 speed has a 25.5% over drive. Poor choice for heavy truck/L18. Probably hold 50-60MPH Noticeable harder to get rolling. First three gears sluggish. RPM drop at 3K 3,000-2,235

 

The mid ratio 5 speed has about a 17% over drive. Might be OK but not up inclines or into the wind. Very slightly harder take off and first 3 gears have less performance. RPM drop at 3K.... 3,000=2,490

 

The close ratio  5 speed ('80 720 truck, identical to your 4 speed) has a 12% over drive. My choice for a small L18. No difference from your 4 speed but has slight RPM drop in 5th 3,000=2,640

[Cardinal Grammeter]

I think I could pull any 5th at 50-60 mph since I could make the Rte 30 summit in 4th at 50 mph albeit floored in a few spots.

 

But the more I think about it, I don't want to give up the 3.5 1st, so the close ratio ZX is pretty much off the table.  (However if I found one really cheap, I would get it.)

 

___________________________

 

I just did some research and it looks like there are 2 different 5-speeds for the L trucks:  EDIT:  only 2, not 3:

 

620 77-78

620 79 and 720 80

 

And the 720 L20B is THE WINNER:  Deep Low and High OD  (3.592 & 0.813)  EDIT:  This is WRONG, the .813 was incorrect on zhome.com - it should have been 0.882

 

In fact, THE LOSER is the 1979 with a Shallow Low and Not so High OD (3.321 & 0.864)   EDIT:  No clear LOSER now that the uber 0.813 is actually 0.882

 

It's almost like for the 720, they put together the best gear ratios for the small L20B.  But it also begs the question, what in the world were they thinking for the 1979 620???

 

Found these on the BeachGarage.com

 

Transmission Gear Ratios

Type 1st   2nd   3rd   4th   5th   Year Range

AT 3 2.458 1.458 1.000             1973-79

MT 4 3.657 2.177 1.419 1.000       1973

MT 4 3.592 2.246 1.415 1.000       1974-79

MT 5 3.321 2.077 1.308 1.000 0.864 1977-78

MT 5 3.592 2.246 1.415 1.000 0.882 1979

 

Rear Axle Gear Ratios

Ratio model     Year Range

4.875 AT & MT   1973

4.625 AT        1974

4.375 AT        1975-79

4.375 MT4       1974-78

4.375 MT5       1977-78

4.11  MT4 & MT5 1979

 

_______________________________________________________

Found these on zhome.com: (I'm thinking #1 is the 1980 L20B 5-speed???)

Special Note#1  There was a 5 speed 720 truck('79-'85)transmission that will bolt into an L-6 car, that also has "lower" gearing. However, there were two other sets of different gear ratios available, depending on the truck model:

   #1         #2        #31    3.592     3.321     3.5922    2.246     2.077     2.0573    1.415     1.308     1.3614    1.000     1.000     1.0005    0.882     0.833     0.813   EDIT NOT 0.813 as per datzenmike's correction

[DanielC]

I have done a five speed swap into a 521.  The 3.3xx first gear ratio was fine.  I used to pull a two horse trailer with it.  But I was running a 2000 roadster clutch pressure plate.

[flatcat19]

I think I could pull any 5th at 50-60 mph since I could make the Rte 30 summit in 4th at 50 mph albeit floored in a few spots.

 

But the more I think about it, I don't want to give up the 3.5 1st, so the close ratio ZX is pretty much off the table. (However if I found one really cheap, I would get it.)

 

___________________________

 

I just did some research and it looks like there are 3 different 5-speeds for the L trucks:

 

620 77-78

620 79

720 80

 

And the 720 L20B is THE WINNER: Deep Low and High OD (3.592 & 0.813)

 

In fact, THE LOSER is the 1979 with a Shallow Low and Not so High OD (3.321 & 0.864)

 

It's almost like for the 720, they put together the best gear ratios for the small L20B. But it also begs the question, what in the world were they thinking for the 1979 620???

 

Found these on the BeachGarage.com

 

Transmission Gear Ratios

Type 1st 2nd 3rd 4th 5th Year Range

AT 3 2.458 1.458 1.000 1973-79

MT 4 3.657 2.177 1.419 1.000 1973

MT 4 3.592 2.246 1.415 1.000 1974-79

MT 5 3.321 2.077 1.308 1.000 0.864 1977-78

MT 5 3.592 2.246 1.415 1.000 0.882 1979

 

Rear Axle Gear Ratios

Ratio model Year Range

4.875 AT & MT 1973

4.625 AT 1974

4.375 AT 1975-79

4.375 MT4 1974-78

4.375 MT5 1977-78

4.11 MT4 & MT5 1979

 

_______________________________________________________

Found these on zhome.com: (I'm thinking #1 is the 1980 L20B 5-speed???)

Special Note#1 There was a 5 speed 720 truck('79-'85)transmission that will bolt into an L-6 car, that also has "lower" gearing. However, there were two other sets of different gear ratios available, depending on the truck model:

#1 #2 #3

 

1 3.592 3.321 3.592

2 2.246 2.077 2.057

3 1.415 1.308 1.361

4 1.000 1.000 1.000

5 0.813 0.833 0.813

 

Take into consideration that the rear end gear for these trucks got change multiple times. Three different transmissions, 5 different rear end gears.

 

 

Each gear set, all of a sudden, changes how the transmissions acts.

[datzenmike]

I think I could pull any 5th at 50-60 mph since I could make the Rte 30 summit in 4th at 50 mph albeit floored in a few spots.

 

But the more I think about it, I don't want to give up the 3.5 1st, so the close ratio ZX is pretty much off the table.  (However if I found one really cheap, I would get it.)

 

___________________________

 

I just did some research and it looks like there are 3 different 5-speeds for the L trucks:

 

620 77-78

620 79

720 80

 

And the 720 L20B is THE WINNER:  Deep Low and High OD  (3.592 & 0.813)

 

In fact, THE LOSER is the 1979 with a Shallow Low and Not so High OD (3.321 & 0.864)

 

It's almost like for the 720, they put together the best gear ratios for the small L20B.  But it also begs the question, what in the world were they thinking for the 1979 620???

 

Found these on the BeachGarage.com

 

Transmission Gear Ratios

Type 1st   2nd   3rd   4th   5th   Year Range

AT 3 2.458 1.458 1.000             1973-79

MT 4 3.657 2.177 1.419 1.000       1973

MT 4 3.592 2.246 1.415 1.000       1974-79

MT 5 3.321 2.077 1.308 1.000 0.864 1977-78

MT 5 3.592 2.246 1.415 1.000 0.882 1979

 

Rear Axle Gear Ratios

Ratio model     Year Range

4.875 AT & MT   1973

4.625 AT        1974

4.375 AT        1975-79

4.375 MT4       1974-78

4.375 MT5       1977-78

4.11  MT4 & MT5 1979

 

_______________________________________________________

 

Found these on zhome.com: (I'm thinking #1 is the 1980 L20B 5-speed???)

Special Note#1  There was a 5 speed 720 truck('79-'85)transmission that will bolt into an L-6 car, that also has "lower" gearing. However, there were two other sets of different gear ratios available, depending on the truck model:

 

#1 #2 #3

 

1 3.592 3.321 3.592

2 2.246 2.077 2.057

3 1.415 1.308 1.361

4 1.000 1.000 1.000

5 0.813 0.833 0.813

Better check the facts in your own post about the '79 5 speed and the gear ratios listed for the '80 5 speed are for the 4x4 truck and as the speedometer is driven by the transfer case and there is no speedometer in them, are not much good for swaps. The '79 620 and the '80 2wd 5 speeds are listed below...

 

 

There were two 5 speed ratios for the 620 and the '80 720.

 

'77-'78 mid ratio with 3.321 first and 0.864 OD 13.6%

'79 620 and '80 720 wide ratio* with 3.592 first and 0.882 OD 11.8%

 

 

* The wide ratio was necessary because these years didn't use a 4.375 differential but a 4.11 so take offs would be easier. 

The difference in OD gearing is barely noticeable, less than 2% different. At 3,000 RPM the difference is 60 RPM. .

[Ranman72]

much wisdom here from mike the guy who loves trannys 

oops i mean mike the tranny guy who loves datsuns 

[Cardinal Grammeter]

Yes, I saw that 0.813  that you marked red - that was copied from zhome.com

 

I also found a massive table of what seemed to be all Datsun transmissions and it listed same ratios for all 620's and also some or all 720's too.  That made no sense.

 

I'm going to edit the red, it should be 0.882, right?  It would be nice to have all the ratios in one place.

_____________________________

 

EDIT:

 

NOTE:  The change in the 5-speed ratios definitely coincide with the shallower 4.11 rear.  However, it doesn't explain that the 4-speed has the deep 1st all the way thru 1979 - whereas the 77-78 5-speed had a higher 1st. 

 

But hen in 79, the went to 4.11, kept the 4-spd low and lowered the 5-sped low to match.

 

Sounds like some indifference between the 2 lows with the L20B. 

[datzenmike]

Well the early 71B 4 speed was behind the small L18 so it was to give it a worst case scenario advantage of taking off on a hill fully loaded. Later 620s also had a camper option and then around '78 there was a Cab/Chassis option for motor homes. Both were expecting heavy weight and use and all were 4 speeds only.  Only the standard '79 got the 4.11 the automatic remained 4.375

[Cardinal Grammeter]

The more I pay attention to driving mine around town, there are nasty short grades at stop signs and lights - way above 10% grades.   And I like my low just the way it is at 3.5 in the 4-spd.

 

I am facing a full 1/2 ton load of pavers and I definitely don't want any part of a higher low ratio.

 

And yes, buzzing around on the interstate with the 4-spd is not really an issue. 

 

So is it worth the expense to buy the 5-spd when I have to replace the clutch?

 

So now I'm on the fence whether to do the wide ratio 5-spd upgrade.  A cheap deal on a wide ratio looks like a requirement now.

 

Oh well... fat chance on the East Coast.

[datzenmike]

 The '79 620 5 speed has 3.592 first gear and a respectable 12% over drive. You won't notice anything if you swap it in until you are out of town on the highway.

[datsunaholic]

I know I'm late to the post, but I have experience here.  My prior '76 King Cab had an L18 in it and I stuck an '83 ZX trans in it when the clutch went out.

 

It was...  slow pulling away from traffic lights, but not unreasonable in my mind.  Was a little iffy when I had a full bed of engines (I think I had 3 Z24s and a L18 in there, all the way from Portland back to Tacoma).

 

But it was really, REALLY good on the freeway.  As long as I didn't let it drop below 60 in 5th  Only on major hills did I have to drop back to 4th, and then it was no different than 4th with the original 4-speed.  The gas mileage was phenomenal though with a light foot on cross-state trips.  I miss that setup, but I definitely prefer the power of the L20B I have now.  Still have the Engine/Trans combo but haven't had anything to put it in, though the L20B in my current '76 KC is getting REALLY tired.  Engine has about 350,000 miles on a REBUILD, how many before that IDK (truck has 450,000 on it, but engine isn't original)

[Cardinal Grammeter]

datsunaholic,

 

what mpg were you getting on the Xcountry?

[datsunaholic]

Around 30 MPG.  Got as high as 32 headed westbound from Spokane to Seattle (not as big of a climb over Snoqualmie Pass that direction, its more gradual).  Best I've gotten with an L20B in a truck was 25, but have to keep it under 65 to do so.  The L18+ZX 5-speed was doing 75 most of the time.  That's with a Weber 32/36 (same carb on both trucks, BTW).

 

 

On the flip side my Mom's bone-stock 73 rarely got 20.  There were years I saw only 18 commuting from Seattle to Bremerton (60 miles, all freeway).  It's those damn 4.88 rear gears.  My '78 510 Hatch w) dogleg got 35 doing the same route.

[Cardinal Grammeter]

Is there any way to identify the 79 620 or the 80 720 3.592 low 5-spd?

 

I had to haul over 900# of Studebaker V8 blocks on back roads and interstate (Pittsburgh to Cheat Lake WV) and had no issues with the 4-spd low (74 L18).   Since I'll rarely haul 1/2 ton, it probably doesn't matter which one I get although I would prefer the 3.592.

 

NOTE:  I'm running 205/75r14's which put my speedometer low by 10% (indicated 50 is actual 55).  Again the previous argument if I get wide tires and normal height, the 3.592 would not be necessary.

 

If anything, the brakes were dodgy.

[flatcat19]

The differences are all so slight it won't matter much at all.

 

And given your location...do you have any options to pick from?

 

Get a 5 speed. Install it. Make another thread just for that.

[flatcat19]

Then make another thread about what kind of fluid to use in your new 5 speed.

 

 

(The answer is StaLube GL-4. Save the bandwidth. Jeff will thank you for that.)

[datzenmike]

From the outside, no. You can identify an '80 from a '79 transmission but not the internals.

 

Place the transmission in first gear and mark the input and output shaft. Turn the input 20 times while counting the output turns.

 

Wide ratio box ..... 3.592..... 5.5 output turns

Mid ratio box .........3.321..... 6.0 turns

Close ratio box..... 3.062..... 6.5 turns

[Cardinal Grammeter]

OT:  Trans lube:  Talked to racer who used 0w20 Mobile 1 in TopLoaders.  On the street too with no wear issues.  However, the light weigh makes them shift noticeably better.  I have on in my Lark and am aging to try it.  Mañana...

[datzenmike]

Racing and street driving is very different. Racing means doing what ever is needed to get you to the end first. The car doesn't matter, parts can be replaced or rebuilt every weekend. That 'racer' probably changed the oil after every race. Here's another thing, races don't go very far. You need protection that will last 100,000+ miles.

 

Nissan calls for GL-4 80W90 gear oil which is about 30W engine oil I think. I wouldn't run anything thinner but synthetic. Try G.M. Delco Synchromesh Transmission Oil. GM dealers have it but Lordco is cheaper. It's a synthetic and quite thin but it will protect your transmission. It's also copper allow safe for your synchros.

[G-Duax]

I would like to hear some results from using the G.M. Delco Synchromesh Transmission Oil.

 

Went through several different gear lubes before going back to a plain old petrolium based StaLube GL-4.

 

The GL-4 stuff is getting hard to find.

20 & 30 years ago (the last times I rebuilt Nissan trans) everyone had the stuff, Castrol, Valvoline, etc., but these days, just about everyone's oil says GL-5, or GL-4 & GL-5. Only the StaLube said just GL-4.

Would like to have a back up source.

[datzenmike]

First it IS a synthetic so it may seep through old oil seals. Also GL-4 compliant. I just replaced the output seal and it's been good. Had it through the 2K trip to Canby last year and (that was it for mileage for the year) checked it this spring and was fine. Went 3K this year and have driven it more. This is not a DD so.... If all it costs is a $5 rear seal every year i'st more than worth it.

 

Shifting is the greatest improvement, down shifting in particular. I never used to slip into first on in town corners, unless at slowest point and a double clutch. Now you can 'shove it in' before even starting to turn the wheel. It would firmly resist downshifting before, and when pushed harder word grind slightly on engagement. Second was the same on the highway. I even started down shifting more now.... because I can.

 

Up shifting is now very 'clicky'. By this I mean the shifter loosely clicks positively into every gear.... very reassuring. Before it was mushy soft and slower. Third and fifth were very hard to shift fast.

 

With the 80w90 the first half dozen shifts or mile or so were very firm, and second would often grind ever so slightly when the transmission was cold. I would rev higher in first and while using the clutch, allow it to rev match for second to avoid this. Even worse as the weather got cooler in October. That is completely gone now.

 

Tried to get it at the GM dealer, but all he said is what's this for? I said it doesn't matter and gave him the proper part number... but he insisted this stuff was a special lubricant and shouldn't be.... blah blah blah. He insisted on looking it up so I told him it was for a '76 Datsun 710. He wasn't impressed and you could see he thought I was the one making him look like a dick. We can order it in he said. I went literally across the street to Lordco and got it for $2 cheaper a liter. It isn't cheap at $17 CDN a liter, but worth twice that in satisfaction. 

 

Getting cooled but no change in shifting.

[G-Duax]

Cool !

I'll have to give it a try :)

[Cardinal Grammeter]

I have some of he Pennzoil Synchromesh that is supposed to match ONE of the GM part numbers... LOTS of discussion about this. 

 

Probably should stop any further discussion since definitely OT and there are better threads for continued discussion

 

_______________________

 

AMAZING DEVELOPMENT HERE IN THE RUST BELT:  In the midst of the Rust Belt, a local guy has a Datsun 5-spd, but doesn't know what it came out of. 

 

So I need to know howl to identify the L-engine 5-spds (I guess his includes the Zcars too.

 

Not knowing what information is relevant, I told him for starters to determine:  (but I still need into to identify)

• Length of case from engine mounting surface to back of tail housing
• # Splines on input and output shaft
• # Bolts attaching to block

This could be an attractive price because it's a bunch of unidentified parts.  Guy has some mirrors too  (great lusting...)

[flatcat19]

Just get a pic and paste it here.

 

Pics of speedo hole and bell housing important.