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I am wanting to convert my 1970 240z from a 4 speed to a 5 speed and understand that a '81-'83 280zx 5 speed is the way to go. Can anyone tell how I can identify the '81-'83 280zx 5 speed (Casting numbers or markings)? I do have a line on a '75 5 speed but understand that is not as desirable?
 

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I am wanting to convert my 1970 240z from a 4 speed to a 5 speed and understand that a '81-'83 280zx 5 speed is the way to go. Can anyone tell how I can identify the '81-'83 280zx 5 speed (Casting numbers or markings)? I do have a line on a '75 5 speed but understand that is not as desirable?
The gear ratios are SLIGHTLY different between the Z and ZX transmissions but I really wouldn't fret over it. If you have a 5-speed ready to go, pop it in and you'll be more than happy with it.
 

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Well in the US we didn't get a 5 speed til 77. I have a 78 in my car its more a 4 speed w/overdrive. The key with that ZX 5 speed is it comes with a 3.9 differential. US 240s came with a 3.54 if I recall correctly. So keep that in mind as well as trans tunnel clearance, might need a mod to get to 5th.
 

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Simplest is to use the 77-78 "5 speed". Outside dimensions are exactly the same as the one you have. As mentioned, Datsun just added a 5th overdrive gear inside on an existing shaft in the 77-78 units. So technically it's not a 'true' 5 speed, but they work fine and will give you a little more top end - or slight MPG increase, depending on how you drive.
 

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the later 5 speeds have a .75 OD, if you have a 3.54 diff then you are turning about 3k at 80mph. Its a nice setup for highway speeds but the OD cant be engaged at anything under 65 on flat roads least you lug the engine.
 

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the later 5 speeds have a .75 OD, if you have a 3.54 diff then you are turning about 3k at 80mph. Its a nice setup for highway speeds but the OD cant be engaged at anything under 65 on flat roads least you lug the engine.
I put the car in 5th below 65 daily but I don't get any shakes/signs the engine is having difficulty. Is lugging the engine something that can be not noticeable?
 

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I put the car in 5th below 65 daily but I don't get any shakes/signs the engine is having difficulty. Is lugging the engine something that can be not noticeable?
If your setup has you going under 2.5k in 5th that is lugging the engine, read that somewhere in one of the owners manuals IIRC.
its not noticeable other than the sluggish nature of accelerating. Generally speaking I don't like the engine to turn less than a minimum of 2.5k under pretty much any driving condition.
 

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If your setup has you going under 2.5k in 5th that is lugging the engine, read that somewhere in one of the owners manuals IIRC.
its not noticeable other than the sluggish nature of accelerating. Generally speaking I don't like the engine to turn less than a minimum of 2.5k under pretty much any driving condition.
Ah, good to know. I'll change my driving practices then, thanks Dave.
 

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actually it was don't drive under 2.0k in any of the 1st - 4th, and 2.5k for 5th. I just cant remember where I read that, but I do know on my 3.54 with a .75 OD and stock wheels that its pretty sluggish below 65 mph. I think my 5speed trans came from a ZX with a 3.7 diff but I never bothered to swap the rear ends. I just stay out of 5th unless I am on a free way going 70. You should just check your RPM, you may have a different setup that lets you run lower than 65.
 

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I have a closed ratio 5 speed rebuilt for 850. never ran went to a 350z 6 speed
you have a 350z transmission in your ZX? what was that swap like? difficult?

or do you mean you went to driving a 350z?

Bon
 

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I am wanting to convert my 1970 240z from a 4 speed to a 5 speed and understand that a '81-'83 280zx 5 speed is the way to go. Can anyone tell how I can identify the '81-'83 280zx 5 speed (Casting numbers or markings)? I do have a line on a '75 5 speed but understand that is not as desirable?
i think the best thing you can do is go find an 82-83 ZX in a salvage yard and pull a transmission from one, if you can source one. that way you know for sure.
also, I do beleive there is a way to itentify one if on the side... the close ratio trans should have one little "ear" sticking out to the side (if I remember correctly) on the tail end of the unit. and the wide-spread trans has two "ears"

unless you are going to swap the diffs, its probably best to stick with an early 5 spd. i got one for my 76 from zcarsource of az for a grand rebuilt and shipped. worth the price in my opinion.

Bon
 

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It was a straight swap in my '72. Evidently the speedometer pinion gear (located where the speedometer connects to the transmission) needs to be changed. I didn't know about that and my speedometer didn't read correctly afterwards, which probably why I got a ticket for going 80 mph when I thought I was only doing 70.
 

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I am wanting to convert my 1970 240z from a 4 speed to a 5 speed and understand that a '81-'83 280zx 5 speed is the way to go. Can anyone tell how I can identify the '81-'83 280zx 5 speed (Casting numbers or markings)? I do have a line on a '75 5 speed but understand that is not as desirable?
Lots of items to clarify on this thread so here goes. All z's from 70-74 came with 3.36:1 gear ratio in the diff. 75-78 came with 3.54. The early 5 spd. trans was used from 77-80 and the easiest way to tell it is the tail shaft housing is a course matte surface whereas the newer style 81-83 uses a smooth surface on the tail shaft housing. The newer style also has an oval shaped plate that is approximately 1" x 2" on the left side of the tail shaft housing and it has a pair of 10mm headed bolts holding the plate in place. That is the reverse lockout plate and didn't come on the earlier transmissions. The newer one uses a taller fifth gear than the early transmission and for most z's both models will work fine. Little known fact, the 83 transmission 5th gear is a little taller than the 81-82 trans and therefore uses different 5th gears. For cars with the 3.36 gearing, going to a 5 speed is going to mean that you're rarely going to be able to use 5th unless you're doing over 75mph. On the 3.54 gearing cars that number is 65 mph. If you're installing a 5 speed you should have at least a 3.54 gear ratio or higher number. If you don't then you should change out the differential to a higher number.
Dave, the minimum rpm on 2nd thru 4th gear is 2K whereas the minimum rpm in 5th is 2500 rpm. Anything below that is lugging the engine. It also puts undo stress on the transmission. I've had to replace gears in the trans before from people that lug the engine so it doesn't just damage the engine. The only place I know of on the internet that gives out that info is on my website at www.zspecialties.com or else on a post that I've done on this forum in the past. I wrote it up and put it on my website about 15 years ago.
To answer another comment, lugging an engine in these cars isn't always noticeable. Lugging the engine on these cars you'll only get the chugging feeling at extra low rpms. These figures are for level ground, if you come to an incline then you should probably add about 300 rpm to the above figures. The power band doesn't start usually until 3K rpm on most z's.
Ken, be advised that to install a newer style 4 speed or both models of 5 speeds you'll have to notch the console for shifter clearance, install a 72-78 style shift boot, with a 72-78 shift boot retaining ring. I have the boots and rings in stock, and I also sell a real leather shift boot that fits nicely. The 70-71 shift boot is square whereas the 72-78 shift boot is rectangular, so the newer style nagahyde shift boots won't work on the 70-71 cars. I also sell a custom shortened shift tower on an exchange basis. I take 2" out of the shift tower so it gives you a faster throw without taking more noticeable force and it still fits the car and shift boot. The weld is beneath the upper shift boot so you don't see it. It's still a linear shift unlike the more expensive short throw shifters that are on the market.
Z man of Washington
360-668-2979
[email protected]
 

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Lots of items to clarify on this thread so here goes. All z's from 70-74 came with 3.36:1 gear ratio in the diff. 75-78 came with 3.54. The early 5 spd. trans was used from 77-80 and the easiest way to tell it is the tail shaft housing is a course matte surface whereas the newer style 81-83 uses a smooth surface on the tail shaft housing. The newer style also has an oval shaped plate that is approximately 1" x 2" on the left side of the tail shaft housing and it has a pair of 10mm headed bolts holding the plate in place. That is the reverse lockout plate and didn't come on the earlier transmissions. The newer one uses a taller fifth gear than the early transmission and for most z's both models will work fine. Little known fact, the 83 transmission 5th gear is a little taller than the 81-82 trans and therefore uses different 5th gears. For cars with the 3.36 gearing, going to a 5 speed is going to mean that you're rarely going to be able to use 5th unless you're doing over 75mph. On the 3.54 gearing cars that number is 65 mph. If you're installing a 5 speed you should have at least a 3.54 gear ratio or higher number. If you don't then you should change out the differential to a higher number.
Dave, the minimum rpm on 2nd thru 4th gear is 2K whereas the minimum rpm in 5th is 2500 rpm. Anything below that is lugging the engine. It also puts undo stress on the transmission. I've had to replace gears in the trans before from people that lug the engine so it doesn't just damage the engine. The only place I know of on the internet that gives out that info is on my website at www.zspecialties.com or else on a post that I've done on this forum in the past. I wrote it up and put it on my website about 15 years ago.
To answer another comment, lugging an engine in these cars isn't always noticeable. Lugging the engine on these cars you'll only get the chugging feeling at extra low rpms. These figures are for level ground, if you come to an incline then you should probably add about 300 rpm to the above figures. The power band doesn't start usually until 3K rpm on most z's.
Ken, be advised that to install a newer style 4 speed or both models of 5 speeds you'll have to notch the console for shifter clearance, install a 72-78 style shift boot, with a 72-78 shift boot retaining ring. I have the boots and rings in stock, and I also sell a real leather shift boot that fits nicely. The 70-71 shift boot is square whereas the 72-78 shift boot is rectangular, so the newer style nagahyde shift boots won't work on the 70-71 cars. I also sell a custom shortened shift tower on an exchange basis. I take 2" out of the shift tower so it gives you a faster throw without taking more noticeable force and it still fits the car and shift boot. The weld is beneath the upper shift boot so you don't see it. It's still a linear shift unlike the more expensive short throw shifters that are on the market.
Z man of Washington
360-668-2979
[email protected]
Zman, this is really great stuff. a wealth of information. i didn't know the 83 had an even taller 5th than an 82, which brings me to this question: what does "taller 5th" actually mean? i've heard that before but couldn't really grasp the meaning. can you clarify that? trans in my 83 feels much smoother than the one that was in my '80.

for me, the late model trans and the 3.90 rear is a great combo on the 83 car. but i can see now why the early diff on the the 240z was best mated to that early 4 spd from factory. makes sense.

Bon
 

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Mr. zman..:

Interesting concept of "lugging". Of course, intrepretation depends a lot on how heavy a foot is plying the go pedal, but my experience is that most any engine (in good fettle) is happy enough at low revs, as long as one doesn't pull any bull moves, acceleration-wise.

And as physics would have it, a straight six is particularly cooperative in this regard. It will happily putter about town at 1.2 to 1.5K revs and the car is slippery enough to roll at 2K at speed on the open road without breaking a sweat.

No engine "loves to rev", despite the claims of would-be Walter Mittys or mechanical masochists. Rather, I would opine that truth lies in "low revs, long life" when executed with artfully light feet and little desire to hurry up to the next red light. And as a bonus, such techniques can make clutches immortal.

Just $.02 from the peanut gallery.
 

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Dave, the minimum rpm on 2nd thru 4th gear is 2K whereas the minimum rpm in 5th is 2500 rpm. Anything below that is lugging the engine. It also puts undo stress on the transmission. I've had to replace gears in the trans before from people that lug the engine so it doesn't just damage the engine. The only place I know of on the internet that gives out that info is on my website at www.zspecialties.com or else on a post that I've done on this forum in the past. I wrote it up and put it on my website about 15 years ago.


360-668-2979
[email protected]
Yes this is where I read about the shifting, thanks for the clarification. I could not recall where but I knew I had read it somewhere, thanks again Zman!
 

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If you're installing a 5 speed you should have at least a 3.54 gear ratio or higher number. If you don't then you should change out the differential to a higher number.

Is there any way to obtain a different ratio without having to swap the entire differential? Can the ring and pinion be exchanged instead?
.
 

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Zman, this is really great stuff. a wealth of information. i didn't know the 83 had an even taller 5th than an 82, which brings me to this question: what does "taller 5th" actually mean? i've heard that before but couldn't really grasp the meaning. can you clarify that? trans in my 83 feels much smoother than the one that was in my '80.

for me, the late model trans and the 3.90 rear is a great combo on the 83 car. but i can see now why the early diff on the the 240z was best mated to that early 4 spd from factory. makes sense.

Bon
Bon, a taller gear means the same as a gear ratio having longer legs. This means that they operate at a lower engine rpm at the same road speed. For instance a 3.36 gear ratio in the diff is a taller set than a 3.70. It's a little confusing because it's backwards compared to the numbers. Took me many years to remember it correctly. Someone with longer legs can usually cover ground faster than someone with shorter legs. Think of a German Shepard vs. a Chihuahua.
Acemon, ring and pinions aren't available for these cars anymore so you'd have to change out the entire diff to get a different ratio. Besides changing the R&P is more work than just swapping out the diff. If you have to clean and paint the outside, that's still less work than a rebuild and replacing the R&P. ZMOW
 

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Mr. zman..:

Interesting concept of "lugging". Of course, intrepretation depends a lot on how heavy a foot is plying the go pedal, but my experience is that most any engine (in good fettle) is happy enough at low revs, as long as one doesn't pull any bull moves, acceleration-wise.

And as physics would have it, a straight six is particularly cooperative in this regard. It will happily putter about town at 1.2 to 1.5K revs and the car is slippery enough to roll at 2K at speed on the open road without breaking a sweat.

No engine "loves to rev", despite the claims of would-be Walter Mittys or mechanical masochists. Rather, I would opine that truth lies in "low revs, long life" when executed with artfully light feet and little desire to hurry up to the next red light. And as a bonus, such techniques can make clutches immortal.

Just $.02 from the peanut gallery.
The L engine by Datsun is one of the most durable engines ever built provided: #1 It does not run at too hot or too cold of a temp, #2 Good oil with extra lubrication added to it if you're using most oils that are being sold nowadays, #3 If the engine is not driven too easy, especially with manual transmissions. All these things considered, the average life expectancy on the L6 is 400K to 500K miles. I've seen them do over 600K. I've taken engines apart with 400K and you can usually still see the factory hone marks in the cylinders and they have almost zero bore taper. I've also rebuilt these engines at 175K miles that I had to bore out as much as 1mm because of cylinder taper. After talking to the customer I usually find out that they've been driving the engine too easy because they had the same idea in their head that you have and they've been lugging the engine. The power band runs from 3K to 5500 rpm on a stock engine. Add a hi perf cam to it and you can run it up to 6500 rpm without any other changes. It won't shorten engine life by driving it harder (within reason) but I guarantee that you can shorten the L engine life by driving it too easy. I've seen it happen too many times in my 4+ decades with these cars to come to any other conclusion. I'm not saying that you have to floor it every time you drive it through the gears, but you need to operate at higher rpm's than most other engines. I never shift before 3500 rpm. I try to drive like the engine and car needs to be driven and that way it will definitely last me longer. The rpm's you're talking about should only be used if you're pressing lightly on the gas pedal and you're going downhill. If you think that you're saving the engine by driving that way then perhaps you should think about getting a vehicle with a slant 6 by Mopar. They're a good long lasting engine that responds better to low rpm's. You should think about driving a z like it's meant to be driven.
I've got 425K original miles on my 82 turbo and when I drive it, I usually drive it fairly hard. I of course know the difference between driving it hard, and over driving it and I never overdrive it because that is abuse just like driving it at too low of an rpm is. I don't abuse Z cars, I appreciate them too much for that. I blew a headgasket in my turbo which happens sometimes especially when you crank the boost up. Surface the head and away I go knowing that I can drive the engine for at least another 100K miles before it needs a rebuild, possibly even longer than that. Like I mentioned before, I've had to replace gears in transmissions due to lugging. It wears out the needle bearing surfaces on the main gears and I've directly linked it to lugging the engine as well.
ZMOW
 
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