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The "Mongrel" gearbox for the 4x4 guy(and the land speed record guy)


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Thats interesting, Lowering the first three gears actually looks like decent ratios looking at the gear calculator.  

 

Its quite closer than I expected, only widening the 3rd -> 4th shift a bit. Actually looks like a really nice gearbox. 

 

http://www.jdmlegion.com/tools/gear_speed_calculator.aspx

 

FYI your stock 2nd gear is a 1.902 ?? not a 2.077.

 

 

See what datzenmike said, I don't think you can mix 71b and 71c components... the later C series trans was beefed up quite a bit.

 

I'm running that ZX box in my 510 behind a L20b.  Thus why the 4.3 diff is going to be usful for me! much less powerful engine.

 

 

Datzenmike!

 

There is a possible 0.67 overdrive ! is it possible to keep the 1-4 gears on a ZX box the same, and add in that 5th? 

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Thats interesting, Lowering the first three gears actually looks like decent ratios looking at the gear calculator.  

 

Its quite closer than I expected, only widening the 3rd -> 4th shift a bit. Actually looks like a really nice gearbox. 

 

http://www.jdmlegion.com/tools/gear_speed_calculator.aspx

 

FYI your stock 2nd gear is a 1.902 ?? not a 2.077.

 

 

See what datzenmike said, I don't think you can mix 71b and 71c components... the later C series trans was beefed up quite a bit.

 

I'm running that ZX box in my 510 behind a L20b.  Thus why the 4.3 diff is going to be usful for me! much less powerful engine.

 

 

Datzenmike!

 

There is a possible 0.67 overdrive ! is it possible to keep the 1-4 gears on a ZX box the same, and add in that 5th? 

 

Your right about that it is 1.902, I have been looking at transmission ratios all day and got the z20 1981 2nd gear in there by mistake.

 

I didn't completely get what Datzenmike said but I think I have a better idea, do you know of any source of information where I could compare 71c stuff? I can easily find info on gears but not  input/counter, I want to see if I could do what you did, maybe with a different transmission.

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I think not.

 

Nissan made two or maybe three? 1,2,3 gear sets with a single 5th gear. To make a wide ratio transmission they simply change the main shaft to counter drive gear set and this adds a multiplication ratio to all the other gears including 5th. Fifth can't simply be removed and changes for another ratio.

 

For example the 720 4x4 uses a 3.592 ratio first gear.

The first gear teeth are 33/14 or 2.357*

The input main and counter gears are 32/21 or 1.5238

Multiplied together we get a first of 3.5916 or round of to 3.592

 

By simply changing the input main and counter gears to 22/31 or 1.409

We multiply by the first gear 2.357* to get a first of 3.321 just like most 620, 280z and Maxima 5 speeds. All the same gears so it cheaper to make simply by changing the main/counter set.

 

 

Yes some of the 71C if not all internals will fit on the 71B main shafts as documented here... http://720world.com/...ransmission-faq

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I think I get it, thanks for the explanation, that makes complete sense, the main and counter gears are all attached and of a set size. So if I change the main all the counters change too, and I am guessing you say it wont work because there are no mains from any other transmission that line up to the FS5W71H ? I hope I didn't derail the thread too much.....

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What I want to do would look something like this:

 

STOCK:            Frankenstien:

1) 3.321            3.592 

2) 2.077            2.246 

3) 1.308            1.415

4) 1                   1

5) 0.759            0.745 <- here I would like to be somewhere from .65 to .67

 

 I am not completely sure about 1st or 2nd but I am pretty sure I will change 3rd. I already have a spare transmission, so I was thinking of doing a rebuild and seeing how things go. Worst comes to worst if it is not drivable I can change things back. but I don't think the changes are drastic enough to mess things up badly. I really just want to improve to 0-70 time. I don't know what your hp/tq numbers are in the zx but in the 240 with my KA I am making about 180 and have plans to bump that to 210-220 and hopefully have 190ish tq. This will be at the crank N/A. 3rd and 4th are ok for very tame driving but I dunno it seems to me if I am on it 3rd gear doesn't pull very hard at all.

 

That and of course the 5th gear, .67  is right around where I want to be and I think with the power I will have it there should be enough tq. So for this to work I would need the 81-83 280zx non turbo input/counter shaft ? Where did you get the 5th gear from? What year is that zx? I haven't seen anything that is .5333 in a 5th gear, unless I am misunderstanding something.

 

 

81-83 280zx non turbo input/counter 29/23= 1.261

5th gear 24/45(non-ZX) = .5333 *.1.261  = .672 Overdrive

 

you cant just change 1,2, or 3 independently from each other. they are stuck together. all you can change are the input/counter gears and 5th gear.

 

 

 

.5333 is the 24/45 5th gear.

 

For the .67 5th you will have to get an 81-83 280zx N/A trans and a 5th gear from just about any other 71B trans with the 24/45 5th gear.

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you cant just change 1,2, or 3 independently from each other. they are stuck together. all you can change are the input/counter gears and 5th gear.

 

 

.5333 is the 24/45 5th gear.

 

For the .67 5th you will have to get an 81-83 280zx N/A trans and a 5th gear from just about any other 71B trans with the 24/45 5th gear.

 

Right, 1-2-3 are all from a 1982 200sx, that had a FS5W71B. Which according to the 720 world FAQ can be made into a hybrid with a FS5W71C or H. I think the biggest part that is causing confusion is that I am not aware of the main shaft size for the 200sx, all I know is that gear set was from the z22e motor, so it was the smaller engine.  The 5th gear was from an 82 280zx

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This is kinda what I am trying to find out 

 

For the .67 5th you will have to get an 81-83 280zx N/A trans and a 5th gear from just about any other 71B trans with the 24/45 5th gear.

 

How do you know which 71B has a 24/45 5th gear? Where did you get the info from? or maybe better what search string should I be using or something.  I am looking to put together as much info as I can on the FS5W71-  series of transmissions as I can, so I know what options there are for switching things around.

 

Also, I want to thank you guys for taking the time to explain what you have so far. You really helped me to get a much better grasp of what was going on....

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This is kinda what I am trying to find out 

 

 

How do you know which 71B has a 24/45 5th gear? Where did you get the info from? or maybe better what search string should I be using or something.  I am looking to put together as much info as I can on the FS5W71-  series of transmissions as I can, so I know what options there are for switching things around.

 

Also, I want to thank you guys for taking the time to explain what you have so far. You really helped me to get a much better grasp of what was going on....

 

Read from the beginning of the thread. I dismantled a lot of transmissions I had laying around and counted the teeth on 5th gears and input/counter sets. That is how I found out. I'd say at least 85% of the 71B transmissions have the 24/45 5th gear.

Its the 81-83 280zx input shaft and counter gear that make the standard 5th gear into the champion overdrive. There is tons of info out there, right and wrong. I don't see how I haven't seen mention of a .672 overdrive yet though. Maybe I'm just the first to have figured it out? Probably not but I haven't seen it plastered everywhere yet.

 

Like I said earlier, don't mix pre-81 transmissions with 81+ transmissions unless its BEHIND the center plate of the transmission (like, just swapping 5th gear). There is something different in there somewhere by about .010" ish. Just enough to bind up a transmission and dig a hole in the case. been there done that got the T-shirt

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Read from the beginning of the thread. I dismantled a lot of transmissions I had laying around and counted the teeth on 5th gears and input/counter sets. That is how I found out. I'd say at least 85% of the 71B transmissions have the 24/45 5th gear.

Its the 81-83 280zx input shaft and counter gear that make the standard 5th gear into the champion overdrive. There is tons of info out there, right and wrong. I don't see how I haven't seen mention of a .672 overdrive yet though. Maybe I'm just the first to have figured it out? Probably not but I haven't seen it plastered everywhere yet.

 

Like I said earlier, don't mix pre-81 transmissions with 81+ transmissions unless its BEHIND the center plate of the transmission (like, just swapping 5th gear). There is something different in there somewhere by about .010" ish. Just enough to bind up a transmission and dig a hole in the case. been there done that got the T-shirt

 

 

Thanks for the info man....I have been looking around ALOT for changing ratios, and I have not seen ANY info as good as what I have gotten here, so if you asked me I would say it probably has never been thought of, most people in to 240 forums don't ever talk about transmissions unless they are swapping from a Z or something...

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Read from the beginning of the thread. I dismantled a lot of transmissions I had laying around and counted the teeth on 5th gears and input/counter sets. That is how I found out. I'd say at least 85% of the 71B transmissions have the 24/45 5th gear.

Its the 81-83 280zx input shaft and counter gear that make the standard 5th gear into the champion overdrive. There is tons of info out there, right and wrong. I don't see how I haven't seen mention of a .672 overdrive yet though. Maybe I'm just the first to have figured it out? Probably not but I haven't seen it plastered everywhere yet.

 

Like I said earlier, don't mix pre-81 transmissions with 81+ transmissions unless its BEHIND the center plate of the transmission (like, just swapping 5th gear). There is something different in there somewhere by about .010" ish. Just enough to bind up a transmission and dig a hole in the case. been there done that got the T-shirt

Mm i have a spare(scap) 79 ZX box... I could use that 5th gear.

 

Now to debate which 5th gear I want! 

 

Thanks for the info man....I have been looking around ALOT for changing ratios, and I have not seen ANY info as good as what I have gotten here, so if you asked me I would say it probably has never been thought of, most people in to 240 forums don't ever talk about transmissions unless they are swapping from a Z or something...

I guess they just go through gearboxes so fast they never bother making one with good ratios.(lol drifting)  The stock 240sx ratios are pretty ideal for a track car to begin with ...

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  • 2 weeks later...

Ok, having finally fixed the Deathmobile this thread becomes of more than passing interest....I'm going to learn myself up a bit on these gear/trans combos and try to hit the following...

 

long tail 5 speed beefy enough to last, and with the 3.5 1st of the truck trans I had, and the .745 5th of the Z trans I just had rebuilt. I wish I could figure out which model the truck trans came from, but all the listings usually say truck 1, truck 2, truck 3, etc, and the 3.5xxx number for 1st is associated with one of those but no details. It is a long tail however.

 

In reading back a few posts it looks like Masteroskillio and I have similar goals.

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Ok I'm retracing this entire thread again.

 

First off I'm picking up that a stock maxima transmission as recommended by MoT gets close to what I wanted with a pretty low 1st and the .745 5th I like. I think I missed what year to look for.

 

Second is I'd like to understand the gear ratio derivations which are mathematically simple but I don't get what drives what yet. It seems some input ratio thingy sets the tone for 1st-3rd (ignoring 4th) and then there's wiggle room on 5th ratios for some reason.

 

I see in the pix the big shaft with four gears on it and I guess some input gear drives that?

 

I'm not getting what turns what yet.

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  • 3 weeks later...

The mixing of pre-81 and post 81 transmissions IS possible and it isn't hard to do...just takes some trimming of the countershaft gear area in the front case half. This is required to do the KA trans swap behind the L28's in the Z cars, since you can't just flip the engine over the 20 degrees needed to get the shifter lined up.

 

Also, the 4-speed housing works fine...just need to move the drilled and tapped hole for the reverse light sensor forward 20mm...the later boxes have this boss already cast into place.

 

I do a lot of these case swaps, and it just hit me what MOT was talking about with the case binding.

 

Also...who wants a L-series bell on a S15 6-speed trans? I'm doing one this coming week, and can modify the bell to fit the standard L-series for you. Just PM me.

 

Ratios of the 6-speed:

 

3.6

2.2

1.5

1.2

1.0

0.76

 

It would be great in a track car with a 3.9 or 4.11 rear end, as a dogleg-1st 5 speed, ignoring 1st gear and taking off the start line in 2nd, then running the circuit track shifting 3-4-5-6 like a 4 speed box. it's the same internals as the toyota IS200 transmission, and the IS200 box has a 0.829 6th...even closer ratios.

 

The new 6-speeds behind the G35 and the Frontier pickup are a different box...but the truck gets a 4.0something 1st gear...

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Ok I'm retracing this entire thread again.

 

First off I'm picking up that a stock maxima transmission as recommended by MoT gets close to what I wanted with a pretty low 1st and the .745 5th I like. I think I missed what year to look for.

 

 

 

My info does not show the Maxima 5 speeds as having the 3.592 1st ratio. My info shows it's the same as the '77-'78 620 truck and 280z and the first year ('79) 280zx 5 speeds with a 3.321 1st ratio.

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Mike you are right, it has a 3.321 1st but 5th is .745 unlike the 620 and early zx. 


When you do the math that's what I got. I guess I had incorrectly stated the 3.59 1st gear...(which is only nice for moving at 2mph in traffic in a car, pain in the butt otherwise.)


Re-posting My first hand tooth counts(will probably do this on every page here lol):
 

Input/counter shaft.

SD22                               32/21

stubby later 720 4x4 5spd. 32/21

720 early 4x4 trans 4spd    32/21

280Z 5spd                        32/21

280zx 5 speed                  29/23

84 Maxima 5 speed           31/22

 

 

Counter/output

1st gear

Stubby later 720 4x4 5spd 33/14

280Z 5spd                        33/14

Maxima 5 speed               33/14

280zx                              34/14

 

5th gear

Maxima                            24/45

280zx 5 speed                  26/44

280Z                                24/45

Stubby later 720 4x4 5spd 24/45

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my maxima trans

 

Input/counter shaft.

 

84 Maxima 5 speed 31/22 (1.409)

 

Counter/output

1st gear

Maxima 5 speed

(2.357) (grosses out to 3.32 depending on rounding error)

 

5th gear

Maxima 24/45
(.533 *1.409)= .751 depending how you want to round off. This was on 2 different maxima transmissions.

you calculate it out this way




HEre is a quick explanation for the datto transmission.
 

power in here                           input gear                             3+4 selector ring            1+2 selector ring         5+R selector ring

CLUTCH====input shaft========H(4)        H(4)==========I========H3====H2==I==H1==PLATE==HR=I=H5====================Driveshaft

                                                    H===Counter Shaft==============H3====H2====H1==PLATE==HR==H5

counter gear

 

 

This is a side view of any 71B trans, as viewed from the Drivers side. H is just a representation for each gear.

for 1st,2nd,3rd,5th, and Reverse,


the input shaft AND the counter shaft spin any time the clutch pedal is not engaged.
When you select 1,2,3,R,5th you are sending power through theinput shaft, to the countershaft before it reaches the Output shaft.

 

So for these calculations you take input shaft ratio (counter gear/input gear) (31/22) to figure out the input/counter gear ratio. The counter shaft is geared down by 1.409:1 from the engine RPM.


Then take your actual gear ratio(counter gear/output shaft gear)(5th which is 24/45)(.53333333333etc...) and factor that into your counter shaft ratio of 1.409.

Input shaft ratio * Gear ratio= final ratio for that gear

1.409 * .533 = .751



On selecting 4th, you are not using the countershaft at all. You are simply connecting the input and output shafts together and the counter shaft freewheels. Thus every 4th gear is the same 1:1 ratio unless you are talking about a 6 speed(Except a T56 with double overdrive) or a close ratio 5 speed with a 1:1 top gear.

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  • 5 months later...

Sorry to bring this back up, I just had more time to look into this, and I was about to start working on it, but I needed to know one last thing. If I was looking to so the .672 overdrive and I was taking the input shaft/counter gear from 81-83 280zx, and I use the stock 240sx 5th that i believe is .5333, that would intern increase the gear height of the entire gearbox, not just 5th.

so if am correct it would work something like this:

 

Stock input/counter:  1.409    

1) 3.321

2) 1.902

3) 1.308

4) 1

5) .759

 

280zx input/counter: 1.261

1) 2.970

2) 1.701

3) 1.17

4) .894

5) .672

 

So basically I would be trading acceleration all around for more fuel efficiency, and a higher top end assuming I am correct. 

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  • 6 months later...

OK, here we go.. The clutch was going out in my '82 Datsun 720 4x4, all gears were shifting fine. I had some guy come over and replace the clutch instead of me having to do it. At some point during the process he removed the guide pin from the top of the tranny and moved the striker back, and now once he got it All back together it will not shift gears!! There is only one gear available and thats 1st gear. Somehow he must have knocked off the linkage or shifting rods or something (I am no transmission mechanic. I have researched this and I have the FS5W71B transmission, so it does not have a plate on the top of it in order to get the shifter back correct again, I think the plate came on the "C" model transmission. I have had some mechanics I called tell me the tranny has to be removed, and some tell me that you can do it without taking it out and apart.. The shifter feels like it will go to the 1st position and 2nd position, but with no "click" in between. If you try to get it into 3rd or any other it will not go far enough right no matter what I try to do.please help me or point me in the right direction to find an article. If you can walk me through it I would be glad to send you some cash in return for your time, or if you could point me in the right direction. ANY help would be greatly appreciated

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I guess the reply didn't post.

 

 

Remove the shifter.

 

The striking rod has a hole in it that the plastic cup on the bottom of the shifter fits into.

 

What we want to try to do is get the striking rod turned or rotated towards the driver as much as possible and at the same time pulled back towards the rear of the vehicle to try and get it to engage the 1st/2nd shift rod when you release it.

 

First is left and forward but the shifter flips that around and left to right. Inside the transmission the striking rod is way over on the right somewhere as shown below. It needs to drop down into the N (neutral) gate between 2 and 1. Once in the N you can shove it 'upward' onto N and out of 1.

 

 

R 4

NN2 (striking rod)

53N

__1

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  • 11 months later...

So I built a FS5W71B gearbox into a stubby case...

I took what seems to be an 81-83 280zx transmisson(only thing wrong with it was reverse was messed up)

and a stubby transmission that came out of a later 720 4x4 truck.

 

Here are the criteria I was going for:

1. had to end up with the stubby tail housing and output shaft because of driveline space concerns

2. as low of a first gear ratio as possible

3. as little overdrive as possible.

 

I had several parts transmissions laying around to pull parts from

here is what I ended up with.

 

SD22 input shaft/ counter gear (1.52 ratio) Same ratio as the 720 4x4 stubby and early 720 4x4 long tail 4 speed but those were damaged and/or worn excessively

 

81-83 280zx full gear set, 280zx main plate and shift rods.

 

reverse gear idler gear off of a maxima transmission to replace damaged 280zx gear(same depth as the 280zx reverse idler)

I ended up with ratios of

 

3.678 1st gear

2.24 2nd gear

1.57 3rd gear

1.0 4th (duh)

.898 5th gear.

 

With the 33" tires currently and 4.88 differential ratios, that puts me at highway speed of 70mph at around 3000RPMs

 

1st gear ratio in 2:1 low range of 3mph at 1000

and 15mph at 5000.

 

This would probably be undrivebale behind an L20B (on the highway) but I'm putting it behind an L28 in front of it so it should have plenty of torque.

 

Just thought I would post this different "Mongrel" setup for the 4x4 guys.

So basically this is 280zx gear set main plate and shift rods in a 720 4x4 stubby 26.5" transmission with the stubby input shaft? Love this set up and would love to put in it my 4x4 for the gear ratios and I need to replace the tranny and would love to put a stubby tranny in with low first. Would it be easier to get a 280zx transmission and a 720 stubby transmission to do this? What is the parts list?
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