DPG Posted March 5, 2012 Share Posted March 5, 2012 Hi guys, I am trying to find out if the 4spd gears from a 72-76 tranny will fit into a 5spd later model tranny. I haven't been able to find anything through searching. I know the 4spd and 5spd tranny's from later years shared the first 4 gears, so I wasn't sure if they changed the gear thickness. Thank you for any help! -David Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 5, 2012 Share Posted March 5, 2012 The 77 - 79 5 speeds have the same 1-4 ratios so the odds are good. The 80 - 83 transmissions have different ratios. The thicker gears didn't come until 1984 with the 300ZX and the 71C transmission. I've seen it suggested that 5th gear should swap easily between the 71B transmissions but never seen someone say that they've actually done it. You might compare drawings from the FSMs. If they use all of the same pieces for 1-4, then the odds should be in your favor. Of course, to get the gears you'd have the whole transmission. Might be easier to swap the tail housing with 5th and reverse on to the 4 speed case, to get a 5 speed. Sounds interesting. Quote Link to comment Share on other sites More sharing options...
DPG Posted March 6, 2012 Author Share Posted March 6, 2012 Yeah, I was noticing the gearing for each year and the earlier models had much better 1st-3rd gears (for NA applications), Tranmission and Gear Ratios, so I think I will have to give it a try. Quote Link to comment Share on other sites More sharing options...
aplyedmind Posted March 6, 2012 Share Posted March 6, 2012 I believe the Nissan 5spd is just a 4 speed with a added 5th gear . I think I read that somewhere here before. Quote Link to comment Share on other sites More sharing options...
sticky280zx Posted March 6, 2012 Share Posted March 6, 2012 Why not just buy a good 5speed for $150...seems like alot easier route to me? Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 6, 2012 Share Posted March 6, 2012 (edited) Here's a link to a current thread that implies the 5th gear swap is doable. No details, it's in a For Sale thread, Post #1. Maybe the poster can offer some insights. http://forums.hybridz.org/index.php/topic/105479-built-l28-and-other-goodies/page__pid__986795#entry986795 Edited March 6, 2012 by NewZed Quote Link to comment Share on other sites More sharing options...
beermanpete Posted March 6, 2012 Share Posted March 6, 2012 The counter shaft for the 5-speed is longer than the 4-speed. Even it the counter shaft from the 4-speed would fit into the 5-speed box there will not be room to instal the overdrive counter gear. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 6, 2012 Share Posted March 6, 2012 So you could only do half a gear set on the first four gears, and only if the ratios were the same. Is that the takeaway? It would be interesting to know what the OP has planned. My post #6 was off-topic, since it's about swapping 5th gears between two 5 speeds, not installing 4 speed gears in a 5 speed. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted March 6, 2012 Share Posted March 6, 2012 Yes, as long as the gears for the main shaft are identical in both. If the goal is to find a source for free or cheap repair parts then it would be worth trying. If the goal is to change the gear ratios it won't work because you need to use the main shaft gear and counter gear as a set. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 6, 2012 Share Posted March 6, 2012 Yeah, I was noticing the gearing for each year and the earlier models had much better 1st-3rd gears (for NA applications), Tranmission and Gear Ratios, so I think I will have to give it a try. I would say that the late ZX 5 speeds 80-83 have the best ratios for NA engines. There is a BIG hole in the 2-3 shift on the 4 speeds and early 5 speeds. Particularly if you have a high strung NA (cam, triples, etc) that 2-3 shift can put you out of the power band. I've seen it firsthand at the track. The 80-83 have much closer ratios and can use a lower final drive. Quote Link to comment Share on other sites More sharing options...
DPG Posted March 6, 2012 Author Share Posted March 6, 2012 Yes, as long as the gears for the main shaft are identical in both. If the goal is to find a source for free or cheap repair parts then it would be worth trying. If the goal is to change the gear ratios it won't work because you need to use the main shaft gear and counter gear as a set. Here is my thought process. I have had other cars to where you could change out the gears to basically a shorter gear car. The 1st 2nd and 3rd gears on the 72-76 4 spds were shorter gears than the later 5 spds. What I want to do is swap out the first 3 gears in the 5 spd with the first 3 gears from the 4spd. I'm not well versed and educated on manual transmission design and build so I don't completely understand what you mean by the main shaft gear and the counter gear needing to be a set. Could you expand on this with some more explanation? Quote Link to comment Share on other sites More sharing options...
DPG Posted March 6, 2012 Author Share Posted March 6, 2012 I would say that the late ZX 5 speeds 80-83 have the best ratios for NA engines. There is a BIG hole in the 2-3 shift on the 4 speeds and early 5 speeds. Particularly if you have a high strung NA (cam, triples, etc) that 2-3 shift can put you out of the power band. I've seen it firsthand at the track. The 80-83 have much closer ratios and can use a lower final drive. I was looking at the gearing again and you are very correct on the later 5spds, much closer ratios. I wasn't looking close enough on those. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 7, 2012 Share Posted March 7, 2012 Here is my thought process. I have had other cars to where you could change out the gears to basically a shorter gear car. The 1st 2nd and 3rd gears on the 72-76 4 spds were shorter gears than the later 5 spds. What I want to do is swap out the first 3 gears in the 5 spd with the first 3 gears from the 4spd. I'm not well versed and educated on manual transmission design and build so I don't completely understand what you mean by the main shaft gear and the counter gear needing to be a set. Could you expand on this with some more explanation? I'm not beerman, and have only taken one transmission apart, partially, but it looks like three of the gears on the countershaft in a 4 speed are either cut as part of the shaft or permanently bonded to the shaft. All of the main shaft gears will come off, but only reverse, and the main drive gear can be removed from the countershaft in a 4 speed. Actually, in the 1978 FSM, Nissan doesn't even call out a counter shaft anymore, just counter gears and parts. It looks like they made some signifcant modifications. There is no distinct shaft just a stack of gears and a splined mini-shaft that all get stacked to work like a full length shaft. The synchro pieces are all on the mainshaft though, so if you had a 4 speed with good synchros, those might be some parts worth swapping, as a gear and blocking ring assembly. Although the different wear patterns might cause some noise. As far as ratios, the 71C transmission has the lower 1st gear and an even spread between gears. 1st, 3rd and 4th are like the early 5 speed, but 2nd has been moved to even out that 2-3 gap. One more option, but requires some work. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted March 7, 2012 Share Posted March 7, 2012 Here is my thought process. I have had other cars to where you could change out the gears to basically a shorter gear car. The 1st 2nd and 3rd gears on the 72-76 4 spds were shorter gears than the later 5 spds. What I want to do is swap out the first 3 gears in the 5 spd with the first 3 gears from the 4spd. I'm not well versed and educated on manual transmission design and build so I don't completely understand what you mean by the main shaft gear and the counter gear needing to be a set. Could you expand on this with some more explanation? There are 3 shafts in the transmission: The input shaft, which protrudes from the from of the transmission and connects to the clutch. The main shaft, which runs from just behind the input shaft (on the same center line) through the length of the transmission, extends out the back of the tail housing and connects to the drive shaft, and the counter shaft, which is parallel to but offset from the main shaft. There is a gear set coupling the input shaft to the counter shaft. 1st, 2nd, and 3rd each have a pair of gears. One gear from each pair is on the counter shaft and the partner for each pair is on the main shaft. When you are in 1st, 2nd, 3rd, and 5th the power goes from the input shaft to the counter shaft through a pair of gears and back to the main shaft through another pair of gears. 4th is not actually a gear per se, it is a coupling of the input shaft to the output shaft and is a 1:1 ratio. When in 4th the counter shaft and all the gears are not used. The counter shaft is made as one single piece and contains one gear each for 1st, 2nd, and 3rd. 5th has a separate counter gear that fits onto the end of the counter shaft on a spline. Each of these gears has a partner on the main shaft that free-wheel on the main shaft. When you select a particular gear the appropriate main shaft gear is locked to the main shaft by the synco hub. To change the gear ratio for 1st, 2nd, or 3rd requires changing all 3 at once due to the counter shaft being one singe part. Since the diameter of each gear on the counter shaft must match with the corresponding gear on the main shaft all 3 of the main shaft gears must be changed as well. 5th can likely be changed independently from the others as its gears separate parts, but the 2 gears for 5th must be changes as a set to keep the diameters properly matched. The early 5-speeds have the same gear ratios as the 4-speeds, the only difference being the addition of the overdrive gear (5th). Just get a 5-speed from the 77 or 78 280Z and you should have what you want. I hope this explains it clearly (and correctly). Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 7, 2012 Share Posted March 7, 2012 (edited) I would say that the late ZX 5 speeds 80-83 have the best ratios for NA engines. There is a BIG hole in the 2-3 shift on the 4 speeds and early 5 speeds. Particularly if you have a high strung NA (cam, triples, etc) that 2-3 shift can put you out of the power band. I've seen it firsthand at the track. The 80-83 have much closer ratios and can use a lower final drive. I concur. I personally feel that the later ZX trans is the best that ever went behind a L motor. 1st can be a little useless if you're running 4.10 or higher with lots of power, but overall the spread is really nice and even. The RPM drops are wonderfully systematic and really doesn't leave much to be desired as far as transmission ratios. And for the record, my personal preference is that I really like these trans with a diff in the 3.5 range if you're running a turbo motor. The stock 3.9 they were common with is wonderful for NA application. And the upside is that I usually see one in the junkyard every time I'm there. Quite common right now as these cars are nearing the end of their consumer life span and progressing into a mostly hobbyist phase. Heck, I got my last S130 for free, pair $500 for another, and regularly find them on craigs for under $1500 in solid shape. Talk about cheap parts donors... Edited March 7, 2012 by Gollum Quote Link to comment Share on other sites More sharing options...
Racer Z Posted April 18, 2012 Share Posted April 18, 2012 I don't have the answer to the original question. I think it has been addressed already. To follow up on the alternative direction the thread has taken: If you want the closest possible gear ratios, you will need the 80 to 84 5-speed. This has the closer ratio spread (gears 1 to 4). You're locked into using the first four gears as a set, you can not just change second gear for reasons already noted. You then need the fifth gear set from the early 5-speed. Put the early (fifth gear) "set" in the later model 5-speed and you will have the closest gear ratios. This may not be ideal for street performance but it will a better track (road racing, autocross) gear ratio set. I have not actually done this myself. I now have all the pieces to do this and plan on doing it soon. I have rebuilt a 4-speed and have some hands-on-experience. Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 19, 2012 Share Posted April 19, 2012 Norm The12SecondSUDude did the cross-pollinational swaps of the counter gear for fifth to split the difference. He posted on it once long ago, more from a matter of necessity from broken gearboxes and 'pick of the litter parts' than with the intent to get a different ratio. Quote Link to comment Share on other sites More sharing options...
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