EricJB Posted January 24, 2014 Report Share Posted January 24, 2014 So I have read all the threads on this here, and they seem to be mostly about 1st gear for 4x4's or 5th gear for highway driving. I have been trying to figure out a way to have a close ratio box in my truck, and most options are out of reach. G force 5 speed $6700.00 any ratio's I want. I fucking wish. T5 with close gear stack about $3500.00 and 1 to 1 4th So I got to thinking about making a 71b close ratio by swapping 3rd gear top to bottom.(28 tooth on top, 26 tooth on the counershaft) This would involve getting 2 sets of gears. cutting the gear off the countershaft, and boring the upper gear to .001 press fit.( tapered) welding it together. Than cutting up a countershaft to get 3rd gear from it. Boring it to .001 press fit and welding it. I dont know if it can be done, but I have welded pressed on close ratio gears on a VW bug trans, and they held. If I did the math right, With a zx input gear set (1.26?) I would get 1st @2.97 2nd @1.7 3rd @1.36 . 4th @ 1.0 Dont care about 5th Thoughts? Quote Link to comment
ggzilla Posted January 24, 2014 Report Share Posted January 24, 2014 With 1.26 input ratio, 28/26 comes out as 1.36. To determine ratios, divide the cluster (countershaft) drive gear by the input shaft drive gear to get the input ratio. Next divide the 3rd gear on the mainshaft by the 3rd gear on the countershaft. Then multiply the two figures. Quote Link to comment
ggzilla Posted January 24, 2014 Report Share Posted January 24, 2014 With a change to a 1.26 input set (29/23 gears) the 1977-1978 620 gearset reportedly work out to: 1st.... 2.972 2nd... 1.702 3rd.... 1.171 4th.... 1.000 5th.... 0.745 It sounds like that's what you are aiming for EXCEPT you want to even up the drops around 3rd. The 29/23 input set comes from 1981-1983 non-turbo 280ZX. This is a GREAT idea for peaky powerband engines so as to keep within the powerband after shifting. To preserve the acceleration which would normally suffer with a close-ratio gearbox you can fit a steeper final gear, for example go from 4.375 to 4.88. First gear will be close to the original acceleration, and the other gears will have more than original. With 5th gear, freeway speeds can still be obtained. 1 Quote Link to comment
Stupid_fast Posted January 24, 2014 Report Share Posted January 24, 2014 Close ratio box for your truck ???? And you don't care about 5th? Why? Rock climbing ? Just get a stock 81-83 ZX BOX. 3.062 1.858 1.308 1.0 0.745 < can swap 5th for 0.864 I believe ... Quote Link to comment
EricJB Posted January 24, 2014 Author Report Share Posted January 24, 2014 If you watch this vid, you can hear the gap I am trying to close up. A zx box would definatley help, but a mongrel box with a swapped 3rd would get me even closer. Already have 4.88's in the back, so it could easily be a bit taller in 1st and 2nd. I dont think I would bother if I could find a good zx box though. But in the case of just finding the input gears, I might give it a try. I dont care about 5th because I dont use it. So it could be whatever. Quote Link to comment
Stupid_fast Posted January 24, 2014 Report Share Posted January 24, 2014 Yeah, the ZX box gets rid of that 2-3 gap. It is getting harder to find the 80-83 box however. If you can swap the gears go ahead, I'm just pointing out the CR ZX box already has what you're trying to get. Quote Link to comment
Farmer Joe Posted January 24, 2014 Report Share Posted January 24, 2014 time to adapt a muncie in this thing... never break a trans again. or maybe find a turbo zx t5 and toss fresh world class guts in it? can you even do that? Quote Link to comment
Stupid_fast Posted January 24, 2014 Report Share Posted January 24, 2014 or maybe find a turbo zx t5 and toss fresh world class guts in it? can you even do that? Simple answer is NO. NWC and WC T5's don't mix apparantly. there is a lot of discussion about it on Z forums. Takes a lot of effort. You can have a good gear shop drop a closer ratio mustang(or similar) gearset into it, but it isn't cheap and you end up with the ratios of a CR ZX box with a taller 5th. The ZX T5 is great on the lower revving L28ET with 3.54 rear end, but the gear spread is a bit much for any higher rpm peak power N/A motor. 1 Quote Link to comment
EricJB Posted January 24, 2014 Author Report Share Posted January 24, 2014 I don't have a ZX trans or gearset at the moment. Just a calculator. I cant remember if a ZX box is a 71b, or a 71c. I have to be able to get the short tail housing ( and shorter mainshaft) on it since I still have a bench seat, and long arms. Not currently having any breakage issues with the 71b, just need to lose the 2nd - 3rd gap as much as possible. Quote Link to comment
datzenmike Posted January 25, 2014 Report Share Posted January 25, 2014 It's a B, the earliest C was the '84 300zx non turbo. There were no Bs after '86.5. Some have stated the '84/'85 is also a C... and it does perhaps have some C parts, but the A B C as far as I'm concerned is the shifter type. The 1st, 2nd, and third gears are all one assy on the counter shaft. Very bottom far right is 1 st then 2nd to the left and 3rd to the left of that. The large gear on the far left is the counter driven gear. Otherwise the counter shaft has the three lowest gears cut from a one piece chunk. Says '87 720 but '77-'78 620 truck, '77-'78 280z and '79 280zx, 810 and Maxima 5 speeds will work. Just swap the '80-'83 280zx input gear set int the transmissions mentioned above. These... Quote Link to comment
deweyharding Posted January 25, 2014 Report Share Posted January 25, 2014 Can the fifth gear be changed to a numerically higher number so that percentage is less than 25%? Also what causes the fifth gear to change from the .833 in box one? Quote Link to comment
ggzilla Posted January 25, 2014 Report Share Posted January 25, 2014 To create the mongrel box, you need to source the input set from a 1981-1983 non-turbo 280ZX transmission. Which is a already close-ratio box, so why not just use the whole transmission? It is also a 71B transmission for L-series engine. Quote Link to comment
datzenmike Posted January 25, 2014 Report Share Posted January 25, 2014 Can the fifth gear be changed to a numerically higher number so that percentage is less than 25%? Also what causes the fifth gear to change from the .833 in box one? Changing the input ratios changes every gear after it. Quote Link to comment
EricJB Posted January 25, 2014 Author Report Share Posted January 25, 2014 To create the mongrel box, you need to source the input set from a 1981-1983 non-turbo 280ZX transmission. Which is a already close-ratio box, so why not just use the whole transmission? It is also a 71B transmission for L-series engine. I would if I had access to one. Especially if I could convert it to a short tail. Honestly just doing math when I couldn't sleep. What I would really like to do is put a gear in between 2nd and 3rd, instead of putting them closer. A 5 speed with a 1 to 1 5th would be optimal. Trying to do the most I can with Datsun parts though. Quote Link to comment
ggzilla Posted January 25, 2014 Report Share Posted January 25, 2014 What I would really like to do is put a gear in between 2nd and 3rd, instead of putting them closer. A 5 speed with a 1 to 1 5th would be optimal. Trying to do the most I can with Datsun parts though.1:1 fifth is available with the Nissan six-speed from an S15. Or more commonly available in USA in the miata (its the same gearbox), but cheaper to get the Nissan version as they take them off the SR20DET. Adapt an L20B auto bell housing to it, a bit of work will get you a first class gearbox. Datsun A-series bell grafted on Quote Link to comment
datzenmike Posted January 25, 2014 Report Share Posted January 25, 2014 There is also the F5C71B NISMO Rally 5 speed 1st... 3.321 2nd.. 2.27 32% 3rd... 1.601 29% 4th... 1.24 22% 5th... 1 to 1 19% Quote Link to comment
EricJB Posted January 25, 2014 Author Report Share Posted January 25, 2014 Not opposed to grafting, or machining to make it work. Where do you get the Nissan/Miata gearbox? Is there an importer in the PNW? Does anyone know what the ratio's are? Quote Link to comment
ggzilla Posted January 25, 2014 Report Share Posted January 25, 2014 From a junkyard. See http://datsun1200.com/modules/mediawiki/?title=6-speed Quote Link to comment
datzenmike Posted January 25, 2014 Report Share Posted January 25, 2014 Found my counter shaft... all one piece. Quote Link to comment
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