I checked the search and couldn't find anything on this, but I'm wondering if it would be possible to add a fifth gear to my 4 speed tranny. I am looking at the CRX HF's fifth gear for fuel economy. It seems to me that the CRX shares all of the same parts up to fifth and it's accompanying pieces.

So my question is this: What would I need in terms of parts to get that extra gear in there?

My list of parts that I'm assuming I need are as follows (part number followed by description):
91108-PL3-008 BEARING, NEEDLE (32X37X23.5)
23626-PL3-325 SLEEVE SET, SYNCHRONIZER (5)
24200-PL3-010 FORK, FIFTH GEARSHIFT
24455-PG1-300 SPRING, SHIFT FORK SETTING
96211-10000 BALL, STEEL (#10) (5/16)
96220-50100 ROLLER (5X10)
23461-PL3-010 GEAR, COUNTERSHAFT FIFTH
23581-PL3-010 GEAR, MAINSHAFT FIFTH

Is that all that I would need? Would it work? Thanks in advance

 

You can buy all of that, and it will work. But it will probably be much much cheaper to find a busted trans to source your parts from. Of all the trans that I've torn down, I've yet to find one with a trashed 5th gear set.

However the 4 speed trans has the HF 1-4 of 3.25/1.65/1.033/0.823 with the 89-00 dx 3.888 final drive. You'll be better off having a DX/LX/Si 1-4 of 3.25/1.894/1.259/0.937/0.771 or if you're one of those that thinks you'll get significantly better gas mileage with a 'taller' 5th gear, you can maybe source a HF 5th of 0.694 or a 0.702 5th from a 92-00 non-SI trans.

But yes, it's definitely possible.

 

Pick up the parts used or find a complete 5spd trans. Too much money buying the additional parts from Honda just to have a long geared trans with a funky 4-5 shift.

 

I currently have the same situation. I have a Civic STD 4sp manual transmission. I found an CRX HF 5sp manual transmission that I will be able to combine with the 4sp and hopefully get one good one since they do share the same parts (LS3). These 5sp HF trannies are getting hard find..

 

Yes they are hard to find at times! I remember when gas prices were low and everyone was quick to swap to an Si trans...now its been the opposite!

 

easiest to put the 3.72 or 3.89 DX/STD FD into the HF tranny.....

But I'm getting 46 mpg with a close ratio ZC tranny, go figure

 

What kind of speeds are tou travelling at bone? I've had the theory that an Si tranny would get you better mileage in town just because you can drive around in 5th (od)

 

oooooooohhhh a 4 speed trans! have not had the time to mess around with one of these. aren't the casings still the same? or are they different?

 

65-70 mph, engine is buzzing above 3000 rpms on the highway. I shift at 3000-3200 rpms so the engine doesn't lug. D16A6/Y8 in a 89 CRX HF.

I can go 1-3-5 on the ZC box, but ti lugs the motor down into the 1600-2000 rpm range where I get some knocking due to the higher compression and stock PM6 ECU.

46 mpg before I've done any of my tuning tricks. I have not touch the motor except for change the oil in the two years I've owned it. The bottom end in "tired" so states the original builder when he raced it in SCCA in 2006-7, seems fine to me

 

From what I have read the 4sp STD and the 5sp CRX HF have the same L3 case and almost identical parts. Makes sense from a cost perspective. FYI, someone said the 4th on the STD is almost as high as the Si 5th.. look at the ratios

88-91 CRX Si
1st 3.250
2nd 1.894
3rd 1.259
4th 0.937
5th 0.771
Final Drive 4.250

88-91 CRX HF
1st 3.250
2nd 1.650
3rd 1.033
4th 0.823
5th 0.694
Final Drive 2.954 (3.250 in California)

88-91 Civic STD
1st 3.250
2nd 1.650
3rd 1.033
4th 0.823
Final Drive 3.888

 

Will take apart a junkyard 88 CRX HF tranny for Christmas! There is a Santa Claus! If it looks good enough, will combine/replace my 4sp STD