I'm finally taking a big step into modding my car for the first time. I never really do much with my cars because I'm not looking for high performance. I just want a good reliable car.
I recently got a '91 STD hatchback with a bad 4-spd (input shaft bearing supposedly failed) and a d15b1 (supposedly has >90K miles. I don't think it's worth running this motor). Since I have the opportunity, I am swapping the motor for a stock d16a6. I have another 4-spd currently being used in an '89 hatch. I want to pull that tranny and add a 5th gear to lower rpms with the a6 when I'm on the highway (because who sees an ancient civic hatch going 75+ and is really quiet?) The idea is to have a nice quiet, comfortable car to take on long trips. Of course, I plan to install a new "cushiony" suspension and I will probably seek out some Del Sol seats (I hear these are very comfortable. Currently I have some ragged 5th gen front seats).

I have a 5-spd from a '94 DX I had years ago with bad bearings all around from running low on fluid one day. I want to use the 5th gear on the 4-spd. With the '94, I would go 70 mph and the engine would be running at ~2500 rpm.
I don't really know much about transmissions. However, I know that my 4-spd has a spot for 5th gear. It's unlikely I can use the 5th selector fork on the 4-spd from the '94. I would have to find one from a 4th gen d-series. I also know that the final drive from the '94 is 4.058 and the final drive from the '89 is 3.888. This will put the rpms lower than 2500 at 70 mph. I'm just not sure how much of a difference it will make. It's possible I may have to modify the mainshaft (and maybe other parts as well) and I also have to add the reverse lockout.

Tomorrow I will disassemble the '94 5-spd and the bad 4-spd and make comparisons and see if it's even possible to do this swap. It's all I have to work with and I really don't want to buy another tranny just to pull parts from it. Who knows? Maybe all I'd have to do is use the 3.888 on the '94 with the '89 bell housing and all will be good.

If my info is incorrect, please correct me on it. I'm really posting this in case anyone else wants to try something like this. I'll post my findings tomorrow.

 

Take plenty of detailed pics. This thread would be pointless in the future without it.

 

Alrighty, so I have the 2 open and found some interesting bits here and there. The 4-spd did indeed have a bad input shaft bearing (or what's left of it...). I've heard if this fails and explodes like this one it ruins the transmission. From what I could tell, however, is after removing a few shards the gears were free and I could finally turn everything. From what I can tell the gears appear ok. A few bearings need to be replaced but I don't see anything too serious aside from the ISB.
I found an awesome tutorial on how to disassemble an s20 tranny. This also worked for my 4-spd. http://www.honda-acura.net/forums/do...ld-89pics.html

 

Comparing the 2 gear sets I found something interesting:
It appears the 4-spd set has what looks like a 5th gear? I'm going by what I found here: https://honda-tech.com/forums/transm.../#post38267670
If it really is a 5th, I certainly could not shift to it. In the pic attached, the top set is from the 4-spd and the bottom set is the 5-spd. I could only find a difference with the forks as seen in the pictures (it might be the forks were in different positions...).

I also compared bell housings and found they are the same with a couple of differences:
the reverse fork mounts are different
there is a slot underneath where the differential sits (seen in the bell housing comparison pic). The '91 is off slightly to the left, while the '94 is slightly to the right. Not sure what this is for or if it makes a difference...

I think I will use the gear set from the '94 inside the '91 case while keeping the 3.888 FD. Looks like this involves disassembling the countershafts and swapping gears over.

So here's my first question: assuming that pic in the thread I referenced is correct, why am I counting 5 gears on the 4-spd?

 

Here is a better comparison of the 2 sets. Top is the 4-spd bottom is the 5-spd.

 

Alrighty, so I took a closer look at everything and confirmed my supposed 4-spd seems to be a 5-spd. I am guessing it is a DX based on this post: https://honda-tech.com/forums/honda-.../#post24613592 (I think it has PL3 A000, not sure since it is dull)
If it is indeed the DX tranny, this means I have a 3.89 final drive instead of the 3.888 (probably makes 5 rpm difference @70...). I will use the test specified by Tyson to make sure it really is a DX.

Where things seem strange:
before I pulled the old tranny, I tried running through all gears (not running) and I got 1-4 and reverse. I could not go into 5th which made me think it really was a 4-spd. I now suspect that maybe some debris prevented me from engaging 5th. The transmission was seized until I opened it up.

You can see from the attached pics that I can slide a 5th gear fork and move the sleeve into a 5th gear. I will probably save the set as I have a 1990 DX tranny that currently works with no issue. Always good to have spare parts

It will be a while before I get to disassembly as I am awaiting arrival of my Helms. Then I will feel more comfortable with disassembly of the countershaft (and maybe identify reverse lockout).
In the meantime, I have to go parts hunting...

 

Posted plenty of pictures... but I can't see any of them. Anyone else having this problem?

 

@JPhilBradley I can see them. Not sure what's going on your end.

This mystery 5-spd is getting even stranger. I followed this https://honda-tech.com/forums/honda-.../#post22442194 and I counted 69 teeth on the differential and 17 teeth on the pinion gear. This gives me a FD of 4.058 This is the same as the 1994 dx tranny!!!!

The gear sets are different between the transmissions, however. The 1994 DX gear ratios are standard:
1st: 3.25
2nd: 1.761
3rd: 1.172
4th: 0.909
5th: 0.702
The gear ratios of the mystery tranny are as follows:
1st: 3.25
2nd: 1.894
3rd: 1.259
4th: 0.937
5th: 0.771
With this info, it appears I have a 4th gen dx tranny with a 5th gen dx FD. I'd say it's a nice compromise between the 4th gen dx and the 4th gen si.

I found a gouge on the 3/4 shift fork on the 4th gen tranny (seen in the pic). It will be replaced along with the usual parts for a good rebuild. Luckily, I can still get it from Honda.

 

Since I've come this far and want to stay with this, I have a question for you guys:
Does anyone here have a long final drive? I want to stay around 3.8 if possible.

 

Nice setup .

 

I have decided to go back to the idea of pulling the 4-spd out of the 1989 hatch. I have most of the parts for a rebuild, though I am having a hard time finding a new friction damper 91212-PL3-T01 (Honda calls it Friction Damper Second). I will disassemble both countershafts this weekend and compare those 2 dampers for compatibility.

 

After some delays, I got the countershafts apart and compared the 2 secondary dampers. As far as I can tell, they appear to be the same. There is no difference in size, no difference in fitment when I swapped them, and no difference in the rubber surrounding the ring. I have come to the conclusion that either there really isn't much of a difference (if any) or someone replaced the damper in the 4th gen dx with a damper for a different setup.
I have yet to pull the tranny out of my '89. I'm almost certain no one has taken it apart so the original secondary damper might still be there. I have to find some time to pull my '90 tranny out so I can swap it in to the 89. In the meantime, I will order a damper for the '94 tranny. Even if it does not fit, it would be good to keep since I'm sure that damper is becoming scarce.
More to come.

Left damper is '94, right damper is '91.

 

My EK sedan has real tall gearing, close to 2500 at around 65 from memory. It might be easier just to source one of those?

 

I believe the Civic Sedan EX had a different FD than the DX and Si.
That might be the FD you have there.

Many conversions were done that took the ZC gearset and plopped it in on the Si FD.
The downside is that the shifting is a bit too quick and 5th gear top speed suffers when using the Si FD.
A lot of the conversions keep the 5th gear from the Si because of this.

However, the FD you have would make for a happy medium.

 

@~sp33~
I am using the transmission from an eg I used to have. Seems it revved in a similar area where yours is. I am trying to get it lower, however, which is why I am transferring my 5th into my '89 4-speed. I also do not want to buy another transmission when I already have 2 spares sitting around...

@4-drEF
I need to look into this. I didn't bother to check if the FD from an automatic could be used. If it came from the EX auto, then that would confirm the countershafts between it and my '94 DX are the same.
EDIT: oops, forgot there was a manual transmission for the EX...

 

The 90-91 Sedan EX manual is what I was thinking.
It is somewhat rare.

 

I haven't found very much about the 4th gen EX transmissions. According to http://www.automobile-catalog.com/ca...oor_sedan.html, it is an SI transmission. I can believe this because my stock 5th gen EX also has an SI transmission.
I haven't found anything about differences in the California versions of the EX.

 

Dunno if this is any help, but the US brochure shows the EX manual as having the same final drive as the SI.

 

Good info. Some sites say there was an automatic available for the STD, though I have never seen one.

 

Interdasting!
You certainly have an odd trans!

 

@4drEF
Indeed it is. I also had another thought the other day. The previous owner was talking like this car was a 4-spd. He said something about it doing ~5k rpms at 75mph. I thought that was a little extreme but I didn't think too much about it. Before pulling it, I ran through the gears and I could get 1-4 and reverse, but no 5th. I am now wondering if the shift rod was ever changed to allow selection of 5th gear. This will be answered when I crack open my 89 4-spd.

Small update: I have pulled my 90 5-spd and replaced the shift rod seal and boot. That leak was getting pretty bad... It's now ready to be installed in my 89. Once that's done, I can finally investigate and begin rebuilding the true 4-spd. Yay!
As a side-note, I found out it may be possible that the synchros from a d-series 5-spd between 1988-2000 might work on my 4-spd. I will see if my 94 synchros will work. Never had a problem with those. My 89 is giving me a little extra feedback in the shifter but it is not grinding yet... I might just order new synchros instead.

 

Tomorrow I will do the swap and my '89 will have an 'upgraded' transmission. On average I was getting about 37-38 mpg, 95% is highway miles. I was getting about 40-41 mpg with the '90 5-spd. I'm curious if I will get the same mileage on the '89...
Before I install it, I replaced the axle seals and the shift rod seal and boot. I didn't find a how-to anywhere and my helms didn't mention about those in the transmission section. Figured I'd post some pics here on what I did to install the new seal and boot. I used a 19mm deep socket and a hammer to press the new seal in. I also sprayed a little WD40 in the area so it would slide easier. The rest is pretty straight forward.

 

I'm worried I may not have enough torque to maintain speed in 5th gear. I am now considering minor mods for the d16a6 to gain more low-end torque. The biggest change will probably be in the cam. I am considering 2 possibilities:
- use the d15b1 cam
- send my a6 off to Bisimoto to have a more precise tune. They say I probably need level 2 for my needs.
I guess the best one involves having a narrower lsa (at least that's how I understand it). Of course either one of these will require the ecu to be tuned for my needs. My ecu is from an 88 crx si. I see others say this ecu cannot be chipped. I wonder if there's a way around this...

I will come back with a transmission update tonight.

 

Is an aftermarket cam going to make any difference at all at 2500rpm? You'd be better off making the car lighter. Lighter wheels, eco tyres, smaller battery.

 

Making it lighter will make a small difference, but I want more than what I would get from 100 lb reduction. I understand the use of the b1 will decrease the hp, but I am thinking it may have a narrower lsa compared to the a6 which might give me the torque I'm looking for. After all, the d15b1 peaks at 3000 rpm and the d15b6 peaks at 2200 rpm. The a6 peaks much higher.