Rep Power: 118

Hello everyone, I am planning on swapping my failing automatic transmission to a 5 speed and I understand that the auto and manual sub frames are different and I need to know what exactly the difference is. One post said the only difference is that the front mount is off by about an inch but another post said the front and rear mounts are both slightly off. If the front mount point is the only difference I can live with that until a local junkyard gets another 5 speed Civic in since I have very stiff Innovative polyurethane mounts, but if the rear mount is different too then that's gonna be a problem.

Thank you in advance as always, any information is greatly appreciated!

 
Rep Power: 125

@mac25

One of the mods can verify but I’m pretty sure this guy manual swapped his so he’ll have the answer. He hasn’t been on in a while though.

 
Rep Power: 118

Cool, thank you. When I find a manual sub frame I will be sure to post an update showing the exact differences in case anyone else needs to know at some point.

 
Rep Power: 223

Looking at pictures of both it does look like the rear is the same but the front is off by an inch or so. It's difficult to tell though. RockAuto does not show different rear mounts for auto/manual so I would guess that mount point is the same.

 
Rep Power: 118

Thank you. That's pretty much what I was thinking but as you said its difficult to tell for sure without trying it or having them both to measure. As long as the rear mount fits correctly I think I should be fine for now until I get the proper subframe as long as I take it easy. With 3 Innovative 75A mounts holding the engine and trans in place on both sides and in the back I'm really not expecting it to fall out.

 
Rep Power: 118

Also, does anyone know what exactly the differences are between the auto and manual ECU? I know that my auto ECU will activate VTEC and let me rev to redline without the trans harness plugged in since I already tried it, so would I get any benefit from changing the ECU other than not having trans codes? I don't mind changing the ECU and paying a locksmith to flash it if I get a benefit out of it, but I don't want to pay for something that won't benefit me. I suspect this is one of those things I will have to try for myself, but if anyone knows the differences I would appreciate the info. Thanks in advance as always!

 
Rep Power: 223

Clutch and park/brake interlocks for starters. Not sure how cruise control would work without everything setup properly.

 
Rep Power: 118

Thanks for the information. I'm not concerned about the starter interlock as I have the common sense to not try to start it in gear. I'm not too concerned about cruise control for now either, but I could also see that being a problem with the wrong ECU. Would you expect the engine to be affected by the auto vs manual ECU? Potentially different tuning?

 
Rep Power: 223

Not that I can think of.

 
Rep Power: 222

Just buy the correct ecu, Honda spent millions making them different for a reason

 
Rep Power: 118

I have the correct ECU, I got it from the donor car with the rest of the swap. I'm just wondering if anyone knows what benefit I would see if I change it and pay ~$100 to have it flashed. I understand that there's a reason Honda made different ECUs, but no one seems to know what the differences are. For all I know the only difference may be that the manual ECU won't set auto error codes, which wouldn't be worth paying for a flash at this time if that's the only difference.

 
Rep Power: 367

just try it
if it throws a transmission code, you know what to do.

 
Rep Power: 118

Update- I found a manual subframe and swapped the trans. From what I can tell the auto and manual subframes are the same other than the front mount. As for the ECU, I think it's confused. Since I changed the trans it sometimes seems to idle higher like it can't bring the RPM back down. It also surges when coasting in neutral or with the clutch in instead of idling normally. I assume the auto ECU is confused since it idled and drove perfectly before I swapped the trans. Other than that it runs and drives perfectly though, the 5 speed is definitely a lot more fun than the auto. I will report back after I get the 5 speed ECU flashed, hopefully that solves the idle issue.

 
Rep Power: 222

IAC may be different between auto and manual as well, can't remember

 
Rep Power: 118

Good point. I'm not sure but I have an RSX-S throttle body so it should be the manual one.

 
Rep Power: 0

vehicle speed sensor is not the same automatic vs manual. Just watched on youtube vtec academy how to convert auto harness to manual harness. Thats why ecu is confused.
theres a few things must do including changing a few pin outs at ecu.

 
Rep Power: 118

The signal appears to be the same, the speedometer reads properly and the ECU reports the correct speed on my Scangauge with the auto harness and no wiring mods.

 
Rep Power: 0

watching vtec academy's videos on youtube is best. Im new to hondas but theres something about speed sensors being diff frequency. Its all explained in his videos. Vtec academy = hasport very trusted source.

 
Rep Power: 118

That doesn't have anything to do with these D series transmissions, it's a K series thing. Some of the K series transmissions like the 02-05 Civic Si and 02-04 RSX have the old style (low frequency) speed sensor and are easier to use for swaps than the transmissions from the 06-11 Civic Si, 05-06 RSX, etc which have the high frequency speed sensor. Never did an auto to manual swap on a K series so I can't say what differences may or may not exit there.