Has anyone followed auto prices to see if they are following manuals upwards? If they don't the increased delta might make this worth while after all.
1991 transmission swap - Auto to manual
- Thread starter 32york
- Start date
Without this, would it be possible that the power steering would work the first time that car is started after reconnecting the battery and then it go away after the car is turned off?
The powersteering would work until you started moving. The Auto ECU looks for 2 speed signals, the diff sensor & the speed sensor.
I'm curious, what did you do about the crank pulley? It is different - the auto has some holes in it all around to view the harmonic balancer, the manuals don't its all solid black; or did you go aftermarket
Thanks.
Thanks.
All the conversions I have done retain the AT balancer. not sure why they do different pulleys. No problems have been reported to date.
great article 
any chance on shedding some lights on how to remove the resistor from the auto ecu so it can be used after being converted to manual ? appreciate any help
any chance on shedding some lights on how to remove the resistor from the auto ecu so it can be used after being converted to manual ? appreciate any help 
any help on which resistor is removed/shorted to convert the AT ECU -> MT?
I am in process of converting from AT-MT. These are an extract of my notes
My goal is a 100% conversion
Falling short of the goal:
1. the main interior wiring harness is different because the AT has solenoid outputs and the connectors for the AT control module.
2. The AT engine has different camshafts, which require the AT ECM. You must change the MT camshafts and MT ECM as a set.
3. There is also an AT engine compartment sticker with slightly different idle speeds (MT JDM version 87533-PR7-J01).
4. The ALB and TCS control units have "AT" on their exterior information stickers. This appears to be cosmetic as everything appears to work just fine regardless of the AT/MT designation. But I am a purist.
I will get to these as time permits. I have a USDM MT TCS, ECU and am awaiting MT camshafts to show up at a decent price.
Challenges of the interior:
If I have to do this job again: I would remove the dash to begin. Just start with that while everything in your garage is clean and space is available.
a. The long hard clutch hard pipe needs to be installed in the front LH corner of the passenger compartment. Very challenging to get the plastic brackets apart, the pipe in place, and back together if the pipe is not perfectly positioned and in factory shape (I spent hours on this). Installation of this pipe through the front bulkhead requires removal of the glove box, control stack+bracket, and a few other bits+bobs that are hard to get to with the dash in place. You must also torture the pipe to get it into position, its not worth it with the dash in situ. The clutch hard pipe also requires dropping of the fuel tank as there is a joint (Clutch joint 46939-SL0-003, bolt [6x25] 95701-06025-05) mounted on the LH side of the body, but that can be done after you have re-installed the interior.
b. Brake/Clutch Pedal conversion is in very tight quarters. Removal of the entire steering column is required.
c. The center console, shifter mechanism, and cables must be removed. It is easier with the dash out of the way.
d. The instrument cluster should be removed to deal with the automatic tach face.
e. An LED brake conversion will require the removal modification of the flasher unit, which is buried (at least on RHD cars).
Doing of the math of adding "a" to "d", it would have been faster, easier and higher quality to do just remove the dash as the first order of business.
Knowledge Base
i. The AT has a water cooling system that requires plumbing the MT does not require. The cooling water manifold thermostat housing (19410-PR7-A00) has an extra port to feed the AT and the oil cooler has a long hard pipe to receive the coolant (19425-PR7-A00). This pipe just makes getting to the speed sensor difficult. It is also more weight and an unneeded extra point of failure. The o-ring on the cooling connector as a special o-ring size that is used on the NSX and Honda motorcycles.
ii. The safety interrupt switch on the clutch pedal (requiring the clutch pedal to be depressed prior to start the engine) and the connector is just rare otherwise. The EU has one switch, and the US seems to have two (both Normally Open, but on top and bottom of the pedal. So one switch will be closed depending on if the pedal is up or down). Get the USDM pedal mount if you want a clutch starter interrupt.
iii. The AT flexplate bolt heads are 1mm shorter than the MT. Any socket misalignment, the bolt will become rounded and you have to get the grinder out. Spend time lining everything up before hitting the impact wrench. A couple of seconds extra per bolt will save you hours.
iv. Hondabond and Urea Grease is considered HazMat or liquid something and cannot be shipped overseas without a lot of hassle. I will have to have this contraband muled in with my next visitors from the States.
v. The AT transmission harness that controls the solenoids can be retrofitted and connected up to the MT transmission for the neutral and reverse lights. There are 4x AT connectors and 2x MT ones, just connect up the MT ones that fit. And the modify the C499 connector that is located on the interior left, just below the DIN stereo connectors.
vi. The AT neutral input goes from the AT shifter, through the instrument cluster and into the ECM. The MT interior harness connects up to the MT engine harness that goes into the MT transmission neutral switch. A wire will have to be run from C499 to the vestigal AT shifter connector to give the ECM the neutral sense.
vii. The key removal interlock can be removed or grounded out at the shifter connector or connected to the hand brake light switch. I connected it to the hand brake (with a couple of diodes to be safe) and it now requires the hand brake to be engaged before the key can be removed. I like this new safety feature.
I will update this post or thread as I get more knowledge and experience.
My car is JDM RHD, but unlikely to be germane.
//wiring change notes:
Locate the brown 2 pin connector, this is the AT neutral switch. The engine will not crank/start if this connector is left open.
Cut the connector off and join these two wires together
Route wires to a Normally Closed (black or white top) clutch switch (optional).
ECM Neutral Switch input
Locate the 12-Pin Connector (C425/6) blue/orange Light Green wire. Connect this wire to ground, the black wire on C425/8).
Or run Blue/orange wire to clutch switch & to ground (Clutch pedal switch optional)
Reverse/Back-Up Lights
Locate connector C499, it a blue 12-pin connector located on the interior rear LH bulkhead, just below the TCS and near the LH seat belt retractor.
Reroute C499/4 to C499/3. This reroutes the former solenoid control, through the MT reverse switch to the reverse lights.
Reroute C499/11 to C425/10 YLW to wire up the power to the reverse lights.
To avoid cutting the original wiring harness, these connectors can be salvaged from a similar year AT Accord/Civic (shifter), Odyssey (under drivers dash). C499 and C425 use the same connector shell. Alternatively, the original shell can be opened up, the pins removed with a pick, connected up with a salvaged pins and wrapped with electrical tape.
Key Interlock (choose one)
Remove Interlock control unit
Route C425/11 Gry/Wht to the ground, nearest ground on the dash.
Connect C425/11 to hand parking brake connector. Non-standard, but will force engagement of hand brake to remove the key.
My goal is a 100% conversion
Falling short of the goal:
1. the main interior wiring harness is different because the AT has solenoid outputs and the connectors for the AT control module.
2. The AT engine has different camshafts, which require the AT ECM. You must change the MT camshafts and MT ECM as a set.
3. There is also an AT engine compartment sticker with slightly different idle speeds (MT JDM version 87533-PR7-J01).
4. The ALB and TCS control units have "AT" on their exterior information stickers. This appears to be cosmetic as everything appears to work just fine regardless of the AT/MT designation. But I am a purist.
I will get to these as time permits. I have a USDM MT TCS, ECU and am awaiting MT camshafts to show up at a decent price.
Challenges of the interior:
If I have to do this job again: I would remove the dash to begin. Just start with that while everything in your garage is clean and space is available.
a. The long hard clutch hard pipe needs to be installed in the front LH corner of the passenger compartment. Very challenging to get the plastic brackets apart, the pipe in place, and back together if the pipe is not perfectly positioned and in factory shape (I spent hours on this). Installation of this pipe through the front bulkhead requires removal of the glove box, control stack+bracket, and a few other bits+bobs that are hard to get to with the dash in place. You must also torture the pipe to get it into position, its not worth it with the dash in situ. The clutch hard pipe also requires dropping of the fuel tank as there is a joint (Clutch joint 46939-SL0-003, bolt [6x25] 95701-06025-05) mounted on the LH side of the body, but that can be done after you have re-installed the interior.
b. Brake/Clutch Pedal conversion is in very tight quarters. Removal of the entire steering column is required.
c. The center console, shifter mechanism, and cables must be removed. It is easier with the dash out of the way.
d. The instrument cluster should be removed to deal with the automatic tach face.
e. An LED brake conversion will require the removal modification of the flasher unit, which is buried (at least on RHD cars).
Doing of the math of adding "a" to "d", it would have been faster, easier and higher quality to do just remove the dash as the first order of business.
Knowledge Base
i. The AT has a water cooling system that requires plumbing the MT does not require. The cooling water manifold thermostat housing (19410-PR7-A00) has an extra port to feed the AT and the oil cooler has a long hard pipe to receive the coolant (19425-PR7-A00). This pipe just makes getting to the speed sensor difficult. It is also more weight and an unneeded extra point of failure. The o-ring on the cooling connector as a special o-ring size that is used on the NSX and Honda motorcycles.
ii. The safety interrupt switch on the clutch pedal (requiring the clutch pedal to be depressed prior to start the engine) and the connector is just rare otherwise. The EU has one switch, and the US seems to have two (both Normally Open, but on top and bottom of the pedal. So one switch will be closed depending on if the pedal is up or down). Get the USDM pedal mount if you want a clutch starter interrupt.
iii. The AT flexplate bolt heads are 1mm shorter than the MT. Any socket misalignment, the bolt will become rounded and you have to get the grinder out. Spend time lining everything up before hitting the impact wrench. A couple of seconds extra per bolt will save you hours.
iv. Hondabond and Urea Grease is considered HazMat or liquid something and cannot be shipped overseas without a lot of hassle. I will have to have this contraband muled in with my next visitors from the States.
v. The AT transmission harness that controls the solenoids can be retrofitted and connected up to the MT transmission for the neutral and reverse lights. There are 4x AT connectors and 2x MT ones, just connect up the MT ones that fit. And the modify the C499 connector that is located on the interior left, just below the DIN stereo connectors.
vi. The AT neutral input goes from the AT shifter, through the instrument cluster and into the ECM. The MT interior harness connects up to the MT engine harness that goes into the MT transmission neutral switch. A wire will have to be run from C499 to the vestigal AT shifter connector to give the ECM the neutral sense.
vii. The key removal interlock can be removed or grounded out at the shifter connector or connected to the hand brake light switch. I connected it to the hand brake (with a couple of diodes to be safe) and it now requires the hand brake to be engaged before the key can be removed. I like this new safety feature.
I will update this post or thread as I get more knowledge and experience.
My car is JDM RHD, but unlikely to be germane.
//wiring change notes:
Locate the brown 2 pin connector, this is the AT neutral switch. The engine will not crank/start if this connector is left open.
Cut the connector off and join these two wires together
Route wires to a Normally Closed (black or white top) clutch switch (optional).
ECM Neutral Switch input
Locate the 12-Pin Connector (C425/6) blue/orange Light Green wire. Connect this wire to ground, the black wire on C425/8).
Or run Blue/orange wire to clutch switch & to ground (Clutch pedal switch optional)
Reverse/Back-Up Lights
Locate connector C499, it a blue 12-pin connector located on the interior rear LH bulkhead, just below the TCS and near the LH seat belt retractor.
Reroute C499/4 to C499/3. This reroutes the former solenoid control, through the MT reverse switch to the reverse lights.
Reroute C499/11 to C425/10 YLW to wire up the power to the reverse lights.
To avoid cutting the original wiring harness, these connectors can be salvaged from a similar year AT Accord/Civic (shifter), Odyssey (under drivers dash). C499 and C425 use the same connector shell. Alternatively, the original shell can be opened up, the pins removed with a pick, connected up with a salvaged pins and wrapped with electrical tape.
Key Interlock (choose one)
Remove Interlock control unit
Route C425/11 Gry/Wht to the ground, nearest ground on the dash.
Connect C425/11 to hand parking brake connector. Non-standard, but will force engagement of hand brake to remove the key.
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If I get another NSX I would get an Auto and build the tranny to handle the J series swap for those days that I am drinking and/or texting when behind the wheel....
I have all this bookmarked for my project. Thanks for posting, Drew.
>I have all this bookmarked for my project. Thanks for posting, Drew.
I have a four-page guide while not comprehensive, but it should be extremely helpful.
I would like to publish on the wiki. I am unclear on how to make a new page, the How To goes to a deleted page, seems like the last modification to the wiki was sometime in 2013?
If one is interested for a copy PM me your email and I'll forward you the latest version.
I have a four-page guide while not comprehensive, but it should be extremely helpful.
I would like to publish on the wiki. I am unclear on how to make a new page, the How To goes to a deleted page, seems like the last modification to the wiki was sometime in 2013?
If one is interested for a copy PM me your email and I'll forward you the latest version.
Converting AT to MT
Hi Drew,
I'm in Australia, and have just picked up one of the few Asutralian delivered NSX's. Like most of them, it's an Auto. How do you go with the conversion, and after a bit of time, would you recommend it? How much did it cost if you don't mind my asking, and where did you source all of the parts? Cheers!
Hi Drew,
I'm in Australia, and have just picked up one of the few Asutralian delivered NSX's. Like most of them, it's an Auto. How do you go with the conversion, and after a bit of time, would you recommend it? How much did it cost if you don't mind my asking, and where did you source all of the parts? Cheers!
The conversion went well, without issue or problems. I left the AT cam shafts, pullies, and ECU. It drives great.
Cost a bit over US$10K. I sourced the "kit" from: EU, UK, US, JP, AU, and NZ.
Is it worth it? Not sure.
Financially, I probably came out ahead as the RHD MT sells for more [than the parts cost of] an AT.
Time, I guess I treated it as entertainment and keep my brain from turning to oatmeal. Though I'm getting older and starting to value my time a lot more.
Would I do it again: probably not...at least not with a functioning AT transmission. The AT version drives really well, it is a lot of fun, and taking out perfectly working items for different working items is a bit foolish.
I drove an LHD MT as a daily driver in the States for almost 15 years and enjoyed every bit of it, it was there for a lot of wonderful milestones in my life. I figured I would want the same thing in my new RHD country, but honestly it doesn't matter that much. Honda did an amazing job with the AT.
I recommend acquiring all the parts in a complete kit, if your AT fails: change it out to MT. A complete kit will only gain in value over time, a lot more than the sum of its parts. The differences in LHD vs RHD is a small number of parts.
There is one big benefit: I am now working on cool collaboration projects with other engineers and makers on NSXprime. This IS the real benefit: the people you meet along the way, help, and become friends with. Well worth it.
I have met other friends in my life when picking up other hobbies like scuba, karting, and owning some unique cars. It's the whole experience that makes it worthwhile.
Source of parts: WhrdNSX, Christian at ATR https://www.nsx-parts.com/shop/, Amayama.com, eBay.com, and auctions.yahoo.co.jp (WhrdNSX facilitates acquisition too). BTW: Parts on jp yahoo for a small fortune for some reason, not sure if they are allowed to use amayama.com
Cost a bit over US$10K. I sourced the "kit" from: EU, UK, US, JP, AU, and NZ.
Is it worth it? Not sure.
Financially, I probably came out ahead as the RHD MT sells for more [than the parts cost of] an AT.
Time, I guess I treated it as entertainment and keep my brain from turning to oatmeal. Though I'm getting older and starting to value my time a lot more.
Would I do it again: probably not...at least not with a functioning AT transmission. The AT version drives really well, it is a lot of fun, and taking out perfectly working items for different working items is a bit foolish.
I drove an LHD MT as a daily driver in the States for almost 15 years and enjoyed every bit of it, it was there for a lot of wonderful milestones in my life. I figured I would want the same thing in my new RHD country, but honestly it doesn't matter that much. Honda did an amazing job with the AT.
I recommend acquiring all the parts in a complete kit, if your AT fails: change it out to MT. A complete kit will only gain in value over time, a lot more than the sum of its parts. The differences in LHD vs RHD is a small number of parts.
There is one big benefit: I am now working on cool collaboration projects with other engineers and makers on NSXprime. This IS the real benefit: the people you meet along the way, help, and become friends with. Well worth it.
I have met other friends in my life when picking up other hobbies like scuba, karting, and owning some unique cars. It's the whole experience that makes it worthwhile.
Source of parts: WhrdNSX, Christian at ATR https://www.nsx-parts.com/shop/, Amayama.com, eBay.com, and auctions.yahoo.co.jp (WhrdNSX facilitates acquisition too). BTW: Parts on jp yahoo for a small fortune for some reason, not sure if they are allowed to use amayama.com
drew said:
This made me laugh out loud. Love it.
drew said:
Having owned/driven both versions, I agree 100%. For [MENTION=37151]allhart[/MENTION], a better and less expense route you may want to consider is to have your AT properly serviced. Honda did a poor job documenting the required services on the AT and, as a result, they have developed an undeserved reputation for being fragile and unreliable.
The NSX auto transmission is quite clever and different than most auto transmissions from other makes. Compared to a traditional "slushbox" style unit, which uses circulating fluid pressure to change gears, the NSX transmission is better described as an automatic-manual transmission. Instead of having one clutch like the MT, it has four- one for each gear. And, instead of pushing on the pedal with your foot to engage the clutch, the AT uses hydraulic pressure to do it. It's an amazing system that delivers much more crisp, sporty shifting compared to a traditional automatic. It shifts with a clutch like a manual, just automatically. However, this novel design raises maintenance issues that are not needed in other types. First is the clutch packs. They are just like the clutch disc on a manual car, except they are smaller and bathed in ATF. They use friction to transmit force to the gears, so just like a regular clutch they eventually wear out. They also make a lot of dust, just like a MT clutch. This dust collects in the ATF, which passes through an internal filter. Eventually, around 100,000 miles, the filter clogs. The clog causes a pressure drop across the filter, so there is less fluid pressure available to actuate the clutch packs. This results in shifting hesitation and a feeling like the car is "slipping" gears. It can also have another bad effect: shattering the clutch packs. Basically, the fluid builds up in the filter until it finally blows through the clog and then hits the clutch pack. It feels like a lurch and it is the same as dumping the clutch on a MT car. Eventually, this shock shatters the clutch discs and boom, your AT goes down. It can also cause your torque converter to break for the same reason. The key to the NSX AT, therefore, is keeping the fluid clean. Frequent fluid changes can help, as it will pull a lot of that clutch dust out of the system. But, you will still have to replace the filter eventually and the clutch packs too.
I think you should keep your AT and just service it properly. That means changing the internal filter and clutch packs, and possibly the shift solenoids too. With a fresh AT box, I think you'll be quite surprised at how sporty the NSX can feel. It's perfectly capable of tracking, and the extra low-rpm torque over the MT is quite nice. The cost will be much, much less than converting to MT. I'm at about $15,000 US, but unlike Drew, I'm doing the full MT engine changes too (cams, ECU, etc.).
Having said all that, I am converting my AT to MT lol, but for different reasons. I happen to think the AT NSX is great.
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Thanks so much [MENTION=5430]drew[/MENTION] and [MENTION=18194]Honcho[/MENTION]. Definitely not as straightforward a decision as I initially thought! Part of the problem has been that if when you read about automatic NSX's online, you get the impression that you don't have a "real" NSX if it's not a manual. Mine is a '95 with the f-matic, and I've only had it for a few months, but it's taught me that the transmission is not terrible at all. I also have a V8 Vantage S Sportshift - also a an "automatic-manual" transmission that cops a lot of flak online, but I love that too, as you just have to learn how to drive it properly. The value difference here in Oz is a big factor too, but while I know the car would be worth more (maybe a lot more) than the cost of conversion, if I never intend to sell it, then I'll never get that money back anyway, so it has to be about the enjoyment of the car.
I've been very fortunate to catch up with [MENTION=10956]whrdnsx[/MENTION] who has done quite a few conversions here, so that's a big plus (very generous guy with his knowledge and time too). I think I'll take both of your advice for now and keep it as is. If the transmission goes, or if I come across a great deal on a manual transmission, then I might progress, even if it is just to keep the necessary parts on standby.
Thanks again for your time, and the effort of your responses.
I've been very fortunate to catch up with [MENTION=10956]whrdnsx[/MENTION] who has done quite a few conversions here, so that's a big plus (very generous guy with his knowledge and time too). I think I'll take both of your advice for now and keep it as is. If the transmission goes, or if I come across a great deal on a manual transmission, then I might progress, even if it is just to keep the necessary parts on standby.
Thanks again for your time, and the effort of your responses.
It may have been done in Japan, but honestly even the early 4-speeds are great from a performance driving standpoint. The AT computer does a good job holding lower gears at the right times (braking into corner and then corner exit). There is an old Acura promo video from the 90's showing an AT 91 just ripping around the racing circuit. I've driven an F-matic 2002 and honestly, I just left it in auto. Not sure it is worth the $$$ to convert it.
A magneti marelli f-1 gearbox is a thing of beauty, crossed with temper of a red headed italian woman. As much as I would love it, it would totally kill the driving experience of an NSX (auto or manual). I hear good things about the NSX 4 speed, yet I never liked the TL 5 speed auto, especially shifting in manual mode. The new generation of DCTs are better, but seems like computer controlled clutch engagement just isn’t as smooth as a human controlled; just a lot faster.
Miner
