Welcome to the DSM community. I've done the swap. Its not that hard but you run into a few hmmm moments along the way even with a guide. I THINK this is the one I used. Its a step by step that tells you what to buy also. If this doesnt link then copy past this link from 2GNT Eclipse forum. 2GNT.com - ATMT
You didnt mention what year the car is. If its a 95 then you should swap to a 95 MANUAL ECU/ECM engine computer. 95 is the only OBD1 year. 96-99 are all OBDII. Its easiest to keep the ECU same year as the car as some minor calibration changes may have been made but 95 is the only one youre really stuck with if you have that year car.
The guide says you need a MANUAL engine computer (ECU/ECM). For test purposes you CAN drive using the automatic engine computer but you will have NO speedometer! This is why the instructions say to get a manual ECU. If its an OBDII car you'll probably have a Check eng light (CEL) after you yank out all the auto trans sensors. Once you swap to a MANUAL ECU you can unplug the auto trans computer and shouldnt have a CEL. And with a manual ECU you should be able to wire in the manual speed sensor to get the speedometer back.
Make sure to get a brake pedal assembly from a manual car donor. You can NOT keep the auto brake pedal. The auto brake pedal interferes with the clutch pedal assembly so when you grab a clutch pedal...get the brake pedal too...and shift cables...and everything else the swap guide says to get.
Transmissions you can use. Eclipse non turbo manual 95-99, Talon non turbo 95-98, Dodge Avenger non turbo 95-99, Dodge Neon non turbo manual but ONLY the RT/ACR Magnum cars with a 3.94 drive ratio transmission (same as the Eclipse NT)!! The standard non performance Neons came with 3.55 gears and although the transmissions will bolt up to an Eclipse...it will be a complete SLUG off the line. For this reason ONLY choose the Neon manual from the RT/ACR Magnum cars. Early Neons came with cable operated clutches but I believe by the time RT/ACR cars were out those were all hydraulic clutches by then. Just BE CAREFUL if going with a Neon trans bcus you could end up with the wrong one. Chrysler PT Cruiser transmissions will also work thru the early 2000s as they have the 3:94 final ratio also. I'm not sure exact years to choose for PT Cruisers. Be aware that some versions of the 350NV-T transmission may use c clips OR cotter pins to secure the shifter cables to the transmission depending on which vehicle it was used in and you may need to make some minor modifications depending on what hardware you have available.
Think the whole swap cost me around... $700 including used transmission, new and salvage yard parts...plus 3 different types of trans fluid til I found the one that worked!! Redline MTL is all I recommend! The factory started with gear oil but later went with Auto trans fluid (Dexron IV) in the manual Eclipses/talons just to save $! I tried DexronIV and mine would hardly shift. Pennzoil syncromesh was better but still very notchy. Redline MTL did the trick and per the tech I spoke with at Redline its safe for the Fiberride clutches in an Eclipse non turbo manual trans (NV-T350). MTL is around $15-20 U.S. per quart and you need just over 2 quarts.
If you do the swap have fun! Its a learning process. Totally different car afterwards too. Auto Eclipses have no bottom end at all and the manual wakes it right up!
Wouldnt hurt to change the output shaft seals since they'll likely have over 100k miles on them! Also your stock auto half shafts WILL fit! If theyre original and have high mileage tho you might want to change them out to avoid a possible CV joint failure due to mileage or age. Remanufactured axles probably run around $50 give or take, per shaft with core exchange.
Oh yeah...get plenty of degreaser to clean the donor trans, brake cleaner, and some nice silver /aluminum engine paint to make it look niiiice. (and kitty litter to handle fluid spills)
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