Geo Metro automatic to manual transmission switch

The project:
Install engine and manual transmission from a 1991 Geo Metro 2 door (with crappy stereo) into a 1994 Geo Metro 4 door with a worn out automatic transmission and blown engine (but a great stereo and air conditioning and red instead of aqua-baby blue). I did this because I really wanted a 4 door commuting car with AC. This is not an endeavor for the faint of heart... That being said, I, with a little help from my friends, was able to accomplish this task on two weekends. Now understand this was strictly a white trash operation with logs for jack stands, a makeshift engine hoist made from logs, rope, and a 6"x6" beam, and plenty of empty beer cans lying about. What I’m trying to say is that a guy could do this in a day or two in a decent shop with good jacks and engine hoist.

This is the first time that I have attempted anything like this and Luckily I had the whole 1991 Geo with the manual transmission to use for extra parts, more parts from the 1991 would be needed than I expected.
We started by jacking up both cars and taking off the CV joints.(remove tires and disconnect hub assembly from struts. Be careful not to damage CV Joints that come out of the manual transmission as they will still be needed) We unhooked everything from the engine-blocks unbolted and lowered the engines and transmissions out from under the front of the car as single units. Note: The Automatic transmission has an additional mounting bracket on the rear.

My friend Jeff (right) and I (left) use some of the "Magic Orange" to get the grease off after successfully removing the 1994 engine and transmission.

I really did block the cars up much better than this before working underneath them! In fact I had giant log rounds under the front of the chassis.

Circled is the rear transmission shock mount used only with automatic transmission. Gosh, the automatic transmission is as big as the engine. No wonder the car was a dog.

Dont forget to disconnect the speedometer cable. Here is the retainer clip.

Remove pedal assembly (brake, clutch and clutch cable) from old car and install it in new car. GRRR...This is a back-breaker. It also requires drilling 3 new holes in the firewall for the clutch cable and clutch cable retainer. These holes are blanked out on the inside of the firewall. I used a center punch to dent these holes from the inside out so that I could see where to drill them from the outside. To drill them from the inside I would have had to take off the dashboard and I wanted to avoid this if at all possible (thankfully it was).

Brake pedal and shifter removed from the automatic.

Remove the automatic shifter cowling and replaced it with the standard shifter cowling.

Hole for clutch cable between vacuum assist brake unit and right-front strut housing.

I had to drill these holes in the in the 1994 automatic metro. Here it is installed.

I found a fellow that has some great shots posted online illustrating this. I hope he doesn't mind that I used his pictures.

Install manual gearshift assembly. This requires the removal of the entire automatic transmission shifting assembly as well as the rear automatic-transmission mounting bracket welded to the underside of the car. It isn't used with a manual transmission and it will get in the way of the anchor rod on the new manual shifting assembly. (cut off or pound flat)

Manual shift assembly.

Shift rod, anchor rod and shift rod to transmission linkage. (pictured here without required nuts and bolts)

Remove left front automatic-transmission shock-mount bracket. I did this with a chisel and a small sledge-hammer, crude but effective (be careful not to damage chassis and rember to paint over exposed metal).

I had to remove the left-front automatic transmission mounting bracket.

Notice the left-front automatic transmission shock mount circled in white in the center of the picture.

Picture of how the left-front automatic transmission bracket we had to remove attached to automatic transmission.

Drill new holes for the left-front manual transmission shock-mount bracket. **They do not match up with the old mounting bracket holes.** The position for these holes is blanked out on the inside of the chassis. Drill 3/4” holes through on the other side of the chassis to find the guide holes. This has to be done anyway in order to thread nuts on the bolts that hold on the new mounting bracket.

Circled in white are the correct position of the holes for the manual transmission shockmount bracket. These holes are not pre-drilled on the automatic chassis. DO NOT screw up when drilling these holes...you may only get one chance.

Again the same fellow that I mentioned above has done a nice website documenting this conversion as well. I borrowed this picture (I hope he doesn't mind) as it dose a much better job of illustrating what needs to be done here. Here is the link to his website. I highly recommend checking it out.

Drilling these holes requires removing the wiper fluid reservoir.

Fabricate a metal plate to cover the hole in firewall left behind by the removal of the automatic transmission shift linkage.

Automatic transmission shift linkage.

Removal of the automatic transmission shift linkage mounting plate will leave a hole in the firewall that needs to be covered with a fabricated blank.

This keeps engine compartment fumes from getting into the passenger compartment, always a good idea.
Hoist new engine and transmission into car. I will not even go into detail on how we accomplished this for fear that someone else might try our white-trash method and hurt themselves. Special note: I had to use the right front engine mounting bracket from the 1994 engine that I took out. For some reason the mounting brackets were different ...maybe a 1991 to 1994 issue.

1991 right-front engine bracket. (slightly different from the 1994 bracket)

Cousin Jill holding up her end of the beer drinking. I wonder why she isn't all greasy and dirty?

We had to install the manual transmission CV joint set from out of the 1991. The automatic transmission CV joint set is offset about 3” from the manual set and will not work with a manual transmission.(at least in my case it wouldn't. Maybe this is a 1991 to 1994 or automatic to manual issue...I don't know)

CV joint set from automatic transmission. The Manual transmission CV joint set is not the same.

I cut off the multi-pin (shifter position) plug from the top of the automatic transmission.

Multi-pin shifter position plug scavenged from automatic transmission.

This gave me a very handy way to rewire the existing 1994 automatic wiring harness to work with the new manual transmission. It was an easy way to get the backup lights working and override the safety relay that allows an automatic to start only when park. (The two center wires needed to be shorted together for the starter to work, the yellow and red wires needed to be wired to the reverse switch leads on top of the manual transmission for reverse lights to work, and the rest of the wires I cut off short and insulated with electrical tape for they serve no purpose with a manual transmission.)

New harness plug scavenged from old automatic transmission and modified to facilitate voltage to the starter motor relay and backup lights.

red-black/red-yellow combo go to reverse switch on top of manual transmission. Two center wires are shorted together and the multi wire bundle is just secured together with tape (these wires could be cut all the way off if desired).

here is a picture of the new wiring harness plug installed. The reverse light switch on the manual transmission is circled in white.

Here is the obligatory finished engine shot. (Oh god...who left that wrench in there?!!) Just kiddin'.

Note: When switching engines from Metros made in different years you should probably change the block only and leave anything hooked to the wiring harness in place. This will eliminate any electronics incompatibilities notably distributor, carburetor sensors, intake manifold sensors, engine coolant sensors and other related vacuum hoses sensors and such. I learned this the hard way. When I got the engine changed over it would turn over but it wouldn’t start presumably because the distributor from the ‘91 wasn’t sending the right signal somewhere to operate the ignition system in the ’94. I re-installed the distributor from the 1994 and it started right up. Once I got this working the car would run but it started overheating because the radiator fan sensor wasn’t turning the cooling fan on. Sure enough the fan sensor from the ’94 was a different diameter (and probably a different spec) than the ’91 fan sensor. This required putting the temperature sensor housing I took out with the old engine back onto the engine I just installed. This wasted a lot of antifreeze..DOH. You will also want to make sure that you have some gasket paper handy in case you damage the gasket when you remove the engine coolant sensor housing.

I have probably forgotten some important points as I am writing this in retrospect but as I remember I will include them. Hopefully this is of some help to someone. My new Geo Metro is running great and getting about 50MPG. With todays fuel prices and my 120 mile per day commute I couldn't be happier.

for all of their suggestions. This project would have been a lot harder without their vast archive of Geo Metro information. You can find my post on this subject there at

87-88 Sprint Turbo,89 & later Metro, Tracker, Storm.
12 Diagnostic function working
13 Oxygen sensor or circuit
14 Coolant temperature sensor or circuit (open)
15 Coolant temperature sensor or circuit (shorted)
21 Throttle position sensor or circuit (open)
22 Throttle position sensor or circuit (shorted)
23 Intake air temperature sensor or circuit (open)
24 Vehicle speed sensor (VSS) or circuit
25 Intake air temperature sensor or circuit (shorted)
31 High turbo pressure (87 - 88)
31 Barometric pressure sensor or circuit (89 -95)
32 Barometric pressure sensor or circuit (89 - 95)
32 EGR system (91 - 93)
33 Airflow meter (turbo)
33 Manifold Absolute Pressure (MAP) sensor (90 - 91)
41 Ignition signal problem
42 Crank angle sensor (except Storm)
42 Camshaft position sensor circuit (94-95)
42 Electronic Spark Timing (EST) (Storm)
44 ECM idle switch circuit open
44 Oxygen sensor or circuit - lean exhaust
45 Oxygen sensor or circuit - rich exhaust
46 Idle speed control motor
51 EGR system (except Storm)
51 ECM (Storm)
53 ECM ground circuit
ON Steady ECM faulty

89 - 92 GEO
13 Oxygen Sensor circuit.
14 Coolant Temperature Sensor circuit. High temperature indicated.
15 Coolant Temperature Sensor circuit. Low temperature indicated.
21 Throttle Position Sensor Signal Voltage High (Automatic Transmission).
22 Throttle Position Sensor Signal Voltage Low.
23 Intake Air temperature (MAT) Sensor. Low temperature indicated.
24 Vehicle Speed Sensor circuit.
25 Intake Air temperature (MAT) Sensor. High temperature indicated.
31 MAP Sensor circuit - Signal Voltage Low Vacuum.
32 MAP Sensor circuit - Signal Voltage High Vacuum.
33 MAP Sensor circuit.
41 Ignition Signal circuit.
42 Crank Angle Sensor.
44 Idle switch open or improper adjustment.
45 Idle Switch Circuit Grounded or Improper Adjustment.
46 Idle Speed Control Motor circuit.
51 EGR circuit.
53 Ground circuit

89 - 92 GEO Metro TBI
13 Oxygen Sensor circuit.
14 Coolant Temperature Sensor circuit. High temperature indicated.
15 Coolant Temperature Sensor circuit. Low temperature indicated.
21 Throttle Switch circuit (Manual Transmission).
21 Throttle Position Sensor Signal Voltage High (Automatic Transmission).
22 Throttle Position Sensor Signal Voltage Low.
23 Intake Air temperature (MAT) Sensor. Low temperature indicated.
24 Vehicle Speed Sensor circuit.
25 Intake Air temperature (MAT) Sensor. High temperature indicated.
31 MAP Sensor circuit - Signal Voltage Low Vacuum.
32 MAP Sensor circuit - Signal Voltage High Vacuum.
33 MAP Sensor circuit.
41 Ignition Signal circuit.
42 Crank Angle Sensor.
46 Idle Speed Control Motor circuit.
51 EGR circuit.
53 Ground circuit.

93 - 95 Geo
13 Oxygen Sensor circuit. Signal voltage does not change.
14 Engine Coolant Temperature Sensor circuit High Voltage Input. Low temperature indicated.
15 Engine Coolant Temperature Sensor circuit Low Voltage Input. High temperature indicated.
21 Throttle Position Sensor circuit High Voltage Input.
22 Throttle Position Sensor circuit Low Voltage Input.
23 Intake Air temperature Sensor circuit - High Voltage Input. Low temperature indicated.
24 Vehicle Speed Sensor circuit.
25 Intake Air temperature Sensor circuit - Low Voltage Input. High temperature indicated.
31 MAP Sensor circuit Low Voltage Input - Low manifold pressure.
32 MAP Sensor circuit High Voltage Input - High manifold pressure.
41 Ignition Signal circuit.
42 Crankshaft Position Sensor circuit - No Signal for 2 seconds.
46 Idle Speed Control Motor circuit.
51 EGR circuit.