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Fitting 4.0L SOHC to stock 1990 Bronco II transmission

Se7enth Sol

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1990
Make / Model
Ford Bronco II
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
At to moment I am pulling the old rusted 2.9L v6 out of my 1990 Bronco II 4x4. I have purchased a 4.0L SOHC replacement engine from a 1997 Ford ranger. I thought I did a lot of research before purchasing but now I am not sure if the bolt pattern will line up to the OEM 1990 B2 transmission. There is a lot of conflicting information online about this. Please let me know if the bolt patterns do not line up at all. If they don't I guess I'm gonna have to sell this engine in order to get a 4.0L OHV.
 


snoranger

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The SOHC and the 2.9l/4.0l OHV bolt patterns are very similar. The only difference is the upper passenger side bolt won’t line up. To run the rear timing chain to the right side head, Ford had to move that bolt up and over a little. I wouldn’t be worried about that... I ran a OHV trans behind a SOHC motor for a year or 2 with only 7 of the 8 bolts.

I wouldn’t trust a 2.9L trans behind a SOHC... I barely trust them behind a 2.9L.
 

tw205

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Bronson Michigan
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1985
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Ford Bronco II
Engine Type
2.8 V6
Engine Size
2.8
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Manual
2WD / 4WD
4WD
Total Lift
6” skyjacker 2” body
Tire Size
33x12.5
The trans will bolt on minus the one bolt however I believe you will run into flywheel /clutch issues. When mixing transmissions on ford 2.8,2,9,4.0 v6 engines you use the peripherals that come with the transmission you are using. Your 2.9 should be an FM146 and the flywheel for that will not fit the sohc engine. Sohc has an 8 bold flywheel while the 2.8,2.9,4.0 OHV have a six bolt. I do t know if the 2.9 clutch will bolt into the 4.0 flywheel or if it does will the trans input shaft seat correctly into the pilot bushing. The trans swap article I’ve read on TRS are all upgrading but your situation is in reverse. I would investigate fitment before installation. Switching to a M50D would eliminate the issues. It would allow for the 4.0 flywheel, clutch and starter index plate.
 

Se7enth Sol

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Location
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Vehicle Year
1990
Make / Model
Ford Bronco II
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
The trans will bolt on minus the one bolt however I believe you will run into flywheel /clutch issues. When mixing transmissions on ford 2.8,2,9,4.0 v6 engines you use the peripherals that come with the transmission you are using. Your 2.9 should be an FM146 and the flywheel for that will not fit the sohc engine. Sohc has an 8 bold flywheel while the 2.8,2.9,4.0 OHV have a six bolt. I do t know if the 2.9 clutch will bolt into the 4.0 flywheel or if it does will the trans input shaft seat correctly into the pilot bushing. The trans swap article I’ve read on TRS are all upgrading but your situation is in reverse. I would investigate fitment before installation. Switching to a M50D would eliminate the issues. It would allow for the 4.0 flywheel, clutch and starter index plate.
Thank you so much for your reply! If I did upgrade to the M50D, would that require moving the transfer case and getting newly sized drive shafts? Aka are both transmissions the same length from front to back?
 

tw205

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Location
Bronson Michigan
Vehicle Year
1985
Make / Model
Ford Bronco II
Engine Type
2.8 V6
Engine Size
2.8
Transmission
Manual
2WD / 4WD
4WD
Total Lift
6” skyjacker 2” body
Tire Size
33x12.5
Fm 146 to M50D use same crossmember and mount. Same driveshafts. I think the length difference is minimal. I think under an inch. The tech build I followed for mine called for same driveshafts. Your flywheel should be good. Get the engine plate (starter index ring) from the 4.0. Starter from the 4.0 clutch for the 4.0. For the master and slave you may be able to use your old one but I’m not positive. The key is keeping the same fittings. My 2.9 master hydraulic line wouldn’t fit on the 4.0 slave so I used the 4.0 slave and the hydraulic from the master to slave from the 4.0. Then had to bleed the system.
 

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