4.0 Swap into 86 bronco II

Im interested in doing a 4.0L swap into my bronco II, I have a 5 Speed and a 2.9L. I know the 4.0 Will bolt directly too my transmission, i know i wil need a 4.0 Fly wheel, what about the cluth and slave cylinder? will i need 4.0 ones? i already have a 4.0 Computer in my B2 and wiring will not be a issue for me, will the 2.9L radiator suffice for cooling a 4.0? and motor mounts are they different? i pretty much just wan too know what i wil need to do the swap, thnks you.

You will need the 4.0 clutch and throw out bearing.

You will also need 4.0 starter.

An M50D is the tranny of choice you might have to grind yours out to get the fly wheel to fit.That motor can break your tranny if your heavy footed.

You can't plug a 4.0 computer in and run the 2.9 wiring.They run a completely different fuel injection system.

Radiator should work they do make a heavier one though if you have to change.

I used my 86 mounts

research to find problems and how to solve them.

Do you need to do the whole dash swap? I really like 1st gen dashes, and for mine I don't want to change it out....

For your application, no. Most of us, me anyways, swapped the dash because of how the 4.0 A4LD is shifted verses how the 2.9 A4LD was. And I wanted the newer dash...

Camshaft said:

i already have a 4.0 Computer in my B2

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Haha. So your computer is telling you non existant coil pack to fire? I couldnt use a 93 ecu on my 94 harness. I'd like to know how you accomplished this.

I suggest you use a radiator from a 4.0 Automatic Explorer. They are much larger and it's a bolt in.

I do not suggest you use your current 2.9 trans with the 4.0. The 4.0 makes a lot more torque and your trans will not appreciate that. I would use an M5OD as previously mentioned.

I swapped the entire dash and wiring into my 86 BII, donor engine came from a 92 Explorer 4.0L.

I used the 2.9L flywheel and clutch disk, pressure plate and throw out bearing, I'm using the original BII fm146/1350 and haven't had any problems with the trans as of yet and I have been beating the snot out of the BII every time I get out wheeling over the last few years, I probably get out wheeling every other weekend.

I'm running full width d44/9" spooled front and rear and sitting on 38" Swamper TSL's. I've power shifted it lots, dumped the clutch a ton and all around beat the wee out of it regularly, if it has a bad rep for being weak, I'm not sure why.

If your BII came with A/C then chances are you have the larger rad, if not I would swap in the rad from an auto equipped 4.0L.

I used the 4.0L motor mounts but they looked the same from the 2.9 to the 4.0 so I bet they will both work, the rubber in my 2.9 mounts were all cracked so I used the newer 4.0L mounts.

The 2.9L had a spacer behind the flywheel that I ended up installing on the back of the 4.0L, this spacer ended up spacing the flywheel further into the bell housing and made me have to use an auto 4.0L starter on my manual trans set-up. Had I not installed this spacer I would have had to use a manual trans 4.0L starter. The 2.9L starter won't fit. I believe the 4.0L flywheel and clutch set-up would be a stronger set-up if you have the choice to use it, do it. Mine has been OK with the 2.9L flywheel and clutch, they were brand new and what I had at the time so I went with it, but the 4.0L stuff is larger and would provide more ware surface and clamping force in the long run.

Although the through-firewall wiring connectors on the drivers side fire wall look the same, the pin layouts are different between the 86 2.9 and the ?? 4.0L. You either have to swap wires around in the connector or replace the entire harness inside and out.

The 86 BII fuel sender will not work with the 4.0L dash either, I swapped in the 4.0L sender to get the gauge working again, if you choose to go the route I went with.

Almost all the wiring connectors between the 2.9L and the 4.0L are different shape, one has round connectors and the other has square connectors, so things like the wiper motor, head light connectors and such won't connect without either changing connectors or changing components. I swapped in the 4.0L wiper motor, did the h4 head light conversion, and what ever else was under hood that didn't connect to the newer engine harness. All the components are a bolt across swap, it's just the connectors changed shape somewhere around 88-89.

Hope this helps, if you have any more questions, feel free to ask.

Some good info. Repped.

I'm going through this right now with an '86 BII. Swapping in a '92 4.0 (I've already swapped the trans to the '92 M5OD and 1354-M transfer case) and am working my way very slowly through the wiring.

I'm trying to do this WITHOUT swapping dashboards and without using the Explorer's power distribution box (under the hood). I think it's possible as I've found a thread on another forum which helped a fair bit - that poster did the same thing I'm speaking of.

As far as the clutch goes, the 4.0 clutch is bigger than the 2.9L and typically is considered an upgrade on the 2.9. I'd use this opportunity to put in the larger clutch as I don't know how long the 2.9 will go without starting to glaze/slip.

Good luck! Keep us updated.

Edit: I forgot, Bones is absolutely correct about the sending unit. The resistance (ohms) range of the BII and Exp. senders are incompatible with their respective gauges. If you use the BII dash, keep the BII sending unit. I've heard the exploder fuel pump can be fit to the BII sending unit, then remove the second pump on the rail, and end up with a simpler and possibly more reliable fuel system. From what I understand (I don't know for sure) the BII in-tank pump uses plastic components whereas the Explorer pump uses all-metal construction.

disciplerocks said:

some good info. Repped.

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thx! :d