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Discussion Starter #1
I have an 1988 with a 302 and a Mazda M5OD. The rear main seal appears to be shot and I leak a lot of oil after a short drive. First, I could replace the seal without pulling the engine, from what I've read, but is it easier to pull it?

Now my other option, I have a 1990 with a running 351efi that I have just for parts. Is it worth it for me to rebuild this engine and plan for a swap/upgrade. My biggest concern with this option is matching the 351 with my M5OD transmission. I hear this is a bad option. I really want to keep a manual transmission but now finding an appropriate tranny with appropriate wire harness seems like a task.

Pulling an engine is above my experience level and current tool level. Is it even worth the engine swap for the spare engine I have? I am fairly happy with the 302 but more power would be awesome. What do you think?
 

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Hearing sound of your engine - I'm pretty sure it won't last much longer. With that - after you "just" replace rear main there will be soon other far more expensive and complicated issues you would have to deal with. If you intend to keep your truck for next 3+ years it is smart to get the engine rebuild and swap it. I've done it on Ford Explorer before without any prior experience - it is not that difficult as it may look. There's very reputable shop in Vegas that can rebuild your existing engine (same shop I took my Explorer engine to) or you can source same engine you now have in your truck from junk yard and take it to that shop (or any other) for rebuild and then just swap it. Having 2 identical engines side by side helps to figure out what goes where when you assemble it, given you'll be working with long block. Engine swap is full weekend task if nothing goes wrong. I can help you with that if you decide to go that route. I can borrow engine hoist and stand from friend of mine. Let me know. Milan
 

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351 with zf5. Thats a pretty durable powertrain
 

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Discussion Starter #4
I figure a major overhaul is due. I just want to do it right if I'm gonna tear it all apart. The choices are pull and rebuild my current 302 or rebuild a 351 and have to swap the transmission too, which itself would be an upgrade...

Sounds like the truck will be out of commission for a while in the near future. :cry
 

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Since nobody mentioned this, the M5OD will match up extremely well with the 351 you've got. From what I understand, all 300, 302, and 351 engines have intercompatible transmissions. ie, you can take a M5OD from an 88' 302 and match up with a 90' 351 just fine.

You can check out the http://www.fullsizebronco.com/forum/showthread.php?t=49569&highlight=tranny for more info on this.
 

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Discussion Starter #7
Since nobody mentioned this, the M5OD will match up extremely well with the 351 you've got.
This means a great deal to me. Thanks! I will look more into it. I did read that you need a matching main harness when swapping engines. So I would need a donor truck that had a 351 with the M5OD, which wasn't even an option I believe. I have a lot of research to do :duh
 

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It is more critical to have a donor harness if you are swapping from a manual to an automatic (especially if it is anE40d).You can use the donor harness from your 351 even if it is an auto harness. All you will need to do is make a bypass for the neutral safety switch and tap in your back up light switch. Though I have never done this swap in a Bronco, I did do one similar in an Explorer and everything worked fine. You will get tranny codes that store in the ECU (unless you use a manual ECU) but they do not set the CEL or affect the vehicle performance.
 
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