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Auto to manual trans swap question

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  #1  
Old 05-30-2018, 04:36 PM
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Auto to manual trans swap question

Hello. I have a 78 bronco with a 400M that I want to convert to a manual since my current transmission and transfer case are going bad right now. I plan on going simple with the t18 or t19 but have seen some conflicting statements about driveshaft length changing. If it does change can anyone tell me what length the new shafts will be and is there another vehicle besides a factory manual bronco i can find the correct lengths on. I can wait and measure if needed but its my current daily driver so I want it to be out of commission for the shortest time possible.
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  #2  
Old 06-01-2018, 11:00 AM
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Hi Cipher,
I don't know what differences there are between the 78/79 and the 80-96 Broncos, but from what I'm finding, the auto driveshaft is 27.312" in length whereas the manual is 37.312". Oddly, the driveshaft for a manual transmission and an auto (non-overdrive C6) for the 80+ Bronco is the same length. So, I'm not sure why there would be a 10" difference on yours. (They're 32" in length).

Your front should remain the same.

However, no matter where I look, I'm seeing that the rear driveshaft for a 78/79 is 'unavailable'. You might be able to have your current one lengthened by a driveline shop.

No other vehicles that I know of would work, since the Bronco uses a double cardan joint due to its short length, whereas the trucks don't. You might be able to use a truck's shaft if you cut it and attach it to your double cardan to make a longer one.
 
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Old 06-01-2018, 02:21 PM
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I dont think mine has the double cardan joint on it. I will double check after I get off work but I am pretty sure mine is just a standard shaft. maybe that is why I am having issues.
 
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Old 06-01-2018, 02:52 PM
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If you don't have the double cardan then you don't have the correct tail housing on the transfer case either, as they're different between the two.
However, someone would have had to have cut a truck driveshaft pretty short to get it on a Bronco (which is within the realm of possibility).

What issues are you having?

The double cardan is necessary for it to make the steeper angle from the transfer case to the differential on a short wheelbase. Without it, I would think you'd be getting a little bit of binding.
 
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Old 06-01-2018, 03:10 PM
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there is a loud clunk noise when I put it in gear and it also does it if i drop off or jump on the accelerator while driving down the road. I have also started to notice a sound at low speeds that sounds like a tooth is missing in transfer case but i guess it could just be everything binding up. I have owned this for a while but only drove it a little until it has became my daily driver in November. I'm just hoping I can get everything fixed before it pukes its guts out.
 
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Old 06-01-2018, 03:38 PM
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I should add that the clunk is not a drive line binding sound. I can make the same sound but quieter by rocking the vehicle forward and backward. It also moves a lot forward and backwards when in park like something is worn out in there causing slack
 
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Old 06-03-2018, 08:24 AM
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I did double check and neither my front or rear shafts have the double cardan joints on them. Is there anyway this could be stock? I know the guy I bought it off of said he had 35s on it before so I had suspicions that he had lifted it and then removed the lift before selling it for cheap so maybe he stuck some different shafts on it as well.
 
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Old 06-04-2018, 06:50 AM
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Originally Posted by Cipher43 View Post
I did double check and neither my front or rear shafts have the double cardan joints on them. Is there anyway this could be stock? I know the guy I bought it off of said he had 35s on it before so I had suspicions that he had lifted it and then removed the lift before selling it for cheap so maybe he stuck some different shafts on it as well.
The clunk you're hearing is descriptive of what you'd get with a blown u-joint and not having the proper joint at the front of the driveshaft could very well be what wore it out.

I'd get under it while in neutral and rotate the shaft by hand. There should be absolutely no slop between either end and the driveshaft. If the shaft moves even a tiny bit without either yoke moving, that's your immediate problem.

As abandoned said, you are supposed to have a double joint at the trans end due to the angle and that requires a certain tailpiece so something has been changed in your setup. You may need be able to have a custom made driveshaft to suit your needs. I had Tom Woods build me a driveshaft, which they shipped to me for a little over $300 I think and they were great to work with. They explained to me how to measure, explained what ends I needed and took care of me really well.
 
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Old 06-04-2018, 10:43 AM
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Originally Posted by schwim View Post
The clunk you're hearing is descriptive of what you'd get with a blown u-joint and not having the proper joint at the front of the driveshaft could very well be what wore it out.

I'd get under it while in neutral and rotate the shaft by hand. There should be absolutely no slop between either end and the driveshaft. If the shaft moves even a tiny bit without either yoke moving, that's your immediate problem.
That was my first thought as well. And when testing it, having it in neutral is very important. The engine/trans will put torque on the driveshaft which will hide the slop.

As far as I know, ALL Broncos came with a double cardan joint. They have to due to the short length. Someone's swapped in a truck transfer case and then had the driveshaft shortened to match.
The bad news is, you're going to have to source either a Bronco transfer case, or at least the tailshaft and then swap that onto your current one (I've done this on an NP-208, it's not that bad). Then, you'll also need a driveshaft with the double cardan joint.
You don't want to replicate the problem or you'll just keep wearing parts out.
 
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Old 06-10-2018, 07:43 PM
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is there a housing difference on the transfer case or is it a completely different model case? I had changed the u joints on the rear shaft about 5 years ago and have only put 10k to 20k on them. I remember the reason I replaced the u joints was because it had a little bit of a clunk then but replacing them took most of it out.

I just put it in neutral and checked the drive shafts. the front shaft has one u joint that I knew was starting to go bad but the rear u joints were tight. The slip joint on the shaft is shot though being I could push the shaft sideways 1/4 inch so it might not be transfer case transmission swap just shafts. If the case under mine is the same as stock I might just order a new stock shaft or see if the bronco in the pick and pull has straight shafts
 
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Old 06-11-2018, 11:52 AM
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The housing will be the same.
And it's possible that I might have given incorrect information.

I'm used to working on the NP-208 (1980+ transfer case). It has a different tailshaft for the trucks.
But, looking at pictures of the NP-205, which you more than likely have, the tailshaft is the same.

This is what I had to swap out when I used a truck transfer case.

You can see the long tailshaft here:


This is what the Bronco uses:


But, looking at pictures of the NP-205, they all show it with the second Y-yolk setup.

You might not need a different tailshaft, just a driveshaft with a double cardan joint. That would take a lot of stress off of the driveshaft and get rid of some of those clunks, and wearing out U-joints.
 
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Old 06-11-2018, 06:58 PM
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there is a 79 bronco setting in a pick and pull around me that i will go check out if the transfer is the same when i go to look at the shafts
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