Zf5 Rebuild or Replace

1993 7.3 idi NA non turbo, 4wd single cab

Howdy hope everyone is running well.

I removed my zf5 42 transmission with the intention of rebuilding it. Had very slow, notchy, double clutching shifting since I got it but on my last drive across country it got really bad, I assumed this was due to failing dmf (also had those symptoms since I got it) and old synchros.

The removal and disassembly went pretty well thanks to the forums on here and fte and video by Bulletproof Garage on YouTube. But upon inspecting the rear case I discovered it is, from what I can tell severely damaged. Likely due to excessive play in driveshaft u joints which I intend on replacing as well. I can only see one place it has cracked through but the inside looks very different from what I’d expect or any pictures of cases I can find.

Ive only found theoretically undamaged cases on eBay for 800 and some for upwards of 1200 on parts websites which seems silly to me on top of 500+ for a good rebuild kit.

I have been recommended a shop near me and called them about a month ago. They quoted me around 2,000 for a rebuilt zf5 47 which I am seriously interested in upgrading to for the strengthened case and lower reverse gear so I’m not sending it so much backing up to trailers. My question is whether or not this is actually a good or affordable idea, I have heard a lot of different conflicting opinions about whether or not they’ll match up due to different case length, input shaft length, driveshaft length, etc. I think I’ve seen all the posts on here about it but none of them seem to give complete or firsthand experience of putting a zf5 47 to an IDI.

I am particularly nervous about this matter because I am now living at 7,000 feet altitude and I feel I need to either put a turbo on this or get a new vehicle for the winter, which I would rather not do but have only so much time and money before it will get cold. Any advice on this would be appreciated. Thanks again for y’all’s help in the past.

To be clear the case is only cracked in one spot all the way through, at least to my knowledge. I planned on use some dye penetrant to fully inspect it.

screwhead said:

I am now living at 7,000 feet altitude

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So you don't live in Austin, TX anymore do you?

@IDIBRONCO its a little flat in Texas for me. I was living in Oregon for a bit and I didn’t notice any difference around 4-5,000ft but here in Colorado now and the performance of mine is definitely diminished. What bugs me maybe the most is how long it takes for oil pressure to drop after cold start. 15 minutes at least before it’s not pushing 50 psi.

Those look like just casting flaws, not a crack. Difficult shifting could be caused by a dmf failing or a weak clutch master/slave

cant help you with the transmission case, but when backing up trailers, I put the truck in 4lo dont even need to engage the front hubs. It just gives you so much more control backing up and you dont have to smoke your clutch. Works great.

screwhead said:

I was living in Oregon for a bit and I didn’t notice any difference around 4-5,000ft but here in Colorado now and the performance of mine is definitely diminished.

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Empty, I see the same thing in mine too. It sure does drop off quickly from there though. Some of it depends on the speed I'm driving at though. I'll get to see it all again in another 5 weeks or so. What's really strange the first few times I saw it was the fact that my vacuum gauge reads so much lower at higher elevations.

asmith said:

when backing up trailers, I put the truck in 4lo dont even need to engage the front hubs. It just gives you so much more control backing up and you dont have to smoke your clutch. Works great.

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I do the same.

asmith said:

cant help you with the transmission case, but when backing up trailers, I put the truck in 4lo dont even need to engage the front hubs. It just gives you so much more control backing up and you dont have to smoke your clutch. Works great.

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I have done this in my 250 before, but my F-Super Duty has 5.13 gears, may as well already be in low range lol

Plus it has a ZF5 S5-47 in it, so lower reverse. The original tranny had a bad 5th gear, I replaced it, but I just keep it as a spare, have another 4WD spare (the F-Super Duty trucks ise 4WD transmissions, because they have driveline brakes) three 2WD spares, and one of each 2WD and 4WD T19.

Lots of spare transfer cases too, and a couple spare engines. I feel pretty well off, in that department…

Bolted right up, I recommend the 47 transmission if you can find one

Another friend of mine had a 1988 F350 that he put an S5-47 in

screwhead said:

firsthand experience of putting a zf5 47 to an IDI

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It’s just like putting an S5-42 in, very easy

@amsmith That is a great idea I will start doing that, thank you.

@Nero that’s what I was hoping when I first saw it but it is cracked, all the way through. Enough to leak fluid on the outside of the case. The crack goes out to where the transfer case linkage bolts up.

@KansasIDI Thank you for your comment and advice. I’ve seen you comment about this swap before, was hoping you’d see this.

Sorry for posting something that might already be settled. But I feel much more confident in the 47 swap and fitment now. Will probably go pick it up in the next week or so. Will update. Thank you all.

KansasIDI said:

(the F-Super Duty trucks ise 4WD transmissions, because they have driveline brakes)

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Unless some Cletus was already there like the front part I picked up over Memorial Weekend.