ZF5 rebuild preferences? DIY, rebuilder, etc.

Heh, the Redline ATF claims 70W80 on the gear oil scale. Pretty close to the MTL.

I cored mine out with a regional rebuilder. I would not recommend the same regional rebuilder again, but the second trans is OK.
The reason I cored mine out is, I wanted "gas" gears in my diesel ZF5. The gas gear pack offer a lower first gear and after I put 3.55 gears in my diffs, I realized starting on a grade with a load required the transfer case. If you are running 4.10 gears the new gear pack wouldn't be necessary. Buying all new gas gears would make the rebuild very expensive, but a rebuilder should have them laying around.

I broke the trans in on the synthetic ATF that they recommended. After 10K miles or so I switched to a 30W Amsoil synthetic trans oil. I'm not an engineer, but I would think 75W would be too thick to get between the bearings. Ford ran the ATF (usually 10w) in order to meet CAFE standard for fleet fuel mileage, but I think it is too thin. 2 tow truck owners I spoke with have had issues with their ZF5 and ATF (10w). After they switched to 30W they doubled the life of the transmission.

264WSM said:

I would think 75W would be too thick to get between the bearings. Ford ran the ATF (usually 10w) in order to meet CAFE standard for fleet fuel mileage, but I think it is too thin. 2 tow truck owners I spoke with have had issues with their ZF5 and ATF (10w). After they switched to 30W they doubled the life of the transmission.

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Great! Then 75w80 is perfect. It seems most people don't know that 80w gear oil is roughly the same viscosity as 30w engine oil. Check this out:
SAE crankcase vs gear oil vs other stuff

Something to watch out for is that gear oils with sulfur can damage brass gears like synchros. Look for a gear oil that claims to be safe for yellow metals.

nelstomlinson said:

Something to watch out for is that gear oils with sulfur can damage brass gears like synchros. Look for a gear oil that claims to be safe for yellow metals.

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Good point for future readers, though I was just trying to point out that the MTL was rated at 75-80 and that was perfect for our ZF's as it's a gear oil rating, equivalent to somewhere between a 20 and 30 weight engine oil.
In addition this MTL is designed specifically for manual gearboxes and wouldn't have anything that could damage synchros.

There are a few rebuilders out there that still rebuild the ZF-5. Below are a couple I have bookmarked years ago. That said, I have never used them nor know what their reputation is. On the plus side my bookmarks are at least 5 years old, so the companies have been around for a while at least.


Midwest has rebuilts and rebuild kits.

If I had a pile of money to blow, I would consider an Alison 6-spd conversion

So I'm finally making a little headway on this.

I ended up looking around for a while over the last couple months and getting even a used ZF5 in this state is bonkers. Can't find anything less than $1000. Even out of state stuff is $700 with blown synchros, besides shipping.

So I pulled the trigger on a rebuild kit with bearings and synchros and I'll see what else I might need once I pull it apart someday.

Part #: BK300ZFWS. For the ZF5-S42.
I actually looked this up on Midwest Transmissions website and then googled the part number. Found it on transpartswarehouse.com for almost $80 less and free shipping.
https://transpartswarehouse.com/bk3...ransmission-rebuild-kit-87-95-w-synchros.html

My ZF is in pretty good shape besides the synchros from what I can tell, so hopefully there aren't any surprises later. It'll be a learning experience for sure!

I’m actually in the same boat as you right now, my zf-5 is on its last legs. I also decided to rebuild it myself after watching a very detailed YouTube video and realizing how straightforward it is. I managed to find a low-mile zf-5 locally that I bought as insurance in case my housing is cracked or the trans is otherwise too far gone for a rebuild. I figure if the rebuild goes well I’ll just re-sell the spare zf-5. I’m planning on getting all the rebuild stuff from rock auto. You can’t get it all in one master kit, but the total price is cheaper that way. Plus I can add on things like u-joints and a rear main seal.

EDIT: I didn’t notice the free shipping from trans parts warehouse, that’s a good deal!

I also looked at RockAuto but I couldn't find every synchro(maybe I'm just a goober). Most importantly I couldn't find the 2-3 synchro on their website and that's my worst by far.
I definitely will keep them in mind for the other bits that are worn out once I have it apart.
I wish I could get a cheap spare like you did so I could rebuild and still have a working pickup. In my case I won't be able to. BUT, I have 3 vehicles so it should be OK.

The_Josh_Bear said:

I also looked at RockAuto but I couldn't find every synchro(maybe I'm just a goober). Most importantly I couldn't find the 2-3 synchro on their website and that's my worst by far.
I definitely will keep them in mind for the other bits that are worn out once I have it apart.
I wish I could get a cheap spare like you did so I could rebuild and still have a working pickup. In my case I won't be able to. BUT, I have 3 vehicles so it should be OK.

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Did you ever get around to rebuilding your zf5? How did the rebuild kit workout for you? Mine is in desperate need of a rebuild. I can't shift into 3rd without grinding.

I wish! I still haven't gotten to it. It was supposed to be my winter project but I can't find a decent core. Everyone wants $1000 for a trashed box. Cause let's face it, if it's not in a vehicle for a test-drive, I'm going to assume it's basically wrecked.

And I don't NEED to have a spare, but it sure would be easier to start that way. Sorry to leave everyone hanging...but no news yet.

I noticed the same thing around here, everyone wants $1000 for a used zf-5 that probably needs synchros. The strange thing is I was having no trouble finding zf-6 trannys for half that.

ROCK HARVEY said:

I noticed the same thing around here, everyone wants $1000 for a used zf-5 that probably needs synchros. The strange thing is I was having no trouble finding zf-6 trannys for half that.

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Dang it's nuts how location makes all the difference. I'd grab a 7.3 ZF-6 in no time if that were the case. But around here they are all 1200+. At least that I can find.

Car-part.com has good deals but even then they want $1000+ for the ZF5.

Sounds like @ROCK HARVEY needs to get into the selling zf6 business. I wouldn't mind one....

One trick I found to find good deals on a zf-5 was to search “ford 5-speed” or “ford truck transmission” rather than specifically “zf-5”.

People who know the model number tend to know that they can get $800+ out of it. People who are just parting out their truck and don’t know specific part numbers will often let it go for cheaper.