Zf6?!

justinray

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Holy Gear Split Batman..
After looking at the splits of a zf6 and knowing they bolted up to a PSD, I want to know.. Has anyone done the swap? Any input on the swap at all? Im strongly considering this. Any input is appreciated. If you want to know what i am talking about, google search 'Zfs6-650'
 

f-two-fiddy

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Yes it's been done. the info is around. It entails drilling new mounting holes, and a custom clutch setup.

The Guy that did it said that in his opinion, it was not a big improvement.

If you look closely there is not much difference between the ZF5/6. You'd get a little lower 1st, 2nd. The final is basically the same. Some say that the extra draw of the pump on the ZF6 is more of a set back on an IDI than its worth.

Most consider it not worth allt he extra effort, and go with a ZF5
 

hesutton

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Yes it's been done. the info is around. It entails drilling new mounting holes, and a custom clutch setup.

The Guy that did it said that in his opinion, it was not a big improvement.

If you look closely there is not much difference between the ZF5/6. You'd get a little lower 1st, 2nd. The final is basically the same. Some say that the extra draw of the pump on the ZF6 is more of a set back on an IDI than its worth.

Most consider it not worth allt he extra effort, and go with a ZF5

X 2! All you gain over a ZF5 is a low gear under first. The gears are Low, 1, 2, 3, 4, OD. You cannot use the trans adaptor plate with the ZF6 and must fab a custom mount of some kind for the top two mounting bolts and need custom parts for the clutch as stated above. That's a lot of work to gain a granny gear.

Heath
 

towcat

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here's some quick and candid notes FROM Jason B. THE GUY WHO ACTUALLY WENT TROUGH PUTTING ONE IN.


Ok, I am still getting occasional requests for info on how to do this swap, so I'll make a post with all the info I can remember on how to do it. It's been almost 2 years since I did it, so please excuse anything I forget to mention.

I now have about 20,000 miles on the truck with the conversion, and could not be happier. My only complaint in that time was with the ceramic puck style clutch disk I used. I have since replaced it with a conventional LUK disk and love it! There will be more on this to follow.

First of all, you have to remove the approximately 1" thick adapter plate the IDI's use in order to get the clutch and flywheel spacing correct. In other words, the bellhousing on the ZF6 is deeper and the input shaft is shorter, so the spacer has to go. The 7.3 powerstrokes have a different bellhousing bolt pattern cast into the block compared to the IDI. The good news is the 2 dowel pins, and 4 lower bolts do match up. The upper 2 bolts are the only difference. I made a stepped adapter to go from the upper 2 bolts on the IDI block to the upper 2 bolts on the ZF6. It was 2 pieces of 1/2" x 2" flat steel bar overlapped and welded together, making sure both bars were parallel after welding. The lower bar bolts to the upper holes in the block, and the upper bar sits behind it and has the upper 2 holes tapped for the tranny bolts. That makes the front face of the upper part of the adapter flush with the rest of the bellhousing in the block. I bought the stock tranny dust plate for a '99 and had to cut a little clearance into it for the adapter.

The next big hurdle is the clutch. The ZF6 has a 1.375" input shaft, and the smallest disk you can find with that spline is going to be 13" diameter. A 13" disk will not fit under any pressure plate that fits an IDI flywheel. My first way around this was to use a custom made 12.25" disk with the 1.375" spline and 4 ceramic pucks per side. This disk turned out to be miserable! The more you tried to slip it, the harder it grabbed sending the truck into convulsions. Backing up to a trailer was virtually impossible. So, I recently went a different route.

I had already used a LUK solid flywheel, so I pulled it back out and redrilled it for a LUK 13" PSD pressure plate. I now have the LUK pressure plate and disk for a '99 PSD and it works great. It reduced the pedal effort, virtually eliminated the gear rollover noise, and is very smooth. This is definitely the way to go. Oh, and you can't use a LUK flywheel for a PSD because they have a different bolt pattern on the crankshaft.

The clutch hydraulics weren't too bad, but not a simple bolt together deal, either. I used the correct master cylinder for my year truck. I used a slave cylinder for a '99 ZF6. The fork, pivot, and throwout bearing were all for a ZF6. The only real problem was trying to come up with a clutch hose that would work. I ended up making adapters that fit into the clutch and slave with a -3 AN on the other end. I then made a stainless steel braided hose to connect them. Bleeding was the typical pain, but it has worked great ever since.

The shifter ended up in exactly the same spot as a ZF5, so the tranny tunnel cover for a manual and boot all bolted up fine. I made my own cross member for the back of the tranny by heavily modifying the one that was in my truck with the E4OD. You might be able to bolt in a cross member from a '99 ZF6 - I'm not sure - was too cheap to buy one.

Of course you'll have to visit a driveshaft shop and get yours modified or a new one made. I also went to a '99 E350 disc brake rear axle at the same time, and had an all new driveshaft built to fit.

The ZF6 does not have a speedo drive gear. This is where a '92 up truck has the advantage. I used a speedo from the '92 up truck and made it fit inside my cluster with some slight customization. The '92 up speedo is all electronic, and I was able to drive it from the sensor on the rear axle.

The 7.3 IDI starter bolts directly into the bellhousing of the ZF6 and works fine. The bellhousing lower cover for the '99 bolted right up.

Oh, I did have to bend the floor of the truck up just a little bit for clearance, but it's under the seat and totally unnoticable.

I think that about covers it... If I remember anything else I'll reply to this post. If anyone wants a flywheel redrilled I could probably take care of that part of the conversion for them.

Jason
 

justinray

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That all sounds pretty positive?
If I can use it, I could also change my rear gears to a higher gear and get drastically better fuel economy.
 

towcat

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That all sounds pretty positive?
If I can use it, I could also change my rear gears to a higher gear and get drastically better fuel economy.
jason/jaybee is always a person with a positive attitude. even when his truck cavitated it's motor, he didn't dump on it.
do keep in mind he is an automotive engineer/mechanic/fabricator with a shop that is capable of building formula 1 race cars. he didn't do this on his own driveway with a indexing drill.
 

seawalkersee

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Are you doing a 4X4 or 4X2? I have a 2wd and need a 4x if you were in a position to make a trade...

SWS
 

Shadetreemechanic

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I know the od is near same.. But with a lower first gear, i can use higher rear gears..
Much simpler to use a later model zf. They changed the first gear out around 95 to give a lower first gear. I believe you would look for a zf with model number ending in 47. The IDI zfs all end in 42.
 

The Warden

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I know the od is near same.. But with a lower first gear, i can use higher rear gears..
FWIW...granted, I got lucky and I have a ZF out of an F-450, but I've never had even the slightest amount of trouble getting started with a heavy load. Everything I've heard about the ZF6 conversion is that, while the tranny is nice, it's really a lot of work for little gain...I toyed with the idea and decided that I would be better off focusing my energy on finding and installing an overdrive unit. I'm pretty sure I'll be money ahead after all's said and done, and I'll actually have more flexibility with my drivetrain...I still have the "lower" 1st gear with 4.10's, while I'll be able to cruise on the freeway at 1800 RPM (the equivalent of having a nonexistent 3.27 gear ratio) in double-OD ;Sweet not to mention being able to split every gear and effectively having a 10-speed. I bought a Doug Nash unit a couple of years ago and am waiting to take my truck out of service before I install it (have a whole bunch of other projects to do as well :angel: ).

You probably already know this, but jus tin case...one other thing to keep in mind is, if you need to move a load around in granny gear and you're not using it to "start out", you can always put your transfer case in 4L and keep the front hubs unlocked...I do this all the time and it really makes life easier. Actually, at this point, it's the main thing I use my transfer case for...I miss off-roading :angel: I'm going to have to get my hands on a second truck someday :D
 

War Wagon

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I have thought that I would like to do the ZF-6 swap someday. Along with it going to 3.55 gears. My current situation is the ZF-5 with 4.10 gears. The way I see it, there is not much advantage in my situation if I should only do the ZF-6. With the 6 and 4.10's I don't gain any more OD, which is the biggest problem with my gearing now. I have excessive RPM at highway speed, limited top speed, and reduced fuel economy. If I leave the 5 and go to 3:55's I will be sacrificing towing ability. The way I look at the difference between the ZF-5 and ZF-6 is that the gears (the way they are labeled on the shift knob) there is an extra gear between L and 4(DD = 1:1) in the ZF-6 compared to the gears between 1 and 4(DD = 1:1) in the ZF-5. In both the top 2 gears are pretty much the same DD and OD. In the ZF-6 the gaps in the ratios are closer from L-1-2-3-4 than in the ZF-5's 1-2-3-4. The way I look at it there is an extra gear in the middle to close the gap. I think it makes the ZF-6 more suited for towing while allowing one to still have a rear diff. ratio suitable for highway cruising. In this way I think you could have a well rounded gearing combo to achieve good towing capability, fuel economy (empty/loaded), better cruising RPM, and max top speed. I plan on doing it with a 3.55 gear swap also.
 
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