i am well aware that swapping a zf6 into our trucks is not a simple matter and requires some firewall and trans tunnel mods. however, since the zf5 i just put in my truck is in need of a rebuild, and since i'll be swapping engines and painting my truck all at the same time anyway, i'm thinking i may just go for a ZF6 and do the required work - if i can find one for a reasonable price and in reasonable shape.

a few questions for you all first - will a ZF6 from a 6.0 truck bolt up to our 7.3 block? i have to figure it would, but not sure.

would a BW4407 t-case bolt up to a ZF6? i think i remember reading that somewhere that the output shaft of the ZF6 is better than that of the ZF5, in which case the answer to my questions is no - is this definitely the case, though.

other than making the darn this fit, and these two issues the other other matters to consider are flywheel/clutch/pressure-plate, but i'm sure that can all be figured out...

thanks!

 

If I'm not mistaken, the input and the out put shafts are larger in the ZF6. The input side would not be a problem, all you would need is a clutch plate for it. On the output side, the the 4407 case will not fit, you need the Xcase from a superduty. In my opinion, the only benifit the 6spd has is the higher torque rating, and the lower ratio in the 1st gear. They also run a pump to cool the fluid that you would have to run lines to the radiator. Those ZF6 trannys are massive compaired the the ZF5. For me, it wouldn't be worth the effort to install one in an OBS.

 

The final drive gear has a different ratio too. Should see a drop in cruising RPMs and theoretically better mileage but you know how theorys are. I've heard of guys losing the cooler and plugging the ports on them too. But I agree, it's a helluva lot of work for very little gain over a ZF5.

 

i agree - the gain in high end RMPs (hence fuel efficiency) is very little, but having driven my zf5 for a while now, I would actually like to have that extra gear in the middle there - without a load on the truck, the ZF5 is really just a 4-speed tranny as first is so low.

i'm not really dead set on it - I may just rebuild a zf5 that I have in pieces currently. but I figured, if I could find a zf6 for a decent price, maybe i'd just go that route and never worry about over-torqueing the trans again! plus, with my plans to have the engine out, fenders off and repaint the cab inside and out, there'd be no better time to cut up and reshape the firewall and trans tunnel.

and yes, I thought the output shaft was bigger, thanks for the confirmation, Tom.

 

So what is the cooler for the ZF6 commissioned for an SD? Is it an in-radiator cooler like an autotragic? A separate cooler out in front of the rad?

 

It's not too hard to install a zf6 in a OBS, I swapped a E4OD for one in my 95. You will need a zf6 from a 7.3, all others have a different bell housing. There is also a 10ga spacer between the engine and trans, you won't be reusing the 1" thick one your truck already has. For clearance I just dropped the crossmember down about 1" and used a manual trans floor hump. The front drive shaft from the SD works and I used the OBS rear drive shaft shortened about 1" with a 1410 yoke to mate to the NP271.

 

GODD LUCK finding a ZF6 at a reasonable price. Junk yard sell them for $2250 as soon as they come in. Also repairing them is Just as expensive

A 6.0 ZF6 will NOT fit the 7.3

 

zf6 OD is like .76, the zf5-42 is .72 IIRC.

 

ZF5 S5-42 OD is 0.77

 

I'm just gonna throw a wrench in here. I talked to my buddy who has a zf-6 in his 97 the other day. He says he didn't have to do anything to make it fit. Just bolted it all up. He used the T-case and all from the SD.

We're not close but I tend to trust the guy.

 

They're on CL here quiet often for pretty reasonable prices.

 

There's actually a full swap for sale up in Portland right now for $3000 if you know anyone Rob.

 

Thats crazy expensive lol! No one I even know has $3000 on hand lol

 

ZF5(s42 and s47) OD is .76
ZF6 OD is .72

Hardly any noticeable difference


Ford4Life7.3, what do you consider reasonably priced?


FI460, yeas it is a direct bolt in, IF you have the new clutch, t-case, trans mount and CUSTOM drive shafts to BOLT in

 

yeah, no way i'm paying $2-3k for a used one when a professionally rebuilt ZF5 is less than that. I got to thinking about maybe using a zf6, though when I came across one on CL yesterday for $600 with tcase included. it was in a wrecked truck and supposedly drove fine. I emailed the guy though and someone is coming for it this weekend - plus its out of a 6.0.

and yeah, that OD difference in the zf5 vs 6 would likely be completely unnoticeable. that extra gear change in there would be 1/6 more awesome, though. I don't know about you guys, and maybe its just my tired old engine, or i'm a big wimp, but I wouldn't mind having that extra gear in there to keep the RPM's closer between shifts.

however, seeing as i'm in the market for another tranny since the used one that I bought last year turned out to have a bad reverse gear, I don't think i'd buy another used tranny without it being in a truck immediately prior to purchase so that I can confirm that it goes into all gears smoothly and doesn't pop out. under engine load.

i'm making my reverse gear work for now, but a rebuild of my parts ZF5-42 or a new tranny is definitely in order soon...