ZF6 Install

[Irishcream]

I am looking to either rebuild my ZF5 5 speed transmission for my 97 F250 4X4. Recently I had placed an ad on a local buy and sell site looking for a core to rebuild and got a response from a guy with a Zf6 6 speed out of an 02 F350. My question is how do I install this? What mods do I have to make from the ZF5 and what are the pros and cons and speedbumps I will likely encounter if I go this route? $500 for the core that will need rebuilding. The guys says it kicks out of 4th when downhill with the exhaust brake on. So maybe syncros or something like that.

 

[Talyn]

I'd stick with rebuilding the zf5.

The zf6 has a cooler and stuff you'd have to plumb in and install.
And your not really gaining anything over the 5 speed.

1st on the zf5 is now L.
and the final drive is almost identical.

 

[superduty4x4]

Final drive on the ZF6 is different enough that it's a good thing IMO, especially if you have 4.10 gears.
As for what you'd need to do to install it, you'll need a ZF6 clutch and a transfer case at least. I'm not sure if the ZF6 is longer overall than the ZF5, hopefully someone with some experience here will chime in.

 

[94.5 Stroker]

I talked to Dan at Midwest about this and he said trans, tcase clutch, master cylinder, and you do have to alter your driveahafts.

 

[jdgleason]

Starter and everything fits the same? Still seems like kind of a pain to have to replumb master cylinder and trans cooler. Unless you did a stand alone trans cooler.

 

[Big Bore]

And your not really gaining anything over the 5 speed.

1st on the zf5 is now L.
and the final drive is almost identical.

I disagree. 1st on the ZF5 was always a compound low, 1st on the ZF6 is just lower, which allowed for a lower 2nd (since they added another gear) which is now renamed 1st. The ZF6 allows you to run a taller differential gear and still have closer ratios than the 5speed. The ratios for a ZF6 with 3:73 axle ratio are closer together than ZF5 with 4:10 ratio. So you have the advantage of lower rpms on the hiway, with the ability to more easily stay in the power band. The OD (6th) is slightly higher also, so in addition to being able to run taller axle ratio, you get even more advantage running a slightly higher OD through it, which combined is in fact significant. It also allows a better takeoff gear than the ZF5, where you were either using compound low which would wind out too quick, or 2nd which required a lot of clutch slipping in comparison to the new "1st" in the ZF6.


The oil lines are easily managed with a remote cooler, or swap your radiator for one from an auto truck.

The other issues like transfer case and clutch master/slave cylinder are significant hurdles but not insurmountable. Worth the effort IMO.

 

[morefuel]

Final drive on a zf6 is .72. Final drive on a zf5 is .76 if I remember correctly.

 

[Big Bore]

Final drive on a zf6 is .72. Final drive on a zf5 is .76 if I remember correctly.

Yes.

 

[Big Bore]

Go here and look at the final drive ratio's. A ZF6 with 3:73's is almost exactly the same final drive (2.69) as a ZF5 with 3:55's (2.70). When multiplied through the diff that .04 is VERY significant.

In fact, If you compare the final drive ratios, a ZF6 with 3:55's is numerically superior through the entire gear range to a ZF5 with 4:10's.

 

[superduty4x4]

Go here and look at the final drive ratio's. A ZF6 with 3:73's is almost exactly the same final drive (2.69) as a ZF5 with 3:55's (2.70). When multiplied through the diff that .04 is VERY significant.

I also know the ZF6 final drive is the same, or awful damn close, to the final drive of an E4OD. My 96 was an E4OD with 4.10's and my 97 is a ZF5 with 4.10's, I'm at least 200rpm higher at highway cruise speeds in the 97. That .04 doesn't sound like much but it damn sure makes a difference.

 

[Big Bore]

I also know the ZF6 final drive is the same, or awful damn close, to the final drive of an E4OD. My 96 was an E4OD with 4.10's and my 97 is a ZF5 with 4.10's, I'm at least 200rpm higher at highway cruise speeds in the 97. That .04 doesn't sound like much but it damn sure makes a difference.

E4OD OD is .71.

 

[Irishcream]

I did the Single mass flywheel upgrade already on the ZF5 so I think the clutch is the same. As far as changing hydraulics, transfer case, driveshaft, and installing a cooler. All this kinda defeats the purpose of me doing the swap. I was merely looking to rebuild a tranny and the only response locally was a guy with a Zf6. I need the truck to be mobile for as long as possible. I am rebuilding the tranny myself on a sort of budget. If I rebuild mine I know it needs syncros. My fear was taking mine out thinking it's only syncros so it may take me a couple days and I'd already have the syncros ready to go then finding something else wrong now my downtime has gone from a couple days to a couple months which i cannot afford. If I gotta save up for gears and stuff then having a core would be ideal. no time restraints. I can rebuild it over a longer period of time making the financial pinch not as bad.

 

[Talyn]

Wow, this thread turned funny.

ZF5 vs ZF6 wars!

The extra gear really doesn't gain you anything unless you haul SUPER large.
I still take off in 2nd while hauling.

And, I don't know many 6 speed SD's that get the fuel mileage I get.
And they running 3.73's vs my 4.10's

 

[superduty4x4]

I did the Single mass flywheel upgrade already on the ZF5 so I think the clutch is the same. As far as changing hydraulics, transfer case, driveshaft, and installing a cooler. All this kinda defeats the purpose of me doing the swap. I was merely looking to rebuild a tranny and the only response locally was a guy with a Zf6. I need the truck to be mobile for as long as possible. I am rebuilding the tranny myself on a sort of budget. If I rebuild mine I know it needs syncros. My fear was taking mine out thinking it's only syncros so it may take me a couple days and I'd already have the syncros ready to go then finding something else wrong now my downtime has gone from a couple days to a couple months which i cannot afford. If I gotta save up for gears and stuff then having a core would be ideal. no time restraints. I can rebuild it over a longer period of time making the financial pinch not as bad.

The clutches are different between the two, the ZF6 has a larger input shaft, and one other difference I'm not remembering at the moment. Just FYI in case you decide to do the swap later on.

 

[Big Bore]

The extra gear really doesn't gain you anything unless you haul SUPER large.
I still take off in 2nd while hauling.

So you choose to ignore the math. Fine. LOL That still doesn't change the fact a 6speed is superior to the 5 speed in every way and that the extra gear makes a huge difference.

BTW, if you are taking off in 2nd, you aren't "hauling". LOL

This is hauling

And, I don't know many 6 speed SD's that get the fuel mileage I get.
And they running 3.73's vs my 4.10's

My two buddies with 6 spds always got 2 mpg more than I did in the same situations.

 

[Buffalo444]

The zf5 is a big trans, but the zf6 is MONTEROUS!, you will definately have to modify the trans hump.

 

[oldbluef250]

The adapater plate that goes on the back of the engine that the transmission bolts to is thinner on the zf6 compared to the zf5. I believe the zf5 has the same adapter as the autos. Someone else could verifty this

 

[Big Bore]

I just did a clutch on a ZF6 and didn't even think to look at the adapter. I'm going out to measure the ZF5, then I'll measure the ZF6 later, that's much needed info for a swap.

The ZF6 is definitely significantly larger (and apparently a lot stronger), but I'm not sure it's any taller from the center line as far as requiring floor pan modifications, I could be wrong. Several people have done this not sure if any of them are here.

 

[Hotrodtractor]

The extra gear really doesn't gain you anything unless you haul SUPER large.
I still take off in 2nd while hauling.

And, I don't know many 6 speed SD's that get the fuel mileage I get.
And they running 3.73's vs my 4.10's

Most people do not consider their girlfriend as a load that needs to be hauled, so what do you consider "SUPER large"?

I consistently got 21mpg running empty at 400+ rwhp in rush hour traffic with my old superduty and ZF6. I can't say that I ever had any good fuel consumption numbers when loaded due to the nature of the usage of a loaded truck around a farm.

 

[Big Bore]

Going back and looking at the final drive ratios, a ZF6 with 3:55's has way better final drive ratios in the first 4 gears than a ZF5 with 4:10's, with final drive ratio in OD WAY TALLER . Which means it will get a heavy load started better, faster and easier, while still being able to maintain lower rpm's on the hiway. I'd say that's a little more than significant. I've been mulling over the idea of an older Ford with a 1st gen 12v/ZF6/3.55's, and the more I think on it, the more I realize that would be the perfect low maintenance high mileage setup. The 6speed would help keep the narrow power band of the 12v in the sweet spot, while capitalizing on it's natural tendency to get good mileage.