ZF 6 speed swap

[pdfhick69]

Will a ZF 6 speed bolt up to a 95 PS block?

 

[79jasper]

Yes. Long as it's from a 7.3.

But you're not gaining anything over a zf5, cept a granny low.

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[Baird Tadeu]

The 1999-2003 Ford 7.3 works well behind a Cummins engine. Ford started using this transmission in ’99. If your truck did not have one of these transmissions originally you may want to consider swapping one in, especially if you are planning to use your truck for heavy trailer pulling.

 

[War Wagon]

'94-'97 OBS 7.3L

ZF 5-speed wide ratio:
1st = 5.72
2nd = 2.94
3rd = 1.61
4th = 1.00 DD
5th(OD) = 0.76


'99+ SD 7.3L
ZF 6-speed

1st(L) = 5.79
2nd(1) = 3.31
3rd(2) = 2.10
4th(3) = 1.31
5th(4) = 1.00 DD
6th(OD) = 0.72

I don't really think of it as adding a granny low the way that it is labeled on the shifter knob. Actually, when you look at the ratios, 1st in the ZF-5 is nearly the same ratio as 1st(L) in the ZF-6. Think about most peoples driving habits, at least mine anyway. I don't normally ever start in the actual 1st gear when empty unless I intend to go slow. If I'm driving a ZF-5 pickup I start in 2nd, and if I'm driving a ZF-6 pickup I start in 2nd("1" on the shifter). If I am loaded heavy I'll use the low 1st gear to start out. The way I look at it you gain another gear between 1st gear and DD, which makes the ratios in between 1st and 5th(DD) in the ZF-6 closer than in the ZF-5 leaving 1 OD gear on top of DD in both transmissions. I personally intend to someday do a ZF 6 swap into my '94 F350 at some point. It has 4.10 gears and a ZF-5 now. I would like to go to 3.55 gears and compensate with a ZF-6 to make up for the widening of the ratios by going to taller gears. I think it would be a great swap all around and shouldn't be to complicated on your 7.3L PSD. Mine is an IDI and is a more complicated swap.

 

[War Wagon]

I pulled the above ratios from another forum. I do find some discrepancies when searching for ZF-5 ratios. There were differences in the gas and diesel 5-speeds and differences in the diesel ZF5-42 and ZF5-47 transmissions. So, the gains would be different depending on what version you were replacing. Some it looks like would be more like stated above and would more so beading a lower gear, but depending on what axle ratio you have and weather or not you want to do a gear swap, I still think there's a benefit it.

 

[79jasper]

Thanks for correcting.
I thought the ratio's were different than what you posted.

In your case (one I had thought of before) would actually make sense.

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[War Wagon]

The way I see that it makes for the best upgrade is if you have low gears and a 5 speed, for example, and want to do the swap with the accompanying swap of higher gears in the rear end. Or, if you have tall rear end gears already and like them, but don't like the gaps between the gear especially when loaded. You don't want to loose you nice highway cruising gears, but would like to lessen the gaps in between your shifts.

These are some more ratios I found but again are not official. I'm not having any luck finding the info direct from ZF. Maybe these are more accurate.

S42 ZF5
Close Ratio
1st Gear:
4.14
2nd Gear:
2.37
3rd Gear:
1.42
4th Gear:
1.00
5th Gear:
0.77
Rev Gear:
3.79

S47 ZF5
Close Ratio
1st Gear:
5.08
2nd Gear:
2.60
3rd Gear:
1.53
4th Gear:
1.00
5th Gear:
0.77
Rev Gear:
4.66

ZF6
1st Gear:
5.79
2nd Gear:
3.31
3rd Gear:
2.10
4th Gear:
1.31
5th Gear:
1.00
6th Gear:
0.72
Rev Gear:
5.23