IDI vs 460 ZF5 gear ratios

[dunk]

My understanding is the diesel ZF5 is a close ratio and the gas ZF5 is a wide ratio. I've owned and driven several small block and big block ZF5s but never a diesel ZF5. I recall with a 302 making it scream in every gear to get anywhere. I have a 460 ZF5 with a tailhousing sans mounts (last relic of my annual ZF5 replacements). Have a diesel ZF5 with good cases. I intend to do new bearings, syncros, and anything else the diesel ZF5 needs to put behind my 6.9 turbo.

I've been told I drive my 460 like a diesel, usually shifting by 2000RPM as torque is plentiful off idle. Ironically with the C6 I let the IDI scream as it's the only way it'll get moving. IDI seems to make about the same power everywhere, which is not much. Thinking wide ratio may help a bit towing with lower ratio first to get moving. Not sure how the other gears compare. Thoughts?

 

[F350camper]

I had a 7.3 idi with the close ratio ZF, the only thing I didnt like was reverse was way too tall.
Now I have the wide ratio gasser ZF5 behind a 4bt. 1st is awesome, and reverse is great. But at times it does feel like there is a gear missing between 3rd and fourth.

 

[LCAM-01XA]

Reverse on the close-ratio ZF is horrible with 3.55 gears, downright useless when you have a good load on the truck - shift t-case into low range if you have one, if you don't good luck and start saving for a clutch job it you back up heavy stuff reasonably often. Maybe it would be somewhat OK with 4.10s, idk, but to me a reverse gear should be nice and low, not allowing you to idle at 25mph...

I think you will like the wide-ratio ZF. Our truck went from 4:1 first down to almost 7:1 first courtesy of a NP435 (lowest-geared transmission you can get in a Ford), and I freakin loved it, just let the clutch off and she starts moving regardless of what she's hooked up to. Especially in reverse, that 8:1 ratio was all sorts of awesome. The gap between the gear ratios was a bit too large, yes, but honestly nothing I couldn't live with, I mean she's no 10-speed so why even bother looking for a "right" gear for any given speed/load - either slow down and hold the lower gear or speed up to catch the higher one, it was never a big deal... Never shifted at over 2500 rpms if I could help it, usually 2k was the sweet spot provided she won't fall flat on her face in the higher gear.

Then we put in a close-ratio ZF5, for the sole benefit of having OD top gear. And well, I don't like it, way too high geared for my driving style, around the yard truck is always in low range now where it rarely was before. Really gotta get my **** in gear and do exactly what you're planning on doing, funny thing our donor 460 trans is also missing its mount right now but I plan on having it welded and beefed up so it will never let go again.

For the record there is a mid-range ZF5 as well, it's one of the S47 models and was found behind Powerstrokes. Has 5.08 first gear, 4.66 reverse. Should be noticeably better than the close-ratio mess yet still not too far spread to be annoying.

All that said, the moment we run into an affordable 4x4 DNE or Ranger box for a 4-speed, all our ZFs will go for sale, regardless of their ratios

 

[The Warden]

But at times it does feel like there is a gear missing between 3rd and fourth.

I haven't driven an IDI with a wide-ratio ZF5 behind it, but my 6.9L used to have a wide-ratio T-19 behind it (IIRC the wide-ratio T-19 was only used in '83 and '84 trucks; I drove an '86 with a close-ratio T-19 once), and I had exactly the same experience with feeling like there was a gear missing between 3rd and 4th. Furthermore, with 4.10's, I was close to the governor at 35 MPH in 3rd gear, which got frustrating when 4th was too tall trying to climb a hill loaded and I had to slow down (with a similar load, I can do 45 to 50 with the ZF5 in 3rd without a problem). 1st and 2nd were really only useful for getting the load started (even with a moderate load, I could start in 2nd easily, but I usually started in 1st to reduce clutch wear), and of course the lack of an overdrive gear drove me crazy on long freeway runs

I know others have gone the wide-ratio route and have been happy with it...personally, I'd consider a wide-ratio box with a gear-splitter, but without that, I STRONGLY prefer the close-ratio.

JMHO...

 

[LCAM-01XA]

Warden, your wide-ratio T19 actually had a 3rd gear quite a bit lower than what a wide-ratio ZF has, 1.8 vs 1.6 or something like that. So then the wide-ratio ZF will fall between your two T19s when it comes to 3rd gear experience, and the mid-ratio (PSD-issue S47 only) will be even closer to the T19 you liked with 2nd and 3rd geared just a lil bit low (but probably not enough to even notice a difference).

Personally I never noticed 3rd gear being "wrong" with our NP435, and it's just a hair below what a wide-ratio ZF runs. We also have a wide-ratio T19 out of a '83 or '84 1-ton IIRC, I'll just take your word for 3rd being too low on that one. But the wide-ratio ZF ain't gonna be quite as bad. To me the 435 felt just right for a heavy truck, the wide-ratio ZF still has its gears closer than that so it should be even better suited for IDI use.

I think this is one of those things that a person has to experience for themselves to decide whether they like it or not. Plus it also depends on axle gearing, IMHO close-ratio can be fine with 4.10s while 3.55s kinda really call for something wider. Naturally wide 4.10s is slow as all heck and you end up having to wind it up a lot (as you found out), and close 3.55s are not gonna be much fun at all when hooked up to a 10k trailer...

 

[A48WillyzGuy]

I have a 460 ZF5 (wide ratio) behind my IDI. I also have 3.55's and 37's. IIRC the 460 ZF has lower gearing all around, compared to the diesel ZF. The lower gears work out very well for my setup, but I haven't had an opportunity to put more than about 2500 lbs behind it. My combination does put a heck of a load on the engine though.

 

[The Warden]

I think this is one of those things that a person has to experience for themselves to decide whether they like it or not. Plus it also depends on axle gearing, IMHO close-ratio can be fine with 4.10s while 3.55s kinda really call for something wider. Naturally wide 4.10s is slow as all heck and you end up having to wind it up a lot (as you found out), and close 3.55s are not gonna be much fun at all when hooked up to a 10k trailer...

I agree 100% that you have to drive it for yourself before making a final decision, although that's not always practical. I haven't driven a wide-ratio ZF behind anything; I was just going off Rob's post about feeling like he was missing a gear and remembering how similar my T-19 was, and jumped to the conclusion that the gears were close enough to make driving them similar (although, going off your post, that was erroneous). By the way, with an 8K trailer, I find the close-ratio ZF and 4.10 gears to be perfect behind the IDI. If I'm maneuvering at low speeds, I'll shift the transfer case into 4L with the front hubs unlocked to give me a granny gear to make things easier and be gentler to the clutch, but I wouldn't say that it's absolutely necessary. I would probably have a different opinion if I had 3.55 gears.

By the way, that T-19 isn't the only wide-ratio transmission I've ever driven...I've also driven a wide-ratio NP435 behind a 352 FE block, in a '67 F-250 my dad used to have (2WD, 4.10 axle gears). The FE block's power band was low enough that it wasn't really all that different from the IDI, really.

I'm curious to see how a wide-ratio transmission would behave with 3.55 gears...I'm open to trying something, but my experience (and the fact that most of my driving's at freeway speeds or close) has led me to a preference for close-ratio transmissions. But, that's just me

 

[LCAM-01XA]

I agree 100% that you have to drive it for yourself before making a final decision, although that's not always practical. I haven't driven a wide-ratio ZF behind anything; I was just going off Rob's post about feeling like he was missing a gear and remembering how similar my T-19 was, and jumped to the conclusion that the gears were close enough to make driving them similar (although, going off your post, that was erroneous). By the way, with an 8K trailer, I find the close-ratio ZF and 4.10 gears to be perfect behind the IDI. If I'm maneuvering at low speeds, I'll shift the transfer case into 4L with the front hubs unlocked to give me a granny gear to make things easier and be gentler to the clutch, but I wouldn't say that it's absolutely necessary. I would probably have a different opinion if I had 3.55 gears.

By the way, that T-19 isn't the only wide-ratio transmission I've ever driven...I've also driven a wide-ratio NP435 behind a 352 FE block, in a '67 F-250 my dad used to have (2WD, 4.10 axle gears). The FE block's power band was low enough that it wasn't really all that different from the IDI, really.

I'm curious to see how a wide-ratio transmission would behave with 3.55 gears...I'm open to trying something, but my experience (and the fact that most of my driving's at freeway speeds or close) has led me to a preference for close-ratio transmissions. But, that's just me

Yes I suppose close-ratio with 4.10s is reasonable enough. With 3.55s it can kinda suck tho, especially if we're talking reverse gear on the ZF.

The '67 you drove sounds like a pretty awesome setup for moving heavy things at low speeds, but under light load IMHO the extra low gears are quite a bit overkill and kinda cripple its drivability. But if you found the 435 acceptable in that truck, that's kinda what you'd see from it behind an IDI, and naturally it would be better with 3.55s. The way we did ours is we offset the lack of OD by switching from 4.10s to 3.55s, and then offset the lack of power with the 3.55s by using a 435 instead of a close ratio T19. Really wanted creeper T19 for its synchronized yet still very low 1st gear (lower than what you had in that '84 even), but these proved to be about as rare as hen's teeth. Still halfway tempted to sell all our ZFs and grab a new Ranger, but the lead time on it sucks.

With mostly freeway driving, have you considered switching to 3.55s? It's a noticeable drop in engine speed, if your regular load levels do not warrant high RPMs for sake of power and EGT management you may find the 3.55s are better suited for your needs. Then you can decide whether you need the wide-ratio or not, but since you have a t-case that you can use for low range I suspect you'll stay with the close-ratio setup.

 

[The Warden]

Yes I suppose close-ratio with 4.10s is reasonable enough. With 3.55s it can kinda suck tho, especially if we're talking reverse gear on the ZF.

I won't argue that; reverse on the ZF with 4.10's is taller than I would like! At the same time, one could argue that that's a design issue specific to the ZF...but, at that point, we're getting academic

The '67 you drove sounds like a pretty awesome setup for moving heavy things at low speeds, but under light load IMHO the extra low gears are quite a bit overkill and kinda cripple its drivability. But if you found the 435 acceptable in that truck, that's kinda what you'd see from it behind an IDI, and naturally it would be better with 3.55s.

Forgive me; I guess I didn't clarify myself...I meant that I found the '67 to drive similar to the IDI, and I found both to be UNacceptable. Granted, I didn't drive the FE block with a heavy load, and the granny gear was nice...but, lightly loaded, it's just as you said...you could start in 2nd (and almost start in 3rd), and drivability left much to be desired. So did fuel economy; I think it only averaged 5 or 6 MPG on an empty freeway run (even on the T-19, my IDI got 12 MPG on a bad day when loaded heavy; I did 14 to 15 MPG on an empty freeway run).

I guess my core point is that I like having gear options at higher vehicle speeds. It's nice to have the gearing at lower speeds as well (I would LOVE a ZF6 ), but if I had a choice, I don't want to be stuck in one or two gears at any speed above 35 MPH. In turn, this is a big argument for a gear splitter or a Brownie Box

The way we did ours is we offset the lack of OD by switching from 4.10s to 3.55s, and then offset the lack of power with the 3.55s by using a 435 instead of a close ratio T19. Really wanted creeper T19 for its synchronized yet still very low 1st gear (lower than what you had in that '84 even), but these proved to be about as rare as hen's teeth. Still halfway tempted to sell all our ZFs and grab a new Ranger, but the lead time on it sucks.

Wow, I didn't know such an animal existed...I thought that any transmission with a true granny gear was non-synchronized (at least for 1st gear). The really sad thing is, I figured my old T-19 was worthless and it ended up getting stored outside and rainwater got into it and ruined it. I hear you on the Ranger; part of me wonders what it'd be like to run an NV4500 with a Ranger

With mostly freeway driving, have you considered switching to 3.55s? It's a noticeable drop in engine speed, if your regular load levels do not warrant high RPMs for sake of power and EGT management you may find the 3.55s are better suited for your needs. Then you can decide whether you need the wide-ratio or not, but since you have a t-case that you can use for low range I suspect you'll stay with the close-ratio setup.

I thought about re-gearing (and I almost did re-gear to 3.54 when I still had the T-19), but I have a U.S. Gear OD unit instead...I also have some other plans that will be unveiled at a later date

 

[LCAM-01XA]

Mkay, whoever asked how much of a engine speed drop there is between gears - well the answer is it depends on how slow your transmission shifts. Ours 5.72-geared ZF seems to shift about as slow as the old 435, meaning if clutched in at 2000 RPMs when she's finally in the higher gear the engine has dropped to about 1100 RPMs. Shifting at higher RPMs slows the gear disengage/reengage down even more, if engine speed of 1500 RPMs is desired after upshift is complete the initial clutch-in should happen at 2500 or so. This is all on level ground, upshifting while pulling a grade is quite futile - the truck slows down way too fast so by the time we're in the higher gear we're back under 1500RPMs which is no good at all. That is not to say uphill upshifts are impossible, 1-3 is perfectly doable even with a trailer but 4th may be a no-go if the grade is steep enough. And one should keep in mind that this particular truck is a fairly gutless wonder on account of lacking a turbo, having the IP turned down (max EGT of 1000F sustained foot to the floor in OD and losing speed), and scaling it at like 8k empty to begin with. Additionally the creeper gearset was not rebuilt in any way, the big-block donor transmission shifted quite acceptably and the bearings were in excellent shape (thing had like zero input shaft play), so we just switched everything over from one case into the other and simply reshimmed the front bearings to restore the proper preloads - maybe new synchros would make her shift a bit faster, dunno and quite frankly we have exactly zero intentions of messing with this again unless it's absolutely necessary. Naturally, YMMV. But after driving the creeper-geared ZF for a while I think for most folks who like the close-ratio setups but want a bit more grunt out of the thing the 5.08:1 PSD ZF S47 would indeed be the way to go.

Warden, the creeper 6.36:1 geared T19 was supposedly only available in '84-'86 F250s with 4x4 and 460 engines. Kinda makes it a rare bird. Being a T19 it is still fully synchronized in all forward gears tho, which is why we're still kinda looking for one. The long-term plans for this truck are that exact 4-speed with a Ranger in front of it, but that may be years from now... Already got the bellhousing and the clutch fork pivot brace ready tho