zf-5 or any transmission with over drive swap

Hello everyone, I'm a new member here, and I'm sure this question has been asked a million times but I'm having trouble finding information on a zf-5 (or anything of the likes) swap, specifically a parts list and a list of possible modifications that need to be done to fit both the transmission, transfer case, and the drive shaft and whatever else needs to be done. My truck is a 1985 Ford F-250 XLT Lariat 4x4 with the 7.5L engine and T-19 transmission. I've searched youtube to no avail, for the 4x4 at least. I've surfed all sorts of forums and still, not much information to go off of. If this question has already been answered, please direct me to the thread with the answers, maybe save me the time from scrolling through 101 pages of the same question lol.

It seems like these trucks haven't picked up in popularity like the 70's era quite yet due to the lack of information out there for the variety this truck came in during it's time. But that's perfectly fine with me, it's my favorite truck and as long as things stay cheap, I'm happy! I'd just really like to have an Overdrive option for this old girl!

Welcome!  Glad you joined!

But, you probably missed the email you were sent asking you to go to the New Members Start Here folder, read the guidelines, and then introduce yourself in that folder.  We ask that because we hold everyone to those guidelines and want you to have had a good chance to see them.  And since they are posted there...

So, have you read them?

And now on to the question at hand.  My truck, Big Blue, started life as a 1985 Ford F-250 XLT Lariat Explorer 4x4 with the 7.5L engine and T-19 transmission.  It is now running Ford's EEC-V EFI system and a ZF5-42 tranny.  Yesterday it turned in 12.8 MPG on a 170 mile trip my wife and I took, so it is running well.

The transfer case you have, which should be the BW1345, will bolt up.  And I think the driveshafts you have work, but I'm not sure about that as I had to change out the front one because I changed the front axle to a D60.  I think I used the original rear driveshaft though.

Obviously you'll need a new clutch as the input shaft on the ZF is a lot bigger.  And you'll need the taller transmission cover from later years as the ZF sits higher.

I'm sure someone else will chime in on what I've forgotten, but you've come to the right place - we've done it.  

I've swapped my T-19 for a Zf-5 as well.
It is the only manual overdrive option with the proper bell housing pattern.

Gary is pretty spot on.
My front driveshaft fit without issue.
The one other thing I can think of is that the transmission cross member needs to be shifted to the rear.

Jim - I forgot about the crossmember.  Yes, it needs to go about 3/4" to the rear.

When I put the ZF in Dad's truck I jacked the cab up and redrilled the frame to take the gussets that far back as well.  But on Big Blue I redrilled the bottom of the frame to take the crossmember and used the original holes in the top of the frame for the top of the gussets.  It did put the gussets in a bit of a twist, but not too bad and it seems to work fine.

I did the ZF5 swap last year and am very happy with it. I have the granny first gear. Hill starts in 2nd without a problem. 4.56 gearing on final drive with 37s and I am at 2000 RPM at 70 mph.

The transmission crossmember (and gussets!) can be reused if you drill the frame which can be a pain. You may just want to find a crossmember and gussets from a donor truck. The ZF5 tailhousing has different lengths (between the S5-42 and S5-47) so I'd get the transmission before hunting the crossmember. You will also need the transmission mount. Match whatever is on your engine mounts either poly or rubber.

The clutch comes in different sizes. Centerforce makes the biggest one IIRC. You will need the pilot bearing, throw out bearing, clutch fork, clutch slave and master (get a prebled unit IMHO as the system is a pain to bleed). If you had a manual already, your electrical harness and existing pedals will work fine.

The ZF5 is BIG. I don't know if the controls for that transfer case will work with the ZF5 in there. I'm not sure if you have to have linkage specific to the transmission. Maybe someone can chime in.

I did the short throw conversion with Midwest Transmission and am very happy with the results. Also, JB Fabrication makes a nice looking shift stick and boot.

I just reread your post and I realized you have an 85, not a 95. Your existing transfer case controls WILL NOT WORK. When the ZF5 was available from the factory, the controls had already been relocated from the transmission tunnel cover to the floor-board in front of it and just behind the gas pedal. You will need to cut a hole to accommodate the controls or go with a cable actuated system.

Frankly, this is probably the most difficult part of the whole project (other than finding a good ZF5 hahaha).

I've managed to move my '87 1356 transfer case linkage over to the '91 Zf-5 in my truck.
I think it's very fortunate that I didn't have to find that funky shift boot and cut a hole in the side of my tunnel.

If it stops raining I may go out and try to snap a pic.

I used the same BW1354 and controls that Big Blue came with behind the ZF5.

Chad - Tell us more about what t-case you used?  Is that the NP205?  I've not played with one of those, but what made it difficult to use the linkage with it?

My existing clutch fork and slave worked just fine.  

I'm not sure why you had all these fitment problems Chad.
What engine and gearbox were in your Bronco when you swapped in your Zf-5?   🤔

Hi Gary. Ya, I've got an NP205 like what would have been found in a 78/79. It is way easier linking up the aluminum t-cases.

The NP205/ZF5 combo has a lot of complications. It has twin shift rails. Technically, it fits the tailhousing bolt pattern, but the housing has to be clearanced to allow one of the shift rails. Plus, there isn't that length of input housing on the NP205 like there is on the 208 or the BW units, so the shift rails are much closer to the transmission case. If you set all the aluminum units on a table next to the NP205, it's shape would stick out like a sore thumb; it is dramatically different compared to the minor differences on the aluminum units. Additionally, that iron transfer case weighs about as much as the whole ZF5 (I've lifted them both so I know first hand). So you have to find a way to mount it to a support off the frame with a bushing or your ZF5 will definitely crack.

Frankly, I didn't have the transfer case shift linkage for either the NP205 or the ZF5, so it seemed like hunting down original parts without knowing how they would fit (or if I could make them fit) would be a boondoggle. There are two bosses accessible on the ZF5 that could probably be used to engineer a linkage solution. I haven't tried using the part from the NP205 that links the shift rails together so I'm not even sure if that would work with the ZF5 even after it was clearanced. Again, since the Bullnoses have the transfer case shifter in the transmission tunnel cover and the later 5 speed trucks don't, once you put the later transmission tunnel cover on the Bullnose, there is no longer a hole to allow access for a transfer case shifter, so you have to choose where to cut one no matter which direction you go with the linkage.

I decided to go with a twin stick cable actuated shifter from JB Fabrication. That way I could take advantage of the dual shift rods. That thing is massive though so I still haven't cut the transmission tunnel cover to mount it. I'm going to have to weld on some framing for the shifter to bolt to. Like I said earlier, I think the t-case shift linkage is the most complicated part of the ZF5 swap and it's even more complicated with an NP205. I created these issues myself by swapping out everything so I'm not complaining. Engineering the solution is part of the fun.

I included a couple pics that shows the trailing edge of the tailhousing where you can see the clearancing I did for the shift rail and another pic that shows the transmission and transfer case bolted together. If anybody is dying for pictures, let me know what you want to see and I will snap some while I am under there this weekend installing a ground strap on my fuel tank.

ArdWrknTrk wrote

I think it's very fortunate that I didn't have to find that funky shift boot and cut a hole in the side of my tunnel.

I cut the hole in the side of the tunnel in my 1980 for the M5OD and the 1356. One, I didn't have the original case and controls, and two, I didn't mind zip-cutting the floor in this truck as it wasn't s how winner anyway lol!




One downside to the location of that transfer case shifter being that far left...at least in the north, is that the screw holes filled up with salt from shoes/boots/floor and rusted to pieces...which made them extremely difficult to remove lol.

Chad - I had no idea the 205 required that kind of work.  Wow!  I'm glad I stayed with the Bullnose t-cases.  From my reading though I understand that the twin-stick approach allows you to use 2WD Low range.  And it also allows you to have front wheel drive only.  Those are intriguing.

And I'd forgotten that I did have to cut the tunnel cover, but since I had the Bullnose cover it was easy to figure out where to cut it.

Cory - I hadn't thought about the snow melt and salt.  We don't have enough snow any more to make that an issue, but I can see how it could be if you did it day after day in the winter.  Anyway, your installation looks (looked?) good.  

As you are looking for a ZF5, keep in mind that since the bellhousing is an integral part of the transmission you need to get one that will fit your big block.  From least common to most common, they made them for small blocks (which won't work at all for you), big block gassers (which would be a direct bolt-on) and diesels.  Diesels are probably the most common, and one MIGHT work on a big block.  I know they are close and I've read that you can relatively easily modify one to work on the other.  But I don't know if you can only put a diesel trans on a gas engine, or a big block trans on a diesel engine or if you can do it either way.  And I don't know what you have to change.

So sorry for not having the answers, but at least it might help you find the right questions.

Good point, Bob, and one we'd forgotten.

But, there's a big difference in gear ratios between the diesel and gas ZF5's.  The diesels have a close-ratio gearset and the gas trannys have a wide-ratio gearset.  

ZF5 - Close
1st: 4.14
2nd:2.37
3rd: 1.42
4th: 1.00
5th: 0.77

ZF5 - Wide
1st: 5.72
2nd:2.94
3rd: 1.61
4th: 1.00
5th: 0.76

Depending on your intended usage that may make a big difference.  For me the low 1st gear of the wide-ratio gearset is the only way to go.  But I will admit that there's a wide jump between 3rd and 4th so going to 3rd at much of a speed is questionable.  On the other hand, when we were running the carb on this engine and climbing the passes around Ouray we found that we could go a lot of places in 3rd if we kept the R's up.  Now, with EFI, that won't be necessary and I'll bet 3rd is going to be "the gear" when in low range.

Bob, only the top two bolt holes are the same IDI diesel- big block gas pattern.
The locating dowels are bigger for diesel and the starter is far different.
Ford used an adapter plate on the IH engines. I suspect they came with an SAE pattern.

I have heard that some people have been able to weld up the gas pattern bellhousing and bore out new holes, but that would take some serious mill (no separate bellhousing on the Zf, so you'd have to fixture the whole trans) and an accurate pattern.
I've never heard of someone going the other way.
And like Gary said, the higher 1st and tighter ratios don't really suit a 460.

I'm not sure what you could do about the starter. They are unique to diesels.
For sure the diesel flywheel is not the same as a 460.

I've definitely heard about people trying to convert the diesel case to a gasser. It ends with a listing on Craigslist for diesel ZF5 with a cracked bellhousing. I'm not saying the successes aren't out there, but I don't see them as much as I do the failures...

Back to the original poster's question. If you are unhappy with your lack of overdrive, why not just install a one of those units as an add on? I think I heard them called gear doublers? Seems like a significantly easier way to go if all your missing is a highway gear.

Dave (fuzzface2) has a gear vendors overdrive under his flareside.

Probably because the units that fit T-19's are $3,200???

https://www.gearvendors.com/4x4fmanual.html

Ouch. I withdraw the question.

I also think since these units go between the gearbox and the transfer case you need to think about additional support and new (or modified) driveshafts as well.