This thread is going to be about my efforts to swap a ZF5 into Dad's '81 w/a 351M. That truck is currently running a C6 and will be getting both a different engine as well as the ZF, but I'll try to contain things to the tranny swap itself.

And, if you think you've read some of this stuff somewhere before then you are probably correct as Chris did his magic and extracted the ZF posts from the thread called Dad's Truck Build. Hopefully that will make it easier in the long run for people to find info on swaps like this.

As many of you know, I'm approaching this not by bolting things together to see if they work, but by drawing the various components up in CAD so I can see if they'll fit or work together. The main reason for that is to minimize the downtime and churn when I actually start doing the swap. And, the main reason for that has been that Dad likes to see his truck from time to time. However, the days when he actually recognizes his truck seem to be dwindling, so I may be able to start the actual work sooner than I thought.

And, as stated somewhere below, my intent on this swap is to make it as simple as is possible so that others can do it also. Toward that end I'm hoping to solve most of the problems with off-the-shelf components.

Anyway, please review what we have to this point and ask questions, make comments, or offer suggestions.

 

Ok, I figured out how to output my drawings in jpg. So, here are two of them. First is the pilot bearing issue. I don't yet have the adapter drawn up that holds the pilot bearing further back to catch the ZF's shaft, but will do and will post that.

Second is the issue of how little the clutch hub engages the splines of the input shaft, which is .304". That's being discussed on another thread in a different forum, but thought I'd show y'all what the issue is and get your input. And, for reference, the clutch hub is 1 1/64" long, so we'd get only about 30% engagement using the 460 clutch that is shown.

And, I apologize for the poor quality of the drawings. I'm no draftsman, but they work for me. If you have problems visualizing them please let me know and I'll see what I can do to clarify them.

 

Part of the problem with the clutch hub, comes from the 460 crank being longer, and therefore protrudes further out from the back of the block, than that of a 351M/400. Which also explians the pilot bearing engagement issue.

Off the wall question, but how thick is the bellhousing where it meets the engine? Could this surface be milled down some while still providing the thickness to allow the bellhousing bolts to properly secure it to the engine? Gaining even .100" there would translate directly into .100" more clutch hub engagement and pilot bearing engagement.
Leaving out the rear plate would also gain engagement depth for both, but you would likely need to cut out the starter area, or make a "shim" for the starter that is the same thickness.
Might not sound like much, but if you could gain 1/16"-1/8" on both, that would become 1/8"-1/4" additional engagement depth......

 

I'm hoping Gary can be a guinea pig for me and get this all figured out and working, I'd like to take what he learns and do the same ZF5 conversion to my own truck someday.

 

I haven't included the 1/16" rear plate/spacer in the drawings or measurements. In other words, I've already planned to leave it off.

As for milling the face of the tranny, the thinnest place on it is .600" and that's at the top 2 bolt holes. But, the 4 other bolts holes have 2.000+ thickness so are obviously stout. I'm not sure how much can be taken off and still have the needed strength on the top two holes, but it would look like a fair amount could. However, the input shaft is .262" back of the front end of the bell, so about the most that could be taken off is .250". And, since my mill can go horizontal that is a possibility, although one I'll put on the back burner at the moment as I've not exhausted other approaches.

Actually, that's my hope - that this swap can be done in a way that is repeatable with relatively little trouble. I can't find anywhere else on FTE, or anywhere on the internet for that matter, that has a complete how-to. In some places one or two of the problems are mentioned but no place that I can find lists all of them. And, in many the solution is done w/o recording how it was achieved.

So, is it time I start a dedicated thread to this swap? There's also one in the 335 Series forum, but it isn't going very quickly - although I'm not moving rapidly either. However, I am trying to approach it in a scientific (terribly-boring?) fashion. And, I've posted twice on that thread w/o any acknowledgement or response of any kind.

Let me put that another way. To this point I've learned, by virtue of reading everything I can find on the subject, that there are these problems and potential solutions:

• Clutch: The ZF5's input shaft is much larger than that of any transmission put behind the 351M/400, so no stock clutch will fit. However, I hope to be able to solve that by getting the 12 1/4" 460 clutch to fit under the 351M/400 pressure plate. And, if it won't out of the box maybe it can be turned down just a bit to fit. Or, maybe a clutch house can make a 12" clutch with a 460 hub.
• Flywheel: A 12" flywheel was used on 400's in the trucks, so that's the way to go since it is a big as is available off-the-shelf for the 351M/400. However, at least one has had the 460's flywheel redrilled to fit the 351M/400 crank.
• Pilot bearing: As discussed, the input shaft on the ZF5 isn't long enough to engage the stock pilot bearing. But, an adapter can be made to space the pilot bearing to the rear to fully engage the shaft.
• Splines: The 460 clutch that I have will only engage ~.300" of the 1.016" of splines, so it would be possible to tear the splines out if the driver isn't careful.
• Throwout bearing: The input bearing's retainer isn't long enough to allow the 460's throwout bearing to release the clutch without falling off the end. At least one FTE'er has found a larger bearing and was able to make an adapter that press-fits on the retainer to provide the needed length. However, what that bearing is or came from isn't known.

 

Is it a good idea to leave it off? IIRC it's involved at the starter motor somehow.

I remember having read about this in the 73-79 forum some time ago, although that may have been only about a conversion to a hydraulic clutch, I don't remember for certain.

You might post in there, too, and see if somebody there remembers more.

The 335 forum is an exceedingly low-traffic forum, always has been AFAIK. There have been some really good guys there in the past, but that was around 5 years ago.

The 73-79 forum here seems to get the most M-block traffic from what I've observed.

 

Which is the reason I mentioned the possible need for a shim of the same thickness between the starter and bellhousing. Without it, the gears could mesh too deep.
However, the distance from the mounting surface to the ring gear *shouldn't* be any different with/without the plate....

 

Chris/RW - Neither of you mentioned starting a new thread re the ZF swap, so I'll assume you don't see the need and continue on in this thread.

Chris - I'm not sure quite how to post in the 73-79 forum. They've mentioned the ZF swap in some threads, but I don't remember one specific to it. I'll look again, but if there isn't one should I start a new thread there and ask how people have solved those problems?

As for the spacer, I agree with RW that I can put a shim between the starter and the tranny if need be to get the starter forward that 1/16". But, I doubt it is needed. And, if I do leave the spacer off I may cut the bottom of it off and bolt it on via the holes in it and the tapped holes in the tranny. That would give protection to the flywheel and act as the inspection cover from the "golden years".

And, I've designed the pilot bearing adapter. I started with info from 1FastGambler, who has done this swap into a 70's truck. But, his adapter doesn't get the pilot bearing all the way back on the input shaft's nose. And, as RW pointed out at the GTG, the input shaft on my ZF is worn significantly at the front so I want to get the bearing as far to the rear as is possible. I've left .075" between the back of the spacer and the step on the input shaft for clearance and movement. And, dimensions like the depth of the bore for the pilot bearing will not be finalized until I have the bearing in my hands.

 

This is up to you...

Think to yourself... if you were searching FTE for a specific topic, would you you hope to find more help when your search term shows up in the title of a thread, or when it shows up in the body of somebody's build thread?

But I don't want to tell you how to write your stuff, it's like telling an artist how to paint.

I would search first, then ask.

I just searched over there on "zf5" and lots of possibilities came up but only a handful with with that in the Title.

Maybe this will help prod you in your decision above.

I did read through some of THIS THREAD, though, and looked at solidrunner's gallery.

He doesn't seem to get real specific, though.

There were lots of other threads mentioned in there, too, none of which I looked at.

I then searched on "zf5 howto" and got pointed to 1fastgambler's stuff, even where I asked him to write up a howto on how he did his.

Not sure if he ever did that, though.

https://www.ford-trucks.com/forums/1...f-5-400-a.html

https://www.ford-trucks.com/forums/1...i-400-etc.html

 

I had read Solidrunner's thread before. In fact, I believe I've read all threads re ZF5 swaps, although I haven't read all posts that mention a ZF5. In any event, I re-read Solidrunners thread just now and found a gem that I had overlooked or forgotten: "If I remember correctly, I used the ZF t/o bearing and clutch disc and the 400 flywheel and pressure plate. The clutch disc was a little bit bigger so it had to "clearance" itself against the edges of the pressure plate when I first started it up. Other than that it's working great."

Basically, what he is saying is that he stuffed a 12 1/4" 460 clutch under a 12" 400 pressure plate and that it trimmed itself off when he first started it up. That worried me a bit, so I called a clutch/brake shop here in Tulsa. From what he said no one in town makes clutches. However, he's been working on clutches for a long time and said that there is plenty of room between the edge of the disk and the "fingers" inside such that I could trim it on the lathe and make it fit.

And, in a way I confirmed his statement about using the 460 throwout bearing as the drawing, below, shows the 460 bearing sitting against the pressure plate and just coming to the end of the bearing retainer. IOW, it looks like it won't fall off.

However, I did discover a problem with my pilot bearing adapter - it shares the same space as the clutch hub. Or, to put it another way, there's a .318" overlap, so I'll have to scale the adapter back a bit in length, which will make the bearing run on part of the worn area. Oh well.

As for the new thread, I'd originally thought I should start one but when you two didn't suggest it when I asked I guessed maybe not. Anyway, I would like to do so. Can I copy/paste a bunch of the posts over to a thread or does that take a moderator?

 

Good explaination so far, Gary. I'm going to subscribe to this thread since I'm interested in a ZF5 swap.

 

So why exactly are you as content on a ZF5 swap as I am on building a 351M/400?

 

In regards to the milling: The top 2 bolt holes would be down to .350 after a cut of .250. In my opinion, that's plenty. Most of the stress is on the bottom 4 bolts, likely the reason for the extra long shoulders on the holes.
Of course, there's also the option of adding some more "meat" around those top 2 bolt holes......

That 1/4" translates into 1/4" more engagement depth for the pilot and splines, even little bit will help.

 

Taking 1/4" off would almost double the spline engagement, which is now my largest concern. I'm not sure the 1/4" makes much difference on the pilot bearing as I'll still have to have an adapter. But, as I think about it, taking .250" off of the .318" overlap of the pilot bearing and clutch hub means I'd only have to reduce the size of the pilot bearing by .068". And that means the pilot bearing would be running on some unused shaft instead of the part that is worn.

Yes, milling 1/4" off the front of the bell would solve several problems. And, I may do it. But, it runs counter to the plan of making this an off-the-shelf swap. However, the only alternative I can see that would gain spline engagement is to find someone to make a special clutch disk that has the hub set to the rear further. Or, use part of the hub off this used disk and weld it to the rear of a new disk. Now, that might be a reasonable approach as I know someone who can weld anything to anything. Hmmmmm

Ok guys, your thoughts on this, please?


I forgot Shaun's dig. To tell the truth, Shaun, when I get into Dad's truck and realize how well it works with the C6 I wonder why I want to change it out. Then I stop at the next gas station and am suddenly reminded - 10.5 MPG! So, I want OD. And I don't think the M5OD was ever put behind a 351M or 400, much less behind the 460, so the ZF5 is the only 5 speed OD tranny I know of that'll at least bolt to the back of the block, if not play well with the flywheel and pressure plate.

 

To be honest, the thought of removing that much bell housing material scares me.

I take my tuck up into the back country (read: way into the mountains, far from civilization) to cut & haul firewood (and a fair amount of it at that, loaded in a 13' trailer in addition to the bed).

That would be a really, really, really crappy place to break something like a transmission.