ZF Swap

[jmurphy]

Hello Everyone,
So I just picked up a ZF S5-42 for $200, feeling like it was a really good deal despite the lower shifter being broken and it not having an upper shifter either. It will probably be a while before I can afford the rest of the parts I need to actually swap it into my rig but couldn't pass up on the deal and now I can start researching about specifics on swapping a ZF

This ZF was just sitting in a yard and don't have any history other than being told that the PO bought it from his brother in law to put into his truck but didn't realize it was a 302 (4.9)/351 (5.8) bellhousing model and not the 460 (7.5) bellhousing model he needed for his truck so he was selling it. I don't know how trustworthy the information is so debating weather to clean up the outside, drain and put new fluid in it and put money towards the rest of the swap or spend the extra money and get a bearing and synco kit and rebuild before swapping in. If going with the rebuild does anyone have recommendations on where to get a good rebuild kit? So far I've found these two places with rebuild kits. 1.manualtransmissionpart.com 2. drivetrain.com

Next I'm also not sure what transfer case setup to go with yet. I want to be able to drive my Bronco to and from the trails so I want to keep my axle gears as high as possible and use the rest of the drivetrain to achieve very low crawl ratios. It seems obvious that the easiest would be an atlas 4 speed but most things easy don't come cheap. The other option I'm considering is getting the Wild Horses supercrawler kit and finding a used NP203. The NP203 should bolt directly to the ZF and the kit will bolt the Dana 20 to the NP203 this would achieve a similar result as the Atlas 4 speed. My concern is that I'm not sure how this will affect the driveline angles and if it would cause any other issues I'm not aware of.

Now on to some really nerdy/technical stuff......According to this awesome Gear Ratio Calculator I found online. If I run the ZF/NP203/Dana 20 (T shift, 2.46 low) combo, 4.11 axle gears and 35" tires I would have a 115:1 Low/Low gear ratio and still be able to cruse down the interstate at 75 mph at only 2300 rpm. My only experience with how crawl ratios relate to trail driving is limited to one trip I took with my sister's Rubicon and was so impressed. Granted we were not on anything hard but there were a couple of steep parts and I actually had to give it gas to go down the hill. I did a quick calculation on her setup and it was a 65:1 crawl ratio.

Just for the sake of discussion I really like manuals and would like to ditch the C-4 and get the ZF into the Bronco ASAP so I'm curious if it would be worth the effort to pick up a NP203 add the conversion kit to make it a part-time T-case and install it behind the ZF so I could get the manual into the Bronco sooner than later. That would buy me some time while I keep saving up to get the remaining parts for the doubler. I did a quick check and my stock setup C4/Dana 20 and 3.50 axle gears nets a whopping 20:1, If I run the ZF/NP203 and 3.50 axle gears I would double the crawl ratio to 40:1 Sounds pretty awesome to me if it makes sense from a budget standpoint. For those of you who are running the ZF does your new crossmember bolt directly to the ZF? If so in theory I wouldn't need to redo the crossmember support I would just end up removing the NP203 so I could split the NP203 and bolt it to the Dana 20 and then mount the whole thing to the back of the ZF? I'm assuming this would require changing the drive shafts both times, is that a big pain in the but or something rather simple to do? Any rough estimates to get driveshafts modified?

I haven't put together a compete budget but from what I've check so far the NP203/Dana 20 would be considerable less and possible to do in stages than going with an Atlas 4 speed. So I figure for a guy on a budget going with the NP203/Dana 20 with a 115:1 crawl ratio should be enough to get me by for several years before I could justify actually needing the crawl ratio an atlas 4 speed provides. But would really appreciate hearing about people's real world experience with different setups and if there are any other options out there that's I'm missing.

Thanks

 

[Joker11]

I touched on this in another thread. There are a few of us going into the ZF on a low budget. Good for you on the deal.
I paid 1000 bucks for my ZF. It came with upper and lower shifters, the shifter boot and the shift knob. I am hoping my guy did me solid on the deal. I am not even going to do anything to it first other than clean, prime and paint it.

I am going with the strong box for a doubler.

Yes, it will affect the driveline. Your driveshaft will have to be shortened. That is cheaper than lengthening. To lengthen it you will have to retube it. You pay by the inch on the tube, plus welds and a balance. To shorten it, just one cut, just one weld and a balance. but no tube.

Your angles can become extreme, especially with a lift. I am dealing with that.

I am with you on the thought process. Get it up and running and work on it as you can afford it. I think more projects get completed when you do it that way. Otherwise it can seem overwhelming and end up sitting as the project that you just never finished.

 

[broncnaz]

Id check end play on the input and output shafts that can tell you something about the condtion also check the oil that come out no metal and your good. Doesnt hurt to rebuild tho.
The OD may not be totally useable depends on your engine but you may need to regear the axles to 4.88 or 5.13 to really use the OD. Your thnking on the transmission gearing to make up for lost axle gearing is a little off while you could survive it wont be the best combo.
As for the 203 doubler once you buy the kit the 203 and a 203 and a HD output shaft for the D20 your close to the price of a atlas. kind of a toss up there.
Overall I woulndt worry much about crawl ratio unless you plan on rock crawling. The 5.72 first gear is plent low enough for most slow speed stuff.

 

[jmurphy]

I'll have to look for your other thread and read through it. Hope it goes well getting your ZF up and running.

That strong box looks pretty cool, are you going with the DIY setup or buying one assembled?

Thanks for the heads up on the driveshafts, am I missing something or won't the front driveshaft need to be lengthened since the t-case is going to be further back? Also can you cut off the rear spring mounts, rotate the axle housing and weld new spring mounts on to help reduce the rear driveshaft angle or does that cause other issues where it's not a good idea? And if so is getting a Hi 9 the only other option to remedy extreme driveshaft angles?

Good to know, I'll definitely check for any end play and the tranny oil.

Oh really? I certainly haven't look into axle gearing enough. Why would the overdrive not be very useable with that combo? What things need to be taken into consideration when figuring axle gears for driving a rig on both highway and trails?

Thanks for the input certainly realizing how much more I need to learn about different aspects of swapping different parts.

 

[broncnaz]

Yes usually both driveshafts will need mods. Sometimes you can use the front drivesahft in the rear but it all depends on the setup you go with. Costs for driveshaft mods varies kinda depends on if you have any local shops that can do the work. otherwise your looking at about $240 ea plus shipping for new shafts. Of course the shops may be similar in price.
Yes the rear spring perches can be cut and the axle rotated to get a better pinion angle but that only solves part of the issue. Steep driveshaft angles are not good for ujoint life and tend to cause vibrations. Steep angles come from high lifts and short driveshafts. Rotating the axle helps slighly reduce the angle but usually not enough you can only turn the axle so far. Not a big deal on offroad rigs but once on the hiway you can have issues.
The Hi9 is a good option for those that run the super tall lifts and have doublers ect. And have steep drivelines and short ujoint life.

Axle gearing is a big part of being able to use OD with large tires. Most factory setups came with about 3.73 or 4.11 gearing and were only expected to run about 29in tires. That puts the engine in its torque range. Once you go with bigger tires the RPM's drops and your out of the torque range. Small block engines need to rev up a little to be in there powerband. They are not lowend torque monsters. Usually you want to the RPM's around 2500rpm at about 65mph. A little extra RPM's doesnt hurt with a small block.
You also have to figure that the bronco is a brick you lift it put larger tires and you increase drag even more which takes even more power to maintain a happy speed the small engine will struggle to maintain speed. So thats where axle gearing comes into play. Most people would probably recommend about 4.88 axle gearing for your combo. Might also want to consider that you may want to go with even bigger tires at some point and will really need the lower gearing even more.
Gear ratios calculators are a great tool but they dont always tell the whole story unless your just looking for crawl ratio.
There is nothing set in stone that say you must do this or that its all up to you. Many people run setups that are not considered to be optimum and they live with it. Many will say its fine and maybe it is to them. But its a whole package that works together to get the best all around setup vs one that just works.
For what its worth you could probably just do a NP435/203/205 setup with 4.11 gears and forget about the OD of the ZF. Or even a NP435 with a atlas as you wouldnt have to put money into adapters and doublers. NP's are cheap and that setup would be shorter than your ZF/doubler/D20 combo
Sorry for the long post and the monkey wrench at the end. But you asked.

 

[GrillMaster]

Just did this swap with a 205 and it's not too bad. Not to hard to take the case apart and check the gears, mine had to come apart as the front seal/input shaft was leaking. Of course I didnt know this till I had it all together and running. I had no play on the input or output and the gears and syncros looked solid when I had it apart so no rebuild. I too was on a budget, hence the 205 vs Atlas. 205 is not as low as the D20 but with the granny 1st on the ZF I have enough gears to do most of the trails around here and I can hang with the atlas guys in most cases (no pun intended). I had to install a 1" body lift and do a crossover 2 into 1 exhaust. Both of hich I really like. I made a mount for the 205 to take stress of the rear of the ZF and used the BC crossmember, braided clutch hose and stock/rebuilt master and slave from the autoparts store. It's a great upgrade as I drive 100+ miles to trails and it does 2k on the freeway vs 3k with my old toploader 4 speed. Also running 4.11 gears, I think 4.56 would be perfect for someone who drives 65-70 on 35s. I need to downshift to 4th on the steep grades.

 

[Broncobowsher]

You should be able to pick up parts off a 2WD ZF to fix the shifter. Worst case, rebuild the 2WD with the 4WD output shaft and tail housing. the 2WD is a lot cheaper to get as the demand is a lot lower.

Now your 4.11 and 35" tire combo. That isn't going to fly. You didn't state what engine you have, guessing a 302? No way will it have enough torque at 2300 RPM to push a Bronco sitting on 35s through the wind at 75 MPH. If you were still running on 29" tires, it might be about right. I would recommend more than 4.11 gears with 35's WITHOUT an overdrive.

Another factor I look at in your plans that looks to be a failure point, low geared transmission, doubler, Dana 20 output shaft. You do plan on upgrading the output shaft at some point?

 

[GrillMaster]

"Now your 4.11 and 35" tire combo. That isn't going to fly. You didn't state what engine you have"

This combo works great for me running a 351C but 4.56s would be better gears. Currently I can drive up most freeway hills in 5th at 70 MPH. Steep hils require a downshift.

 

[76Broncofromhell]

Why are you calculating crawl ratio when I'm not even sure if it's going to be a wheeler? I've been running a ZF to D300 in my rock crawler with good results for going on 5 years now. I'm running 1 tons, 5.13s and 42's for reference. I use 1st and Low range only on extremely difficult obstacles, most of the time I'm in 2nd or 3rd in low.

My EB ran with 35s and 4.11s for years with no issues - then I took it apart.

Going too deep on the gears is a big mistake in something you drive on the street and do light wheeling. Doublers on something like that are an even bigger mistake in my humble opinion.

Do you have any plans to do hardcore trails in this? Or is it just going to be moderate trails? I'm in the process of swapping this exact same drivetrain into an FJ60 at the moment and I went through all of the same exercises regarding gear ratio. I decided on 3.73s and 35's namely because I'm realistic about the freeway speeds around here. I chose 4.10s and an AX15 on my other truck and it leaves me wanting a bit less RPMs at 75-80. If I have to downshift up a hill, so be it.

 

[Joker11]

I can't imagine having a bronco and NOT going out on some difficult trails and crawls.
Seems silly to do a bunch of upgrades if they aren't going to be used.
I guess it never occured to me that someone would build a streeter.
That may sound dumb, but I live in an area 5 minutes away from the Glamis sand dunes. I am also in the open desert where we have washes and rocks and hills. It is just what we do out here.
I now see where I went wrong. Not everybody lives in Yuma.

 

[broncnaz]

There are many people that build broncos up but dont really use them. Some even put some high dollar parts that are really only suited for trail use becuase they think its cool or its what others are running. Overall it doesnt take much to do difficult trails in a bronco. Many times all the hard core stuff is not needed.

 

[76Broncofromhell]

I can't imagine having a bronco and NOT going out on some difficult trails and crawls.
Seems silly to do a bunch of upgrades if they aren't going to be used.
I guess it never occured to me that someone would build a streeter.
That may sound dumb, but I live in an area 5 minutes away from the Glamis sand dunes. I am also in the open desert where we have washes and rocks and hills. It is just what we do out here.
I now see where I went wrong. Not everybody lives in Yuma.

I would consider Glamis (and the whole Calexico area) to be "light wheeling", in that it is very possible to run the local trails without beating the hell out of your rig. I've run both my EB and my daily driver SR5 Toyota down there without destroying it. In neither instance was I wishing for 100:1 low range or at major risk of body damage. In contrast, I would never take my more streetable rigs to the Hammers or Fordyce. Many EB owners are body damage averse, so for them a deep low range is mostly a waste.

To my original point (and to answer the OP's question) - if you aren't sure you need a doubler - you don't need a doubler. This goes for many offroad-specific parts as well.

 

[Joker11]

I was just pointing out recreation areas. Like Picacho. Not that it is rough wheeling, but that it is so close that we all go out there.

The first time I went wheeling I learned what I needed pretty quick. 35s, a lift and more gear. But you are right, a set of paddle tires and glamis is easy wheelin.

 

[jmurphy]

Do you have any plans to do hardcore trails in this? Or is it just going to be moderate trails?

While I do intend to drive my bronco around its main purpose will be to push the limits while wheeling. I'm sure that I will be doing quite a bit of touch up/complete overhaul on the body from time to time. But I just don't want to have to trailer my bronco to and from places.

The plan is for my brother and I to each take our Bronco's and go wheeling anywhere in Moab, The Rubicon Trail, Holy Cross Trail etc. I'm not sure if you would consider these in the Hardcore class or if in your opinion one would need a high crawl ratio on these types of trails?

To my original point (and to answer the OP's question) - if you aren't sure you need a doubler - you don't need a doubler. This goes for many offroad-specific parts as well.

I wasn't originally questioning if I needed a doubler but certainly brings up a good point to think about given I have such little experience with what I'd actually need on the trail. Since I have never built a rig I run a lot of scenarios in my head. I could buy the 3.15:1 low gear for the Dana 20 for approx $825 or buy a used NP203 and adapter for $600-750. From a cost side of things it seems to make sense to go with a doubler but I'm just not sure if the doubler caused any other major issues that I'm not aware of. I want to have the most gear as possible and don't want to have a doubler just to say I have one but it is very easy to get sucked into things not needed. That's why I figured I should get some advice from people and their experiences to help me decide so please keep opinions coming.

 

[broncnaz]

Id swap in the ZF for now then start wheeling and see if you think you actually need a doubler or lower gearing. Minds can change 10 times before you end up with the setup you want.
Really if your going to be pushing the limits while wheeling then your probably going to need a trailer. Bronco parts are not always easy to comeby out on the trail and some custom stuff may be ever harder to get. Along those lines lower gearing makes it easier to break parts. So in a sense higher gearing may be a better choice.
Most all the trails you listed can be run in fairly stock rigs. But yes modifications can make it easier and allow you to go more places. Whay you need is more up to you than what we say.
Although Id say your better off doing a atlas. Or a 203/205 setup either way costs will be close. Even if you stick with a D20 as was said before double and D20 your going to need a HD output shaft for the D20 All said and done your still weaker than the 205 or atlas and still close in price.

 

[Pat B]

Something I've learned about the ZF.....
Don't waste your time and money trying to use Mercon, go right to the Red Line MTL 75-85 wt synthetic oil. It's a heckova' more quiet than Mercon

Pat

 

[76Broncofromhell]

While I do intend to drive my bronco around its main purpose will be to push the limits while wheeling. I'm sure that I will be doing quite a bit of touch up/complete overhaul on the body from time to time. But I just don't want to have to trailer my bronco to and from places.

The plan is for my brother and I to each take our Bronco's and go wheeling anywhere in Moab, The Rubicon Trail, Holy Cross Trail etc. I'm not sure if you would consider these in the Hardcore class or if in your opinion one would need a high crawl ratio on these types of trails?

I can answer specific to the Rubicon - on 35s with a rear locker you can run the trail with no body damage if you take the bypass lines. One of my friends has taken a Toyota Tacoma on 31s with open differentials from Loon to Tahoe sustaining minimal damage. His only modification is never lifting off the throttle -ever.

My flat fender (seen here) runs a 351W-ZF-Dana 300 and runs just about every trail you can throw at it. Insanely low crawl ratios are mainly reserved to the small underpowered rigs like Samurais and Toyotas.

I wasn't originally questioning if I needed a doubler but certainly brings up a good point to think about given I have such little experience with what I'd actually need on the trail. Since I have never built a rig I run a lot of scenarios in my head. I could buy the 3.15:1 low gear for the Dana 20 for approx $825 or buy a used NP203 and adapter for $600-750. From a cost side of things it seems to make sense to go with a doubler but I'm just not sure if the doubler caused any other major issues that I'm not aware of. I want to have the most gear as possible and don't want to have a doubler just to say I have one but it is very easy to get sucked into things not needed. That's why I figured I should get some advice from people and their experiences to help me decide so please keep opinions coming.

I go through this exercise every time I see a set of TeraLow D300 gears go for sale on Pirate. Stock Dana 20 will do you fine, don't invest in low range gears until you are sure you need them. The reason guys prefer doublers over low gear sets is because deep low range gears in a single case rule out any ability to do things like sand or loose hill climbs with any sort of wheel speed. That's my father's only complaint with his '12 Rubicon. He has to be in 6th and Low to actually climb up hills with a lot of loose gravel or sand. I can go up in 3rd. A doubler means you can keep the stock low range, and still go lower.

Once you put a ZF-D20 adapter on, you can pull the stock case in a matter of minutes on a Bronco. It's actually quite easy and doesn't require much more than disconnecting the shift linkage and drivelines. You don't even have to drain the oil out of the case.

 

[roundhouse]

I can answer specific to the Rubicon - on 35s with a rear locker you can run the trail with no body damage if you take the bypass lines. One of my friends has taken a Toyota Tacoma on 31s with open differentials from Loon to Tahoe sustaining minimal damage. His only modification is never lifting off the throttle -ever.

My flat fender (seen here) runs a 351W-ZF-Dana 300 and runs just about every trail you can throw at it. Insanely low crawl ratios are mainly reserved to the small underpowered rigs like Samurais and Toyotas.





I go through this exercise every time I see a set of TeraLow D300 gears go for sale on Pirate. Stock Dana 20 will do you fine, don't invest in low range gears until you are sure you need them. The reason guys prefer doublers over low gear sets is because deep low range gears in a single case rule out any ability to do things like sand or loose hill climbs with any sort of wheel speed. That's my father's only complaint with his '12 Rubicon. He has to be in 6th and Low to actually climb up hills with a lot of loose gravel or sand. I can go up in 3rd. A doubler means you can keep the stock low range, and still go lower.

Once you put a ZF-D20 adapter on, you can pull the stock case in a matter of minutes on a Bronco. It's actually quite easy and doesn't require much more than disconnecting the shift linkage and drivelines. You don't even have to drain the oil out of the case.

Amazing fab work on the flatty !