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78 Custom 460 NP435 NP205 Sniper EFI HyperSpark Ignition 4.56 Gears Front/Rear Grizzly Lockers
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· They call me "MR FLAT TIRE"
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Maybe time for an engine upgrade too? You kno, being a matched set.
Sometimes that works for management encouragement.
It’s just like when a new purse = a new dress, belt, shoes, necklace, and maybe a new jacket. Oh and don’t forget the little earrings. You want it to match right?
 

· Moderator and Scrounger Extraordinaire
85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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For a 400, you will need a big block ZF5. Meaning from behind a 460.

Then you need a hydraulic clutch assembly since the ZF uses a concentric slave cylinder vs an external one. You will need an 11" clutch.

Transmission crossmember will likely be custom to some extent. You will also likely have issues with the transmission tunnel being too short, height wise, for the ZF shift tower. Not sure if a 92+ tunnel cover will fit.
 

· Driving Stuff Henry Built
*90xlt,351w,e4od,1356m*79,400,C6,205,19donors*73,400,np435,d20j twin
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Looks like that ^ came through some sort of electronic translator. I took a "best guess" on the meaning in the quote below. I'm not sure about the portion in italics. Maybe it means that the case is weak.

Alright. I was bantering on which to trade in my C6 79 (460 engine) Bronco. I was picking the ZF5 since I will utilize this Bronco to drive on the highways. However I would like to also go on rough terrain with it. Nothing too wild. I'm trusting the ZF5 would get better MPG for my 460 since the RPM would be lower at higher speeds. Which would be better? - The NP435 will have the lowest first gear. - The ZF5 will have the OD fifth gear in addition to a low first, however not so low as the first in the NP435. - The NP435 is known to be indestructible. - The ZF5 is known to be acceptable for moderate stuff yet the packaging of the transmission is powerless. - The NP435 will be a less complex trade in the 79 Bronco. - The ZF5 will require a few changes. - The NP435 could deal with the NP205 transfer case. - The ZF5 would require the NP205 to have a support because of the weight of the NP205. The Borg-Warner transfer case wouldn't need tge suppprt and would have a lower low gear and be light. Yet the NP205 could have lower gears installed into it.
I have no experience with the Zf5.

The NP435 is a heavy duty truck transmission. I have one in my 73 Bronco. It is strong. But it is stiff & slow to shift. Some people do not like it on the street because of the stiff shifting. Offroaders seem to love its very low first gear & strength. And that is a short transmission, which works well in short vehicles like Broncos

I have the NP205 in my 79 Bronco & the Borg Warner 1356 in my 90 Bronco. The 79 is not driveable yet, so I have not tried the gearing of the NP205 yet. I like the low gearing of the Borg Warner 1356 a lot. And I am considering using a 1356 in the 79 because of the lower gearing.

I like to go offroad, but am not as rough on my vehicles as some people are. I don't think I will need the additional strength of the 205. But if I do use the 1356, I will keep the 205 in the garage just in case.

Which you choose will depend partly on which ratio gears you use in your axles & your tire size. With higher axle gearing (like 3.50:1) & bigger tires, the NP435 combined with Borg Warner 1356 might give you what you want, both offroad & on the highway. Or with lower axle gears (like 4.88:1) you might prefer the ZF5 & NP205.

A gear ratio calculator is a good help in determining the best combination for your individual use. I like the one linked below. It has dropdowns to choose which transmission & transfer case & other components. It shows the RPM at various road speeds so you can see what effect the different combinations will have. It also allows you to enter 2 different combinations side by side, so you can compare their outcomes.

Please ignore the skulls & crossbones. The guy built a great calculator, but seems to like a "grimm" theme.
 

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1978 bronco xlt .030 351m zf5 35’s 4:56 gears locked front & rear 4” lift deaver springs sport cage
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70 Posts
I put one in my 78 bronco with 351m. I used a spacer to move the flywheel back 3/4”. Tim Meyer makes the spacer. He also can machine your flywheel to accept a 460 clutch and plate. I used the hydraulic clutch from an 96 f250 if I recall correctly. It is an external slave. I modified the stock pedal assembly to use a pushrod for the clutch master. I also used the stock crossmember. The zf is almost the exact same length as a 435 with the bell housing attached. I did have to notch the tailhousing of the zf to clear the shift rods for the transfer case. The zf case is huge so a body lift of at least an inch will be required unless you do like me and cut out the tunnel and firewall and fabricate a new one. The biggest problem I’ve had is starters. By moving the flywheel back you need a starter with a long snout. A 351W automatic transmission starter will achieve almost full engagement of the ring gear. That is the only starter I have so far that works. There were no conversion kits available when I did mine so there was a lot of trial and error. PM if you have specific questions.
 
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1978 bronco xlt .030 351m zf5 35’s 4:56 gears locked front & rear 4” lift deaver springs sport cage
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Well it didn’t help mpg. I changed gearing from 3.50 to 4.46 and jumped tire size from 33 to 35 and beadlocks so in my case I actually lost some mpg. If all else had remained unchanged im guessing about 2 mpg improvement based on the drop in rpm’s at cruise. (65 mph with 33’s and the 435 was around 3000rpm, with the zf same speed rpm is 2100). I’d probably do it again in a stock truck and I would add more sound deadening. The zf case is aluminum and there is a lot of roll over noise from the main shaft that transfers through the aluminum case. I’ve talked to a lot of people about this and all have the same issue.
 
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