3speed to 4speed
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Senior User
Joined: Jul 2002
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From: Anchorage
3speed to 4speed
So I've decided to swap in a 300-6 and np435 into my '58 F250 using the mid engine mounts from the '78 4wd F150 that donated the engine and the trans crossmember from the '76 F350 that the 4 speed came from.
In the interest of keeping the truck as cosmetically (if not mechanically) original as possible, will a factory 4speed floor hump work with the np435 or will I have to break out the TIG and do some fabricating?
In the interest of keeping the truck as cosmetically (if not mechanically) original as possible, will a factory 4speed floor hump work with the np435 or will I have to break out the TIG and do some fabricating?
Post Fiend
Joined: Mar 2007
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From: springfield il
i swapped { not completely like what you are doing ! } my light duty 3 for a t-89 four speed much the same size , weight etc. i'd imagine as your np435 . i just modified the oe tranny cover for now , and have picked up one with the 4 speed hole { rusty pig in a poke after i got it ! no good . } you will probably have to do as i in the 53 { flathead v-8 } and the biggest change , is to run a two peice driveshaft due to the unique ujoint " cup / holder " whatever you want to call it . which means finding an oe carrier bearing crossmember , or for now i have improvised one , and am going to make a better , much more sturdy one out of an extra crossmember i have . the np435 is not od i beleive and had a couple in early 90's late 80's trucks me thinks and the shifter comes up in the same spot on the t-89 and them . so take it for what it's worth .........
I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
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From: Northshore, MN
Maybe not too much work. The shifter hole may or may not be in a different spot, and a patch put in over the old one, but shouldn't be too hard. The NP435 (and 300) is my favorite tranny and I've abused a couple and they never failed. Two things to look at first. The trans cover that the NP435 sits under in most all trucks have the front half angled upward as thecab front and firewall angles upward as well. My '48 doesn't, but maybe the '58 does? Secondly, the majority of the NP435 hangs downward, so make sure you have clearance there. A carrier bearing might not be needed if your truck is a shortbed. if it's a longbed, you might....if it was original to your truck, I'd consider using one. I assume the 4 sp. from the F350 is 2wd? if so, the speedo gear will be there. Sounds like a good combo for all around driving.
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Senior User
Joined: Jul 2002
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From: Anchorage
From what pictures I've been able to find, the factory 4speed transmission hump is significantly higher than the basically flat cover for the 3speed trans and does slope up in the front before it meets the firewall. I suppose it wouldn't be that big of a deal to modify a factory cover if the hole doesn't line up. It just be nice if I could use a proper rubber floor mat.
I could use the 2wd M5OD out of my '92. It already has a hydraulic slave cylinder and should be plenty heavy duty enough for what I plan on using the truck for: mostly driving around town looking cool and maybe pulling a trailer every once in a while. If the M5OD proves not up to the task, I could always bolt a ZF in its place.
In any case, I'll have plenty of time to plan the project out; I fly up to Alaska next week to work for 9 months.
I could use the 2wd M5OD out of my '92. It already has a hydraulic slave cylinder and should be plenty heavy duty enough for what I plan on using the truck for: mostly driving around town looking cool and maybe pulling a trailer every once in a while. If the M5OD proves not up to the task, I could always bolt a ZF in its place.
In any case, I'll have plenty of time to plan the project out; I fly up to Alaska next week to work for 9 months.
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