4r100 compatibility

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Jan 5, 2025 | 08:41 AM

#46

carlsson

Mountain Pass

Joined: Oct 2005

Posts: 145

Likes: 2

those 4r100 had a defective front seal design. my 99 had to be done 3 times, twice at ford, and the last time correctly but independent shop. when towing a heavy load, when reversing a huge amount of fluid dumps out, and actually caught fire on exhaust. install the updated seal, and a good experienced trans shop will know how to drill and enlarge the oil return passages to prevent seal failure.

Oct 1, 2025 | 11:15 AM

#47

B-Rad88

More Turbo

Joined: Dec 2016

Posts: 538

Likes: 42

From: Southwest Missouri

Found this thread when doing research. I am curious if all 4R100's are identical to each other blueprint wise. The answer I am trying to solve is could i take a 4x4 4R100 behind the 5.4 and completely rebuild the entire thing to then fit behind a 4x4 7.3? I would like to think yes because of the fact that it is the same family 4R100. I think the ZF5's from the 351 and 460 are the same size dimensionally as the ZF5 behind the 7.3 but had different gear ratios and bolt pattern on the bell housing. I don't want to assume this however, and saw this thread already exists and wasn't quite what the OP was asking about. i would like to get my hands on a 4R100 and learn rebuilding it myself. Currently my truck is at BTS getting a rebuild, but it would be nice for me to learn for when I may one day buy another truck. Just general curiosity. I know you can rebuild a 2wd 7.3 4R100 to work with a 4x4 7.3 and that requires complete disassembly to swap the output shaft and tail housing i think it was.

Oct 1, 2025 | 12:03 PM

#48

m-chan68

Lead Driver

Joined: Mar 2010

Posts: 5,504

Likes: 256

From: Woodbridge, Ontario, CA

Quote:

Originally Posted by B-Rad88

The answer I am trying to solve is could i take a 4x4 4R100 behind the 5.4 and completely rebuild the entire thing to then fit behind a 4x4 7.3?

NOPE. The 4R100 behind a 7.3 uses a bell housing bolt pattern similar to what's used by Ford's 385 series V8's (370/429/460) while the 5.4 uses a seven bolt pattern used by Ford's 4.6, 5.4, 6.8, 5.0 Coyote, 6.2 and 7.3 gas engines. Therefore the two transmissions use completely different transmission cases.