View Full Version : 4:10 to 3:55 interchangeability

06-17-2005, 09:08 PM
will the guts from a known good 3.55 rear swap directly into the casing that had 4:10's?
Is it a direct part for part just gut the tubes and hog head and put the guts from a good rear in it?

We already determined that both the front and rear drive train are bad due to a visual inspection.

we have a known good front and rear drive train standing by but would like to know if the guts interchange. the truck is pretty heavy and sits up so high that im afraid i dont have a jack or jack stands to get it up on.

i just figured if the guts will interchange,, it would make more sense to do it this way rather than all that heavy and possibly dangerous work.
help anyone?

06-17-2005, 11:07 PM
as long as the housings and carriers are the same, then yes

06-18-2005, 12:40 AM
as shawn said, if the housings and casings are the same then its no prob

been putting the bronco trough some abuse ;)

06-18-2005, 01:12 AM
may be more of a dog with less gear to move those big tires and heavy truck just remember that. part about it

06-18-2005, 07:45 AM
I would not try it... Getting the pinion depth correct is critical, each housing and gear set is a little different. I'm bettin it'll howl, or the gear won't last because of incorrect tooth pattern or backlash.

Get out your service manuals and check out what is needed(tools and parts) when chainging a gear set.

06-18-2005, 08:34 AM
I've done this. A mechanic friend of mine informed me that Ford has very strict tolerances on their rear axles. I researched this and found more info to back his claim up on the net. What this means is that (with care and proper checking after) you can swap different gears from same style (i.e. 7.5 to 7.5 or 8.8 to 8.8) housings without a lot of fuss. Generally if you obtain the used pinion with the bearing still pressed on - leave it and the shims on. install it this way using a new pinion nut/crush collar. Install the ring gear onto the carrier and reinstall the carrier using the old shims from the car you are fixing. Do not mix them up side to side. Check the wear pattern with white grease or similar. I've done this twice with excellent results. Maybe I got lucky, but maybe I've found a way to save $150 for myself. If it didn't work I'd have had to pay out anyways and all I'd have wasted was my time.

06-18-2005, 03:37 PM
you guys all are on the same path im thinking. I knew that if this were done, id need to carry all the parts from the new differential to the old ***********including shims. Im not comfortable nor have the smarts to poperly tune a rear so i figured if the casings were the same,, id make darn sure each part from the new went into the old housing.

see,, im just trying to figure out a way were we dont have to pull the entire front end and the rear end.

this is not for my wifes bronco,, this is for a friend who asked if i would lend a hand doing this. I just thought if we gut both the front and the rear, it would work if the casings were the same.

maybe i did not explain that properly the first time.
does it still seem possible and ok for a work truck considered to be a throwaway?

06-18-2005, 03:45 PM
if its just a temp fix on a work truck I think it should still work. But only as a temp fix. It sounds like it would not line up all rightand just slowly shard away metal. It shoud still be okay for a good couple hunderad miles. Maybe more.

06-18-2005, 03:52 PM
if it wont last that long,, its a no go.

tom,, ive heard the same about each differential being different. My brother in law works for Dana and he says the same. Tuning a rear is pretty tricky stuff from the warnings ive had handed to me. Ive never worked on one or had the fortune of being around someone who would consider it to be easy.

06-18-2005, 09:17 PM
not a temp fix on my 7.5 -- 30 000kms and going strong!! These are hard drivin' miles BTW. Also J, not all shims are carried over from the donor to the recipient, just the pinion shim. The carrier shims are reused from the recipient as stated in my previous post. best of luck!

06-18-2005, 09:25 PM
BTW - how do you think Ford assembles these things on a moving line if they aren't all the same? Do they spend hours micing everything ? not likely. If you are using Ford parts, install them and then check the wear pattern - if it looks good/sounds good, drive it. Read my sig. I drive the shit out of my car with gears installed in my driveway with no probs- even the last gears I put in there looked great when I swapped them out for shorter ones(no sign of wear after 2 yrs). If they weren't right they'd be noisy and my wife wouldn't stand for that. She's never complained.

06-18-2005, 09:42 PM
no , no no,,
your taking me wrong here,, im not privy to the shade tree mech way vs the OEM way. Im not at all familiar with whats possible to get away with and whats not.
trust me,,ive came up with some off the wall crazy crap you can get away with on our cars and have no problem telling others they can as well with no issues.

i appreciate you advice, im listening to all the advice here. If this were my car, i would have already begun the swap shim for shim and gear for gear but his is not my vehicle so i dont want someone coming down on me for crap work.

im not even sure if the housings are the same, i was hoping a ford truck type would chime in.