Swapping limited slip between axles

[Brain75]

Ok so lets start this off by saying I am looking for something that is cost effective - something that will pay for itself, not interested in throwing money to the wind.

I have a 1990 2.9L M5OD-R1 2wd that is bone stock as far as engine/trans/axle. Door Tags - Trans: M (M5OD-R1), Axle: 84 (7.5" 3.45 Open), and during paint/rehab I checked both of those and they match.

A F4 axle (3.45 LS) showed up in the junkyard and I thought about grabbing it just to add the limited slip to deal with Colorado roads. Rather than grab it without thinking, I checked a few other things to see if I still wanted a 3.45 or something else would be better.

Obviously my truck was built when 55 mph was the speed limit and no thought to going 75 was on the engineers' minds.
I have read repeatedly that the best economy of a 2.9 will be between 1500 and 2500, so maybe I don't want a 3.45.
I'm definitely going to change tires (switching from 14" to 16"), so we have a lot of variables to play with...

The most cost effective for me to do an axle or gear swap would be to grab a complete axle from the junkyard - the yard wants the same price for gears/center section as they do whole axle, and they want 1/3 what summit/jeggs/yukon wants for bare gears.

So here's my thought, find a 3.27 axle and slightly bigger tires. Problem, no 3.27 was made with factory limited slip in a ranger (the only 3.27 door code is "91" which is 8.8" open).... but the explorer 8.8" did (door code "D1").


So here's my thought, tell me if this is possible or not, dumb idea, or what.
Option A) find a 3.27 LS axle from an explorer (D1) and do the explorer swap (grind off perches and flip them over) - https://www.therangerstation.com/tech_library/Explorer8_8.shtml
Option B) ..... haven't figured this out yet... no way to get a 3.27 or 3.08 in the lighter 7.5" in a limited slip without opening up the wallet to bleed for retail.
Option C) swap the M5OD to a T56 (6 speed double overdrive, final drive ratio 0.5) or similar - probably cost a lot more.
Option D) add a brownie box, gear vendor, etc - anything add on to drop the final ratio - probably cost a lot more.
How common was a D1 axle tag in a 90-94 explorer? (I have drum now, and switching to disc opens up a lot more things which equals cost)

FWIW, I recompiled this chart https://www.therangerstation.com/how-to_pages/gear_ratio_tire_size_chart.shtml

into something more applicable to our gear ratios offered w/o all the chevy and 9" ratios and with the addition of a few stock tire sizes. Also made the whole thing a calculator (interactive with user input) in an excel spreadsheet instead of a static grid (as well as the speed being user input instead of static 65mph, and the final drive ratio a user variable instead of being 1:1.

If someone wants a javascript project I think it would be an ideal add to the tech library.

 

[Brain75]

My original option B, before I thought about it a lot (and the reason for the title "LS swap between axles") was I thought I could find a open axle from a ranger (right perches) and a LS axle from an explorer and put the center section in to the ranger (in the yard) and then walk out with only paying for 1 axle... that wont work because all explorers were 31 spline and almost all rangers (except FX4 L2) are 28 - so you can't just "swap the traction lock in the yard", right?

 

[lil_Blue_Ford]

The Explorer axles are all 8.8”

The center chunk would probably swap, you would have to change the side gears to the Ranger ones

 

[Brain75]

I got the 8.8" issue - the one only 3.27 (door code 91) in a ranger is also an 8.8, but I think that is a 28 spline 8.8 where the explorer is 31 spline 8.8.... understand what you are saying...

Sorry if this is a total n00b not getting it question, but... A guy couldn't swap the traction lock out of any 7.5 into a different geared 7.5 could he?
For example I know for a fact the junkyard has a F4 axle (3.45 LS 7.5"), and I would bet money there is probably a 3.08 open 7.5" (door code 82) - moving just the "locker" over to the 3.08.
I know locker is not the right word for factory LS, just using it as a placeholder word.

 

[superj]

I wonder If ford axles are like jeep axles, from 3.73 and numerically higher all fit the same carrier while the numerically lower (3.55 and down) interchange into the same carriers.

 

[Brain75]

I started before this search with a check of summit/jegs/etc and there seems to be a division at 4.10 if I remember right.. but at this point I can't remember if that was the 7.5 or 8.8"... also seemed that 3.73 was the most common ratio everyone carried a rebuild kit for which includes gears.

 

[alwaysFlOoReD]

So, for the cost of oil and 2 side gear shims, you can make a poor mans LS. Ad a shim on both sides behind the side gears...
I've personally done this with a 9" (Torino) and a d-28 (b-2).
Downside is accelerated wear and a remote possibility of grenading the gears.

 

[Brain75]

I think if I was doing that (no ratio change) I would just go to the 'yard and trade my 84 for F4 - probably have no oil in it, but would be an actual LS for only a little more money (my junkyard is dirt cheap).

 

[Brain75]

fwiw, the prices I am seeing of stuff online I am considering pulling stuff from the yard to resell it here hesus...

 

[sgtsandman]

Option A is probably going to be the easiest. I strongly suspect C and D are going to cost some money. The other question with the Explorer axle is whether ABS is going to be an issue or not. Did 1990 even have ABS as an option?

You might also want the master cylinder from the Explorer if you get one with disc brakes since the proportioning will be different for disc vs drum. If you get one with drums, you won't have to worry about that.

 

[scotts90ranger]

Going to explorer disc brakes is as simple as swapping the axle while grabbing two passenger side soft lines while you're at the yard then cutting and crimping on nuts in the middle of the explorer hard line at the top of the diff so you can use the stock Ranger soft line and just calling that done once it's in, the Ranger master works fine... sure might be different than it should but it works great on my '90...

In your shoes to make things simpler I would just get the 3.45 axle from the yard and when you get new tires go up in size to drop the rpm then change the speedo gear to get the speedo reading right afterward... that is way simpler than any other option if all that is planned anyway... if you are wanting better winter performance you want taller tires not shorter anyway so you can increase your contact patch... myself I would go 15's not 16's as I like sidewall height, you're still talking pretty short tires no matter what with that gear ratio...

 

[Brain75]

Scott,
As far as rear discs not taking a different master "the ranger master works fine" that one has been beat to death in the '48-56 crowd... some real smart fellas there explained it pretty clear... disc take more pressure as well as holding a residual pressure in the line. If you don't, what happens is the discs are there but they never ever wear out, seem to last forever (cause they aren't doing anything useful). I'd ask how much your rear discs are wearing, I bet they are just riding around doing nothing and since 80% of the brake happens in the front wheels anyhow you just don't realize that on your truck 99.5% of the brake force is happening up front.

I'm pretty sure the T56/6060 is out, it requires enlargening the tunnel or a body lift to fit (big tranny). More work and money than I want to do... and I ran the calculator with it's final gear #6.... 0.5 ratio drops way too low, you would want 3.55 or 3.73 with that kinda final drive, which is a really nice combo (probably the best) but that is replacing 4 parts to fix the problem instead of 2 (trans, axle, tires and a new driveshaft). For you guys wanting a stronger tranny, no weak slave cylinder, and a real wide trans that means you can still drive your lifted crawler on the highway that is probably the way to go.

Cost of the custom driveshaft alone probably kills both T56 and brownie box - not gonna come up with anything out the yard that is "just right".

I think I have kinda decided a short term path that will help me decide long term better.
Gonna grab the radiator out of an Explorer 4.0 w/ AC that is on my todo list (improve cooling system for the 2.9L), and while I am there scout everything out. Probably get the 3.45 LS 7.5" and do that swap... then drive it for a good while and figure out what my fuel mileage really is. I'm figuring a trip to Austin (901 mi one way) will show me what highway mpg is pretty definitely. The front tires are a little dry rotted, so I might not be waiting as long as I hope for tires, might get pushed into that sooner than later. I won't be putting anything so low profile that it is impossible for a guy to dismount em at home with a handyman jack and a bumper... I've figured out that is like 60 series or 65 - no rubber band 40 series tires for me.

I'll also be adding running boards/nerf bars and just tell my sweet thing to climb on the step to get in.

Further down the road if the MPG is still bad enough that I can justify the cost, go to the yard and get just the ring and pinion of a 3.27 or 3.08 and learn how to do a rear end rebuild.

On my '48, I have a 9" axle with 3.00 gears and a non world class (common) T5 trans. It turned it into a grocery getter... and at 68mph you hit an aerodynamic wall and can't go any faster, the rpms are there, the engine is happy - plenty of space before redline, just not enough ponies to push all the air out of the way. I'd say it took the fun out of it, but the original axle was a 4.86 or 4.27 which coupled with the original trans was slow marching speed for infantry (ford was still using up surplus trannys well into 1949 from the war) so I didn't really have a lot of fun with it to begin with. I know I went too far with that one (it was the only 9" older than 1972 in the yard), and it is on my list to find another set of gears for it 3.50 or 3.75.

I'm a little gun shy of going all the way to 3.08 because of my experience with my '48. The tires on the "full size pickup" 48 are bigger than the ranger but not much. F-1 is basically a small truck, they use S-10 and Ranger parts on em a bunch (like the bench seat is typically from a Ranger anything "full size" is way too wide).

Either way, I probably will end up with 6 different speedo gears when this is all done , thankfully the 'yard looks at that as "junk plastic" they would have to pay to recycle and they let it out $1 / ft - so I bet those are $1 each for me.

Before all this started I read every thread with the 2.9L and "mpg" or "fuel economy" in em - nobody really said what kinda mileage they get bone stock doing 20mph faster than Ford designed for. And those threads that collected fuel mileage had highly modded crawlers and dropped minitrucks, but the details were filtered out to just raw mpg numbers... not really useful.

 

[19Walt93]

I would go to higher(lower numerical) gears unless you drive in absolutely flat country and that's not how I imagine Colorado. If you swap the limited slip differential into your housing using the same gears all you'll have to set is the backlash and bearing preload.

 

[superj]

Driving to austin?

 

[Brain75]

I have driven the 3.00 geared '48 up to the mountains (bandimeere speedway) and some waterfalls up truly in the mountains, it is tolerable but only really because there is so much traffic you are rowing through the gears all the time anyhow, yes 3.00 is too low to climb a big hill... heck my 3.45 looses 6mph out of 65 on the one big long hill east of Sterling and that is hours away from the mountains.

Everything I own (including all my tools) except my GM car, 15 pairs of clothes and a computer is in a storage facility in Austin. I moved wholeheartedly to Austin 10 years ago and about 3 years ago landlords raised the rent 50% with nearly no notice (the Texas minimum legal 60 days)... it happened about a month after Elon announced he was bring Tesla and SpaceX to Austin. I refused to take that kinda hike in rent and put everything in storage. I'm operating on borrowed shop, borrowed tools, and borrowed time kinda... I have to go back to Austin at some point, even if all it is for initially is to get some more winter clothes and some tools.