Hey, so I have a 1992 F-150 4.9l with the 5spd and was wondering whether I could stick a limited slip diff in the rear to have a bit more fun. I am led to believe that the truck has an 8.8 axle with 31 splines and a gear ratio of 3.08. Now my question is whether the gear ratio of the lsd needs to be 3.08 as my truck is 4wd however some sites say that the lsd fits all gear ratios? I don't understand how one size fits all when some are specific. If anyone has any experience in this field or has done something similar to this any help is awesome and recommendations to which lsd would suit my need are more than welcome.
Thanks.

 

The differential is a separate part from the ring and pinion gears. The ring gear is bolted to the diff so if you want the easiest swap then you need to find an axle with the same gear ratio, but your ring gear can be transferred to the LS diff with a little more work.

 

stock units used clutch disks and to my understanding "fun" would mean you probably be toasting them rather quick. there may be a more robust replacement option or you may be interested in getting a 3.55 or something axle with an aftermarket setup or soemthing that doesnt have a shorter service life s o you can have more uninterupted fun

 

The 8.8 rear is designed in such a way that on the same diff unit you could use gears at least between 2.73 and 4.56 ratios (same applies to the Sterling as well where you can go from 3.08 up to 5.13 iirc). Other axle types, namely pretty much anything Dana, each diff carrier has a range of gear ratios it will work with, once you go out of that range you'll need a new carrier with different offset of the ring gear mounting flange. Basically it's all in how the gears are machined - with its own axles Ford was perfectly okay with using a thin ring gear and large pinion for the 2.73 ratio and thick gear with small pinion on the other end of the range at 4.56 so that's why you can use the same carrier for all standard-issue gear ratios.

So put a limited-slip diff in a factory-open-diff axle, you leave the pinion alone, you take the diff and ring gear our of the axle, then you take the ring gear off the old diff and put it on the new one, and then stick new diff with factory ring gear back in the axle.

But as AuroraGirl said, if burnouts and drifting is what you're after you want both the LSD and some numerically-higher gears. In which case you're getting the whole diff case, and replacing pinion and all that as well.

By the way the factory Ford LSD can be packed with more clutches to make it grab better. Think you can go up to 4 per side (been a long while since I've done one) and the way you arrange the clutches and plates makes a difference as well.

 

Doubt the poster is after a speed demon with a 4.9, just reliable power and more traction than two open axles provide.

Best deal to me on a 31 spline clutch type 8.8 is a https://performanceparts.ford.com/part/M-4204-F318C They seem to sell for $240-250 new and already have carbon fiber clutches. Pop on carrier bearings, swap the ring, verify pattern, verify backlash, drive on. BUT you may want to see if you even have a Traclok to begin with before buying anything. I have seen 4x4s with two open axles, but not common. I would think the axle door tag would be H8, but research some. H9 for sure is 3.55:1 LSD and 18 is my 3.08:1 8.8 in my 1992. If you have one, just install fresh clutches.

On the front, I would probably install a used Dana 44 Powerlok if fitment available.

 

"whether I could stick a limited slip diff in the rear to have a bit more fun"

I admire your heart hit man, but the man said fun and 4.9 and LSD and my mind wasnt on speed

It was on torque and breaking traction and in his case either wants to be able to do it for more than a try or two before needing to get in 4wd because his fun activities just dug him to an ice patch and now he dont move haha!

But I suppose it doesnt have to be ice or snow, dirt and gravel are year round where its warm

I, personally, do not love the 3.08, e4od, open diff combo in my life. wet grass never seemed so intimidating

But now its like prime numbers. **** keeps me up at night.

 

Is a D44 powerlok like a GM G80 (gov-bomb as its known) where under slip at low speeds it will engage the other wheel but has a replaceable part / can be broken by abuse easily or is it just something better than that design lol

 

My '01 Z71 came with that G80. Makes sense for light duty use, but the actual locking mechanism is crap in it. That went away long ago on that truck. I think it took X amount of wheel spin on the opposing side to generate enough centrifugal force to engage that lockup pin within in it.

Unsure what traction devices Ford had available or what fits for the D44 TTB in these years. 4x4 guys will know more. I know Dana had a Traclok available too, which I would not want for the install hassle. Powerlok is a pretty beefy traction device for the cost.

 

If I was to ever do a 4wd swap or straight axle swap to a f150 from these years I would use my 78 k10 d44 front (6 lug) and 12 bolt rear because I would also, mark my words, find a way to take the NP203 with it all no matter the effort. and then I would enjoy 3.73, hate my 6 lugged life, enjoy a great 4wd, hate my gas mileage BAD, and eventually get to expereicne the gov bomb failure so I can hate that too LOL

 

Funny you should mention that as guess what the Ford factory LSD looks like in the Sterling axles - yup, a Dana Traclok 😂 Actually I'm having some vague memories of using D60/70 clutches in a Sterling Traclok, or the other way around, been a long while now but there was definitely some interchangeability there.

Also a Traclok in the front axle is actually quite nice, I got one in my SD D60 (not a factory setup obviously) with beefed up spring tension or extra clutches or whatever I did few years back to make it stronger then factory and it's definitely noticeable in winter and muddy field conditions, both wheels keep spinning without hopping or skipping as they fight for traction. Understeer doesn't seem to be an issue either (but there's a diesel right on top of it, plus some other heavy bits).

PowrLoc might be a bit too aggressive for a front axle, had a 70s truck with one and it was not fun at all taking sharp corners in slippery winter stuff, understeer was noticeable and quite annoying once you got used to it and tbh reasonably dangerous before that.

 

Was it a kingpin axle or balljoints? was it a always engaged hub like an NP203 vehicle would have or was it just engaged hub locks and you were either in 2 or 4 wd but i guess itwould still fight you a litttle bit lol


I have work ahead of me next year.. I have 2 axle shafts about ready to pop their u joints they are so worn... but the passenger side isnt the right shaft apparently a 77 d44 from a chevy had different bearings, specs, machining than a 1980 d44 from a chevy(gmc) and my truck is the 80... I also have limited experience on straight axle systems other than being an expert on dana spicer locking hub install(had to redo 2 times for different reasons on the one side on year lol...)

I think there is a bearing in the spindle or suposed to be on the outer shaft that supports it in the hub nose area stuff so its kept at good angles and not throwed around, and also possibly something in the axle tube i need to verify because the thing feels sloppy and im like oh no let me guess that was smaller or had a different bearing size than the one it came out of

I already ruined the first shaft when I had bald bias plys and clutch dumping trying to plow with

its partially cut off in the pic but this ultra lightweight 10.5ft plow Apparently the weak point was the passenger axle shaft in that equation those many moons ago. open diff I suppose only needed to lose traction for a second while not moving fast but under throttle and a weak old u joint that was abused said nope and the shafts yokes had a suicide pact

the shaft thats good there is for a jeep size d44 I think.. bought it by accident trying to replace the one you see to the left. which i salvaged from my spare d44 but has different enough stuff that Im in this pizza roll

 

The TL in my '09 Superduty was dead around 14k, pretty sad. Dealer tried to spin me some song and dance regarding its operation...aka not interested in warranty repair. Pulled it and popped a True Trac in there. Loved it, split the Ford unit and smoked clutches.

I guess a TL up front would not be awful if all available, the hubs are open most of the time anyway.

 

Fun fact. That did not work. but it fit and allowed me to get stuck in mud thinking i had 4wd lol

 

Oh the TracLok is too weak for the rear, totally agree with that! TrueTrac is what mine will be getting eventually as well, I think it's the only proper choice for trucks that see heavy axle loads. Not that a Detroit would come apart, but is be concerned about it shock-loading the shafts (well the bolts really) and I love the seamless operation of the TrueTrac.

 

The one with the PowrLok that understeered like a mother? Ballpoint, standard-issue 78 Ford D44 with locking hubs. Not problems with hubs disengaged, but lock them in and she'd wanna go straight regardless of 2wd or 4x4 at the t-case. Pretty normal given the reason why there's a diff in there in the first place. Big wide tires didn't help either.

There's a needle bearing on the inboard side of the hollow spindle thru which your stub shaft passes, it's right next to the U-joit yoke. The other end of the stub shaft, with the splines for the locking hub, is centered and supported by the locking hub itself - there's usually a bushing in there for that, and with '96 & '97 Ford hubs (the one with only 3 bolts instead of 6) you get a second needle bearing instead of a bushing, but honestly either type does the job fine.

There ain't nothing inside the axle housing tube. Both the long and the short shafts are supported by the diff on their inboard side and by the wheel U-joint on the outboard side. So really the needle bearing in the spindle carries the weight of both the stub shaft and the axle shaft.

This is how all disc-brake Ford D44s are, also all pre-Superduty D60s regardless of ballpoint or kingpin setup at the knuckles. Superduty axles with unit bearings are near identical, with the exception that there ain't no hollow spindle and instead the needle bearing is pressed into the inner bore of the unit bearing assembly - functionally it works the same way as far as shafts are concerned.

With your GM axles, if there's no center disconnect like your NP203 truck should have, the setup is identical to the Ford described above. With CAD axles it's almost the same, except your long axle shaft now pilots inside the CAD unit on its inboard end, instead of in the diff. The short axle shaft is the same as the Ford's above regardless CAD or not.