Hey Guys. I've got an '86 F150, 4.9, C6, Flareside.

I'm wanting to replace the rear differential with a limited slip to aide with slippery grass and muddy conditions, my one-wheel-wonder isnt doing the job and i've almost gotten stuck several times.

This whole truck has been a great learning experience but I've never worked on a differential before. Should I simply pull one from a Junkyard? Any good guides for diff identification?

 

Yes, see what you have first. More than likely it is a Ford 8.8. If it has a rear cover with lots of bolts holding in on, it's a 8.8. You can find lots of aftermarket parts to make a 8.8 limited slip, since it's basically the same rearend used in the 5.0 mustangs. You just have to make sure what axle spline count you have.

If the back of the rearend is smooth with no bolts, only bolts or nuts in the front, then it's a 9 inch. Another popular rearend, though Ford was phasing them out around your model year. But you could still have one. Lots of aftermarket support for a Ford 9 inch also.

 

Do you have a 9 inch or an 8.8 inch?

9er = drop out carrier

8.8 = tin cover bolted on the back side.

Setting up a differential is an "advanced" job. You need some dial indicators and possibly a press. I don't know the percentage of people who end up doing it twice or three times, or who silently endure a howler or end up at a shop.

Skip the drama and have it done. Figure $1000, which will give you new gears and ratio if you want and new bearings.

Junkyard stuff--if you can get the whole assembly, especially with the 8.8, that would work. Junkyard 9ers are a thing of the past. Still there, but picked over and questionable condition.

There's a tag on these as OEM. If you find the tag, you can probably at least read the ratio. 3 55, with the 3 slightly hidden but the bolt holding the tag on--wll be a 3.55 open 8.8". 3.50 open if a 9 inch. 3L55 or 3L50 will be a limited slip.

 

Looks like i've got an 8.8. Looked all over but no tag, so unsure of ratio. Cover has probably been off at one point as there seems to be RTV behind it.

I used to be a machinist and am comfortable with "precision" work if that's what it takes, however the budget is the real limiter here. If I can simply ****** the whole thing from a junkyard that would be ideal. My local yard commonly has stuff back to ~88, i dont generally see bullnoses there though. Can I just steal the complete rear axle assembly off of any older F150? I should be able to just jack it up and make sure the wheels turn the same direction to identify a LSD right?

 

You can decode the door sticker to see what ratio your truck has as a start.

I dont see what you could not find a JY unit just measure the spring pads and wheel to wheel and bolt pattern size.
You should look for the tag on the JY unit but you would need to hold the drive shaft when trying to turn the wheel.
Could also pull the cover to see what the inside looks like, metal in the oil and no milk shake etc. with cover off you can see if it is a LS or not.
Dave ----

 

What about one of these units?

 

I can tell you they are easy to install, nothing to "setup" like you do with replacing a carrier unit.

They have good and bad with a "locker".
They lock the 2 axles together when under power, going straight or around a corner.
This can be a problem, if straight and the road is pitched to the side of the road and there is ice / snow the rear will kick out or slide to that side of the road.
Going around a corner under power and it is dry the tires will make noise and if the law is around to hear it may bring them on.
If wet out the rear will kick out if not careful. With a long wheel base it is not too bad as you can catch it but a short wheel base you really need to be on your toes!

With a LS / clutch type carrier it kind of locks the axles till the "break away" of the clutches are reached then it is 1 wheel peel of sort.
In ice / snow it acts like a locker as the tires dont have high grip to the road but going around a corner in the dry the tires have grip, the clutches slip and no tire noise.

They each have there place as I have used a Lock Right Locker in a short wheel base car both on the street and drag racing with street tires. This also makes a banging noise that others outside the car can hear when going around corners when not under load.
A Detroit Locker in my drag car with 9" slicks
And factory LS in a 86 K5 4x4 diesel Blazer had to upgrade to a better one as the clutches went thru the carrier and got on in my 02 Durango 4x4 with 292K miles.
So I know a little of what I talk.
Dave ----

 

Most of your post is talking about the pros and cons of a limited slip rear axle. He said he wanted a easy way to get limited slip, I assumed he knew the pros and cons of any limited slip axle. The unit in the link would be a easy way to get limited slip. The only drawback I have heard with this type of unit is the clicking noise it makes when going around turns.

 

OK thing is what you posted is not a LS but a locker and yes that type dose make noise, mine was like someone hit the rear axle with a large hammer and people would turn and look what happen.

I also dont ***-U-ME he knew the difference.
Also if others find this in a search, now they know the good, bad & ugly
Dave ----

 

When prowling a junkyard for a limited slip, typically you only need to remove the fill plug. Peek inside with a strong flashlight (I've got some recommendations for rechargeables...) and maybe an inspection mirror for a better viewing angle. Or just stick your finger in there. A stock open diff will have a rough casting with a tapered or bell-shaped profile, open on the sides. A limited slip carrier will be barrel-shaped and almost entirely enclosed, often with a smooth machined surface (depending on the brand).

A quick peek like this will go a lot quicker than pulling the cover on multiple vehicles. You might miss a retrofitted lunchbox locker that fits inside the stock carrier, but that's no big deal if that's not the style you want. If there's any doubt about what you're seeing through the fill port, you can always pull the cover to be sure.

 

I dont know if you can look thru the fill plug hold or not as I never really looked into it
I would think you would see the bolt side of the ring gear and carrier and you really need to see the other side or where the spider gears would be.
I dont even know if one of them boar scopes that work with your phone would work as you need to get around the ring gear.

Then again would you want to gamble on a used LS that may have warn clutches?
They do make rebuild kits for them if you want to go that route.
Dave -----

 

Oops, I stand corrected. I'm mostly familiar with Dana axles, and those have the fill plug in the cover, on the side where the spider gears are located. I just searched for "Ford 8.8 fill plug location" and I see the location is in the axle housing, not the cover. As Emily Latilla would say...

 

Thats ok I had a brain fart and was thinking Ford 9" and did not know where the 8.8 fill plug was but got lucky
Dave ----