94 Ranger rear diff? Help!

[Jabberwocky]

Ok so I tried sifting through the site to find what I need, because I'm sure it's on here, however I've come up dry.

Here is the deal. New to me truck. Looks like the maint has been immaculate, it's sat for about 5 mo. on a dealer lot so when I get in and drive it and it shifts late and hard I'm not surprised, there is also a growling noise in the rear and I can't be sure if it's diff or brakes.

Took it to my mech for a full check up after purchase and he said the truck was great except I needed a new trany and a new diff, apparently my current are shot.

I obviously didn't like this diag so I started doing some work myself and got to here. Trans is fine, just needs valve body rebuilt, gears clutches and bands were all fine, fluid flow was just all jacked up. Now I'm diving into the growl and I find two things:
1.) Rear brakes are adjusted too tight and dragging.

2.) I have no idea what I'm doing on this diff. I've done a quick change Chevy and a ford 9" and this looks nothing like either. Can anyone point me to, or get me, a pic thread or good how-to? I'm specifically looking for how to drain and check the fluid, what fluid I should use to replace and what critical parts and problems I should look for to diag it myself since my wrench was sooo wrong about the trany. (Yay extra $1500 in my pocket just for being skeptical!)

Any help would be appreciated, I'm good with tech stuff so it doesn't have to be a hand holding adventure, it's just that all I know about rear ends is enough to get in trouble and cost myself money. Thanks!!

[EDIT]
As a side note. Any thoughts on why my brakes were so tight? If there is any lip on the drum it is the slightest of lips so I don't think that's a factor. I can see that these are self adjusting brakes, but not sure how they work. I know ford has had a history of making some goofy sustems (92 full size conversion van: With vehicle running and in park depress and hold the parking brake, depress brake pedal, release parking brake.) So not knowing how this one works I thought I should ask, don't want to overlook something that is a potential problem. Thanks!

 

[arco777]

To check fluid, remove the drain plug with a 3/8 square drive; a ratchet with a good foot and a half extension or more makes it easier. The check/fill plug is on the forward top side of the diff housing, and the extensions will make it easier. Lifting the truck at the frame will help as well, and is a must if doing a drain and fill with gasket change.

Pull the plug; the fluid should be to the level of the threads.

To drain fluid, you could use a suction pump to suck the fluid out through the hole but it's easier and more effective to take the diff cover off. Just pull all the bolts, leaving two, then loosen the bottom one up a little and stick a putty knife in to break the seal and the fluid will pour out. It won't come too fast to handle if you leave the two bolts in and take it slow but you will want a deep pan for the fluid.

Do you have a limited slip differential? You can tell by looking at your door sticker and converting the axle code or reading the tag on the diff cover itself to find out. Search the site for charts listing the axle codes, which will list ratios and whether it's a limited slip or not.

Once drained remove the cover. You'll be able to tell for sure at this point if you have a limited slip differential. If so you'll need to purchase Friction Modifier (LSD additive) as well as oil. Most auto parts stores (O'Reilly's for sure) can tell you how much gear oil your differential will need to fill it and what weight (i.e. SAE 80W-90), and can suggest a friction modifier, which usually comes as a tube. Get a new diff cover gasket at the same time. You will need to know if you have the 8.8" or 7.5" rear end on your Ranger to get the proper gasket. The axle code on the door may indicate which you have.

Check the inside of the differential housing for debris and sludge that accumulates in the bottom ribbing. Clean out as much of it as possible.

Use the putty knife to get all the old gasket residue off the sealing surfaces of both cover and housing. I use a thin layer of silicone RTV to help hold the gasket in place and make a bit better seal on both sides of the gasket. Others may say yes or no to that but I've never leaked a drop doing it that way. But don't go ghetto and seal with RTV only and no gasket.

When you torque the cover bolts down, you don't want to go too tight and damage the gasket. Tighten in a criss-cross pattern like lug nuts and if you have a torque wrench, set it to something low. I don't recall the actual figure, something like 20 ft/lbs or a bit less. But either way just use your best judgement and don't reef the bolts down, let the gasket do the work.

Re-fill the diff through the check hole. Add friction modifier if you have an LSD. A cheap pump that screws onto the oil bottle is helpful as they have a length of tube you can run into the hole and just pump it in. Or, if you have only got the bottle with a nipple on top, slip some clean fuel tubing over it and squirt it in the hole the same way. Once oil comes out the hole the diff is full; re-install the plug tightly.

Hope this helps.

 

[RangerX]

arco gave you some great info ^^ so I'll just say these 8.8 axles are stout and rarely break in any way. Did the mechanic give you any details on WHY your diff is shot and you need a new one? Was he blaming the tight brakes on the diff?

 

[Jabberwocky]

No explanation from the tech on why they thought the diff was shot, I did ask if it was worth a rebuild and he chuckled and said, "Your going to want to just replace it." However that was his statement about both the diff and the trans.

Door code says F6, and Diff tag reads L 37 75 ... So if I read all that right I have a LSD 3.73 ratio and a 7.5 ring gear, yes? With that info, do I need to know anything else? Does anyone know a preferred oil weight or friction modifier?

On to the noise. I dropped the tires and adjusted the spinner on the brakes to where there is a slight rub taking the drum on and off, with no grab. I then jacked each side up independently and spun the wheel, the sound was nearly impossible to pinpoint as it is reverberating off the truck bed. It's too low a noise to really call a hum, but too smooth for me to say it's a grind. Closest thing I can relate it to is the noise you hear when you spin a disk brake, that kind of "hooshhhh" that comes from the pad contact. If this helps identify or clarify great if not, enjoy the ramble

 

[Jabberwocky]

Dyslexia strikes again… diff tag actually reads L 73 … sorry bout that.

 

[RangerX]

Well, I agree with him that it's easier to replace than fix. You should be able to pick up a used 7.5 dirt cheap, as they are not desirable. You could also use an 8.8 as a direct bolt-in.

For gear oil, it just calls for 80W90 for your year. You can add the LS additive if you want, but the LS is probably so worn out after 16 years that it would be pointless.

 

[arco777]

80W-90 is what I use too. As for brand it's not as important as motor oil in my opinion, but I use the Castrol since it's a good midrange and I can't afford Royal Purple. For friction modifier I use the Equa-Torque stuff but whatever's available should work. Some gear oils are available with the additive already mixed in.

True that a LSD will wear out over time and Ford's Trac-Lok already had a low lock torque (LSD tightness). But it may still be worth maintaining. Lift both rear wheels off the ground and put your trans in Park; rotate one wheel by hand and you should be able to get an idea of how much your LSD is working. If both wheels immediately spin opposite of each other without effort your LSD is worn out; if there is resistance or both wheels turn together your LSD is probably still somewhat functional.

LSDs can be rebuilt but it usually requires an axle shop to properly shim the differential when it's put back in the housing. If you have the extra cash or are considering a performance build, an 8.8 rear axle is a good investment. A junkyard unit from a Ranger or Explorer shouldn't be hard to find, considering all Explorers use the 8.8 and are available with disc or drum brakes depending on year. You can also use a Mustang LSD or aftermarket locker (remember to check axle spline count) and you can rebuild any Ford 8.8 LSD with aftermarket carbon fiber rebuild kits that will improve the locking torque capability.

 

[Jabberwocky]

So I'm heading to the jukyard today to pull some parts that I already need, I know they have a couple rangers and Xs there and I might be able to get a decent rear end. A couple questions firts.

You could also use an 8.8 as a direct bolt-in.

I'm assuming I already know the answer but I'll ask anyway. Can the 'guts' just be swapped or do I need to swap the whole rear end assembly and roll it out?

Also, if there is another 7.5 that is in decent shape can that simply bolt into my pumpkin or am I looking for trouble doing that?

 

[arco777]

The 8.8 housing and guts are both different I believe; even if the insides were interchangeable, you'd still have to pay to have the differential shimmed (axle rebuilt) which makes a complete 8.8 a better buy. Just slapping the parts together will end up with ring and pinion getting torn up if you don't have the mesh set perfectly using the right shims. Most people don't have time or patience to shim a diff themselves but it can be done. A complete used 8.8 will be ready to go of course. Same with the 7.5. If the diff itself is swapped out, you'll need to get it shimmed up for it to last.

A used 7.5 axle in good shape is fine too for light duty applications. If your Ranger is equipped with a 4.0L, you're towing or off-roading, etc, you should probably go 8.8 but for just light utility work the 7.5 should be fine.

 

[Tony H]

First thing I'd look at is the fluid level. If it low then I'd look at the Brake pads to see if the seals are leaking on them. Low fluid would cause a hum in the rear.

Rear brakes: Drums are supposed to drag a bit. So it's hard to determine if they are too tight.