I had my rear diff cover off today to fix a leak. I was blown away. Take a look at my rear in my album. The window sticker for my truck says 3.55 LS. It's an '01 4x4 with the Off-road package... And this is what i find? An open rear end? I hope that somebody can tell me that the ford Trac-Lok is some weird design that looks like this. I can't see how this can be a locking set. There's just not enough parts. What a downer.
If anybody can decode the tags, that'd be awesome. I've only been able to find older model info.

 

doesn't look like an open to me.

 

L55 975 = Limited Slip 3.55 ratio 9.75 inch axle

If it was open it would say 355 975.

Yours is a limited slip. That's what the stock Ford LS diff looks like.

- Erik

 

Wow, where'd they put all the guts?

Thanks Erik

 

One way to check if you indeed have a LS rear is to raise the rear wheels off the ground. Put it in N and release the P brake and turn one of the wheels. If both wheels turn in the same direction, you have an LS. If they turn in opposite directions, it's open.

Oh, and you still could have an open diff with the "Off Road" package... LS is still an additional option box you have to check (or at least was for your year truck) for just about all option packages...

Mitch

 

For reference, this is his differential.






Look here for the clutch packs.

 

I thought they all used an S spring like this, but I guess not...?

 

thts open diff for sure

 

Seems to be 50/50 still. Dang I wish I would have had more time to dig in and search for numbers on it. I rolled it over once but didn't see anything.

I was just remembering years ago when I had the truck in ND and I got "stuck" in 2wd on a patch of ice under just one wheel. It made a growling sound from the rear as only one wheel tried to pull. I got on this website and searched and searched and read about a torque bias or something and a way to get around it. I read that you had to put your parking brake on, give a little throttle, and slowly let off the parking brake in order to keep both wheels locked. I tried it and it worked most of the time, but I was always disgusted at how pathetic this rear-end was. I've always thought of it as more of a limited GRIP than a limited slip.

Anyhow, I keep looking for pictures of a trac-lok and most have that S-spring but some don't. Who knows. The tag said limited slip, and the cover didn't seem like it had ever been off before, so I guess that's that. Ford did a great job with hiding both the works and the function of this limited slip.

 

That is pretty much it.
Get a locker.

 

Well, I suppose it could be an open if someone had changed it out, or changed the tags. Now that I think of it, I remember seeing the S clip a bunch too, but sometimes not. I'm not 100% that an LS needs to have the S clip though. I'm especially sceptical because the tags say LS. Usually, people don't switch LS diff's to open as that's kind of a downgrade. Even more commonly they don't even put the tags back on. So I'm saying its LS because that's what the tags tell me.

Another way to tell is can you tell me what your door jamb sticker says under axle? It should say H9 for a 9.75 axle with 3.55 LS. I know this for a fact because that's what I have. If its an open the code would read 19 instead.

- Erik

 

It's most likely a limited slip. Kind of hard to tell on a 9.75 just from that picture since the ls and open diffs look pretty much the same, but if the e-brake deal worked for you at some point I would say it is. The 8.8 would have an S spring, 9.75s use "conical spring washers" (for lack of a better term) behind the clutch packs which are behind the side gears.

 

Not really 'for sure'.... That's what my diff looks like and it's a LS 'for sure'..

Even an LS will spin one wheel on un equal traction situations. Say one wheel is on gravel and the other on pavement.. Punch the gas and the wheel on the gravel will spin... Put both wheel on the gravel, and they will both spin...

I used the E brake trick with my old 1971 LTD that had an open diff 9" rear with 2.73 gears in it... I know it was open, because the wheel spin test proved it. Yet, I could do the E brake trick and both wheels would turn when I was stuck... I was a 16 year old kid living in a rural area with a lot of dirt roads and open fields!! Of course I ventured out there!

Mitch

 

That's seems to be the case, but it shouldn't be right? That nullifies the whole point of having a limited slip. My old S-10 and my brother's blazer would let one wheel spin about 2 rounds and then it'd lock both in. Granted it sounded like two hammers knocking together, it would grab both wheels and get you going. It served it's purpose well. It seems like this rear buckles under pressure and doesn't do it's job, so what's the point?

Anyhow, I checked my door jamb sticker. Axle code H9.

 

Unless the LS is brand new, the clutches wear over time and this is usually the result in such a case. The E brake trick would work well in this case.

What you have to do is keep the less traciton wheel from spinning too fast so the clutches will catch. That's why using the E brake works. It slows down that spinning wheel, giving the clutch a chance to grab and then it'll send some power to the other wheel.

That's the compromise of a LS compared to a full on locker type of rear end. Try to turn a corner with a full on locker, and you will hear the loud clicking of it as it has to give to go around the corner. Pros and cons to both solutions... You just have to decide which ones work best for you..

My LS still works, even after 207,000 miles, but I can tell it's losing it's grip compared to when I first got the truck...

Mitch