My 3.55LS limited slip diff. is not working. Can this be repaired by changing the carrier? Also can an open diff. be converted to LS by changing the carrier?

 

What do you mean it's not working? Is the rearend blown, where it locks up or makes horrendous noises when you try to move the vehicle? Or are you just talking about the LS? The Ford limited slips are notoriously crappy, and the clutches regularly wear out at 60k miles. So either the limited slip is working normally, and it just sucks, or you need to replace the clutches.

You could replace the whole carrier, and this may end up being cheaper than paying somebody to pull the carrier out, pull it apart, replace the clutches, then put eveything back together. You really just need to call around and compare prices.

And yes, an open differential can be replaced with a LS.

 

The LS is not working. When I jack up the rear and spin one wheel the other one does not turn.

 

Have you checked the LS by having one tire on pavement or hardpack and the other on loose gravel and accelerating hard?
Seeing that it takes a difference in the torque on each axle to engage the clutches in the LS and with both tires in the air there is very little torque when one tire is spun by hand I would think only one tire would spin, but I may be wrong. I do know that with an open diff the other tire with spin the opposite direction and with a locker both tires will spin the same direction.

 

No, I haven't tried that. I will today. What result should I expect if the LS is working?

 

With a Limited Slip diff if you jack up the rear and turn one tire, they both should turn if it is functioning properly.

The "Limited Slip" simply means that in a turn the clutch packs on the inside wheel will slip allowing that wheel to turn at a slower rate than the outside wheel.

That out of the way you CAN NOT simply pull the carrier out and replace it with a new one. Granted you won't have to worry about setting pinion depth but you will need to adjust the carrier for backlash and add or remove shims for propoer bearing pre-load.

If you suspect that the clutches need to be replaced you can do that easily with the carrier still in the truck. You can buy a diff rebuild kit for about $50.00. Its a bit more involved but I will give you the short and sweet here. Remove diff cover, remove cross pin bolt, slide out cross pin, push in on axles to remove c-Clips and slide axles out of diff housing. Pull S-Spring, rotate diff to remove spider gears, then you can remove the side gears and clutch packs. Replace clutch packs and steel friction disc. Re-Assy. is opposite.

I have done this more than a few times in the car with 4.10 and 4.30 gears which are taller than 3.55's and make it 10x's harder to get the S Spring back in. Overall it takes me about an hour to do a rebuild.

Call around to a few shops, it will be cheaper for them to re-build your diff in the truck than it would be for them to replace one as the steps are pretty much the same but with re-building you don't have to measure anything out so it saves time = less cost.

 

If your LS is working both wheels will spin about the same speed, if it is not then it will act like an open diff and the tire on the gravel will spin like hell and the one on pavement will not spin.

 

I did some tests today.---Both wheels on gravel-right wheel spins. Right wheel on gravel,left wheel on asphalt-right wheel spins. Left wheel on gravel,right wheel on asphalt-left wheel spins.

 

Sounds like you just need to re-build the diff. It seems that possibly the clutch pack on the right side is in better shape which is why all things equal it spins and when there is less traction available to it it spins. The only time the left spun was when it had the least resistance.

Like I said a $50.00 re-build kit will get it working again.

 

Thanks everyone for the input. The reason that I brought this up in the first place is that the guy I bought the truck from told me that he had replaced the rear end. Now, I suspect that the LS is not working but I don't know if the replacement rear end was LS or not. The tag says that it is 8.8 3.55LS. Is it possible to tell if it's LS by looking inside the case?

 

Well if you pop off the rear cover you should be able to tell.

First off remove the bottom 4 bolts then just loosen the rest a little. Pry back the bottom of the cover and let the gear fluid drain into an oil pan or something similar. Once the cover is off you should see something similar to this provided you have a Ford rear diff.



That is the inside of my diff. yours should be similar. If you look on the right side of the picture you will see the side gear which I outlined in red. If you look to the right of that you will see where I put a few yellow lines. Where the yellow lines are represent where the clutch packs for that side are. They are inside of the housing under the side gear. Depending on the design of the diff you should be able to rotate the housing to see the tabs of the clutch pack showing through the housing. Now if your diff is LS then you will have the clutch packs under BOTH side gears.

 

Thanks a lot TruBluGT! I'll open it up and look. Maybe this weekend if I can. Thanks again for your help!

 

After I open my differential, what's the best way to reseal it? Gasket,RTV?

 

https://www.f150online.com/forums/sh...d.php?t=276840

 

I opened up my differential and found that it is NOT a LS! The code on the door tag is H9 which indicates a LS, but the tag on the rear end does not have the LS. Also I did not see any clutch pack where Jbrew indicated. Appearently the previous owner did some swapping. Now I'll have to figure out what to do to restore the LS to my truck.