Limited Slip Differential Question

I just bought a 3.73 clutch style limited slip diff/third member off a 2005 TRD sport to install into my 2005 base model (5 lug) 5 speed. I got this off eBay for $200 and wasn't given much information about the condition of the truck that it came off but figured I would take a chance with it.

I noticed that when I try to turn the gears it feels stuck/bound up until I apply enough pressure. Once it finally starts going it feels like it turns relatively smooth but still a bit harder to turn than my old open diff. Is this normal of a clutch type LSD style differential?

Any tips on how to tell if it’s properly functioning aside from installing it and driving around or taking it to a gear shop?

(It was also quite dirty when I unpacked it so I was curious if maybe some small pieces of the moving blankets that it was wrapped in are stuck inside or something? )

thanks!

 

Is it stiff when you turn the ring gear or try and spin the side gears in opposite directions? Pic?

 

Yea it’s just when I turn it at the pinion flange. It feels like it sort of sits in a groove but once it gets turning it’s ok. When you stop turning it it finds a groove again, but not necessarily at the same spot.

 

Hmm I may have found the problem, it looks like the gap between the flange and the differential has one part where the gap is smaller compared to the other side where spacing is consistent.

 

That's just a thin dust cover. The gap is irrelevant. Typically the preloaded bearings will have have stiction especially when new and before breaking in. But even after that it can be felt. Not saying it's perfect but not saying there's anything necessarily abnormal either.

 

Sounds normal to me also.
Every differential I've set up has had some amount of stiction like that. As long as it's smooth-turning (no roughness as you rotate it) you should be fine.
It does look like that member could potentially have history of a pinion seal leak, given the oil coating on the nose of it, but that could also just be from the way it was packed & shipped too. Unless the seller claimed it had a new seal, you'd probably want to change that anyway since you don't have much history on it.

 

Did this work out?

 

No progress yet. I think I want to have a differential shop give the 3.73 a quick check before going through with putting it on. I did check the preload with an inch pound torque wrench, the starting (breakaway) torque was around 10 inch pounds, which seemed fine but maybe a bit high for a used diff? but yea I still feel like there is something up with it. It still feels like there is something a bit too notchy/bindy about how it turns. I’ll let y’all know if it works out.

I also have a 4.08 open diff as a second option, it spins super smooth. It’s breakaway torque was only 2 inch pounds. Do the LSD units need/create a significantly higher preload?



On another note, has anyone swapped the mechanical LSD into a (previously) open 8.4 diff? I feel like the 4.08 ratio open diff (49/12) is in good shape and might be a better ratio but I love the idea of having a mechanical LSD. I was curious about the possibility of swapping the mechanical LSD into that? I know the mechanical LSD only ever came with 3.73 and 3.91 ratios which both have smaller ring gears (41 and 43). So maybe there is would be an issue fitting it onto the 49 tooth ring gear? Not saying that would be easy or worth it, just curious.

 

That is exactly what I did to get an LSD into my rear diff. I just switched the open carrier from my factory 3rd member, and swapped my 4.10 ring gear over to the LSD. It bolted up nicely, and putting the factory shims back into place resulted in the gear backlash/pattern to be spot on (I dropped off the 3rd member at a driveline shop to check it over after I assembled it, and an hour and $50 later, they said it was good to go!).

 

Keep in mind that the pre-load torque is usually specified as a rotational torque, not breakaway so you have to read it live.

 

Awesome, how was it removing the ring gear? I imagine the ring bolts are red locktited in there, did you have to use a torch to remove them? Also, did you reuse the same ring bolts when you reinstalled?

 

the only FSM I could find for the 8.4 diff with LSD was from a Tundra with the 3.91 LSD but I imagine it should be the same, the service manual shows “Preload at Starting” which I imagine is the breakaway torque?

 

I used an impact, as at the time, I had no way to hold the carrier and use a breaker bar to loosen the ring gear bolts. Yes they did have loctite on them, so I cleaned them before reusing them, and obviously used new red loctite when reinstalling the 4:10 ring gear on the LSD carrier.