Was the factory LSD's breakaway torque any good?

[hawairish]

I rebuilt the LSDs over the weekend...a few times actually...and my 1st go-around produced 137 ft-lbs. Not bad I suppose; a bit above my projected amount. But when I built the 2nd one, I only got 80 ft-lbs. These were presumably supposed to be identical, but it's possible I put one additional new friction disc into the first one. After re-shuffling the discs around, I got more even numbers of 103 and 97...this time being (more) certain of the parity.

 

I feel like I want more, maybe around 150. I tried cross-ref'ing side gear shims, but it's a crap-shot finding something with the right ID/OD. Best hope would be checking my open diff, but I'm not ready to pull it from the truck yet.

 

I'm wondering if adding another spring plate (3 per side instead of 2) and pulling a friction disc to keep the nominal stack height would give me some extra clamping force, though I'd lose some friction surface. I'm kicking myself for not trying it earlier, but it'll have to wait a while a couple weeks. There's not an OE setup like that, presumably for a reason. Think it would exert too much extra force on the spiders? I can't imagine it being any more stressful than simply having a much higher break-away force with an OE configuration. Thoughts?

 

 

[hawairish]

A little update on this...

 

I opted to get a set of the thicker friction plates, and two more normal discs. The spring plate idea was a no-go due to parts availability. Each LSD is ending up with 6 new pieces. After assembling one of them the other week, I got somewhere over 300 ft-lbs, exceeding what I could measure. That basically means I tripled the break-away by adding only .1mm to each stack, despite adding .3mm previously and seeing only about double at that point.

 

But that didn't seem right, so I broke it back down and swapped in some thinner (and unworn) plates to bring it back down that .1mm...and it went back to around 100 ft-lbs.

 

Thinking that maybe the first build was a fluke, rebuilt it to that setup. Same thing, except I bent my torque extender, again somewhere over 300 ft-lbs. Thinking maybe it was just that one LSD, I broke down both again, swapped around parts, rebuilt it. Rebuilt my torque extender...bent it again.

 

The extender isn't much more than a 1/4" thick--yet apparently not thick enough!--steel bar with two holes to fit over the wheel studs, and another wheel stud located further up the bar with a lug nut tightly on it so I can put the torque wrench on it. I need to get some angle iron or channel iron instead of a flat bar.

 

Supposing I build a better extender and still hit the 300-mark, I may just replace a disc with a plate...that keeps the same thickness but removes 20% of the friction surface.

 

Also, here is a chart I compiled before I began working on things:

 

 

 

Edited June 12, 2018 by hawairish

[Precise1]

Damn, good information Bud! Keep it up...

 

 

I got somewhere over 300 ft-lbs, exceeding what I could measure. That basically means I tripled the break-away by adding only .1mm to each stack, despite adding .3mm previously and seeing only about double at that point.

 

But that didn't seem right, so I broke it back down and swapped in some thinner (and unworn) plates to bring it back down that .1mm...and it went back to around 100 ft-lbs.

 

Thinking that maybe the first build was a fluke, rebuilt it to that setup. Same thing, except I bent my torque extender, again somewhere over 300 ft-lbs. Thinking maybe it was just that one LSD, I broke down both again, swapped around parts, rebuilt it. Rebuilt my torque extender...bent it again.

 

The extender isn't much more than a 1/4" thick--yet apparently not thick enough!

 

So this tells me that there is something else going on between the plates where .3mm doubles the break away, and .1mm triples it. I don't know what, but there has to be another factor as well.

 

Yeah, I have lot of experience making manufacturing fixtures, and it is surprising how easily/much mild steel will bend under load with only moderate pressure. When you start adding hundreds of lbs of pressure... Square or rectangular tube would probably be ideal for this purpose, and you can always put a solid bar inside if it starts to bend.

 

B

[hawairish]

Damn, good information Bud! Keep it up...

 

 

So this tells me that there is something else going on between the plates where .3mm doubles the break away, and .1mm triples it. I don't know what, but there has to be another factor as well.

 

Yeah, I have lot of experience making manufacturing fixtures, and it is surprising how easily/much mild steel will bend under load with only moderate pressure. When you start adding hundreds of lbs of pressure... Square or rectangular tube would probably be ideal for this purpose, and you can always put a solid bar inside if it starts to bend.

 

B

 

Yeah, it's a real fine line. I was definitely pissing me off, too. Must've rebuilt them at least a dozen times trying to find that happy medium. For one rebuild, I swapped the entire stack to the other carrier, and the numbers carried over...somewhere way over 300, and some lousy 100 number. So .1mm per side made a 200 ft-lb difference.

 

I thought about dumbing down the stack by swapping a pair of discs with plates, but it wouldn't have given me any spares to add .1mm to the other LSD build...so I'd have one LSD at less than 300, and still one at 100 with nothing I could do to improve it.

 

I ended up doing what I didn't want to do, and that was to make the stack uneven. One side in each LSD is .1mm thicker than the other. I kept trying to rationalize it: what difference could it make?!?! I stared at my digital calipers set to .1...as thick as a sheet of paper; 0.0039". Unbelievable the difference it makes.

 

I don't think it will break anything, but theoretically should lead to a little more wear on the thinner side. However, with both sides seeing pressure from the springs and spiders, I can't imagine it will be significant enough to worry. With this setup, I got one diff at 175 and the other at 150. Given all the pairings that I tried, it seemed that I should be able to produce some total between 300-400 for both LSDs combined, so I'm settling for those numbers. It's the most even pairing I've had.

 

I literally just pulled it off the jacks, need to tackle one more thing up front and then will take it for a test drive. I installed the Lokka and front 4.636 last weekend, LSD and rear 4.636 today...and a few other things (a spare donor axle comes in handy!). I took the 175'er, buddy's getting the 150.

 

I ended up using a length of 2x4 lumber to create a new bar. Worked out well...the steel bar that had broken off the previous bar became an insert on the 2x4 that I bolted to it. This particular 2x4 has been my multi-tool through this entire process...used it to mount the R200A flange so I could disassemble it for the Lokka, used to keep the wheel hubs stationary during torque tests, and then made it the torque bar. Who'd have thought...

[hawairish]

And next time (never!), I'm just buying a f*#%^@ Xterra diff... I had to settle for R50s locally.

[hawairish]

So wow...forgetting about the LSD for a moment, what a surprising difference the 4.636 gears make!

 

The LSD did great, too. Very good street manners, definitely noticeable. Some gas around the corner and it gives a very firm grab-and-go. Despite all the effort, a worthy upgrade.

 

 

[Precise1]

Cool, I'm glad you got some results that you are happy with. Personally, I would have gone with the 300lb version, but that is all that I am used to on both my 1995s (the 1999.0 is open diff). It only was an issue a few times until I learned not to accelerate hard while turning in the rain in first and second gear, unless you like getting dizzy...

 

Well, it is going to be a great upgrade for others, especially since you did all the work!

As I said before, good job and thanks for documenting it.

 

(you really should be using mics though, not calipers; I doubt they have good resolution if you can set the display to .1mm)

 

B

[hawairish]

Yeah, I would've liked to stick with the 300 ft-lbs as well...but I had mental conniption since I had bought 12 discs/plates to rebuild two LSDs, and 6 were adding 200 ft-lbs to one LSD, while the other 6 (at the exact same thicknesses) were adding only about 40 ft-lbs to the other. Financially, I just couldn't accept that. I probably could've gotten the same numbers by putting warn discs back in.

 

What I really needed was another 4x 1.6mm pieces, but I had settled on 4x 1.5mm pieces because of national availability. Of course, should I plan to revisit this, I means that I should be able to swap in another 1.6mm piece and get back up to 300...hmmm.

 

Agreed on the mics over calipers. The mm resolution was in hundredths which is probably fine for this (cheapo HF digital calipers...but they've served me well), but the real problem is that the discs have just a slightly smaller diameter than the plates, so the plates don't see constant wear at the edges, and the calipers pick that up a little. The FSM does indicate to use mics on specific points, in particular the centers vs. inner/outer tabs, to measure wear. But the pieces aren't a perfect uniform thickness anyway (even brand new), so I measured at about 4-6 points to determine what I could as a min, max, and average. Kind of an arbitrary process altogether...I started pairing things up to make the stack as perfect as possible, but it really became a lost cause once it was in the axle and being tested.

 

I'd also like to think that the LSD will improve over time, for some time anyway. The raised areas of the new discs appeared to more rounded...as these flatten out (before they were too thin/smooth), perhaps the friction area increases a little. I'll give it a few more days and pull a tire off to retest.