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GTV6PASSION,

You have initiated a great thread that has been expanded into specific details with information from some people having real world experience:

1. While there is nothing wrong with spending the $ for new discs, I think it is clear that two new discs in a stock setup will only produce the 21% lockup as specified for new cars. Your initial question has been highjacked into the topic of modifying LSD's for more lock up.

2. Jim K. has stated that new discs will wear faster than a LSD set up with used discs, but mentions the "pre-load" that can be acomplished by adding shims.

3. Richard Jemison recommends using an additional two discs and shims, but cautions against using pre load, and identifies undesirable consequences.

4. Richard also discussed the attractive lure of changing ramp angles, and advises against this.

Great stuff, everyone. Thanks...please keep the information flowing.

Richard you seem to have a bit of experience what is you take of new LSD vs "rebuilding" used ones. Is the cost saving worth not getting new?
 

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Bacci make their own friction plates and they do them in various sizes for different applications. I got 4 last week but they were too big, probably for some older BMW diff. I sent them back along with a used Alfa disk for reference and called them on the phone. Giulio said the big ones are what they use for Alfas but I very much doubt this, they probably just packed the wrong stuff. They also have something very clever which I have only seen in ZF BMW LSD's: flat plates shaped as conical springs for applying constant preload, used one per side, on the end of each clutch pack. With these, adjustment doesn't have to be so critical any more. I've also ordered 4 of them! They're the same price as the friction ones, less than 20€ each.
Back to your question, they said they can supply the same size as ZF so all is well, as this is what I want them for anyway.
Jim K.
 

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Oh boy, the experts are coming through with more good information. Thanks.

Jim K: I had a discussion with Jim Steck last year, and he described the very kind of shallow conical LSD plate you mention. I remember him mentioning their use in some GM LSD differentials. I guess these are really "Belleville washers", which I know are used for many non-automotive applications (and are included in most spring force calculation programs).

...They also have something very clever which I have only seen in ZF BMW LSD's: flat plates shaped as conical springs for applying constant preload, used one per side, on the end of each clutch pack. With these, adjustment doesn't have to be so critical any more. I've also ordered 4 of them! They're the same price as the friction ones, less than 20€ each.
Back to your question, they said they can supply the same size as ZF so all is well, as this is what I want them for anyway.
Jim K.
 

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a little bit "off topic" but interesting question :

the recommanded oil for the transaxle / lsd is 75w90...

some suggest that a 75w140 "special lsd" (motul FF for exemple in europe) really improves the lifetime of the frictions plates , giving also a more postive gearchange, crucial subject for the alfa transaxle...

i'm thinking about switching for this oil on my 75 3.0 v6 quadrifoglio, but advices are welcome...
 

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Discussion Starter · #28 ·
Okey, so I opened the differential yesterday. Frankly speaking I can not say if my LSD discs are worn or not. If you guys could look at the photos and tell me what you think about them. I didn’t find any oil deposits on their surfaces and solvent washing which I applied haven’t changed their appearance much.

I found that thickness of the external blades and internal ones (LSD discs) is the same. So I don’t exactly understand the shimming issue. If I replace two external blades with two additional LSD discs, the total thickness of the setup will remain the same. So what is the reason for applying brass shim?

I discovered that AR 75 limited slip differential has one more external blade when compared to AR 105/115. The part has number 9 on the drawing and is on the right on the photo. Does it change anyhow the shimming issue?
 

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Hi Tomasz,

Any additional shims are to increase the lockup of the LSD. This can be done with the original two plates, and also if you add two more plates. Also, the shim can be brass or steel. Variations are:

1. Two friction plates = original lockup from factory literature as 21% (until worn)
2. two friction plates and additional shims. Lockup depends upon shim thickness
3. Four friction plates= additional lockup, but this is fixed at whatever results from the additional plates.
4. Four friction plates and additional shims. lockup depends upon shim thickness.

... So what is the reason for applying brass shim?
 

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Discussion Starter · #30 ·
Hello,

George thanks for explaining. Now I finally got it:) So to sum up, most of you suggest using two 0.01 - 0.02 inche brass shims, that can be easily cut form brass roll. They should have a shape of external blades and will give propper preload to the assembly. Right?

Does anyone have opinion on the lsd dics on my pictures? Are they worn or fine?
 

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Tomasz,

I used .002 in. steel "shim stock" for my shims (this can be purchased at a machine tool supply). I also left some clearance rather than pre-load. This is the difference in height between the stack-up of plates and parts and the cavity and cover they fit into (see the exploded view in your post #41). When "Little italian" (Bud Feigel) and I worked on our LSD's, we mounted the LSD in a vise where we could measure the resistance to lock-up. Bud also had a differential cover with the axle housing cut off and made a short "test" axle from old pieces.The best result seemed to be with some small clearance. If we shimmed the pack to no clearance, the LSD was completely locked (I have notes from these sessions, and will try to provide more information).

And... we used existing plates with no work other than to clean off old lubricant.

Hello,

George thanks for explaining. Now I finally got it:) So to sum up, most of you suggest using two 0.01 - 0.02 inche brass shims, that can be easily cut form brass roll. They should have a shape of external blades and will give propper preload to the assembly. Right?

Does anyone have opinion on the lsd dics on my pictures? Are they worn or fine?
 

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I'm with Richard. And...if shims are used, the resulting clearance / free play must be measured. Don't just throw shims in the LSD without knowing the numerical result.

[Disc springs....
Best are the sinus wave shaped springs.

/QUOTE]
Sorry:
I`ve been building LSD units for race use (and street) for many years and I disagree. They need to be free with no preload. I keep track of all the competition transaxle units & I have not had one LSD unit fail or been returned for adjustment. When the boxes are in for gear changes etc. the units are checked & cleaned, but when the correct fluid is used & changed there is no problem.

What is your history of building with these springs? What gives them the "best" status?
This is where I say "PHOOEY"!:(
 

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What is your history of building with these springs? What gives them the "best" status?
No history at all.
I was referring to the "Belleville washers", used them a lot in bearing applications and hate them, very difficult to predict/get the right pretension when stacking, very large spread in the disc spring stiffness. I prefer the sinus waved washers for pretensioning.

In theory I don't see why the LSD need to have play.
A small pre-load with a spring washer will give a nicer transition from moving from the "on throttle" to the "off throttle ramp".
 
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