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Discussion Starter #1
Hello All,

1991 Spider Veloce with 99K miles.

I was recently chasing down a clunk that I was getting from the rear. I thought it was the Diff but turned out to be in the driveshaft.

During my adventure, I saw this video from Wheeler Dealers, where they had a 1987 Quad. Its an interesting show, but for the diff, you can skip to 12:30.

https://www.dailymotion.com/video/x6kuvcm

Here he talks about then proceeds to replace and even adds an additional friction disk to each side of the differential.

With 99K miles, I am thinking that my friction plates are in need of replacement.

Are there any tests that can be done without opening the diff?

What are your thoughts on adding the 2nd friction plate?

Thanks in advance for the learning opportunity.

Vin
 

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But Mad North-Northwest
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I was recently chasing down a clunk that I was getting from the rear. I thought it was the Diff but turned out to be in the driveshaft.
If you ever wonder if I get tired of being right all the time the answer is: no. No, I do not :D

There was some discussion of that episode when it came out, and the consensus was that adding plates on a street car was a bad idea. I do not know any good way to test the Alfa LSD statically. The stock LSD is set up without preload, IIRC, so basically it acts like an open diff until under load. So while I'm willing to be educated on the subject, I've never been told a good way to tell how limited-slip your LSD still is (besides peeling out and looking for parallel stripes, that is!)

Unless you're racing or really, really, bored my suggestion would be to just not eff with it. But you seem to be looking for excuses to rip open your differential, so knock yourself out, man :D
 

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Tom is correct. Wheeler dealers got it wrong.
 

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Discussion Starter #4
Unless you're racing or really, really, bored my suggestion would be to just not eff with it. But you seem to be looking for excuses to rip open your differential, so knock yourself out, man :D
Now that made me laugh! :grin2:

No, I'm not looking for an excuse to open the differential, but I am looking for ways to improve my ride.

The friction disks are items that get used up like the clutch don't they?

Vin
 

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Ill throw my 2 cents in, having rebuilt a few diffs. I did actually put a 4 clutch pack in the 4:10 I am currently driving in the GTV. I did this 2 + years ago before the WD guys had the show. It locks up too easily. I will probably at some point go back to the 2 clutch plate setup. On the spider, I kept the 2 plate setup and it is really nice with no early lockup at all.

Vin, unless you are tracking or crossing the car, the hassle isnt worth it. Fire it up, dump the clutch in first and see if you lay down two black strips. If so, then good to go.
 

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But Mad North-Northwest
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They wear, yes. If you set them up with preload they'll wear fast. But since there's no preload in the stock setup they're only engaged when one wheel starts to slip. So really dunno how worn they get in practice.

Probably depends how hard you've been driving. Like I said, I don't know a way to test beyond the burnout method.
 

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Discussion Starter #7
Ill throw my 2 cents in, having rebuilt a few diffs. I did actually put a 4 clutch pack in the 4:10 I am currently driving in the GTV. I did this 2 + years ago before the WD guys had the show. It locks up too easily. I will probably at some point go back to the 2 clutch plate setup. On the spider, I kept the 2 plate setup and it is really nice with no early lockup at all.

Vin, unless you are tracking or crossing the car, the hassle isnt worth it. Fire it up, dump the clutch in first and see if you lay down two black strips. If so, then good to go.
I appreciate all the replies. Again, its a learning moment for me.

I am off the 4 clutch pack thinking. Thanks everyone.

"Fire it up, dump the clutch in first and see if you lay down two black strips. If so, then good to go"

Now there's a test I am looking forward to doing :wink2:

Vin
 

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The clutch plates pick up a glaze that makes them less grippy. Alfar7 media blasts them when he rebuilds LSD's.
 

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Discussion Starter #9
Ok,

Went for a drive and did the test. in 1st gear, RPM about 4000, dropped the clutch and laid down 2 black stripes.

That was fun!

So, looks like I'm all good for now.

So, for learning purposes, what are the signs that the friction disks are worn? Doing the above test and no stripes?

Thanks,

Vin
 

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Richard Jemison
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LSD builds

The WD video is misleading on a bunch of fronts.

Can`t do it in an afternoon? They must be drinking tea all f`ing afternoon!

Takes about an hour..
But you have to have the correct thickness of floater plates to set clearances so the lock up occurs as it should. You Never preload.

All that oil! If you do it correctly you set the clearances dry so you know what true clearances are.

The friction disk are very rarely damaged. The burned oil carbon coats the surface of the "clutch disk" reducing the grip on the floater plates. Media blast them with "black diamond" media, and the clutch disk are like new unless the teeth that engage the drive coupler`s splines are worn beyond use. These have a texture as they are moly plated as with later syncro bands. And FYI the correct lubricant as with transmissions and transaxles to use is Redline 75-90 NS.

As well the clutch disk will grip better if the floater plates are media blasted as well. I do this on all my LSD builds, both 4 disk (racing) and 2 disk for street. You really do not want 4 disk LSDs for street use. You will be blessed with oversteer at many inopportune occasions (rain...)

Typically there is an optimal clearance for the assembly based on application. The looser (more clearance) from those levels results in a more aggressive lock-up. But that can result in push (understeer) coming out of a corner on a race track. Best to have a gentle application of lock-up so power can be modulated during the exit. Once the ramps are off the bottom of the "V", lockup is a function of torque application when setup is correct. Both with 2 disk and 4 disk.
 

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Discussion Starter #11
Can`t do it in an afternoon? They must be drinking tea all f`ing afternoon!
Wow! I laughed twice in one thread :grin2::grin2:

I was really hoping to see you chime in Richard. Thanks.

Do you have a picture of measuring the clearance?

And measuring without oil makes total sense.

Thanks,

Vin
 

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Richard Jemison
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Measuring clearance

I`ve never bothered to take a picture or video during set-up, but it`s easy.

When you are setting up the assembly (dry) first using the "probe" end of a digital or dial caliper and measure the depth of the raised section on the underside of the cover that fits into the main housing, over the plates. Remember to to "zero" out that end of the caliper on a flat surface for accuracy.

When the assembly is where you think it is right, using the caliper again measure the distance from the top mount edge of the housing to the top plate. The difference will be clearance. The measurement of the inside of the housing should be about .010-.016" (dry) for a 2 disk, and .014 to .020" for a 4 disk, larger than the top plate`s thickness.
In both the smaller number is fine for street use and the larger clearance for track use.
 

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Discussion Starter #13
Richard,

As always, thank you for sharing your knowledge with the group.

Vin
 

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Here’s what happens when I don’t check clearance —

I rebuilt a 4:10 to put in GTV. All bearings changed and preload and pinion depth set. Changed clutch discs in LSD unit and thought I had it wired! When installed with axles in, turning the rear wheels resulted in notchy movement. This translated to vibration in the drive train — reasonably severe.

Knew it was the LSD as the culprit so sent to RJ. He expertly diagnosed my setup as 7 thou preload! The notchyness was stick-slip on the plates! After RJ set it up with mix-n-match parts from his stash I ended up with 4 thou clearance ( total delta 11 thou).

Installed and notchiness is gone. 1000 percent this is how to set up. Locks up great when needed—and nice and smooth !

I’m a believer — No preload at all!! Unless you like vibration!! Thanks RJ !

Now with the longer diff it clearly shows I need more ponies under the hood!
 

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I believe what you're describing as notchiness (sometimes called chatter) is normal for LSDs. There are additives that can be used to reduce it. Some people believe the additives affect (limit) the LSD's performance; I am not convinced of that.

Does your LSD have cup springs, also called Belleville washers? Cheers,
 

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Kevin, yes I agree there is a slight notchiness in any spider gear driven LSD but it should be barely (if at all) detectable. The situation I was describing was severe; and it was no doubt caused by preload. There are no belleville washers that I recall in an Alfa LSD.
 

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Richard Jemison
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LSDs

I believe what you're describing as notchiness (sometimes called chatter) is normal for LSDs. There are additives that can be used to reduce it. Some people believe the additives affect (limit) the LSD's performance; I am not convinced of that.

Does your LSD have cup springs, also called Belleville washers? Cheers,
Share
Additives absolutely reduce effectivness. As do any common GL5 lubricant.

These units should have no device as a Belleville washer that caused any degree of preload.
 

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Measuring clearance

I`ve never bothered to take a picture or video during set-up, but it`s easy.

When you are setting up the assembly (dry) first using the "probe" end of a digital or dial caliper and measure the depth of the raised section on the underside of the cover that fits into the main housing, over the plates. Remember to to "zero" out that end of the caliper on a flat surface for accuracy.

When the assembly is where you think it is right, using the caliper again measure the distance from the top mount edge of the housing to the top plate. The difference will be clearance. The measurement of the inside of the housing should be about .010-.016" (dry) for a 2 disk, and .014 to .020" for a 4 disk, larger than the top plate`s thickness.
In both the smaller number is fine for street use and the larger clearance for track use.
Hello,

I have been following this thread for a few weeks to plan the re-assembly of a donor 2L rear end while cleaning everything very well for inspection and assembly. This 2L lsd will be insralled in my street gt for occasional Alfa club track outings. I have decided to do the 4 disk modification and have been for the past few days assembling and measuring clearances. I have measured and documented all disks and have concluded they are all within an acceptable thickness range just as the spyder gear parts and sleeves as being pretty close to one another. The problem I have is that I can measure a wide range of clearances between the top cover and the top smooth plate (method Richard describes and I well understand) purely as a function of how I place the spyder gears in place. Also, I can sometimes lift the bottom packet by pushing up through the openings (next to the bearing) with my fingers and other times there is no play even with the cap not installed.

Does placement of the spyder gears and related parts and sleeves have only one way or I do need to "mix and match" until I get the proper clearance? I have obtained the proper clearance a few times but also way off many other times with the bottom packet of disks sometimes with play and other times without. Pretty random.

I hope this makes sense to someone.

Thanks.

Rich
 

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Discussion Starter #20
I have obtained the proper clearance a few times but also way off many other times with the bottom packet of disks sometimes with play and other times without. Pretty random.

I hope this makes sense to someone.

Thanks.

Rich
Can you please post pictures of the measuring procedure?

I'm sure it will be helpful.

Vin
 
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