Differential Friction Disk Change? - Alfa Romeo Bulletin Board & Forums
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post #1 of 18 (permalink) Old 05-14-2019, 09:00 AM Thread Starter
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Differential Friction Disk Change?

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

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #2 of 18 (permalink) Old 05-14-2019, 09:17 AM
But Mad North-Northwest
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Quote:
Originally Posted by Vintre View Post
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

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
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post #3 of 18 (permalink) Old 05-14-2019, 09:51 AM
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Tom is correct. Wheeler dealers got it wrong.

Ed Prytherch
79 Spider
76 Suzuki GT500
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post #4 of 18 (permalink) Old 05-14-2019, 09:53 AM Thread Starter
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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
Now that made me laugh!

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

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #5 of 18 (permalink) Old 05-14-2019, 10:22 AM
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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.

74 GTV with 10548's and Ingram pump
71 Spider 1750 BOMBER ; 1995 LS 78K tight fast car
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post #6 of 18 (permalink) Old 05-14-2019, 10:30 AM
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.

Tom

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Last edited by Gubi; 05-14-2019 at 01:49 PM.
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post #7 of 18 (permalink) Old 05-14-2019, 11:46 AM Thread Starter
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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.
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

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #8 of 18 (permalink) Old 05-14-2019, 02:00 PM
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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.

Ed Prytherch
79 Spider
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2011 Jaguar XKR

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post #9 of 18 (permalink) Old 05-14-2019, 04:07 PM Thread Starter
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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

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #10 of 18 (permalink) Old 05-14-2019, 07:38 PM
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.

Richard Jemison
RJR Racing

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post #11 of 18 (permalink) Old 05-14-2019, 08:03 PM Thread Starter
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Can`t do it in an afternoon? They must be drinking tea all f`ing afternoon!
Wow! I laughed twice in one thread

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

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #12 of 18 (permalink) Old 05-15-2019, 06:05 AM
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.

Richard Jemison
RJR Racing

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post #13 of 18 (permalink) Old 05-15-2019, 06:09 AM Thread Starter
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Richard,

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

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #14 of 18 (permalink) Old 06-18-2019, 07:29 PM
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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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post #15 of 18 (permalink) Old 06-20-2019, 02:55 PM
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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,

Kevin
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