12-02-2007, 05:10 PM
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How To Identify An LSD (Limited Slip Differential)
Well - a bit of a loaded question here (since I already know the answer), but I am posting this for a friend here who may be a bit too embarrassed to ask the question himself...
In a traditional "locked" rear differential setup (or with any American-type LSD), you can raise the drive-wheels off of the ground and turn one wheel forward and watch the other wheel turning forward with it and that is one sure-fire way of knowing that you have an LSD in your differential or not!
Without coaching anybody here, can someone please tell us what happens when you perform this simple "test" on an Alfa Romeo transaxle WITH an installed LSD?
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12-02-2007, 05:34 PM
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ive asked this one a few times and NEVER gotten a straight answer......your right tho..traditional units are obvious
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12-02-2007, 06:10 PM
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My way of testing an LSD transaxle is, put your car on a first gear rev the RPM at 5000 then release the clutch, if you see 2 black tire marks on the ground then you know you have an LSD transaxle. This is the old school way.
Giorgio
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12-02-2007, 07:15 PM
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Well, my '85 BMW 535i with an LSD, and when I jack it up and start it the rear wheels spin a little (in neutral). Does this have anything to do with the LSD?
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12-02-2007, 11:25 PM
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The only way to be really sure is to open the tranny and look.
Lifting the wheels and spinning isn't really going to give you anything, it will only work if your pinion is not tight enough. i.e. you can see weather the drag torque in the speedgears/bearings are larger then the clutch packs. 
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12-02-2007, 11:39 PM
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I always thought the best way was to park one wheel on gravel (or grass), the other on tarmac, and dump the clutch. Either you sit there and spin one wheel, or you start to accelerate. Always worked for me.
I've never been game to dump the clutch in my transaxle Alfas on a dry road. Do people actually do that? maybe if I could drive someone elses?
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12-02-2007, 11:53 PM
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I do that all the time in my racecar...
The "one wheel on gravel" approach doesn't really give you the whole story, the LSD will transfer 25% extra of the available torque on the slippery wheel. So if you are on ice with one wheel you can transmit next-to-nothing+25% extra to the other wheel, i.e. you will spin the wheel anyway.
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12-03-2007, 12:02 AM
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You'll spin the wheel, but still accelerate surely?
But with a non-lsd on gravel/grass/ice you'll get nowhere?
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12-03-2007, 02:32 AM
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 Quote:
Originally Posted by C&S
I always thought the best way was to park one wheel on gravel (or grass), the other on tarmac, and dump the clutch. Either you sit there and spin one wheel, or you start to accelerate. Always worked for me.
I've never been game to dump the clutch in my transaxle Alfas on a dry road. Do people actually do that? maybe if I could drive someone elses?
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I do.
Often.
And always at redline...also, a clutch kick to get 'er nice and sideways on a wet road too...
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12-03-2007, 06:08 AM
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I've heard that one way is to be in an emtpy parking lot turn the wheel to one direction and drop the clutch. If the car snaps around then its LSD if it doesn't snap then no LSD
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12-03-2007, 08:15 AM
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Quote:
Originally Posted by C&S
You'll spin the wheel, but still accelerate surely?
But with a non-lsd on gravel/grass/ice you'll get nowhere?
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12-03-2007, 08:58 AM
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Quote:
Originally Posted by BigSwede
The only way to be really sure is to open the tranny and look. Lifting the wheels and spinning isn't really going to give you anything, it will only work if your pinion is not tight enough. i.e. you can see weather the drag torque in the speedgears/bearings are larger then the clutch packs. |
There are no physical visual/discernable differences between a standard and an LSD Alfa transaxle - at least not externally! You have to open it up to be 100% sure. In fact, you can take an LSD "pumpkin" and install it in a previously (non)LSD transaxle, shim it properly and now have an LSD in a transaxle that previously was not an LSD transaxle!
Here's the smoking gun question in all of this: Can you simply put an Alfa Romeo transaxle car with (suspected) LSD up in the air on a lift, turn one of the drive-wheels in one direction, watch the other wheel - either remain motionless, or even tend to "want" to move in the opposite direction - and conclude that the vehicle in question does NOT have an LSD in it?
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12-03-2007, 09:23 AM
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Quote:
Originally Posted by junglejustice
Can you simply put an Alfa Romeo transaxle car with (suspected) LSD up in the air on a lift, turn one of the drive-wheels in one direction, watch the other wheel - either remain motionless, or even tend to "want" to move in the opposite direction - and conclude that the vehicle in question does NOT have an LSD in it?
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Jes
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12-03-2007, 11:33 AM
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Quote:
Originally Posted by junglejustice
Well, while the key (last) part of my original question wasn't quite answered yet, I think that Mats' answer came closest to what we were looking for; you CAN'T!
There are no physical visual/discernable differences between a standard and an LSD Alfa transaxle - at least not externally! You have to open it up to be 100% sure. In fact, you can take an LSD "pumpkin" and install it in a previously (non)LSD transaxle, shim it properly and now have an LSD in a transaxle that previously was not an LSD transaxle!
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Quote:
Originally Posted by junglejustice
Here's the smoking gun question in all of this: Can you simply put an Alfa Romeo transaxle car with (suspected) LSD up in the air on a lift, turn one of the drive-wheels in one direction, watch the other wheel - either remain motionless, or even tend to "want" to move in the opposite direction - and conclude that the vehicle in question does NOT have an LSD in it?
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No, it's only a brake, the diff itself will work just like intended, in gear (engine shut off) - you can't spin one wheel in one direction and have the other one stand still. If you can that differential is in bits and pieces.
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