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Is this normal operation of the limited slip?

Discussion in 'Technical Q&A' started by f355spider, Dec 31, 2003.

  1. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    16,562
    USA
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    Hugh G. Rection
    I am a little confused as to whether I might have a problem or not. When starting out from a stop, if I make a hard left or right turn and am on the gas pretty good (not spinning the tires, but moving briskly) I feel a little bit of vibration or shudder from the rear of the car....no real noise per say....I used Mobil 1 gear lube, and had the same issues (it has a limited slip additive). The limited slip additive apparently was too slippery for the synchros, and I started getting "crunches" when shifting. So I ditched the Mobil 1 for Redline 75w-90NS which means "no slip" for the limited slip. Shifting is perfect now, but I still get the vibration under the very specifc conditions posted above. I called Redline, and they suggested adding a bit of slip additive (1%) which I did, and this seemed to help a bit, but not completely. I am hesitant to add more, as it might effect the synchros (and why they recommeded not using their standard Redline 75w-90 gear oil which comes with 4% slip additive already in it).

    Hans has me thinking this is perhaps the "normal" operation if the limited slip locking and unlocking? I'm not familiar with how the thing works, so I am asking you more learned folks out there.

    Thanks!
     
  2. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    David - welcome to the club. I do not know which car you are referring to, but I assume it is a Boxer or TR.

    What you are experiencing is the LSD metal clutch plates sticking and skipping on each other. They sit in the transaxle. This is a common symptom, and I experienced it in my Testarossa (1986). The solution was to add MOPAR (from Dodge) LSD additive. If that alone does not solve the problem, then I would go back to the Mobil-1 plus the MOPAR additive.

    Whatever additive you use, go to a large, empty parking lot, and drive the car in reverse with the steering wheel locked first to one extreme and then to the other. This applies maximum stress/shear on the plates and the sharp turn helps to splash the transmission fluid (with additive) on them. It will not hurt the car.

    This is how I solved my problem. End of story.

    Jim S.
     
  3. f355spider

    f355spider F1 World Champ
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    May 29, 2001
    16,562
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    Hugh G. Rection
    Thanks Jim,
    Car is a 328. I already have the slip additive from Redline, sounds like I just need to add a bit more (1 tbs already added). So I will try adding one more tablespoon. And drive as suggested.

    Dave
     
  4. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    David - the Mopar comes in a pre-measured plastic bottle of approximately 100 cc. Not very much. It took a drive to Las Vegas and back to work the stuff into the plates, but now the shudder associated with starting from a stop with the wheel slightly turned is gone. I did not have to accelerate as hard as you describe. A very slow move from standing still, with the wheel turned slightly, resulted in a shudder.

    How far have you driven since adding the additive, or have you tried the locked-wheel in reverse trick?

    Jim S.
     
  5. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    I have probably driven at least 1,300 miles. The car is getting new fuel injectors, o-rings and the co adjusted this week. When I get it back, I will try your recommeded procedure. If no difference, I will add one more tablespoon and see what happens.

    I was told by the guy (Dave) at Redline, that it was not a huge deal, more of an annoyance. He said he would prefer to not use the slip additive and keep the gear oil balanced toward the synchros rather than the limited slip, since the two characteristics of the gear oil are opposed to each other. (the slip additive can make the synchros "crunch")
     
  6. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,849
    Dave - I understand your reluctance to add the additive vis-a-vis its impact on synchronizers. However, the vibration caused by chattering LSD clutches cannot be great news for the transmission housing, which in the Boxer and Testarossa have a propensity to crack at the half-shaft support. I do not know if this is seen in the 3x8 series, but it is a well recognized failure mode in the 12 cylinder interpretations.

    I did not find the additive to impact synchronizer crunch. Shifting did not seem to change with the additive.

    As I write this the Ball in Time Square is falling. Perhaps we should worry less about our transmissions and more about the safety of the 750,000 people standing unprotected on a New York City sidewalk.

    Happy New Year.

    Jim S.
     
  7. Peter

    Peter F1 Veteran
    Rossa Subscribed Owner

    Dec 21, 2000
    6,340
    B.C., Canada
    Dave, I used Canadian Tire's house-brand of tranny lube, 80W90 with the LSD additive already in it. No experiences with this shudder you mention and shifts fine.
     
  8. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
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    Hans E. Hansen
    Dave: In my former 'muscle car' life, the posi shudder occured at slow speeds, light throttle. Tight corners in parking lots, etc. Any heavy application of throttle will cause one tire (the inner) to grip-slip-grip. This is certainly influenced by the posi and its lubricants, but if operation at light throttle is OK, I'd ignor it. FWIW, I just changed from [Redline 1 qt 75W90, 3 qt 75W90NS] to pure 75W90NS. A slight 4th gear crunch when luke warm (didn't do it either cold or very hot) disappeared, but I have a definite posi issue. Jerking in sharp corners *with light throttle*. Heavier throttle gives me the tire grip-slip-grip treatment. Even more throttle and "Yeehaw!"
     
  9. AJS328

    AJS328 F1 Veteran
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    Apr 23, 2003
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    Augustine Staino
    Dave,

    I just added the Redline 75W90NS to my car last week but I really haven't had much of a chance to drive it since. The next time I'm out for a ride I'll check to see if I notice any of the LSD chatter.
     
  10. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    Steve Magnusson
    I too tried the straight Redline 75W90NS in my recent TR service and the low-speed turning chatter was pretty significant (i.e., really not acceptable IMO). I have since added 2% of the Redline "friction modifier" and the LS chatter is greatly reduced, but it's still not "zero". Can't say that I noticed any difference in shifting behavior between the 0% and 2% levels (both were/are excellent compared to where I was, but for a different reason), and I'll probably go back to the typical 4% friction modifier content.

    Sort of chased a red herring on this one -- I was having difficulty selecting either 1st or 2nd when cold, but the real problem was that one of the clutch disc hubs was "rust frozen" onto the splined shaft so that it wasn't really disengaging well. Anyway, just another NS data point...
     
  11. atheyg

    atheyg Guest

    The shudder is not normal, I don't have it on my 328

    I recently changed my gear oil to Valvoline dino oil, It didn't shift perfect till the trans was warmed, I had a leak in the plug so I drained it and put in Slick 50 gear oil which the shop that did the last service put in and it shifts better now than the regular Dino oil, actually shifts perfect.


    I would dump the Redline and go back to Mobil one or the SLick 50 dino, it sounds like its causing problems, any LSD
    additive you add will only last so long anyway so if it cures it by adding more now it will happen again
     
  12. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    Hugh G. Rection
    Thanks Hans, I only get this mild shudder in certain situations, I basically have the wheel cranked over pretty hard, and accellerating briskly to induce it....otherwise, never notice it in normal driving.

    I just notice it making a very sharp 90 degree turn, either starting out from a stop (right turn) or maybe in a parking lot. So it only comes up once every third drive or so. If I am out with the FCA club on a drive, then I notice it at least two or three times. :)

    So, ignore it, or should I add another tablespoon of slip additive? This is one thing I like about Redline NS, you can control the amount of slip additive verusu going with whatever the manufacture pre-determines.
     
  13. Mike328

    Mike328 F1 Rookie

    Oct 19, 2002
    2,655
    Boulder, CO
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    Mike
    I too had the differential "chatter" issue in my 78 308 around tight corners after adding Redline 75w-90NS. However, 3,000 miles later the problem is not as noticeable.

    As some of you may have read several months ago, due to a completely worn 3rd gear syncro, and tired 2nd gear syncro, I'm pulling the gearbox to replace these. I'll also replace all of the others, as well.

    I'm beginning to wonder if all of our 308s--with their age and mileage--just are beginning to see worn syncros that "crunch" easier and more frequently, causing us to look for more exotic gearbox oils so much that our differentials are suffering. Alternatively, it could be years of the use of a "wrong" oil that's causing the syncro problems in the first place. One other thing to note is that while the 328 transmissions were fundamentally similar to 308s, all along the 308 and 328 line I undertand small incremental improvements were made to the transmissions, possibly helping the syncros last longer and crunch less, and this may be particularly noticeable with age.

    I will consider going back to Mobil 1 when I replace the syncros in the next few months...

    --Mike
     
  14. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
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    Malcolm W
    Jim S's advise is correct - the problem is finding a large car park !! - however the problem is as described above, there is a lack of lubrication between the plates inside the differential causing the plates to judder instead of slipping. Unless your're very lucky the only way to fix is to remove the differential, strip the diff and re-lube the surfaces of all the plates, that is assuming that they have not worn below the wear limit, which is 0.12mm.

    MW
     

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