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Diff project

Discussion in 'Boxers/TR/M' started by tuplakoo, Feb 19, 2021.

  1. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    21,333
    Texas
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    Steve Magnusson
    #101 Steve Magnusson, Sep 11, 2021
    Last edited: Sep 11, 2021
    See the cross-section drawing on page E38 of the TR WSM and the text on page E40:

    "...keeping the bearing lubrication holes toward the top."

    (Although something looks wacky in that cross-section drawing on page E38 as the relationship between the removable LH side cover and the ring gear seems reversed to reality -- the teeth on the ring gear point away from the LH side cover on page E38; whereas, on a TR, the teeth on the ring gear point toward the LH side cover. Wonder if they reused a drawing from a different model like a BB?)
     
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  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    21,333
    Texas
    Full Name:
    Steve Magnusson
    My mistake -- had the LH-RH reversed in my head. E38 OK.
     
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  4. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    romano schwabel
    the hole comes to the top. so oil can get to the bearing
     
  5. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Thanks to all. Fingers crossed the preload on the bearings will be good. Between the torch and the freezer, it was a hard job to replace bearing races.
     
  6. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    romano schwabel
    what was hard? it takes some time and with the right temperature it is done in less than 5 seconds each side
    so check the preload very well
     
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  8. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Using an oven gets the entire bearing carrier warm which makes it easy (next time!) We did not have an oven, but went through a lot of propane using a torch to get the side carriers warm. As soon as they heated up, they cooled down (especially the driver's side). As well, a -20c freezer does not get the new bearing race cold enough to simply drop in, even after using the torch for 5-10 minutes on the carrier.

    Now that that is done, I will trial install the differential (I have to assume I do it without the ring gear mounted otherwise I would get a false reading), to check preload on the bearings (I think 3-3.5 Nm torque to turn the differential inside the cases when everything is tightened but without the ring gear installed.

    Once the bearing preload is ok, I then will need to check the pattern on the pinion / ring gear.
     
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  9. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Test fit of differential today shows that it is hard to spin, with the side differential carrier bolts torqued to 25 Nm and the axles seals yet to be installed. Once initial friction is overcome, it does spin with some resistance, which might be in the ballpark.

    The manual gives no figure for tightening torque for the 8 17mm nuts on lock washers that hold each of the differential carriers to the sides of the transmission, but as the studs are just threaded into soft aluminum I would think the torque figures would not be very high. 40-50 Nm would seem far too high.

    The possibility is that it is too tight for the new differential case and bearings with the 1.6mm shim in place; I may order a 1.8mm one to see if that improves things; before going down that path, I want to check the pattern on the teeth.
     
  10. pshoejberg

    pshoejberg Formula 3
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    Dec 22, 2007
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  11. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Thank you, I believe that is correct - I actually keep a 512TR manual around for my Testarossa which can be helpful, as it has a little more detail on some things which the cars have in common.

    The 512 manual suggests 53 Nm for the gearbox 'side covers'. At that level of tightness, the differential will not turn in the bearings, so I guess I need that 1.8mm shim. I hope it is still available.

    No sense it checking the pinion to ring gear clearance and pattern until I have that shim.
     
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  13. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
    7,194
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    romano schwabel
    why trying a 1,8 mm shim? and then may be try again other shims?
    now you have a 1,6 mm shim and when you fasten the 8 nuts with 53 Nm the diff will not turn anymore. so loosen those nuts and put between the cover and the shim or between the shim and the gearbox housing 4 fealer gauges, so in 3,6,9 and 12 with 0,2 mm and tighten again the nuts, then you see if it works fine. if not you may use thicker or thinner gauges. so finally then you know what shim you will need.
    I still have here some shims in stock, self made. also some shims with nearly 3 mm what you could grind to the exact size you need.
    later, when you check the pattern, you may use again other shims both sides then equal thicker or thinner to keep the preload.
    you may use the search function. I have written once how I always do this, but just now can not find so fast anymore.
     
  14. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    romano schwabel
  15. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Many thanks for your response - my thought was to try a 1.8 and if too loose (0.2 is not that much?) I could grind it thinner. I will need to find (or buy) more feeler gauges to test as you suggest.

    Happy to buy shims from you, but delivery is always interesting in Dubai. I will pm you.

    As delivered, the car only had one 1.6mm shim on the passenger side. Do most people need to shim both sides to make the pinion and crown gear fit properly?
     
  16. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    most people - don´t know
    when I rebuilt a gearbox I always had to do so. until now I never only changed the diff. but may be when you only changed the diff it will work fine? so first adjust the preload without the crowngear and then check the pattern. but you not touched the layshaft with the pinion, so I think you not have to check the pattern, only the play what the crown will have to the pinion. you need a very little play only but you need a play ! ! !
    good luck
     
  17. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Thanks. I get 3 hours each evening to work on this, it is amazing how fast the 3 hours goes. The plan this evening is to place 4 thin feeler gauge strips on top of the right side shim to approximate a thicker shim, torque everything to 50Nm and check the bearing tension. If that works, will install the ring gear with the feelers in place, torque it again and check the pattern and free play. Fingers crossed it all works without needing to put a shim on the left side (I will then contact you about a shim).
     
  18. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    romano schwabel
    wish you good luck john
    but you may use 4 equal feelers of course
     
  19. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Four 0.2mm feelers on top of my 1.6mm stock shim tightened with 50Nm of torque on both carriers gives good bearing tension (tight, but turns smoothly) and an 'in the ballpark' wear pattern on the teeth (the driven side looks better). As I do not want to touch the pinion, it may be hard to improve. Thanks to Romano and Paul Newman for their suggestions and guidance. A 1.8mm shim should serve me well.


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  20. qwazipsycho

    qwazipsycho Formula 3

    Oct 30, 2004
    1,165
    Utah
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    Scott
    I can tell you from experience, that's a perfect pattern. As good as it gets. I could never get the coast side to center. And I went so far as to tear the whole gearbox apart to try and move the pinion. I disassembled/reassembled that gearbox at least 6 times before I decided it was as good as it gets the first time I set it up.
     
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  21. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,207
    Dubai, UAE
    Thanks (and many thanks to Romano for making a shim for me, as well as Paul Newman for making the quality differential case). I am really lucky that it fit together so easily with some helpful tips (also, maybe my gearbox case was not originally made on a Friday).

    I am travelling this week but looking forward to finishing the differential and mounting the engine back on the gearbox when I return to Dubai. Meanwhile, I am in Toronto, getting to enjoy driving my BB512 this week. No plans to replace the differential in that one, just saving up to buy more fuel. Actually, when I step on it, it makes clouds of black smoke, even when warm. Does anyone have BB jetting experience? (Perhaps a new thread)
     
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  22. samsaprunoff

    samsaprunoff F1 Rookie
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    Jun 8, 2004
    3,397
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    Sam Saprunoff
    Good day JohnMH,

    Just a heads up that simply changing out the jets may not sort out your rich condition. I have spent a fair amount of time on my BB's carbs and in the process I have a ton of respect for the original designers of these carbs... They are infinitely tune-able ... which is both a blessing and a curse. In addition to jets you may have to consider float levels, emulsion tubes, air correctors, and even review the size of the accelerator circuit return bypass valve (locatedin the float bowl). The bottom line is that there are lots of things going on which are interrelated and so any changes in one can affect others. Also... just a heads up that the "typical" manual float level adjustment (bending of the float tab that the needle vale sits against) is woefully inaccurate and is quite time consuming to get right. Having done this countless times I recently found a much superior measurement method which uses a calibrated sight glass that is affixed to the float bowl drain bolt. Doing this allows you to see and verify the float levels quite easily and accurately.

    Given my experience... and I still have a lot to learn ... I would suggest you find someone who is an absolute guru on these carbs, as there is a fair amount of knowledge and experience needed to truly sort them out especially so given the continually changing fuel formulations at the pumps.

    Cheers,

    Sam
     
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