Yet another differential thread, and it's a puzzle | FerrariChat

Yet another differential thread, and it's a puzzle

Discussion in 'Boxers/TR/M' started by ExtraTx, May 13, 2020.

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  1. ExtraTx

    ExtraTx Rookie

    Jan 25, 2019
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    Austin, TX
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    Jon
    Decided to branch the @PA32Pilot thread because this is a different animal.

    I recently purchased a 1990 Testarossa with 30k miles from an estate. PO appeared to have taken care of it, pretty clean car, but most of it's miles came early on, and only achieved 1k or so for the past 15 years. No miles in the past 5 years. Still starts and runs great, but I didn't drive it due to the assumption that the belts were original. Engine is out, belts were most likely original.

    I've been casually looking for a Testarossa since 2011 or so. Have some other cars that I maintain and play with. I was well aware of what I was getting into.

    Now for the TWIST!!! I was watching the @PA32Pilot thread, and the engine is already out. I'm doing the usual, belts and waterpump because it was leaking, and various gaskets and seals because the engine was basically one big ball of oil collected dirt. I went magnet fishing in my diff case, and find two of the crown wheel bolts. Now, figuring the diff blew up, I dig further. Here is what I found.

    Appears to me, the diff did blow up, and was replaced with an OEM? Installer did a very poor job torquing and locking the crown bolts? Is the 2nd picture the welding, and is the 3rd picture the damage from the previous failure? That's all I can surmise.

    Now what do I do?
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  2. flash32

    flash32 F1 Veteran

    Aug 22, 2008
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    Not sure if the question is to replace the diff ? Atvthus point you already 80 percent there .. I would

    Sent from my moto g(7) using Tapatalk
     
  3. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    #3 turbo-joe, May 13, 2020
    Last edited: May 13, 2020
    OH NO ! ! !
    again a broken diff :( :( :(

    you posted already photo from those screws somewhere, but can not remember where. but I remember that I was writing already those screws are for tighten the crown to the diff.

    very poor ! ! !
    not even bend the locking plate right. or does the screws already got loosen? I think so because of the 2 missing. even if he used the right torque this may happen with used screws.

    photo 1: this seem that the mechanic who did this diff before used the old bolts again, not used loctite. those screws are only for 1 time use ! ! ! same as the flywheel bolts

    photo 2: can not see right if the welding is broken or not. bu tthe roles from the bearing look not good - or is it only dirt?

    photo 3: you mean the "grinding" right on the right side? don´t worry, only optical, nothing serious, except something below is broken. so inspect carefully

    as I see you work by yourself and did this all until now?
    then I suggest:
    have a look first at the CP if you see something unusual, if all ok then get a new diff ( of course not an original ), new bearings, new screws and put all together. adjust right and take your time to do this.

    good luck ;) and happy working :)

    you are lucky that you found this before more would get damaged. so save a lot of money
     
  4. ExtraTx

    ExtraTx Rookie

    Jan 25, 2019
    22
    Austin, TX
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    Jon
    First, I'm assuming this is an OEM diff. Is that correct? This one is fine, the welding is not broken.

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    Second, better picture of the inside of the case. This doesn't look like regular machining marks. Looks like a previous diff came apart.
     
  5. flash32

    flash32 F1 Veteran

    Aug 22, 2008
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    Dominick
    It does look like the ring gear did come in contact with what you are pointing out .. it is very close so if there was a diff failure which caused bearing and side cover to break the original ring gear may have touch/grind against it .. does the ring gear look good ..

    Sent from my moto g(7) using Tapatalk
     
  6. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    yes, looks like
    I would only grind away the edge and inspect if below something is broken would I not think. have seen more bad grindings and had no problem

    I would say it is an original when I see this welding. as I know all the other rebuilders of such a diff not weld this. but may be I will be wrong?

    ring gear is the same as crown?
     
  7. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Are the ring gear and flywheel bolts single use on a Testarossa? Makes sense to me (the flywheel bolts are at least on other cars I know). I priced a set (I intend to upgrade the differential at the time of my next major service) and amazingly Eurospares sells these bolts both new and used(!)
     
  8. versamil

    versamil Formula 3
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    Apr 28, 2013
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    The contact on the bottom of the pan sure looks like the crown gear hit it at some point. Thirty minutes ago, I was really looking at this same area in my TR differential. The shiny surface at the top of where the crown gear appears to have made contact, I think is an integral and important surface. There's also a mating surface at the TOP of the differential housing with the same radius. The left side cover, I think is really pretty fragile, for what it is tasked for. It's machined, to make contact with both the top and bottom cradle. My undamaged differential has a left side cover that I can't completely remove, because it's just ever so slightly raised, or burred where it contacted the lower and upper cradles.I'm sure the same tool that bored the main housing hole, continued in and bored both these "saddles" at the same time. Directly under the bearing, I think these are an important part of the support system for the bearings and ring gear. Anybody who does have a failure, should probably install the left side cover, with no O-ring as a cautionary prefit, just to make sure the two surfaces are contacting each other, and there are no BURRS from the differential grenading. The crown gear coming into contact can very easily raise a burr. Looking at the carnage in the other post, I would think this surface has damage that must be corrected.

    Your welded housing has had a bit more weld ground off than the one in my car. But it certainly is a welded part. Hard to believe someone could do such crap work inside a Ferrari differential. Almost looks like they reused the same bolt locking tabs too. Dumb!
     
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  9. flash32

    flash32 F1 Veteran

    Aug 22, 2008
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    Yes ring is same as crown

    Sent from my moto g(7) using Tapatalk
     
  10. turbo-joe

    turbo-joe F1 Veteran

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    I don´t think so.
    as long as the diff will not break this cover also will not break

    how do you know then when you not removed this cover that your diff is not broken?
     
  11. versamil

    versamil Formula 3
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    I have everything apart, but this cover is just loose in the housing right now, I'm going to lightly sand it tomorrow in an attempt to get it completely out. I have the entire gear unit out of the housing right now. On both the bottom and top surface of the cover, where it contacts the "saddles" in the housing, it has SLIGHTLY raised areas, where it was obviously making contact and moving slightly.

    I manufacture many different sizes of gearboxes, and have machined and built HUNDREDs of them. I feel personal failure if one of my machines fails in less than twenty years, and build them accordingly. As a manufacturer, you can make machines bullet proof, or you can make them so they have a finite life span.The left hand bearing housing in the testarossa, may be up to the task, but Ferrari has made a decision as to how much metal they want to have in the part. The WALLS of this cast aluminum part are NOT very thick, it tapers down in size where it doesn't have to. The bearing is supported quite a ways from the flange, so it has the cast in and machined support in the differential case. Ferrari has to make a decision as to how much a part weighs, as it all adds up. As long as it works and gets a car through warranty, then they are successful. Since this part DOES fail, albeit after the weld breaks, if I was to make it out of a solid chunk of aluminum, I would LEAVE as much material as I could, especially where the driveshaft flange is located. Ferrari very carefully cored that area out, taking out as much material as possible.
     
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  12. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    I think so too brian that F made this so
    but until now I never had a broken left cover and the diff still has been ok. so I think the cover has been not too weak for normal use ;)

    I also have sometimes problems to get this cover out of the gearbox. but this then only when I edge this cover a little. when you try to get it out straight it mostly works fine. that is one more reason I only do this job when the engine is out
     
  13. Newman

    Newman F1 World Champ
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    Just to add a little worry to the diff concern, I find most times the crown bolts are not tight when I take a crown gear off. With a lock plate you would think this wouldn't happen but my theory is the bolts stretch so they lose their torque setting. Ive seen bolts come out before as well so I had them tested one day. The results came back as barely meeting grade three specs. I had the head of one come off at 30 lb-ft too so I replace the bolts with grade 12.9 socket head cap screws and use blue loctite on them.
     
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  14. Newman

    Newman F1 World Champ
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    Ive seen the side support crack between the hole for the propellor shaft and the bearing cup hole. They couldn't get the two holes closer together if they tried which shows the confines of which they were working in trying to make this transaxle work.
     
  15. Newman

    Newman F1 World Champ
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    The saddle support in the gearbox doesn't look unusual to me. Maybe take more pics at different angles. When you look at the saddle in the 365 gearbox its huge compared to the 512 / TR version and you'll find witness marks on the left support of any testarossa or 512 showing that it moves on that saddle as the load is applied and things start moving around in there! The pinion is always trying to spit the crown gear out through the rear cover. Fun stuff :)
     
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  16. ExtraTx

    ExtraTx Rookie

    Jan 25, 2019
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    Thanks for everyone's input. Playing with it this morning I found that EVERY crown bolt was loose. Finger loose. Based off Newmans advice I will source adequate crown bolts to replace these, as it was pure luck they didn't get sucked up between the crown and pinion, and the OEM bolts can't be trusted apparently.

    I'm not worried about the saddle in the case, I just find it interesting that there was some unplanned machining going on in there. I'll clean it up and call it good.

    Has anyone had the OEM diff re-welded? There is a ZF location local to me and some friends have had them do some custom work in the past. Obviously i'm not putting this diff back in as is, but if it can be made adequate I don't have a problem with it.
     
  17. versamil

    versamil Formula 3
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    Newman, "witness marks" is a good term for the very slight raising of material on the back side of the left side cover. Nice to hear you've seen this in all of the cars, as I feel just like you said, that this occurs because every part of this flexes as torque is applied. Naturally the ring and pinion is trying to push things apart.

    There's something about peace of mind, that makes it worth spending about three grand to absolutely remove the apprehension brought about by realizing the part can still grenade. Having your car torn down this far, and NOT buying an upgraded part, after this many failures, doesn't seem worth saving the money.
     
  18. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
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    Anyone ever consider drilling and lockwiring the crown bolts?
     
  19. PA32Pilot

    PA32Pilot Formula 3
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    I am thinking about that. I’m sure I can find aviation bolts that are spec with holes. In aviation we safety wire everything.
     
  20. PA32Pilot

    PA32Pilot Formula 3
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    OP you have everything apart. Spend the $3500CAD and buy a Newman differential.
     
  21. turbo-joe

    turbo-joe F1 Veteran

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    aviation uses metric sizes?
     
  22. PA32Pilot

    PA32Pilot Formula 3
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    A lot of modern composite planes are built out of the US. Diamond aircraft are based and designed in Austria.
     
  23. Newman

    Newman F1 World Champ
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    Countach crown gear bolts are safety wired. I look at it like this, even the loose grade 3 bolts with lock tabs usually don't fall out. It happens but rarely. I think its more likely that a head would fall off an OEM bolt and with grade 12.9 bolts and loctite I don't see one falling out ever.
     
  24. pshoejberg

    pshoejberg Formula 3
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  25. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
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    Yes they are, hence the idea. Countach differentials seem to have no issues, but the differential case is ready for tractor duty.

    My Newman diff is still sitting on my desk waiting for my next TR major. Soon...
     

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