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Loose diff and sheared bolt(s) on Indy 4900

Discussion in 'Maserati' started by Froggie, Apr 6, 2019.

  1. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Hi colleagues,

    While attempting to remedy to a small oil leak coming from the diff of my Indy (we though due to a dry seal because of lengthy storage), it was discovered that the crown assembly was loose and that at least one of the bolts was sheared/broken inside the crown:

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    The good news is that this was discovered in advance of using the car and that apparently the diff is not damaged apart from the bolt(s) and possibly holes.

    My mechanic will dismantle the diff and examine what are the ways to repair: replace with new bolts and/or enlarge the holes, etc.

    By searching in F-chat, I have discovered that the issue is feared in the community of Boxers/TR's and that a very similar situation was reported and analysed for the transaxle of a 308:
    https://www.ferrarichat.com/forum/threads/where-is-a-10mm-bolt-used-in-in-the-308-transaxle.43305/
    https://www.ferrarichat.com/forum/threads/bolt-failure-thoughts-hardcore-engineers-please.217673/

    My questions to the community are the following:
    - was such an issue already reported for the diff of Masers, in particular for the high torque V8 4900?
    - what in your opinion would be the best approach to safely repair/reassemble the diff?
     
  2. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Wow, 100 views and no comment?
    I would be surprised that never ever was a Salisbury diff loosening issue (and broken bolt(s)) noticed by owners of classic Masers.
    Or would I be the sole victim of a badly made assembly or of a defective bolt?

    If such issue was noticed and repaired, I would appreciate any info on the approach used, such as replacing all the bolts or only the defective one(s), sourcing OEM bolts or going for alternatives, eventually redrilling larger holes, etc.

    Thx in advance for the help
     
  3. AM101

    AM101 Rookie

    Mar 11, 2015
    9
    Hi,
    It is very difficult to suggest the best remedial action without inspecting the components.
    This fault is more common on ENV rear axles where access to the bolts is limited when tightening. The result is one or two bolts shearing as has happened in your case. The cause of the bolt breakage on the ENV is a fatigue failure due to insufficient tightening of the bolts, leading to increased cyclic stress loading.
    Failure on the ENV sometimes results in catastrophic failure, or has also been known to cause more rapid wear as the crownwheel flexes so after a few months irreparable damage has been done and a new crownwheel and pinion are required
    The least you need to do is replace all the bolts, as they will have all been stressed beyond there elastic limits. The fit of the bolts must still be good in the crownwheel, if not then a new crownwheel and pinion needs to be considered, and the threads in the diff carrier must also be examined for the same reason.

    Regards,
    Mark
     
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  4. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Mark, thank you very much, I appreciate your reply.
    I have now come also to a similar thinking from the thorough reading of the two threads in link, even though I am not a mechanic.
    Also just learning what an ENV differential is...
    I have understood though that my diff is a Salisbury and can be disassembled for easier repair, a good point then!

    I have asked my mechanic (as I am unable to do such a job myself) to closely examine the bolts and the fit in the crownwheel to see if there is more damage than what was already observed, hopefully not.
    I hope also that OEM bolts can be sourced, otherwise it will be more challenging.
    Of course, if there is more damage in the crown or the spider disc, it will be even more complex, requiring new drilling and bolts...
    At least, the visible parts of the crown and pinion looked in good condition.
    Fingers crossed.

    I am still very surprised that apparently the bolts were not torqued to spec by the factory...
     
  5. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Bad news...

    The diff was disassembled by my mechanic and it turns out it was butchered in the past: it was badly reassembled using a number of shims (now destroyed) between the rounded seat at the base of the disc axle and the conical bearing that should directly seat on it:

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    That of course could not work properly and was probably the cause of wear and fatigue.
    The axle is now worn out and the bearing is moving on it...
    So at the very least, a rechroming of the axle should be made and new bearings sourced.

    In addition, because of such fatigue, the holes in the disc are not round anymore and should be redrilled and maybe sleeved.
    The surprise is that only one bolt was broken, though certainly all of them will have to be replaced because of the increased cyclic stress loading.

    The alternative would be to source a new diff, possibly an LSD...
     
  6. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    25,752
    Austin TX
    Full Name:
    Brian Crall
    Excuse me if I'm wrong but it looks like a common Dana Spicer 44/45 differential. It was used in a lot of things in the USA and Europe like Jeep products among others. I'd contact someone like Yukon Gear and see about getting a new carrier.

    I would get ring gear bolts at the same time and throw those lock tabs over the side. Italians love lock tabs but torquing a high torque fastener through a hardened piece of steel, threaded into another piece of hardened steel and putting a soft lock tab into the sandwich is a terrible piece of engineering. It assures that bolt will not retain clamping force and break. Happens in Ferrari differentials with regularity. If there is concern about the bolt remaining tight, that is why Budda invented Locktite.

    You will need a case spreader to properly set the bearing preload. They are not expensive and can sometimes be rented. Job cannot be done properly without it.
     
  7. GrifoS2

    GrifoS2 Rookie

    May 20, 2007
    29
    Dana is different, but you can take parts from Jaguar diff,
    I had Salisbury Powr-Lok limited slip differential installed to Ghibli SS rear axle, it is from 1975 Jaguar XJ12.
    We also changed ratio from 3.54 to.3.31.
     
  8. AM101

    AM101 Rookie

    Mar 11, 2015
    9
    Thank you for the update, and sorry that you have such a damaged differential.
    It can be a common misconception that previous work carried out on our vehicles in the last 50 years has been carried out correctly, in my experience it is usually not the case. If you are lucky to have a car with a known history that has not been touched for 50 years you must also remember it is now well beyond the designers original service life.
    Rifledriver is correct that the lock washers fitted are the weak point, being made from mild steel. These over time crush, and reduce the pressure from the torqued bolts. From my experience with ENV axles the common wisdom is to remove the lock washers, loctite the nuts (they use nuts and bolts, not the threaded holes as in Salisbury) then drill, and wire. I do not suggest this is the best course of action, just an alternative. For the use we give the cars, if not raced then the original set up should be fine.
    The bolt breakage is caused by the axial loads caused by the crownwheel flexing hammering under the head of the bolt, hence the usual one or two broken. It is unusual for the radial loading to shear all the bolts.
    Regarding your axle I would suggest sourcing new/ good used parts especially if they are common to Jaguar. I am sure experts racing cars with Salisbury differentials could suggest the best way to build one up.
    Regards,
    Mark
     
  9. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Thank you again for your helpful comments.
    @Rifledriver: I understand that Dana44 diffs are very similar to Jaguar diffs but that the latter are considered stronger, in particular with thicker bolts
    @GrifoS2: interesting to know that you successfully installed a Jaguar Powr-Lok LSD to your SS, especially knowing that these items are not that rare in UK.
    So that means that the Jag/Salisbury Powr-Lok diff can withstand the high torque of the 4900 V8, a good point!
    I read that there are 44HU and 44 HA models, dunno what are the differences and whether both fit dimensionally in the Maserati diff casing. I will ask to my mechanic (italian classic cars), hoping he has experience of these...
    My current crown/pinions setting is already a 43/13, so a 3.31 (was standard on European 4900 Indy's), better I think to avoid too high rpm's
     
  10. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    I have now sourced a Salisbury 4HA Power-Lock (or Pwr-Lok) diff that was reconditioned by a Jaguar diffs specialist.
    In principle that diff should be a straight fit in the Salibury casing, subject to careful shimming to ensure the correct pre-loadings.
    It has 45/45 ramping angles that should be suitable for spirited road use.

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    The Jaguar workshop manual for E-Type's provides all the required infos for assembly using the case spreader and backlash clearances dimensions to ensure the correct pre-loads.

    Of course new 12.9 bolts will be necessary to fit the crown ring on the diff and new bearings also.
    @Rifledriver and @AM101 , I will discuss with my mechanic the possibility to avoid the lock tabs and use Loctite instead, seems to me a good advice. Drilling the bolts to safety wire them may be quite difficult however as the heads are not that thick...
     
  11. Froggie

    Froggie Karting

    Sep 27, 2017
    160
    Belgium
    Just discussed with my mechanic.
    It was agreed to not put the mild steel lock tabs.
    It was decided however to insert washers of hard steel to better spread the load between the bolts and the carrier.
    And to put Loctite!
     

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