F355 (5.2) Gated Manual Gearbox 2nd Gear Issue | FerrariChat

F355 (5.2) Gated Manual Gearbox 2nd Gear Issue

Discussion in 'Technical Q&A' started by Qavion, Apr 23, 2022.

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  1. Qavion

    Qavion F1 World Champ
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    #1 Qavion, Apr 23, 2022
    Hi, folks
    I thought it was about time I moved this problem to the Tech forum (from the 348/355 forum) as I'm getting desperate.

    About 4 years ago, I had a gearbox mainshaft bearing failure, which damaged the mainshaft and several gearsets (4th, 6th and, I believe, 2nd). I suspect the damage was caused and hidden by previous owners as when the gearbox was opened, there were less broken bits and pieces in the bottom of the gearbox than there were missing from cogs.

    My tech replaced the mainshaft and mainshaft bearings. The broken gearsets were replaced. The synchros for 1st, 2nd and 3rd were replaced. Of course, all the gearbox components were inspected for damage. All the replaced items were new. The clutch was also replaced. U$20,000 in total.

    3~4 years later, but less than 1000 miles, I noticed that my gearlever would jump out of 2nd gear (hot or cold). I noticed that it was getting harder to engage 2nd (even when warm). I had the linkages adjusted a few days ago and selection became much. much easier. However, it is still jumping out of gear. When I tried to stop it jumping out of gear, there would be a loud clashing of gears (and I had to let it jump into neutral or I think the box would have destroyed itself).

    Would anyone have any suggestions on what might be broken? It was suggested that it might be "dog-teeth, otherwise known as syncro hub, and slider", but I'm not sure what these components are.

    Why would the gearbox suddenly decide it doesn't like second gear? What keeps the gearbox in a particular gear other than the gear lever?

    Thanks!
     
  2. wmuno

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    #2 wmuno, Apr 23, 2022
    The linkage adjustment is the correct place to start. Small adjustments to the length and/or the angular rotation can make a big difference in how the gear box shifts. Also, internal to the gear box are detents on the forks. There is a spring with some type of ball or roller that keeps the forks in position as they move foreward and backward. A weak, broken, or missing spring might be the source of your problem.
     
  3. Qavion

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    #3 Qavion, Apr 23, 2022
    Interesting. Thanks Bill. I'll try to find these in the parts manual.
     
  4. Qavion

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    #4 Qavion, Apr 23, 2022
  5. yelcab

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    #5 yelcab, Apr 23, 2022
    The inability to shift into a gear, and gearbox staying in gear can also be worn out slider, dog teeth (syncro hub), or bad syncro (even new) that was not in spec when new. You did not say that the 2nd/3rd slider and 2nd gear dog teeth were replaced. Perhaps they should have been ...
     
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  6. wmuno

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    #6 wmuno, Apr 23, 2022
    Look at Part 23; these fit into the section that is in light gray. This might be the ball and spring assembly that fits into the detents that are shown on the rods to which the forks are attached.
     
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  7. Qavion

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    #7 Qavion, Apr 23, 2022
    No sliders or dog teeth were replaced. I assume all the parts were inspected before installation because of all the broken bits floating around.
    Are the slider and dog teeth parts #15 & #14 and in the diagram below?

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    Item 15 (P/N 161015) is U$181 new (if available). Item 14 (P/N 161015) is U$222 (if available). The smaller parts are a few dollars each (20, 19 & 18). Of course, most of the cost is in labour.


    #23 is just labelled a "pin".

    1 x item 42 in the post #2 (upper diagram) was replaced for cosmetic reasons (it contacted the ground at some point). I don't know if this part was replaced after the gearbox was assembled.
     
  8. Steve Magnusson

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    #8 Steve Magnusson, Apr 23, 2022
    Last edited: Apr 23, 2022
    No, #15 on that SPC page selects 3rd gear or 4th gear. #12 on the Lay Shaft SPC page is what selects 1st gear or 2nd gear:
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    so same sort of issue -- is #12 misaligned because of some sort of upstream shifter linkage foo, or is something wrong in the mechanism for moving (and holding) #12 in place (but, for that, it's usually something wrong/broken in the little #15, #16, #17 pieces rather than something wrong with #12 or #10 themselves)?

    PS Have to give F some documentation praise for putting the gear number labels on the gears themselves in the figure ;)
     
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  9. Qavion

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    #9 Qavion, Apr 23, 2022
    Ah, thank Steve. I missed that.

    That's the big question. I guess there's only one way to find out... pull the box to pieces again.

    I should have taken closeup photos of the individual components instead of a group shot:

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    Are the items in the bottom right hand corner of the photo below the sliders (dog rings)?

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    They look like they are wrapped new items. Perhaps these were changed. Although, I only see two there, not four.

    The workshop manual goes into great detail on gearbox assembly. I'm not sure if anyone in Australia has the expertise and tools to do this kind of work. There are about 50 specialist tools listed in the WSM.
     
  10. Qavion

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    #10 Qavion, Apr 23, 2022
    I really recommend that all PPI's should include the pulling the gearbox mag plug... You never know what surprises you may find...

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  11. yelcab

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    #11 yelcab, Apr 23, 2022
    Those brass rings are not sliders, me thinks. Taking pictures alone is not inspection. You pull out the calipers to inspect the syncro at installed positions. You look at the inside of the sliders to see what is worn out. Normally, if you replace gears, you also replace syncros and sliders because you are paying for expensive labor just once.
     
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  12. yelcab

    yelcab F1 World Champ
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    #12 yelcab, Apr 23, 2022
    Oh damn. If I see that big of a piece, I would take $15,000 off the price.
     
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  13. Qavion

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    #13 Qavion, Apr 23, 2022
  14. Steve Magnusson

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    #14 Steve Magnusson, Apr 23, 2022
    +1 -- but that's not enough of a $ discount ;). Even the smaller chucks still held on the magnetic plug in that photo are really unacceptable/un-ignorable, and such a gearbox should never continue to be used before investigating/repairing. Only a small amount of very fine (steel) material (coincidentally known as "fines") should be on the magnetic plug -- it's like a finely-ground (usually black-appearing) paste that you wipe off -- no chunks allowed!
     
  15. Qavion

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    #15 Qavion, Apr 24, 2022
    Sooo.... we assume, wear and tear, misadjustment, broken pieces, etc are stopping the following sequence.....

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    1) the gear lever control rod (#9) rotating the 1st/2nd GEAR CONTROL ROCKER ARM (#2) which contacts the 1st/2nd ROD CONTROL SMALL FORK (#32) which moves the 1st/2nd CONTROL ROD (#14) which moves the 1st/2nd GEAR SELECTOR FORK (#20)
    2) This prevents the SELECTOR FORK (#20) moving the SYNCHRONIZER SLEEVE which engages with the SYNCHRO which engages the 2nd GEAR PINION.

    Prior to my tech adjusting the control rod, 2nd gear seemed to put up a lot of resistance to engagement (irrespective of gearbox oil temperature). Sometimes it would feel like 2nd gear was engaged, but when you looked down at the gear lever, it was only 3/4 into the gate. I don't know if this is a clue.

    My tech took about a dozen tries at getting all gears to engage properly by adjusting the lever gear lever linkages. The sweet spot was really difficult to find. I don't know if this is a clue.
     

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