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Thread: My gearbox revision thread

  1. #1
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    Default My gearbox revision thread

    The input shaft of my gearbox (totally 190k km but revised with short gears/4.23 at 80k km, so untouched for the last 110k km) makes some noise at idle with the clutch pedal up and the 5th gear was making some kind of the sound of marbles at 1500 rpm cruising around.

    First taking the gearbox out. Special thanks to Sylvian for borrowing me his lift.

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    Opening the box, at first sight:
    - snap-ring ok
    - countershaft bearing (the one at the snap-ring) ok

    Not sure what to think about the gears. There are spots and even rust ??? on them? I didn't lend my car to 007 for diving in the sea...

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    5th gear: mysterious signs of wear. I've to admit that it popped out on the German Autobahn 2-3 times but that was back in 2008 or so. Something is wrong here. Of course, I use the 5th gear a lot (a lot of cruising). Opinions?

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    I already have new main bearings and all synchros for sure to go in. Will do a lot of measurements by the SM tomorrow.

    Expert advice warmly welcome, thanks in advance!

  2. #2
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    Default

    Reverse gear synchro teeths. While the synchro ring looks good the reverse drive gear looks strange. The sleeve looked ok. I've compared it to another gearbox we did in the past and it looked about the same.

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  3. #3
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    Default

    Hi, goldnsx.

    As you went for the final ratio change, you were forced to replace the countershaft, final driven and oil pump. I presume you replaced the countershaft bearing at that time.

    With the short gear ratio, you were forced to replace the mainshaft (main 1st, reverse, 2nd directly machined on it), counter 2nd, main/counter 3rd & 4th gears.

    I don’t know the base gbox no. of your NSX but looks like there is no washer between the main 2nd/3rd gears so I believe you got the later spec mainshaft which is good.

    I'm afraid that main 5th gear needs replacing.
    As it looks like you are replacing all of the synchro related parts, not much to say but that damage is the typical sign of driver accelerating to the limit in 4th gear and then quickly shifting up to 5th.
    As you opened the gbox, you will notice that compared to the 3rd and 4th synchros (both using the same capacity), 5th one is much smaller for some reason and that is the main reason for the damage.
    Addition to this, the inertia of the CL will play the big part against the synchro capacity but I'll leave it for now.
    Just a matter of interest, what CL were you using when you first noticed the 5th gear issue?

    I can't tell the spec of your 5th shift fork.
    Could you take the photo of it to show the shape of the craw/fork?
    Honda did change the shape/spec of this fork as there were some reports of broken 5th fork in the past.
    Since you opened the gbox, best to replace it if you are using the old spec one.

    I believe you selected the proper shim thickness for the new mainshaft but may want to double check it.

    What MTF were you using?

    Personally, I don’t like the Honda own synchro design without the synchro key but no options…..


    Kaz

  4. #4
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    Default

    Kaz, thanks for your reply.

    Back in 2005, my tranny (1003042) of my 1991 was built with new bearings, FD4.23, new mainshaft, new countershaft and short gears 2-4 (1st and 5th not changed), new synchros and main bearings and new snapring. I always had the OEM twin-disc clutch kit, being the first one, so will replace it now too. Always filled with MTF III, changed every 20k km.

    I only have a bad picture of the shift forks but they never have been changed so far. EDIT: I've measured them and they are about 0.05mm thinner than the standard. The clearance between the shift fork and it's corresponding sleeve is still within specs (around 0.60 mm). Service limit would be 1.0 mm, so I think they're good to be used again.
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    Thanks for the hint for the 5th fork failures. Is the newer design interchangeable with the old one?

    I just got home and am still upset (and depressed too) because something is wrong with the countershaft I've been working on today. I'll have no sleep tonight...
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    I've changed the 1st/2nd synchro/hub/sleeve as a complete set. Before, I've measured the clearance between the 2nd and the 3rd gear (according to 13-30) and found no play at all but the 2nd gear was turning. The standard clearance is 0.04-0.10 mm. I've pressed the 3rd gear onto the shaft and now the 2nd gear is NOT turning, neither so the synchro ring (this are expensive new parts!). The synchro also looks too far of the gear. Now, it looks like the 2nd gear synchro is pressed and it that's the case it's damaged I think. If I'm lucky the spacer collar is just a tiny bit too small.
    In the first two pics is the 1st/2nd gear hub/sleeve. One side is 6.5 mm deep and the other is 7.5 mm. I've installed it the way the old one came out and backed up the the installation with the pics I've taken before. The tiny groove on the outside (pic 3) is towards the 1st gear. The SM doesn't mention anything about that.

    I'll need some motivation before I go on working on it...

    Thanks for listening.
    Last edited by goldnsx; 28-12-2016 at 06:18 PM.

  5. #5

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    Hi,

    Honda 5th Fork change

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    Left Old
    Right New
    Last edited by ozon02; 29-12-2016 at 09:28 PM.

  6. #6
    Join Date
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    Default

    Quote Originally Posted by ozon02 View Post
    Hi,

    Honda 5th Fork change:

    Attachment 12780

    Left Old
    Right New
    bad pic link.....
    aka Jonathan!!

    '92 charlotte green auto.... as a daily
    '37 Ford Y street rod......... something for the weekend!

    ...... if a photobucket pic is foggy, click it, and it'll take you to the clear version, yes, it's a clicking faff....

  7. #7
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    The mystery with my 2nd gear has been solved.
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    The new synchro ring was damaged while pressing the 3rd gear on the shaft. Even after doublechecking every step and consulting the manual (and my brain) it must have misaligned when I was fidling with the 3rd gear. I regard it as bad luck or as a puncture in a new tire, it's only money... I'll get a new one. I testfitted the third gear and there's a space of 0.05 mm between 2nd and 3rd, that's fine.
    I'm glad that no other parts were damaged.

    The hub/sleeve story ended like this: there are small pictures (on the left) in the exploded diagram. By most of them you have to think about a minute or two what area they could refer to and what they are willing to tell you. I don't blame the SM but I guess I was expecting a note or a word of caution. Anyway, it was installed correctly.
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    Mainshaft adjustment
    I was verifying the selected shim(s) that the former installer choosed. It had two shims in it (1.00 mm and 0.65 mm = total of 1.65 mm) with the old mainshaft assembly. There's a note in the SM that you should NOT use two shims (I don't know why and the former installer didn't care). I've removed the ISB and measured:
    Averaged 2.35 mm - 0.12 mm (bearing higher than case) - 0.99 = 1.24 = max shim. ...-1.06 = 1.17 = min shim. So it needed 1.20 but it had 1.65 mm. Not sure but that's my guess why my input shaft bearing made noise. Both main bearings are still fine but under too much pressure. Comments are welcome.

    Question of the day: I need a 1.20 m shim and the thickest shim in the parts catalog is 1.15 mm. Should I install 2 x 0.60 mm? Is it really important to check the mainshaft clearance with the special tools where you pull on the mainshaft and check if the clearance is 0.14-0.21 mm (page 13-42)?

    Another question: how to get these two babies out?
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    The oil seal is already out.
    Last edited by goldnsx; 29-12-2016 at 06:16 PM.

  8. #8

    Default

    Hi Goldi,
    I have SM from USA (Acura) is writen:
    "Do not use more than two thrust shims" (ist geschrieben)

  9. #9
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    Yes, that's what I've read in the SM too but I'd like to know what the reason is. The former installer took two shims and he did a lot of NSX gearboxes. I don't see a reason against using two shims.

    As the bearing I measured with was used for 110k has more play than a new one (actually even a new one has some play built in), I guess that the clearance will be reduced with a new one. If it's reduced by 0.20 mm I can go with the 'standard' shim (1.00 mm). But I'll have to measure again as soon as the mainshaft is rebuilt with new parts.

  10. #10

    Default

    as I understand you write two issues:
    1.
    "makes some noise at idle with the clutch pedal up"
    2.
    "the 5th gear was making some kind of the sound of marbles at 1500 rpm cruising around."

    1.
    may be ball bearing in flywell issue?
    2.
    I would go in the direction of Kaaz mentioned

    and I am doing all the measurements according to the instructions (needle bearing surface etc.)

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