gearbox overhaul

[goldnsx]

My gearbox seems to be dying on me. I'm at about 120k miles now. It sounds like a bearing failure (in neutral and at idle and with the clutch pedal up (so the mainshaft is turning) it sounds like marbles in the tranny, with the clutch pedal down it disappears). I guess it's the input shaft bearing at least. So I'm preparing a full rebuild over the winter season. Try to organize the parts in the meantime (from the US and Japan as some parts are discontinued in the US).
- new clutch (full kit 91)
- new big bearings
- maybe selected synchros and gear hubs
- maybe shift forks
- adding Type R diff plate
- gaskets and o-rings

All good with the gearbox except the noise and it popped out of 5th once. It has been rebuilt at 50k miles with new bearings and synchros (went with the shorties/4.23 then). So I don't know if I should replace everything all over again. This rebuild should last more than 100k miles. I know I'll only be able to inspect it in detail as soon as the box is open. But maybe someone can give me a hint what to change for sure. Thanks!

[NSXGB]

Definitely not the TOB?

[Pride]

Definitely not the TOB.

What does TOB stand for???

[The King]

What does TOB stand for???

Throw out bearing

[Pride]

Throw out bearing

In that case I'm assuming that NSXGB was asking the question as to whether it could possibly be the clutch release bearing because that's what I think it could be, they can get very noisy but not give gearbox issues that goldnsx describes.

[goldnsx]

Now I understand the post of NSXGB. :)
Well, I'm not sure if it's the TOB making the noise. It's still the first with 120k miles on it and it will be changed with the clutch for sure. What I've read is that the TOB is prone to make noise when the clutch pedal is pressed. But that's not the case. There is a slight vibration in the clutch pedal when pressed which is a sign that the TOB is not 100%. But the main noise is with the clutch pedal released. When driving at 40 mph in 5th (revs around 1500 rpm) it sounds like marbles in the gearbox. Above 2k rpm the gearbox sounds ok. So I'm pointing at one of the main bearings like the input shaft bearing which are prone to break on Hondas.

Either way, which the gearbox out I'm going to overhaul both: clutch and gearbox internals. Just not to have do it again in the near future.

[Pride]

Now I understand the post of NSXGB. :)
Well, I'm not sure if it's the TOB making the noise. It's still the first with 120k miles on it and it will be changed with the clutch for sure. What I've read is that the TOB is prone to make noise when the clutch pedal is pressed. But that's not the case. There is a slight vibration in the clutch pedal when pressed which is a sign that the TOB is not 100%. But the main noise is with the clutch pedal released. When driving at 40 mph in 5th (revs around 1500 rpm) it sounds like marbles in the gearbox. Above 2k rpm the gearbox sounds ok. So I'm pointing at one of the main bearings like the input shaft bearing which are prone to break on Hondas.

Either way, which the gearbox out I'm going to overhaul both: clutch and gearbox internals. Just not to have do it again in the near future.

Usually the only time the TOB makes excessive noise when worn out is when it's NOT depressed not when it is.
IMHO almost certainly TOB and when you rev over 2k the TOB bearing noise just becomes inaudible.

[goldnsx]

Usually the only time the TOB makes excessive noise when worn out is when it's NOT depressed not when it is.
IMHO almost certainly TOB and when you rev over 2k the TOB bearing noise just becomes inaudible.
Just for clarfication: not depressed = TOB under load?
The marbles can be heard with the clutch pedal depressed while normal driving in 5th gear at 1500 rpm (below 2k). So I might have two faulty bearings, maybe the TOB and maybe one in the tranny.

[Pride]

Just for clarfication: not depressed = TOB under load?
The marbles can be heard with the clutch pedal depressed while normal driving in 5th gear at 1500 rpm (below 2k). So I might have two faulty bearings, maybe the TOB and maybe one in the tranny.


When clutch pedal is depressed TOB IS under load but should be silent because the ball bearings are under load.

And when the clutch pedal is NOT depressed (released) the TOB bearings will rattle like loose "marbles" because the ball bearings are not under load.

The excessive marble type noises you hear at 1500rpm in 5th gear could be diff or backlash noises.
Have the noises got progressively worse over time???

[goldnsx]

The excessive marble type noises you hear at 1500rpm in 5th gear could be diff or backlash noises.
Have the noises got progressively worse over time???
Hard to say if it got worse over time. All I can say is that I've compared it to another NSX and the other one was silent either way.

[darock]

Cool Thread. My Gearbox also has some bearing noises. 160k Miles. Other than that it is totally fine. I will leave it like that for now. Will have to remove the engine any way some time in the future to replace the clutch. With just 3000km per season it will easily last another season :)

You can test if it is the input shaft bearing by pressing the clutch and wait until the gearbox is silent. Then really fast release and press the clutch again. No gear selected obviously. This way you will hear the input shaft spinning one or two seconds until friction stops it. With the clutch depressed there is no throwout bearing sound. All you hear are the input shaft bearings.

Bernhard

[goldnsx]

Thanks for the input and testing suggestion. The noise is there for some years now. I'm planning to open the gearbox next winter. I've ordered a bunch of parts yesterday. All main bearings will be changed. After having opened the gearbox I'll order a second batch of parts that need to be replaced too. I expect the countershaft bearing to be bad as well. I'll let you know what went wrong. Biggest obstacle now is to how remove the gearbox. I have an engine crane and plan to simplyfy mounting an dismounting by hanging the gearbox by the default hangers hoping they are the center of gravity of the gearbox. The crane will be used for lowering the gearbox, not to lift it over the rear end. :)

You have to order a second batch because there are shims and tolerances that need to be adjusted. The most expensive way is to order every available shim but this adds costs.

[darock]

Thanks for the input and testing suggestion. The noise is there for some years now. I'm planning to open the gearbox next winter. I've ordered a bunch of parts yesterday. All main bearings will be changed. After having opened the gearbox I'll order a second batch of parts that need to be replaced too. I expect the countershaft bearing to be bad as well. I'll let you know what went wrong. Biggest obstacle now is to how remove the gearbox. I have an engine crane and plan to simplyfy mounting an dismounting by hanging the gearbox by the default hangers hoping they are the center of gravity of the gearbox. The crane will be used for lowering the gearbox, not to lift it over the rear end. :)

You have to order a second batch because there are shims and tolerances that need to be adjusted. The most expensive way is to order every available shim but this adds costs.

Thats also what I would do.

Replacing the bearings. Inspecting all the other parts. Measuring the clearances and the shims. Buy the appropriate shims and other stuff needed. Perfect winter project.

I will do that during winter 2018/19. Taking the engine out. LMAs, Valve clearance, water pump, timing belt, clutch and gearbox.

Did the timing belt 2 month ago with the engine in the car and I know that I will NEVER do that again for sure.

Hope to see some nice pictures from your overhaul :D

Bernhard

[goldnsx]

I will be a one man project. Some pics are taken but don't expect a complete photo story. :)

TB: I understand your decision. Did you tilt the engine? With tilting it should be feasable. My TB will be in 2 years or so...planned to let it in the car. As you also speak German I might like to contact you about this...