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Knocking Input Shaft Bearing, Repairable?

Rolls
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Rolls Grand Master

Rolls

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So my input shaft bearing started knocking badly last night, I am planning on rebuilding the box with the help of a mate (has done them before) replacing it and the other 3 main bearings as the box whines a bit.

If the race has completely shit itself will it have sent metal through the whole box meaning it is only good as scrap metal? Or does it usually contain the failure and make repair possibly?

I am going to dump the oil tomorrow and see if theres any chunks coming out, if not though I guess I won't know the extent of the failure until I pull it apart.

How many guys here have replaced a failed input shaft bearing and found no further damage? The knock is reasonably bad and went from being ever so slightly noisy to being f**ked within about 2 seconds.

Risking Grand Master

Risking

Posted
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How did you come to the conclusion its am input shaft bearing?

I don't think I've ever heard an input shaft bearing knock. I'd be more inclined to say your knocked teeth off a gear and that's causing the knocking noise as opposed to a bearing.

The bearings are encased in the bell housing casting and center plate so they can't exactly explode and fall apart. Typically the input shaft bearing whines.

Rolls Grand Master

Rolls

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It knocks identically in all gears and neutral with the clutch out, driving in all the gears also makes the same noise. clutch in and it is gone, it increases in revs with engine revs, imo it can't be anything BUT the input shaft bearing

Risking Grand Master

Risking

Posted
Posted

Lay shaft is also turning which is rotating tooth over tooth with the cluster shaft (nothing is engaged but in neutral with clutch out the fixed 4th gear on the input shaft must rotate the layshaft)

Broken gear teeth give a distinct knock as they run over each other. Which will increase with engine rpm as the layshaft is being rotated faster buy.

Risking Grand Master

Risking

Posted
Posted

Usually they strip a tooth or so then rip the whole lot of teeth off. The inertia that's slammed into the next tooth after a missing one is massive and they just get a domino effect.

It's not exactly hard to pull the bell housing off once the box is out to confirm what's wrong with it.

Rolls Grand Master

Rolls

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Just put a 25 box in. Not worth the head ache for a 20 box. Sounds like youve done serious damage.

Not at $1500 I can keep putting $200 noisy rb20 boxes and freshen up the bearings every 3 years for a long time! If you know of a 25 box in Adelaide that is less than $800 I would consider it though (never seems to happen) plus all the second hand 25 boxes my mates have put in have the same noisy input shaft anyway.

Risking I will be removing the box on wed and investigating what has broken, hopefully it is the input shaft as I have heard other people say theirs failed and starting knocking instead of whirring. I'm guessing if it is the lay shaft gear and metal has gone through everything it is a scrap job?

Will see if I can find anything second hand now in that case.

Rolls Grand Master

Rolls

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Last box lasted 3 years and it was untouched, my mate bought a noisy rb20 box for $200 and did the input shaft bearing for $80 on it, have it sitting in the shed as an option, there are only 4 other bearings in the box which add up to about $200 tops.

$200 vs $1500 for a 25 box that needs the same rebuild? How does $80 == $1300 ?

I don't plan on keeping the car more than another 5-6 years so forking out $1500 + tail shaft mods + rebuild doesn't really make sense imo.

Edited by Rolls
Rolls Grand Master

Rolls

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Pulled the box out and dropped the gearset and found 3rd was missing a tooth which was stuck to the drain plug.

Surprised it didn't get stuck and demolish the entire box. Guess time for a replacement box then! New gearset isn't going to be cheap, I know all my syncros are good though so will keep it for spares.

R31 POWER Mentor

R31 POWER

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Posted

I've been there dude, and i had a rb20. I know the extra price of a 25 box, modding gearbox mount, vl turbo/z32 yoke, speedo sender and modding tail shaft seems like a lot but it does pay for it self.

Scott Black Rising Star

Scott Black

Posted
Posted

or you could try this for not much more than the rb25 box would cost after you factor in mount and tailshaft
http://www.par-engineering.com/sections/products/products.aspx?typeId=gearsets&manId=nissan&sectionId=5

Rolls Grand Master

Rolls

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I've been there dude, and i had a rb20. I know the extra price of a 25 box, modding gearbox mount, vl turbo/z32 yoke, speedo sender and modding tail shaft seems like a lot but it does pay for it self.

Yeah I can see how if you keep the car for some time, this 20 box lasted 6 years though and I would be lucky to keep the car for another 6 years so the ~$1500 to do the conversion just isn't worth it so far when I can get a 20 box for ~400

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