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Rb20 box, cold = bad, warm = :D

dangerous_daveo
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dangerous_daveo Grand Master

dangerous_daveo

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Ok, what I would think to be a really odd sort of problem.

Good old RB20DET gearbox, its got brand new bearings in it, and when all that happened the sincs were also deglazed, and in general I was given a gold medal for my gearbox (selector broke, hence the semi rebuild, much cheaper to do both at once). So going by that its is NOT sincs.

Anyway, the problem is the gearbox is horbile until the car is warm (ie, 30mins or so of driving) and the gears mostly 2nd & 3rd crunch rather badly, more so 2nd on down shifts. (3000rpm, will not go in to 2nd at all). You can all so feel it being a bit notchy on the other gears.

Then once it is warm, it will do whatever I like fairly easy. Still isnt too keen tho until about 1-1.5hours of driving.

So, today the gearbox oil was changed, this makes the changes smoother once its warm, and the whole feel of the box better, but didnt do bugger all to stop this crunching.

So my question is, what the hell could it be!?

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dangerous_daveo Grand Master

dangerous_daveo

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We put in some fancy pants motul stuff.

I dont see how it is "tired" tho when its been basically rebuilt other than the syncros as they were in tip top shape.

My point is after 1hours driving or so, not even giving it any, just sitting at say 60-80kmh its 100% fine, no crunch or anything. This is what made us think it was the oil, as its still crunching even after fancy pants oil, its got to be something else, just using logic and process of elimination.

someonestolecc Grand Master

someonestolecc

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But with a semi-rebuilt gearbox that daveo described he should be able to put in servo gearbox oil and still be ok.

Daveo is it possible something wasn't installed back in correctly ie. bearings in clutch, mis aligned clutch plate etc? I guess this wouldn't make sense that it's ok once warm.

Just out of interest how much did you pay?

dangerous_daveo Grand Master

dangerous_daveo

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But with a semi-rebuilt gearbox that daveo described he should be able to put in servo gearbox oil and still be ok.

Daveo is it possible something wasn't installed back in correctly ie. bearings in clutch, mis aligned clutch plate etc? I guess this wouldn't make sense that it's ok once warm.

Just out of interest how much did you pay?

It was $900 all up including labour to take and put the box back in, and also the 5th gear selector fork. But as they had to pull the box apart anyway for the selector it would be approx the same.

But anyway, back on to the topic in hand. We igorne its the bloody oil ok. As WHEN IT IS WARMED UP IT IS OK!!! The gearbox is smooth other than that crunch. After thinking about it a bit more today i noticed its almost like a switch, it does it, then gets to a point and goes away. It doesnt creep up getting better. (or so I think, it could be me just hear CRUCNH, then I shift like a full on pansy for the next 30mins)

R31Nismoid Grand Master

R31Nismoid

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im thinking it wasnt rebuilt right either if you say everything is new.

either that, ot the new parts in the worn box... ie shafts and stuff would be worn somewhat... it just needs to warm up that little bit.

one way around it i found, was to revmatch it on a change. Rather that just changing willy nilly till its warm. Worked for a while for mine till it got really sck

dangerous_daveo Grand Master

dangerous_daveo

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im thinking it wasnt rebuilt right either if you say everything is new.

either that, ot the new parts in the worn box... ie shafts and stuff would be worn somewhat... it just needs to warm up that little bit.

one way around it i found, was to revmatch it on a change. Rather that just changing willy nilly till its warm. Worked for a while for mine till it got really sck

Still crunches rev matching, as I almost always do that anyway.

I had a thought today that maybe its the clutch over extending, and when it warms up the clutch line expands more therefore canceling out the over extention? Im going to get it back in next week try and get an idea on what the hell is going on with it.

  • 2 weeks later...
dangerous_daveo Grand Master

dangerous_daveo

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Just a quick bump with for this with some new info.

mechanic has had a bit of a play and a drive, and he seems to think it would probably be the gearbox. And more specifically the 2nd gear syncro being too tight.

Now my question is how/why does this happen??? Such as would the rebuild have caused this, or is it just something that can happen.

2nd question, is there a 'band aid' fix for this problem? Such as thinner oil, some kind of additive etc? Or even something so the box just warms up quicker to lessen the time I cant get it in to gear.

Roy Grand Master

Roy

Posted
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Serious suggestion this time...about 2 years ago i thought my gearbox was dead as it was having trouble shifting into gear. Turned out it was a broken gearbox mount that was causing me drama when shifting...since your box has been freshened, it could be one of those silly obvious things that hasnt been checked:)

dangerous_daveo Grand Master

dangerous_daveo

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Serious suggestion this time...about 2 years ago i thought my gearbox was dead as it was having trouble shifting into gear. Turned out it was a broken gearbox mount that was causing me drama when shifting...since your box has been freshened, it could be one of those silly obvious things that hasnt been checked:)

Hmm yeah, could be... but would that really be effected by heat?

I mean thats what gets me, and should be a big giveaway to someone, once it heats up it is smooth as, shifts fast and fine, with NO crunches.

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