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Gearbox rebuild

JimX
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JimX Grand Master

JimX

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I just read Sydneykid saying in another thread that the gears on the RB25 and 26 box seem to be exactly the same strength-wise, just with different ratios. So that's $1000 extra just to change the ratios, doesn't look too appealing anymore :D On the plus side, the RB25 box is stronger than I first thought :(

I think I will need more advice from a gearbox specialist before I take the box out, just to find out what parts exactly I will need to replace and how much they will cost. And gearbox shops wanting to do the work themselves, probably aren't going to be too helpful :)

But I will definitely do a post up about it if/when I do drop the box myself.

Ronin 09 Grand Master

Ronin 09

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Seeing that the RB25 box is fairly common and would likely be put through a fair bit of punishment on tuned cars, aren't there strengthened synchros available? Reason being if you're going to spend the x-dollars on rebuilding the bugger you'd want it to last more than another 50,000k's. And again, i'm another skyline owner with stuffed 1-2 and 2-3 synchros... (they're not so much stuffed that they crunch, but they bauk quite badly when cold and it doesn't go away completely when warm) even redline isn't really enough

Cubes Grand Master

Cubes

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What is designed different that the R32 RB20DET box's don't crunch or you don't hear about them crunching as much?!?

I've done many a gearbox removals/installs/conversions in a pit.

Dropped an auto once when removing it and got auto trans fluid from head to toe and it was hanging with full weight by the kick down cable.. Couldn't believe it held actually.

The reason I dropped it is I forgot to remove the kick down cable, I realised this once I already had the box away from the motor. I then tried to put it back in when a little bit of trans fluid dribbled out hand slipped gearbox smacked me in the head and fell. Auto trans fluid then poored out of the torque converter. :)

Gearbox removals = lots of stress. Unless you have a hoist and a gearbox jack that jacks the gearbox up the the height of the car and you wiggle it in. No weight, no strain easy.... :)

I wouldn't even attempt it on car ramps. The tunnel hugs the gearbox tighter than you would imagine.

I fitted a 5 speed to my old VL NA 3ltr. I had to drop the engine mounts out just to get the thing hooked up. I then broke a couple of exhaust manifold studs in the process. Made it go better compared to the Auto, so it was worth it :D

Cubes Grand Master

Cubes

Posted
Posted

A hoist with a gearbox jack is nothing compared to working in a shoulder width pit.

Two people in there trying to fit a gearbox in to a tunnel that has been press fitted around the gearbox.. Well thats what it felt like with the VL any how. ;)

Yer it is a job that definately sucks though.

Busky2k Veteran

Busky2k

Posted
Posted

Hey there JimX, its probably not what you want to hear, but Heavyweight Shockproof wasnt really primarily designed to give you good shifting. Its bloody thick. Redline's MTL/MT90 are the fluids which help boxes with dead synchros.

I reckon you should give the MTL a shot before you pull the box out. And if it doesnt make enough difference to convince you not to pull the box, at least you can drain the oil and use it again when you get your box rebuilt!!!

Jetdat Veteran

Jetdat

Posted
Posted

I have driven dozens of r33's with various km's on the clock while i was searching for my r33 over an eight month period.

I noticed that all had similar shift problems, although some were more obvious than others. I came to accept that either the japs really hammered their gearboxes in japan and therefore the gearboxes deteriated prematurely or the skyline boxes are one of their weakness'.

After puchasing my r33 i immediately changed the oil to the forum recomended VMX80. I am very glad i did as the oil that came out of the box looked very gluggy and to my suprise was under 3 litres.

4 litres of VMX80 went in, and sure enough did help a lot, but learning to drive the skyline, that is changing gears at the right revs, having the seat at the right distance to the pedals and getting the feel to where each gear was the key to smoother changes.

I must say i am not a beginner manual driver, nor am i a newcomer to turbo and modified cars, but it took a while getting used to the skyline engine/gearbox combination.

My next step is to use the redline stuff as most of you have mentioned, and perhaps bleeding the clutch to make sure no air or water is present in the system.

What i still cannot comprehend is though, regardless of the ambient and engine temperatures the gear changes can be very inconsistent; i.e sometimes very smooth other times a bit rough.

I just wanted to share my experiences in the hope that it may help regarding this issue.

Thanks.

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