Gearbox Or Clutch?

[BMX666]

So I've developed a problem in my C34 series 2 rs4s. When changing from 1st to 2nd and 2nd to 3rd at high revs it seems to grind/crunch. It's worse 1st to 2nd than 2nd to 3rd. Not sure if it does it 3rd to 4th as I'd be doing about 160km/h at that change and public roads tend to not let you go that fast haha. Just cruising around town with normal changes there is no issue whatsoever. I don't notice any clutch slippage at all. Any ideas from anyone would be great. Syncro's or clutch?

[KiwiRS4T]

Its not a slipping clutch that would cause a problem but lack of disengagement. If you are sitting at rest in gear and you let the pedal up slowly does it bite very early or come up quite a way? If it bites too early check for fluid levels and leaks. If its ok most probably your synchros are worn.

[wolverine]

Synchros.

What clutch are you using out of curiosity?

[BMX666]

It bites fairly early. I had the clutch adjusted by a workshop when they did a full service on it about 8000ks ago as I was making a weird noise. Now that I think of it the box was doing a similar thing then but nowhere near as bad. The noise and crunching/grinding went away after a few weeks. The concrete in the carport is bone dry so I don't think it's a leak.

As for what clutch is in it, I have no idea and there's a longish story that goes with that which ends with me still not knowing what clutch it is. I'll hazard a guess and say stock or something similar.

If synchros, what would be the fix? Full box rebuild? Or can you just replace synchros and freshen up the rest?

Also, why would it be completely fine one day then start doing this the next? I could understand if I was smashing through gears and missed a change that resulted in grinding a gear but I haven't done that at any time around the issue developing.

Cheers guys.

[C34S2STAG]

Depends on the teath on the gear it self that the selector goes over. The more you drive it the more it damages it. How many kms has your car done?

[BMX666]

It's just ticked over 100,000. I'll be buying the kit and getting the service done soon.

[wolverine]

The synchros in the Stagea settled down after I pissed off the cushioned button clutch and changed to an NPC organic.

There is some talk that you can load it up in the gear in question and gently slip the clutch off the line to de-glaze the synchros but I have no idea is this is an inspired or stupid idea. If it works it certainly saves a box R&R.

[Raysboostin]

Definately syncros. Its only gonna get worse over time. Its rebuild time unless u want to roll the dice on a 2nd hander. If u want them to last longer u may want to take up granny shifting and no more high rpms.

[BMX666]

As I said it's done it before (not quite this bad) then stopped and it's been fine for ages until now.

A gearbox rebuild is not the next mod I had planned!! Haha. If it has to be, it has to be I guess.

Might take it to a mechanic or gearbox joint if it doesn't settle down over the next couple of weeks.

Thanks guys.

[BMX666]

Does anyone have a rough estimate on how much a rebuild would be worth?

[RS4-S]

I had the clutch adjusted by a workshop when they did a full service on it about 8000ks ago

Had it adjusted???

Does it say what oil they put in your box? Could be the issue

[BMX666]

By adjusted I mean I asked them to diagnose/fix the clutch noise while they were doing the service. They couldn't diagnose the noise without dropping the box out to actually inspect the clutch but did find that the free play was all up the shit so they adjusted that. I believe that was pretty much what the invoice said. I'll try and find the invoice tomorrow (am at work atm) to check what fluid they used. I believe it'd be right tho as they know their turbo cars. They get a lot of Skylines through and specialize in Subaru's.

[pipster11]

you should probably change the gearbox oil at 100,000kms anyway

get something good and synthetic and it may help keep them going

also, making sure that the revs are matched between shifts will lessen the crunching too as the synchro's will be working less

edit: probably don't use redline as its been known to glaze synchros from over-lubrication

Edited September 26, 2012 by pipster11

[BMX666]

So I found the invoice and they defintiely drained and replaced the gearbox fluid. Valvoline 75W-90 is what went in I believe. And that was only about 8-9000ks ago. I guess i could get some Redline and throw that in to see if it helps. From what i've been reading (in the skyline section and other places on the interwebs) that's what most poeple are saying to do. As for Redline glazing the synchros from over lubrication, if they're already fu@#ed I don't see the harm.

Keep the ideas coming if there is anymore.

Thanks

Edited September 27, 2012 by BMX666

[pipster11]

http://www.toymods.o...proof-r154.html

I'd read that first

and from redline themselves:

LightWeight ShockProof™

A unique gear oil designed to lubricate racing transmissions and transaxles which see serious loads (not recommended for most syncro-type transmissions)

Edited September 27, 2012 by pipster11

[Daleo]

you should probably change the gearbox oil at 100,000kms anyway

get something good and synthetic and it may help keep them going

also, making sure that the revs are matched between shifts will lessen the crunching too as the synchro's will be working less

edit: probably don't use redline as its been known to glaze synchros from over-lubrication

I have worked in an engineering trade for over 20 years, and have never heard of this "Glazing" of synchro rings. Frankly it sounds like bollocks to me.

Can you provide an example (not just an anecdotal forum quote from an unconfirmed source) of how lubricating oil can cause the surface of a toothed bronze ring to "glaze"? And why would this "glazing" prevent a bronze ring from engaging with a steel gear.?

Using an oil grade that's too thick can cause synchro issues (much like cold oil in a gearbox) but the number of people who swear by Redline Lightweight Shockproof in Skylines and Supras (both well known for being notchy) suggest that this alleged "glazing" might just be a wives tale.

The synchro ring is essentially a freewheeling gear on the shaft, and it assists the gears in matching speed before engagement; if it is effectively locked to the shaft by a very thick oil film; it doesn't work properly.

Also, as they wear (being bronze; they are designed to) they lose their sharp edges and this also reduces their ability to engage. This is also a source of engagement noise.

The lighter the grade of oil; the better synchro engagement (less crunching) will be; go too light, and you lose the damping effect of the oil and the gearbox will be noisy. Shift action will improve.

Go far too light and the oil can't protect the metal components in the gearbox, as the oil film gets forced from between the metal surfaces, polymer chains get broken down, excessive heat gets generated and components wear prematurely.

I'm not trying to give you a hard time Tom, but bad information is just as useless as no information at all.

[pipster11]

No worries mate, glazing is probably the wrong word but i'd heard tales of redline helping synchros and others saying the opposite

pretty much all of that previous information was regurgitated from the toymods thread

with the exception of the excerpt from redline about not using in in synchro boxes

a lot of the toymods guys were rating castrol vmx80 as being much better than previous oils

[C34S2STAG]

Redline kills syncros

[BMX666]

Read and taken under advisement. That's one negative experience against quite a number of positive ones. I think my point is still valid tho. If the synchros are screwed and it requires a rebuild, what's the harm with throwing some Redline in? I'll do some research and see what I come up with.

[wolverine]

Redline lightweight shockproof screws synchros eh...really?

I must be driving a miracle R33 for >200,000km