Gts25t Synchro Probs

[Dale FZ1]

Thread search here has not come up with heaps of information, so here goes:

Over 9 months of running I found two gearbox problems, normally only surfaced when the ambient temps were high >30 deg C and giving the car a squirt. Quick on/off throttle movements and/or changing gears at rpm >6000. The probs were only occasional and not repeatable at will.

First prob was it tended to pop out of 3rd gear on decel.

Second prob was it would occasionally baulk at upchange either 3-4 or 4-5, as if I hadn't used the clutch.

Changed box oil with 75-90 mineral oil, no change in box operations under the stated conditions. Original oil as it came off the boat did have some metal filing contaminants and was a bit dirty but not overly so.

Changed box oil with ATF for 1000 km trial. Did not experience baulks, but did get a couple of 3rd gear pop outs. This was during a South East Queensland winter (cool but not cold). Removed the AFT and returned to the Shell mineral gear oil, deciding that there may be an issue with detents and probably with synchros. Extra preload on the detent has given heaps better shift precision but a bit slower action. The baulking problem remains so I'm about to start planning a box rebuild pending a trial of Molybond additive.

Here's the question: given the differences between the RB25 box and either RB20 or RB30, are the seal/bearing kits and synchros readily available? Anybody with first hand experience I would be interested to hear.

Also other advice I've had suggests genuine Nissan synchros are made to more consistent tolerances with better results (if more costly). Any experiences here are also wanted.

cheers

[Mumbo#5]

I too would like to know if anyone has done it before...

[RANDY]

Mine is crunchy going into 2nd, more on the upshift from first to 2nd, but crunchy nonetheless. 3rd doesn't feel totally smooth on upshift, but is fine on shifting down to it. 1st and 4th are perfect.

It'd be interesting to see how much a synchro change would cost!

EDIT: Mine's an R33 s2 GTST also, with 160,000 on the clock.

Edited September 22, 2005 by RANDY

[Abo Bob]

Have you guys tried putting some Redline Lightweight Shockproof in there yet? It looks like smurfs blood.

That seems to fix heaps of skylines gearbox problems.

[Bl4cK32]

Ive enquired with Nissan how much for both a bearing kit, and how much for a full syncro rebuild.

From memory its about $450 for a bearing kit, and about $520 ish for the whole syncro replacement.

Most people i have heard only replace the syncros that are gone to keep the costs down. Me on the other hand, like the idea of a new fresh box.

If i could find a workshop manual with the gearbox in exploded view, i'd do the rebuild myself. It has the GTR one in the manual, just not the rb25det box

Anybody got a workshop diagram for the 25t box?....please<sniff>

And in my case, no an oil change wont help as the box whines on decelleration...bearings ar rooted!

[Dale FZ1]

Abo Bob I know/understand many people rave about the qualities of Redline products. I suspect that they really are very good, as well they should be at the cost. Smurf's blood? Is that stuff blue?

Basically my fault diagnosis has examined the value of replacing the oil a couple of times to purge contaminants. Even tried ATF just to see how a really light lubricant might work on suspect synchros. With minimal impact even with that (temporary) trial, I would say playing with brands of oil is likely to be an exercise in buying time. Having said that, the Molybond I put in the oil has made the change quality better.

I've bought this car to do a few track days per year, and if I can't expect that the box will change flawlessly at high rpm and temps in those conditions, it is painful to use only for gentle commuting.

I would replace the synchros that NEED replacing, but closely examine the condition of all to see if they were suspect at the same time. My bearings etc are not at all noisy but the idea in an overhaul is to disassemble/correct/avoid problems only once.

Any links to the necessary workshop manual would be great please.

cheers

[Russco]

Have you guys tried putting some Redline Lightweight Shockproof in there yet?  It looks like smurfs blood.

That seems to fix heaps of skylines gearbox problems.

<{POST_SNAPBACK}>

This seems to be an urban myth, I have personally tried redline in 2 boxes & while it fixes very minor cold change problems it will not help "crunches" where there is an obvious synchro problem. Better to save your $$ & get the problem fixed properly the first time i.e. replace the synchro.

[TokyoTaxi]

All the parts you need for your G/Box can be supplied from NISSAN. Some may have to come from Japan but that doesn't take long. You can even get a whole NEW G/Box through NISSAN !! But that will hurt your bank account a bit more than a rebuild.

I'm just about to get my G/Box ( RB20DET ) back from a full rebuild. All syncro's, bearings ( including the needle roller bearings from under the gear clusters ) and seals will set you back around $1,100 unless you've got someone on the inside RB25DET box will prol be a little more.

IMHO, if you're going to do something, do it right. The last thing you want to be doing is pulling the G/Box out in 3 months time cause some part that you decided not to change has died !!

I'll be going back to Redline Shockproof with this reco'd box as it's the best I've used so far. Currently using Castrol Syntrans ( I think ) and it's not as good as it was with Redline.

And F.Y.I. the syncro's in the 31 and 32 GTS-T G/box's are 3 piece and I'd be shocked if anyone else ( other than NISSAN ) sold them. Can't confirm the exact contents of an R33 G/Box but I'd expect it to be a very similar style of build ( just bigger and tuffer bits ).