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Cunching Syncros At High Rpm


NYTSKY
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Ive noticed that at high rpm my gearbox crunches a little into forth and fifth.I assume its the syncros.Is this a common problem? What would be the cost in getting this fixed?

CHEERS

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iv got the same problem at high revs in my s2 33 going from 3rd to 4th aswell, and once it has done it going from 4th to 5th, i went to a couple of places and they sed it might be cheaper to get a new box :P they say it a lot of work replacing the syncros ;) i brought up that changing the oil to redline will stop it but they sed it will just hide the noise and will result in the gearbox needing a rebuild down the track

i have yet to go to a few other places and suss it out :huh:

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I had a similar problem in my 33. Was crunching slightly going into second and third... i put in Redline Shockproof (yeah the blue stuff... red bottle if i remember correctly) and after a few days the crunching completely went away. It is heaps better to get into any gear and certainly justifies the cost (i think it was like $125 for the bottle or something :laugh:)

Just my 2c :)

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very common problem for skylines to crunch going into high gears at high RPM. My R33 has very low k's and even with good synthetic Motul gear oil it isn't perfect into 5th at big speeds (and the Motul was still a big improvement over the original gear oil!).

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Ill try the redline blue stuff and get back to you all.By the way i just had a new clutch fitted,when the box came out they found the clutch pivot pin at the bottom.It had sheered in half.Took forever to find another one.Now the crunching is worse into 5th anything over 2000rpm an it will crunch.So now im driving like a grandma until i can figure something out.

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well one would ask where you would be redlining 4th anyway.. im going to assume a track or dragstrip..

Redline shockproof oil is not recommended for gearboxes with syncros... even redline state this.

Castrol VMX80 is a better alternative.. all you're really doing is masking a problem that ultimately needs to be fixed

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  • 2 weeks later...

at high speeds I sometimes crunch going into 4th, but only really at 150 or more, so it doesnt really phase me as a rarley see that sort of speed.

If im paitent on the gear change it go's in fine anyway. I just dont think the synchros can keep up at thoes speeds.

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Just a quick question. I dont have anything wrong with my GB. But i got some VMX80 cause i am planing to change the oil. Will this make the GB worse if there is nothing wrong with it in the first place?

No, VMX80 has been tried and recommended by many people on here.

My S2 had a genuine 34,000km on it when I bought it and I noticed a marked IMPROVEMENT when I dumped the factory oil and filled it up with Motul Gear 300. You will probably notice a difference in shifting quality when you put fresh oil in, too.

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Yes it is very annoying, my car crunches in forth when entered with high rpm from either second or third, anything over about 4k and crrruuuunnnncchhhh, even when i wait a while with the clutch pedal depressed and still crunch.

I put the redline oil in and found it makes gear changes generally smoother put only really masks the problem as it definately did not go away. Anyone know how much new synchro's would be to put in? or how much a rebuild is?

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the RB25DET boxes have dual synchros 1st-3rd and single synchro 4th-5th, 4th seems to be very common synchro to let go in these boxes.

Cost of rebuilding varies greatly depending on what is needed. If you are replacing all bearings and couple of synchros expect to pay just under 1K or up to 1.5K for all new synchros. (plus R&R of box itself)

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  • 3 weeks later...

The 33 box is common for this, the fourth gear synchro gets a little tired and eventually wears the input shaft. If you are hard enough on them the selector fork will break in half. I rebuilt one with new bearings, synchros and 3rd/4th selector fork and it lasted just over 12 months, in the end it broke another selector because the worn input shaft wouldnt allow a smooth meshing.

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  • 2 weeks later...
^ how much did it cost?

if you have f**ked synchros and are prepared to have it rebuilt.

as if you would choose the same damn gearbox!

i dont know exactly what a good gear box ugrade would be for the 33 but its not practical to put the same gear box back in and rebuild it... obviously the 33 synchros cant handle the shifts

my 33 got this problem from fast 1st - 2nd shifting. now it crunches slightly only when i shift as quick as i can.

but that was my old car.. i have a new 1 now doesnt crunch but it hasnt been given anything yet.

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