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This thread, is about gearoil and the aditiv Slick50  that came out in the 90's?  Some stuff that has PTFE  in it..  After 20 years of driving a 5 speed (30000km) the gears are making a lot of shifting noise..  again..  Going back from 4 or 5 to 2th is almost impossible to do.


you askt: Are you double - clutching your downshifts? I sure would be. It greatly reduces the work of the sync rings. I do it now by reflex on my ZX.

I drive z and zx now for almost 30 years and never double clutched gears..    i have tried it with my problem gearbox but it's so bad it does not help much..  the gears seam to be rolling long after i activated the clutch..

from another thread,


@Zed Head

ZED HEAD sayd:

  On 10/10/2020 at 12:42 PM, dutchzcarguy said:

i put in SLICK50  does someone here know that stuff? 

I remember.  It has PTFE particles in it to minimize friction.  Synchros need a balance between friction and viscosity to allow the speed matching to occur.

If you want to take a chance with $50 I'd try the AC Delco Friction-modified Synchromesh before tearing the transmission down.  I'd just let the other stuff drain out and refill with Synchromesh.

Otherwise, there's a post on Hybridz about modifying Porsche synchros to work in the steel synchro 5 speeds.  I think that FS5C has steel instead of "brass" (yellow).






zedhead says: Slick50.  Based on how synchro gears work, that seems like a not-good choice for transmission fluid.   

Yes i agree, now after 20 years the slick50 stuff with it's PTFE  (polytetrafluoroethylene)  is much to "slick" for the datsun gearboxes..

If i go back some gears i can hear clearly how the gears are still spinning after a few seconds hitting the clutch!  After that i push the lever carefully in the direction of the gear i want to get shifted into and it will without any bad noises.

It is absolutly possible that a refill with proper GL-4 oil could make a big difference..  As my 240z is at the moment in storage i will test this next year.. (Next year my 240z will be 50 year old and doesn't need anylonger a APK  (a dutch MOT.) it's... if you ask me crazy but true.. ( In the Netherlands cars over 50 are so good they don't need a check for safety...  but that's a different story.)


Zedhead also sayd (in other thread):

Pennzoil's brand seems to work just as well.  Internet has it that Pennzoil developed the formula for GM (AC Delco).

I wonder how Dutchzcar managed to find Slick50 in The Netherlands.


If the ac delco is like pennzoil , i could try that.

The slick50 was for sale at a dutch autoparts store.. (were i get all my oils and stuff.)

The gearbox i use here is a FS5C71B, (orig 5 speed euro 240z gearbox)  it's about 50 years old and Never restored or taken apart..  i know it's got the Porsche synchro's in it.  (I don't know it those are brass or steel..  i somehow think i seen some in brass somewhere...)  


Edited by dutchzcarguy

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My analysis of this discussion is that the Teflon in the SLick-50 probably reduced friction in the transmission to the point where the sync rings could not do their job and instead slipped too much. 

Double-clutching done well should work even if there are no sync rings at all - that's one reason the technique was developed. 

A change in lube ought to help, although I rather doubt it will be a total solution.

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Hi Mat,

If you do plan on rebuilding the FS5C71 you might want to try contacting SW Motorsport in Sydney, Australia. They did have the 1st to 4th gear porche type synchros. They still have the 5th gear porsche type synchro for $145 Australian dollars which is about €95.



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