Gearbox oil change / flush | The Z Club of Great Britain
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Gearbox oil change / flush

Discussion in 'S30 (240Z,260Z,280Z) Drivetrain' started by AliK, Mar 29, 2020.

  1. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    Need some advice please gang.

    Before I pour in the red liquid gold that is Redline’s finest gear oil, I was thinking of getting the car properly warmed up, putting her on stands, draining the oil and then doing a flush by filling, then running through the gears while on the stands, then draining again.

    My question is, would it be OK to use a tin of 20w50 classic engine oil I have sitting around (for the flush only) or should I be buying cheapo GL4 for this purpose?

    Everything I’ve read says engine oil is even tougher stuff and the classic oil is designed to be kind to yellow metals / more viscous.

    Or do I just pour it in and change oil again in a couple of thousand miles!?

    What think yea oh wise ones?
     
  2. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I bought a gearbox that was so glued-up I had to put engine flushing oil in it and run on stands for an hour to get any gears. Yes it was a desperate situation and the box came out of a running car ( no chance!). WORD OF CAUTION - if you jack the rear wheels only and run the car No 6 Cylinder will overheat.

    You shouldn't need to flush your gearbox.
     
    AliK likes this.
  3. toopy

    toopy
    Z Club Member

    I would do the same as you mention above for a gearbox that hasn't had a fluid change since you've had the car. After a couple of thousand miles, if it comes out relatively clean, you know there are no issues and the re-fill will then be good for many thousands more.
    If it's pretty shitty, investigation needed and you know where you are with it going forward.

    Incidentally i will soon be approaching the same situation :D
     
    AliK likes this.
  4. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    Good advice on cyl 6!!!

    Please elaborate on why you think it doesn’t need flushing? I was thinking it would get the crud out a bit more than just draining alone would.
     
  5. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Where is this crud coming from and what is it? An engine is a different matter.
     
    AliK likes this.
  6. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    I'd agree with Rob. As well as no way in for crud, there's also not a lot of places in a manual box for crud to hide when you drain it.
     
  7. Albrecht

    Albrecht Well-Known Forum User

    If your gearbox is a proper UK market item, it should have Servo (steel) synchros instead of Warner (brass/bronze alloy) synchros.

    Is the Redline oil you intend to fill it with designed for Servo or Warner synchros? Was it recommended from a US-based source?

    Best stuff for Servo type synchros is SWEPCO 201.
     
    AliK likes this.
  8. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Yep, it happened to me - burnt the exhaust valve out. When you jack the rear No6 is above the header tank and the revs were low so poor water circulation.
     
    AliK and Paul_S like this.
  9. AliK

    AliK
    Z Club Member
    Staff Member Moderator


    Thanks Alan. Yes it was a US source but equally, I don’t know if mine is an original box + the PO told me that he replaced some synchros but never said what with, so I thought to play it safe. Is the Redline going to cause a problem with steel synchros?

    Ah! Sorry to hear that - it makes sense.



    @jonbills Thanks Jon - I just assumed there will be fine metal shavings / dust in the oil from any gear crunching sins so I was playing it safe.
     
  10. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    The drain plug is magnetic, so you might find some iron filings on it.
     
    AliK likes this.
  11. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    Excellent! Good to know. Let’s hope it’s still magnetic after all these years and heat cycles ;)
     
  12. Albrecht

    Albrecht Well-Known Forum User

    I should think the Redline would be absolutely fine, even if not the theoretical 'best' for steel synchros. But then, it's difficult to define what is 'best' anyway. I just followed the recommendation for the difference between synchro types. USA-based Z people are generally using Warner type synchros...

    I was shocked (in a good way) when I switched to the Swepco 201 for a Servo synchro 'box. Shift quality (via synchro efficiency I guess) just seemed so much better than before. I'll be using it on the FS5C71-B I've just put back together for the white 240ZG project car. Might be worth trying next time you change the oil?
     
    AliK likes this.
  13. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    Always great to hear first hand experiences like that Alan! Thank you.

    After home schooling is over tomorrow I will try to lay under the car to see which ‘box I have.

    My only concern is, looking through my notes from the conversation with the PO this eve, he said the synchro on 5th went and he had to go to Australia to find one; which is why he decided to sell the car in the end. So I can’t be sure if he may have used a brass one. Sadly I’ve lost touch with him now.

    The gear change has always been pretty sweet, with the odd bulk getting into first or reverse. In fact, when Mr Toopey drove my car he was pretty impressed how slick and quick the change was compared to his. So let’s see what the Redline does to it. If it gets worse then the redline becomes a flush and Swepco gets poured in very soon after. Based on what you’ve said I will definitely have a go at the Swepco 201 in a couple of thousand miles. If a yellow synch was used and ends up dissolving over time, then it just gives me a perfect excuse to rebuild it or wheel out the S14a from storage!! ;)

    All I can say is, thank God for the lack of a synchro in reverse - I sometimes find myself looking for 6th on the motorway :eek: !!!
     
  14. atomman

    atomman
    Z Club Member

    One of the only places I found steel syncro's being made was in Oz , so sounds like a Steel type synro box NOT a brass type,

    I don't think they are interchangeable ? But Allan would know ?

    I used the Redline MT90 75w90 in my rebuilt S14 box and i'm very happy with how it shifts etc , (but that does have brass syncro's )
     
    AliK likes this.
  15. franky

    franky Well-Known Forum User

    Hi Alan, with the gearbox I had off yourself i'd need SWEPCO 201 then?
     
  16. Albrecht

    Albrecht Well-Known Forum User

    Yes, it's a Japanese market flange-output FS5C71-B with Servo (steel) synchronisers. The Servo patent synchros are used in many Porsches, and you'll find the SWEPCO 201 recommended for them.

    Anecdote: When the S30-series Z was being planned, the steel Servo synchro FS5c71-A transmission was considered 'unsuitable' for the North American market models as its sporty, positive - slightly raw - synchro action was thought to be a little bit too uncomfortable for the mass market buyer. Therefore Nissan gave them the brass Warner synchro FS4W71-A with its smoother but slower action. All other markets got the Servo synchros...
     
    Chris159, atomman, franky and 2 others like this.
  17. Paul_S

    Paul_S
    Z Club Member

    I'm in the market for some gearbox oil. I've got the FS5C71B (steel synchros) 'box.

    Albrecht recommended SWEPCO 201 above which I found for sale here. It sounds great, but I will be putting this into an untested box so would prefer something cheaper for the first few miles until I know I'm not going to drain it and start all over again. If it's all good then I will probably go for some of that.

    Are there any other recommendations to get me started?

    And what about any additives such as the Molyslip gearbox stuff?
     
  18. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Molyslip. I was told by a Rootes mechanic years ago not to put Molyslip in a gearbox ( I had an Imp) he said that the reduced friction stopped synchros working properly.
     
    Paul_S likes this.
  19. Graeme - CZ

    Graeme - CZ
    Z Club Member

    Hi all. Is there a consensus on what gearbox oil I should use in my ‘73 240z?

    Thanks, Graeme


    Sent from my iPhone using Tapatalk
     
  20. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    I believe we said Swepco201 for steel synchros and something like MT90 if you have brass synchros (the latter being in North American cars).
     
    Last edited: May 22, 2020 at 7:18 PM

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