280ZX Gearbox S14a Swap | The Z Club of Great Britain
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280ZX Gearbox S14a Swap

Discussion in 'Drivetrain' started by Huw, Mar 18, 2016.

  1. Huw

    Huw
    Z Club Member

    The subject of S13/S14 gearbox swaps into S30’s is pretty much old hat now and covered quite well in other threads. However, I thought I would share my experience of doing the same thing but on a 280ZX 2 str Coupe. I replaced my faulty manual gearbox, after attempting to repair it and failing, with a low mileage S14a box.

    The first thing to notice when compering the two gearboxes is the length, the S14 gearbox is a lot longer and the need for shortening propshafts etc. is a given. Other things such as the gearbox mounting adjustments and internal trim are less well documented, so that what I wanted to share.

    Old and new boxes:

    [​IMG]

    The machining necessary to the bell housing of the original gearbox is covered nicely here: http://zhome.com/ZCMnL/tech/240SX5spd/transmission.htm
    A local firm undertook mine as a favour to my father-in-law. The box was given a good clean and inspection before bolting it up to it newly machined bell housing.

    The speedo drive needs to be swapped out with the original. The one from my 280ZX had the blue drive pinion with 18 teeth; luckily this matched the one from the S14a box. However, because the 280ZX drive is slightly offset it had to be rotated 180 degrees for it to engage the drive in the gearbox itself. Because of this a new locating slot needed to be cut into the speedo drive body with a small file.

    [​IMG]

    The rear gearbox cross member needed to be altered as the position of the mounting is now about 2” further back to the original position. To achieve this, I cut out the centre section of the cross member and welded it back together as pictured. I used 5mm thick steel bar to reinforce the assembly, welded across the bush holders. I also added additional fillets welded across the cut surfaces to reinforce the box sections.

    Cross member:

    [​IMG]

    To get the correct position of all the pieces I had the gearbox bolted to the engine and supported by a jack. I bolted all the individual pieces onto the body mounts and gearbox mounting points and tack welded them in situ. The final welding was then done on the bench.

    Welded Cross member:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    When fitting the gearbox to make the mounting bracket, I did not have the shifter installed in the box and it all fitted perfectly. When I fitted the shifter assembly after welding up the cross member, things did not work so well. I used a B&M short shifter and the top of the shifter assemble where the gearstick slots in fouled the transmission tunnel. This would not allow the gearbox to be fully raised to locate the mounting bolts on the cross member.

    The transmission tunnel requires to be trimmed back to allow this clearance; I removed about an inch of material as in the picture below.

    Tunnel fitting before and after:

    [​IMG]

    [​IMG]


    The prop shaft again is something that is well documented, however the way to measure the correct length is not so well documented and I got that wrong. I measured from the flange on the differential to the rear seal on the gearbox. When discussing it with the company I used in Bristol it turns out I had measured it incorrectly. The company kindly lent me the front part of a propshaft (the bit that goes into the gearbox) and instructions to "stick into the box as far as it will go and measure from the middle of the joint to the dif flange". For my car that length was 576mm. The prop needed 52mm taking out of it to fit the new box.

    With all the mechanical bits done the interior needed to be sorted. Fortunately most of the interior console bits can be reused. The trim around the gear stick has a plastic coin tray as part of the centre console. With the new position of the gear stick this will no longer fit. The answer is to turn it around 180 degrees so the coin tray now sits under the ashtray. However, the mounting holes that are used to screw this piece into the console itself will not line up to allow this. They need to be clipped off the plastic, a large washer can be used with the screw to hold the trim piece in place see picture below.

    Coin tray:

    [​IMG]

    [​IMG]

    Next issue is the inner gearshift boot seal, again it cannot be reused in it original position. To fix this it can be rotated 180 degrees and it works quite well. However, the metal clamp which screws to the tunnel to hold the rubber in place needs to be moved about an inch and a half backwards. This will require the holes to be re-drilled in the tunnel to suite. Finally the gear stick gaiter can also be reused by again turning it 180 degrees. I did try a leather gaiter, but it did not look right and I actually prefer the retro 70’s rubber bellows – personal choice. The only part that could not be reused was the gear knob as the thread is 10x1.25mm on the new gearstick. Which is a pity as I rather liked the old one.

    [​IMG]

    [​IMG]

    [​IMG]


    Working on the car I could only raise the car up on wheel ramps. So I did find it a struggle to do due the box swap mainly to the space constraints. The whole conversion itself however, is pretty straightforward to do.

    [​IMG]

    Having driven the car, only up and down the road a bit to see if it works, I would say the car feels much better. Looking forward to giving it a full road test in due course. :driving:
     
    Last edited by a moderator: Aug 3, 2017
  2. candy red

    candy red Well-Known Forum User

    Well done Huw great the way you've done this thread with plenty of detailed pics great job :bow:

    Derrick ;)
     
  3. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Great write up Huw.
     
  4. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Nice one.

    How does it feel now (comparison) driving especially with the quickshift fitted?
     
  5. MaximG

    MaximG
    Z Club Member

    Huw great step by step write up. I would be interested to know what gear knob you went with as I still need to get one for my car.

    Mike
     
  6. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator


    FWIW,I got the shifter thread turned down to m8 and used my original gear knob.
     
  7. Huw

    Huw
    Z Club Member

    Sean

    From the limited drive I have had so far, the gear changes are very positive, no slop a huge improvement over the old box. Most importantly the box is virtually silent no whining at all. Looking froward to driving more when I get MOT this week.


    Mike

    Got the knob off of eBay here:
    http://www.ebay.co.uk/itm/201425793720?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

    Went for that one for the blue detailing - because Im shallow :)

    I didn't think of having the stick turned down Jon, Might do that at a later stage. Cheers.

    Huw
     
  8. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Ok - why go for the quick shift (when it's not obligatory) ?
     
  9. Huw

    Huw
    Z Club Member

    Hi Sean

    Couple of reasons;

    1. The box came without a gear stick and I couldn't find cost effective standard replacement
    2. Standard shift not as positive in terms of shifting
    3. Mainly and most importantly, it's what I wanted.

    Huw
     
  10. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Just curious as I've deliberately gone the other way for my road Z.:)
     
  11. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator


    You got a slow shifter Sean?
     
  12. samuri-240

    samuri-240 Well-Known Forum User

    Excellent thread Huw :thumbs:
     
  13. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Well, yes.:eek:

    Already driven with a quick-shift and if I was building a track-day car, I wouldn't hesitate but I'm doing a nice, comfortable granddad road car and I don't want a notchy/mechanical gear change - more of a soft-fluid motion.

    The box is brand new.
     
  14. Ped

    Ped
    Z Club Member

    Hey Huw really useful thread and well written too. I think the decision to go for the S14 box will make the car a lot nicer to drive altogether. I liked your solution to rotate the trim around the gear stick it has worked out neatly.

    Just a thought... rather than get the gear stick turned to suit the knob thread, could you not get the gear knob drilled out and sleeved and threaded to match the stick - or is there too big a difference?
     
  15. Lurch

    Lurch Active Forum User

    Huw, Why didn't you just fit an R32 Skyline GTS-T gearbox?

    FWIW they are internally similar to the S14 unit, except they are the same length as your original 280ZX 71B unit.
    You wouldn't have had to hack up the gearbox cross-member, shorten the TS or stuff around with the centre console...
     
  16. Huw

    Huw
    Z Club Member

    Probably because I didn't know about that option. Nice too know for next time.
     
    Last edited by a moderator: Mar 26, 2016
  17. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Much less common than 200sx aren't they?
     
  18. Lurch

    Lurch Active Forum User

    Quite common here in Oz. I'm not sure about the UK???
     
  19. Lurch

    Lurch Active Forum User

    Brain fart - R32 box still has the gearbox mount 30mm further rearwards, so a modified cross-member is still required.
     
  20. Huw

    Huw
    Z Club Member

    Pictures fixed with Imgur - thanks Photo Bucket....... for nothing
     
    Last edited by a moderator: Aug 4, 2017

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