View Full Version : Gearbox strength

06-03-2007, 02:13 PM
Wondering how much hp the 240Z box can handle before going pop? Is the late 280ZX box a direct swap, can I use my own driveshaft and how much power can it handle?

Also can I have some tips on removing the gearbox, currently engine is out. Do i firstly remove the driveshaft? WIll consult the FSM but thought i'd firstly get your tips from your own experience.

Particularly interested in how the box was supported, have some idea but any info appreciated.


06-03-2007, 06:34 PM
Having personally destroyed a number of boxes I can speak with confidence on this subject. However, please bear in mind that I do a lot of brutal standing starts & gear changes, and I am also running slicks. In my case about 220bhp is enough to break the damn thing.
Someone like Skiddel could give you a better road going comparison.

My solution to breakages has been to fit a Borg Warner T5 box which ran in the 280ZXT in the states. Get hold of a bellhousing and you can run a box from a Cossie or TVR. Be warned that the clutch plate and prop will have to be altered.

06-03-2007, 09:22 PM
Thanks a lot Ken for your input.

I would like to look into this further, when you say source a bellhousing do you refer to the T5 280ZXT bellhousing? I wonder how heavy they are to ship over..

Anyone done this Cossie TVR swap? Any other major headaches to overcome other then the new propshaft and clutch plate?

06-03-2007, 11:16 PM
I purchased the whole gearbox from a 280ZXT and shipping cost approx $250 from Florida. The bellhousing bolts to the front of the box and would be much cheaper to ship. In hindsight I wish I had only bought the bellhousing. I simply posted a wanted ad on some of the US Zed sites and got a reply within a month.
A T5 has a different input and output spline shaft to that found a Z box, hence the need to alter prop and clutch plate. The only other mod we had to carry out was a slight tweak to the rear box mount. Other than that its a straight bolt in. 2nd hand Cossie T5's come up for sale all the time (e-bay, Motorsport News,etc) and are reasonably priced. You can also source parts and find uprated parts pretty easily.
I think the TVR T5 has a slightly larger casing so I could not comment on how easy it would be to fit.
Oops, missed a mod. The pilot bushing in the back of the crank needs to be bigger, so we had one machined.

07-03-2007, 12:23 AM
Thanks for sharing all of this great information.

I will start hunting for my 280ZX Turbo bellhousing and then at a later date will look for the cossy box.

Do you happen to know if it matters if the T5 box is from a 2WD or a 4WD Cosworth and is there any preference for a late or an early box?

07-03-2007, 09:09 AM
2wd only. 4wd has additional output shafts for front wheels.
I don't think they changed much, if at all, during their manufacturing lifetime. Try some research on a Ford owners forum just to make sure.

07-03-2007, 11:00 AM
The strength of the gearbox is always of concern to the higher horsepower users....its difficult to get any definative figures but I suspect that somewhere around the 200ft/lbs of torque and 250 HP is all you could expect to run. Of course all this depends on how you are going to drive the car and for what purpose, if your car is unlikely to see any hard drag strip launches or racing downchanges at 120mph then the stock unit should perform ok.

At some point in time I expect mine to depart of this mortal coil....thats why I keep a spare

I did look at the T5 route but it would mean that I would have to swap out an expensive clutch, modify a custom prop (soon to be carbon) sure the T5 gives you more strength and many more gear/rebuild options at a much reduced cost, but the gearshift is (so I am told) no better...small price to pay for a box that will withstand 400Hp I guess....maybe I might end up that route when my spare is used and gives up the ghost, who knows. Until then keep us posted George and Ken, any info is greatfully received

07-03-2007, 11:37 AM
Keeping with the Nissan splines / spigot bush should be possible using the T5 core from an early Z31 Turbo...

Black Bug
07-03-2007, 12:27 PM
Sorry Mike, got to disagree with you on that one, been there, ain't going to happen. The problem is the Z31 input shaft is about 3 inches longer than the 280ZXT input shaft, but you can't swap the 280ZXT shaft in to the Z31 box as the 280ZXT has 24 teeth on its lay gear whereas the Z31 has 23T. I tried for ages to source a different input shaft of the right lenght with 23T gear which in theory exist but with a different clutch spline pattern (so hassle getting a matching clutch), but I just couldn't get hold of one for love nor money. The other suggestion was to do a cut'n'shut on the Z31 input shaft to get it to the right length, but that's hardly adviseable given the desire for it to handle more power. Final nail in the coffin for the Nissan T5s is that they're the 'Non-World-Class' version (the Cossie box is the 'World Class' version), that means they're nowhere near as strong as the WC boxes, my research even turned up people swapping them out of their 280ZXs to put the Nissan box in as that was stronger.

I went down the 200SX gearbox swap. You take the front half/bellhousing of your original Zed 5 speed, do a bit of machining on that, then it's a direct fit on the the 200SX gearbox. Some fiddling needs to be done to the rear mount (I'm about a lifetime away form worrying about that admittedly!) but you have a much stronger box than the original Zed one, that can be rebuilt to handle lots more power - check out http://www.phattransmissions.com/PhatTrans/transmissionBuilds.html

Fitting a WC T5 to the 280ZXT T5 Bellhousing is also a good alternative. The bellhousing apparently needs some machining to fit the WC input shaft retainer but that's pretty straightforward. You can get a WC T5 rebuilt to handle mucho power to:


24-03-2007, 12:32 AM
anyone know anyting about moding the 280zx auto box to shift faster and launch harder, poss trans brake

24-03-2007, 05:53 AM
Nothing aside from talk to Mr F ....he and I discussed it (several times) as a possible option

24-03-2007, 08:49 AM
Cossie T5 box is 2wd version 4x4 box is MT75 stonking box, this is also available in 2wd format from the sierra GT 2.0i model even has a synchro on reverse. This box is silky smooth but would be a nightmere to mod to fit.
Most standard Sierras use a Type 9 box.
Just so you know...

24-03-2007, 09:18 AM
Thanks for that Nick, great info. has emerged from this thread, thanks loads to those who have contributed.

24-03-2007, 12:13 PM
moding the 280zx auto box

Years ago, B & M (well known USA auto box performance specialists) used to provide a valve body kit for harder shifts and extended rpm (or indeed, full manual shifting if required). Not seen this recently, but someone probably has an unopened box on a garage shelf somewhere in the world...?

Auto box specialists should be able to split the torque converter and modify the blades to raise the stall speed - or there may may a smaller diameter torque converter from another Nissan that could be used. This will compromise street driving, but will improve launchability!