5 spd transmission ?

[Daryl Smith]

Some info on transmission ratios of the various transmissions which are/could be used.
The 'B' transmission was used in many of the Nissan/Datsun models, including p/u's, some of which are listed earlier in this thread.
The 'C' transmission was also used in p/u's with similar ratios, but I believe is a shorter transmission.
If you know any of these are incorrect, let me know so it can be editted. Thanks.

[fj20spl311]

Thank you for the update

[Daryl Smith]

Some good information here on measuring/matching up your clutch and throwout bearing setup with a transmission/clutch swap.
Relevant for those considering a 240Z clutch, or the diesel trans swap....
http://ace240z.com/transmission-swap.html

[tangoterje]

This is a great thread!

I recently found two diesel pickup bellhousings, one with a 56mm countershaft bearing hole and another with a 62mm hole. The 71C boxes are beautifully built, shift great and are made to last. But stock gearing is unfortunately dull!

I’m currently building a 71C with OS Giken gears for my 240Z with a 3.9:1 or 4.11:1 rear, but I have no idea yet if it will be happy with the 2.717:1 first gear. Will find out in a few months. But this could also be a good solution for the 2 liter roadster, if at least a 4.11:1 is used. I’m trying not to pile up too many projects at once, but it’s hard not to. Found a H190 from a Laurel C32 that has 4.11:1 gears, but no idea if they fit the splines of roadster axles. Guess I’ll find out

OS Giken gears (3-speed kit):
1: 2.717:1
2: 1.722:1
3: 1.232:1

I’m keeping the tall overdrive (0.759:1) for cruising, so I think it should be a fun little rocket that shouldn’t be afraid to be caught by some stop&go traffic.

[Pjackb]

For my U20 stroker build, I’m putting together a 71B transmission from an early ZX, combined with the front portion of an SD22 diesel 5-speed. I originally wanted to use the C version, but the SD25 front portion, which I would have needed, is nearly impossible to find in Canada. This setup will be paired with a 3.9 rear end. It’s the same combo I have in my Z, and in my opinion, it works extremely well with a revvy, torquey engine.

While I do have a freshly rebuilt 71A in my roadster, I’m not a fan of the sloppiness and lateral movement of the roadster 5-speed compared to the B or C versions of the transmission.

[Daryl Smith]

Pjack,
Are you saying the SD25 bellhousing is a direct bolt up to the C transmission?
I have seen no info to denote a difference between the 22/23/25 bellhousings, just that the diesel bellhousing needs to be modified at the inside front around the input shaft bearing.....unless its the above noted bellhousing with the 62 mm bearing? Don't remember what bearing was in mine, but it was larger.....

[tangoterje]

Is that the lovely EFI thingie you’re working on?

I think the 280ZX boxes with a 3:1ish first and a tall 5th sounds perfect, much better ratios than stock 71C imo. Strengthwise, I’m sure you know a competent machinist who can increase the bearing hole to 62mm? I haven’t thought this through, but if you avoid grinding down that 1mm (or so) lip, then perhaps you can use a 62mm bearing as is? Or if the lip is already ground down (I don’t think it is), then perhaps the thin 71C front «scissor gear» can be used? The counter gear that use the scissor gears have a thin groove around on the front side, might need machining then.

I also thought about using a FS5C71B box and convert 1-4 gears to warner, but even if I managed to find the 26/44 teeth 5th gear from the latest 280ZX box, it would still only be 0.833:1. I’d like it to be at least 0.8:1.

Four fun forward gears and a lazy overdrive is my ideal setup.

[tangoterje]

Daryl, these are the two diesel pickup bellhousings I picked up this summer. One counter bearing hole is 56mm (71B size) and one is 62mm (71C size). None of these have the lip around the counter hole removed, so if a 71C with the front thin scissor gear is to be used, some additional milling needs to be done. Also can’t remember if 1-2 shift rod hole is enlarged to 16mm here either.

[tangoterje]

Front scissor gear on a 71C

[tangoterje]

And Pjackb, the tailshaft mod that Lou Mondello do on the 71A make them a LOT tighter! Highly recommended if keeping the A box.

[Pjackb]

Pjack,
Are you saying the SD25 bellhousing is a direct bolt up to the C transmission?
I have seen no info to denote a difference between the 22/23/25 bellhousings, just that the diesel bellhousing needs to be modified at the inside front around the input shaft bearing..

Take a look at the pictures Todd posted
The SD22 engine use a version of the F5W71B version of the 5 speed and the SD25 has a F5W71C version so if you're doing the swap you have to use the right transmission model , I'm not familiar with the SD23
Take a look at the pictures Todd posted for the differences

Is that the lovely EFI thingie you’re working on?

Yes it's for it
I'm not 100% sure where i'll land but as we discussed before I love the way my ZX tranny pairs with the light flywheel, 3.9 rear and torque delivery on the Z and since my drivetrain will be almost identical I expect to have similar powerband I think

[Pjackb]

And Pjackb, the tailshaft mod that Lou Mondello do on the 71A make them a LOT tighter! Highly recommended if keeping the A box.

I reached out to him about it but haven't gotten the information yet

[Daryl Smith]

A consideration for the R motors is that the flat tappets/cam may have lubrication issues at extended low rpm cruising. It has been brought up on different forums as another issue in flat tappet cam failures.
With the 71C transmission and the .838 OD/3.7 rear gear, I'm quite happy with a cruise rpm of ~2500 rpm.
Probably not an issue with the OHC engines.

[tangoterje]

A consideration for the R motors is that the flat tappets/cam may have lubrication issues at extended low rpm cruising. It has been brought up on different forums as another issue in flat tappet cam failures.
With the 71C transmission and the .838 OD/3.7 rear gear, I'm quite happy with a cruise rpm of ~2500 rpm.
Probably not an issue with the OHC engines.

Hmm, interesting, I never considered this. I make sure my idle is high (1000?) for a highish lift cam on my L6, but good point regarding cruise rpm!