300zx Transmission behind a RB26 in a 260z

[garvice]

Hi guys,

I am putting a RB26 in my 260z with a 300zx transmission (RB26 bellhousing, 300zx transmission). I found very few photos of custom transmission mounts so wanted to share what I had done in the minor chance it might help someone else in the future. I included lots of photos as they tell the story far better then words. I have sat my engine completely vertical to allow more exhaust space, this is why my transmission is on an angle.

As most are away, the 300zx transmission is longer then the existing L series 5 speed and and the mount is further back.
My original transmission mount was the later style with two ears off either side of the tunnel and a crossmember between.

I started by cutting the ears off (spot welded on). This is the passenger side, don't have a photo of the drivers side.


I then folded some 2mm sheet to make the drivers side mount parallel to the existing mount (essentially taking the thought of extending the existing mount base). The existing mount is 2mm and is spot welded to the transmission tunnel (which is much thinner) so I felt this was an appropriate thickness. To get the mount to marry up to the tunnel I used a profile gauge (quick google search will bring up what it is). Worked a treat and got the profile spot on first time.


I plug welded it to the existing mount and then seam welded around the edges. I hope I never have to remove this as it will be a complete pain to remove.



The drivers side was a bit more difficult as the tunnel actually narrows rear of the existing mount rather then getting wider like the passengers side. So I just plated the tunnel with some 2mm sheet (it is not parallel to the existing mount like the passengers side is). To weld this on, I plug welded through the tunnel from the inside, then again seam welded around the mount.




The next couple of photos are of the existing crossmember and two different isolation mounts. The first is the L series isolation mount and the second is the GM mount (that I bought for the diff). I had to move the fixing hole in the existing crossmember over to allow for where the transmission sits in the tunnel. This created an issue with the crossmember hitting the transmission bolts. In the end I decided to go with the GM mount as it felt like it had a better construction. The white pipe is 90mm water pipe to simulate an exhaust and the blue tape is in line with the chassis rails.



I wasn't overly happy with how the crossmember sat on the GM mount in relation to the new tunnel mounts (sat a bit low at the mounting points).


So after a bit of deliberation I decided to make my own crossmember (also didn't want to have to burn out the isolation mount, burning rubber stinks). The original is a 2mm pressed mount (a top hat construction with a small bridge over the bottom), so I built mine out of 2mm sheet. The 2mm sheet is rather easy to bend over some pipe. Here is how I made it. Cut a 40mm strip of 2mm sheet, bent to the shape of the mount I wanted. Laid the shape on a sheet and drew a line offset 20mm from the top sheet. Bent a 60mm strip to match this line. Held them together with magnets to offset them 20mm and transfered the shape onto some 2mm sheet. Cutout the shape in two pieces and then had my four sides. Used some 30mm pipe for the isolation mounts. Ok here are the pictures that really explain it.


Reinforced the bolt hole section with more 2mm sheet



Measure twice cut once people, I drilled some holes in the bottom sheet and then realised I had drilled too far over, had to weld the hole back up.


Had to turn down the isolation mounts as my pipe is a bit smaller then the existing crossmember.


The new crossmember although larger is considerably lighter then the original (not quite as wide).




Cardboard templates for the mounting ears

Made the ears out of 4mm sheet (existing ears where a folded piece of 2mm sheet and then a second piece of 2mm sheet to reinforce), notched and seam welded from both sides.









Finished crossmember and mount

[handsandwhich]

Nice work, looks very "stock" looking.

Does the gearbox line up with the existing gearshift hole when you use the 300zx one that has that remote gearshift position?

What are you doing in regards to the tailshaft?

[garvice]

No it sits too far back. However I have cut out the rod that goes between the two uni joints and welded the uni joint yokes together. I also have a shifter mount that 240hoke built for the gearboxes. This places the shifter at the back of the original hole. Will try and find some photos.

Also, just a not to people, this would be much easier with an early 260 or a 240 as the original mount is very different.

EDIT: Will need a custom driveshaft.

[mtopxsecret6]

i like your fabricating work. Definately got some heat in those welds, what sized plate did you use?

[garvice]

Cheers, the ears are 4mm, everything else is 2mm sheet.

[peter mc]

Hi garvice
 did you mount the rb strate up an down in the engine bay ?

[garvice]

Sure did.
Going to add an oil drain at the back of the head to make up for any oil drain issues I might have created.
Only photo I could find, will get some better ones later.


Here are some ones I just took.

[RB30X]

I would've thought you'd need more clearance on the inlet side than exhaust? Ever tried to work on a GTR.
You must be planning a large high mount with a disco potato

Looks awesome.

[garvice]

Inlet side has heaps of room, will also have remote oil filter mount so wont be too bad to work on.
Wont be a disco potato, far too small. I sold my GT30/40R so anything new has to be bigger.

[peter mc]

 i like 35 40 with 86 housing they feel grate after 4000 on the 26  350kw on stock motor at 18psi on 98 ulp makes for a grate ride

[garvice]

You read my mind Peter with the 3540.
Was thinking of aiming for the 400hp mark to start with.

[peter mc]

make shore to use a good manifold like 6boost  with external wast gate for good boost control and 3in exh will make that hp no problem

[KatoKid]

Good work garvice.

I was faced with the same problem if I was to use the Getrag 6 speed in my conversion. The 5 speed ZF fits exactly in the same position as the original crossmember and is a nicer shifting box so that made the decision for me.

[NZeder]

The 5 speed ZF fits exactly in the same position as the original crossmember and is a nicer shifting box so that made the decision for me.

I also thought the fact the 6 speed is almost a non serviceable item would have been in the 5 cog favour too. Back on topic.....great work on the new mount setup. I too would have thought the engine would lean more to the exhaust side like a factory RB install.

[peter mc]

the only reason i run rb on the angle is so you dont upset the sump pick up .but im sure you will mod the sump to fix the problem