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RWD Subaru Boxer Transmission

RWD Subaru Boxer Transmission

RWD Subaru Boxer Transmission

Okay, I'm pretty sure Subaru never made a RWD transmission for the EJ20 engines. But to get back to the reason I posted this:

I want to put a EJ20 in my soon-to-be heavily modified Datsun 260Z chassis. I've been looking for factory RWD transmissions that could possibly bolt up to the EJs block but as I suspected I haven't found anything. Does anyone here have any ideas on how to mount on to it? Know of a transmission with suitable ratios for the engine?

I'm suspecting I'd have to find a transmission, the kind with a separate bellhousing, and have a custom bellhousing made and possibly get the input shaft machined to fit the pilot bearing. Even then I still don't know what transmissions would have the proper ratios, a 240SX trans might but the pictures I've seen of them the bellhousing was integrated into the case. The only one I've found close so far to might working with the custom and machining idea is the T5 from a 1983 Datsun 280ZX Turbo.

Thank you all for any of the help that's sure to follow.

RE: RWD Subaru Boxer Transmission

Your best bet would be to weld the Subaru transaxle's center differential and use that.  For weight savings you could remove the front differential and replace the output seals with plugs.  Apparently this is a very common modification for people who want to make rear drive Subarus.


RE: RWD Subaru Boxer Transmission

But judging from pictures, if I use the Suby transmission the shifter would be at my elbow. That wouldn't be very comfortable to drive.

RE: RWD Subaru Boxer Transmission

Solutions to gear leaver position problems vary from bending the lever to fabricating a simple linkage, or moving the seat, steering wheel and pedals or moving the motor/gearbox.

Another solution would be to use a more physically suitable engine gearbox combo.

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RE: RWD Subaru Boxer Transmission

Put an Allison in the back seat and omit the transmission.


Mike Halloran
Pembroke Pines, FL, USA

RE: RWD Subaru Boxer Transmission

It is not uncommon to adapt a transmission to an engine using an adapter plate. For this to work the transmission bolt circle needs to be slightly smaller than the engine bolt circle. The transmission bolts are installed first, which are countersunk into the plate. The plate is then bolted to the engine.

An automatic is much easier to hook up, because all you need to do now is get the torque converted bolted to the engine's flex plate or old pressure plate.

With a manual, the trick is now getting the input shaft to work. Since you now have a little more room you might be able to put the pilot bearing into the pressure plate. Obviously you can get the pressure plate redrilled for a clutch that will fit the transmission. Now you just have to figure out how to connect a throw-out bearing.

The manual transmission that came to mind first was a Borg-Warner T-5. They were available in many different cars for many different brands in many different power ratings. There were apparently at least two different bellhousing-to-trans bolt patters. A quick search shows that the ford versions had cable operated clutches.


RE: RWD Subaru Boxer Transmission

I know all about the T5s that came in the aero-nose Foxbody Mustangs since I do own a 1990 5.0 Mustang. I have two T5s in fact because I blew up the one that came with the car. Not a big fan of the cable-clutch, especially now that the tension from the cable destroyed my bulkhead (currently trying to get it welded back up and reinforced).

I tore apart the transmission I blew up hoping that I just needed to replace the bearings for the counter-shaft but when I opened it up I found out that there's no more teeth on any gear (I broke it during a hard down-shift to 3rd around a bend).

What I want to do is maybe have the crank from the EJ machined to accept a pilot bearing for the T5 input shaft. Then hopefully the EJ pressure plate being big enough to fit a 10-spline clutch disk inside of, or find a disk small enough to fit the pressure plate. Use a hydraulic throw-out bearing like from Quarter Master, I think Tilton has them too but not sure. Looking at aftermarket bellhouses I saw that the Lakewood ones are made from 1/4" think steel so I feel like I could fab one myself (with tons of careful measurements because alignment has to be PERFECT) and make sure to leave a recess and a secondary mounting surface for a mini high-torque starter since the starter has to be mounted on the trans side. I don't know if the Subaru starter is hooked into the factory ECU for any given reason, but the engine I want to buy won't be coming with an ECU which is ok with me because I want to do the MegaSquirt route.

RE: RWD Subaru Boxer Transmission

Tremec TKO?

But then, I'm still baffled with why you'd want to put a Subaru engine in a 260Z? Just to be different? Is this really a turbo version of the engine like an EJ257? All the N/A version seem very anemic. Personally, I'd be looking to use someething more along the lines of an all aluminum LS series engine with a T56 bolted to it.

If the transmission has an integrated front cover and bellhousing you can often cut off the bellhousing and install a new one just by using the ring of bolts the hold the front cover on the case. This is often done with auto's when installing a safety rated bellhousing.

RE: RWD Subaru Boxer Transmission

I want to use the EJ20 twin-turbo because I can find them easier and for a lot less, but the extra displacement of a 2.5 is an attractive idea (to be turboed of course). I want to put it in my 260Z because it's a lot lighter than the other engines I've thought about, since its a short engine (front to back) it sits well behind the front axle center-line therefore making it a mid-engine car. I also want the very low center-of-gravity that the engine has, not to mention have the fuel economy of a 4 cylinder. The whole front end of the car is being replaced and I know how I'll be re-routing the frame rails to be able to take advantage of the low center-of-gravity of the engine.

RE: RWD Subaru Boxer Transmission

If you want to be that ridiculous why stop there. Use a 2 litre VW rear engined Kombi gear box in the rear and a Suburu engine in the front and pretend you are building a poor mans Skyline GTR.

Look at Formula Ford for gear linkage ideas.

I hope you own a machine shop, metal cutting equipment and a mig or tig welder.

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RE: RWD Subaru Boxer Transmission

Given that the Subaru shifter is on a long linkage, relocating it to a more suitable position shouldn't be much trouble.

I would personally worry less about the shifter position and be more concerned with trying to fit the engine between the chassis rails.


RE: RWD Subaru Boxer Transmission

The engine is almost 31 inches wide at the widest point, but from the widest point of the exhaust manifolds it's only 20.7 inches, the frame-rails are 25 inches apart on the inside. Instead of having the new rails go up the firewall about 6 inches and then go out to the front of the car I was going to run them straight out without raising them, running them under the heads and have mounting tabs going around the exhaust manifold for the engine mounts. Then before the engine have the rails kick inwards and actually be the crossmember so to speak, from there it's just making additions to the frame for spring and upper control arm mounting. I'll try to draw up a pic later tonight to show what I mean.

RE: RWD Subaru Boxer Transmission

Pilot bearing:
I would be checking the bearing spec books for a bearing that has an ID o fit the shaft and an ID to fit the flywheel. If the shaft diameter is so great as to make this unfeasible please RF this post to avoid confusion.

"Why not the best?"
Jimmy Carter

RE: RWD Subaru Boxer Transmission

Yep I would bin the subaru trans' front diff, plug the output holes and weld up the center diff.

Of course Subaru has had their share of transmission failures in may stock cars so they might not be the strongest thing out there.

However that would solve the trans to engine interface issue.

Also, there are surely companies out there that may make upgrades for the weaker stock stuff.

RE: RWD Subaru Boxer Transmission

Most of the reason the Subaru transmission is weak is because all wheel drive tend to prevent the tires from acting as a fuse.

The rest of it is because they're a clamshell design dating back to vehicles that weighed roughly half as much and had as little as 12% of the horsepower.  They're certainly no Audi 016.

The synchronizers don't take well to ham-handed shifting, but I don't think anybody can make one that will.  Or rather, there will always be someone out there who can break it.


RE: RWD Subaru Boxer Transmission

Use the 5-speed gearboxes, they're the strongest. Be aware that the early 5-speed boxes that came with the STI engines didn't have hardened teeth on the 4th and 5th gear sets.
The centre diff can be easily replaced with a solid piece of axle.
Pull out the front diff and weld up the exits.
Now the gearbox is rather empty, so you need to fill it up with more oil than standard!
Also, the engine and gearbox are slightly tilted backwards to ensure that there is enough oil reaching the 5th gear.
There are versions with an internal oilpump that bring oil to the back of the box.
The shifter can be modified easily.

check www.sakereurope.com or www.silvermine.nl

they both use Subaru engines with modified standard gearboxes (only these are modified to be a mid engined configuration)

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