T50 No More - W58 Gearbox Conversion Pt.1

Ah.. the old T50s.. Words are not enough to express just how legendary they are.. These gearboxes come paired with any longitudinal 4A-GEs ever been produced by Toyota, making them just as renowned to any Toyota-head all across the globe.

Funny thing about T50s, though, Toyota seemed to deviate from their habit of over-engineering when they designed these boxes: they are notorious for blowing up at the wrong time and place. I should know that.. after 4 hours and just another 10 minutes of drive before i reach home, my first T50 decided to get stuck on 3rd gear. Mine was behind a turbocharged smallport.. if you lurk the internet forums like i do, you'll even find guys that break their T50s with just bone stock bigports!

Perhaps it's just bad maintenance on my side and that T50s don't suppose to break that easily, however, i'm not keen on finding out (again). That's why i'm ditching my T50 in favor of a stronger monster, the W58. W58s are commonly found in non-turbo Supras and, especially in Indonesia, Cressidas. They are said to withstand 300-400 HP easily, numbers i'm not planning to reach with my 4A-GTE, so hopefully it would last forever on The Dog. Besides, T50s worth more than W58s here in Indonesia. I'm hoping with the cost of the conversion would be covered by the cash i'll get for the T50.

This conversion will be detailed into three parts. This first part covers the adapter plate fabrication, the second part will cover the details found during the swap process and final part will give some comparison between the T50 and W58. Apparently, W58 conversion is quite popular among AE86 owners so you'll find a lot of info on this on the web.

The conversion was started with these..

A spare bellhousing from my 1st T50, the W58 gearbox and a driveshaft with front yoke that fits W58 output splines. You don't need the whole drive-shaft as i found out later the yoke will replace Charmant's easily. Also, if you have a spare 4A engine, that would be great as it will be explained later, you'll save some swap process down time.

I got the idea from Andrew a.k.a Assassin10000's thread on Toymods forum.. so my steps will be very similar to his with just some minor differences. His method is the most cost effective and feasible for me. The idea is to make an adapter plate that sits between the W58 gearbox and T50 bellhousing. Why bother when you can buy custom bellhousing that couples W58 to 4A engine (or any W5x series, as they share common bolt pattern)? First, they're hard to find with decent quality and second, spending some 400 bucks for them and another nearly the same amount getting it past customs seems unjustifiable for me. Another way to get W5x behind your 4A would be to cut both T50 and W58 bellhousing somewhere in the middle and weld them together.. As these bellhousings are aluminum, welding them together can be tricky. I can't find any decent aluminum welder close-by so obviously i'm left with the adapter plate method.

Before i start detailing my conversion process, i'd like to point out something..

Bellhousings from T50 and W58 are placed next to each other and a driveshaft is laid on top. The gap found above T50 bell proves that they're NOT of the same height. I've read somewhere saying otherwise so this just disproves it.

First, take off W58's clutch release bearing carrier guide and draw the outline on 20mm thick steel plate with a chalk. This plate will be your adapter. Drain the oil first before you do this as it will spill when you take the guide off from the gearbox. Then cut the plate using a welding torch.

Next, refit the bearing carrier guide and drill the holes for the dowel pins on the gearbox so that your adapter plate can sit flat. I found out the best way to do this is to dab some paint on the dowel pins and place the adapter on top of them so that you have the marks to drill.

To drill the holes for the bolts to hold the adapter to the gearbox, make some dowel pins for the W58 bell. This way, you can secure the bell on top of your adapter and drill out following the bellhousing holes. Accuracy is important here, as redrilling a massive chunk of steel is no fun.

There're nine holes to drill but for reason to be explained later, you may want to leave one out. Anyway, i drilled all nine holes.

The adapter will be secured to the box using hex bolts so the next step is to enlarge the holes so the bolt head will fit, allowing the T50 box to sit flat on the adapter. Take care not to drill all the way through the holes..

As i have mentioned before and will explain later, you may want to leave the top left hole un-drilled. Eight out nine is still strong enough, i believe.

Next is to drill the holes for the T50 bellhousing bolts. First you need to make sure the T50 bell is centered to the W58 input shaft. For this purpose, a centering tool is machined out on a lathe by opening up an inner diameter the size of W58 bearing guide and reducing the outer diameter to T50's center opening.

You need to know how to align the T50 bell to the W58 box so that later on the car, the shifter stick will sit upright and not tilt to the side. The part of the T50 bell that you need to align to W58's shifter stick center line is the part exactly across the bellhousing drain hole. This is what you'll see when your bellhousing is aligned to the box.

Be very cafeful on this part as mistake here will be costly to fix later.

Once the bellhousing is aligned, drill and tap one hole first to hold the bellhousing firmly to the adapter. Once it sits firmly, you can drill and tap the other holes.

Remember when i said that you may want to leave one gearbox bolt hole not drilled? Here's why..

The bellhousing bolt hole sits on top of the gearbox side of the adapter's bolt hole so you can't drill and tap there. If you leave that particular hole not drilled, you still have eight bolts to fix the adapter to the gearbox AND are able to drill and tap the holes for the bellhousing side. Andrew and I decided to just oblong the hole and use long bolt to fix the bellhousing directly to the gearbox. Here's after i oblong the hole.

and that concludes the adapter plate part of the conversion.. Here's the end result after the outer side is trimmed.

Keep in mind that there's one hole on below right for the bellhousing that you can't drill on the adapter as it sits just on top of the hex bolt head beneath it so you end up using only six out of seven holes on the bellhousing.

One disadvantage from using adapter plate is that your input shaft will be shifted back the same amount as the adapter's thickness. There are two problems raised from this fact.

First problem is that the gearbox input shaft will be floating in the air as it no longer reach the pilot bearing. Leaving it this way is a bad idea as you may risk breaking the shaft later. To solve this problem, you need to make a spacer for the pilot bearing. This spacer will shift the bearing back about the same amount as the shaft offset. Here's the design for the spacer.

Notice the tapered sides? That's to clear the flywheel bolts. The problem with this spacer is that you can't space it out too much as you'll hit the clutch disc but if you space it too little, the gearbox shaft will not reach the bearing. I started with numbers:

a = 36 mm

b = 8 mm

c = 4 mm

d = 12 mm

i then try fitting it in and reduce as necessary so that i have about 2-3mm of space between the pilot bearing and clutch disc. The clutch disc will wear and gets thinner so you need that space. Keep in mind that the pilot bearing is #6001 having 12mm ID x 28mm OD x 8mm T. I didn't have a spare 4A so i had to go back to the machine shop a few times to get it to the right size. A spare engine will save you some time during the swap process.

The second problem is the risk of the clutch release bearing carrier falling off the guide because now the carrier has to sit further forward to engage the clutch. Solution? Lengthen the rear tail of the bearing carrier the same amount as the adapter's thickness.

Here's Before VS After shot..

That concludes this part. Head on to Part 2 for the swap process details.