Full Spool 8" Differential

[DiscoQuinn]

Sadly I'm having trouble finding info for this, I'm getting lost in turbo threads instead of differential talks.

'17 BRZ. I'm aware our cars use a Toyota 8" differential which is shared with the Supra, X-chassis and many other Toyotas, including 4x4's.

I'm a drifting instructor, and I'm not liking the feel of, what I believe, is a torsen in the back. It's locking and unlocking at inopportune times.

My last E7-Corolla was a Kaaz 2 way which was great, but is far too expensive for this car which multiple people will end up driving.

Welding is an option, but I've used full spools in some of my AE86's and other corollas in the past with decent success.

My question is: Will the Toyota truck 8" full spools work in our rear pumpkins? Is it the same ring gear bolt pattern, bearings and splines? Or is there some dimension that will require modification or dismissal of the idea?



If you've run one, which one?

Thank you.

[DiscoQuinn]

I'm going to bump this thread as I don't have a stock axle to count the splines on.

Does anyone have a BRZ axle to check how many splines the axle into the diff are?

[Turdinator]

Originally Posted by DiscoQuinn

I'm going to bump this thread as I don't have a stock axle to count the splines on.

Does anyone have a BRZ axle to check how many splines the axle into the diff are?

I'll check that for you today.

As a starting point it might be worth looking at the part number used by KAAZ and some other popular LSDs and seeing if that same number is listed for other vehicles. It would be a quick way to then look for spools in those vehicles.

[DiscoQuinn]

Picked up a spool today and a spare IS300 diff and we'll see how she fits! <3


Edit: IS300 diff apparently fell out of the truck on the way to meet me....

[DiscoQuinn]

Took me a while, lots of measuring and some good friends.

[DarkPira7e]

So it fits? It functions?

[DiscoQuinn]

Today was day 2. Our local track is closed due to health restrictions so I've not had a chance to do anything but some daily driving to test it out. I don't have a good spot to go do some big skids and feel the differences in a proper manner. But it is working, took a lot of adjustments to make it fit as there were some differences in the Toyota truck and toyota car 8" diffs, but it was close enough to make work.

[Berserker]

Any side notes on what you needed to do for fitment? Just playing with shims more or less?

Appreciate any extra info. I wouldn't mine having a spare diff with a spool for the 1/4

[DiscoQuinn]

Oh man! There was so much I had to change to make it fit.

I did some digging and found that the toyota 8" truck had two versions of spools, and the one of them was the same as the FRS in 3 ways:
-Bearings
-Ring gear pattern
-Spline count

So my brain assumed I just needed to press on some bearings, pop a ring gear on and slap it in. It didn't turn out that way sadly.....





I didn't expect:
-Spring clips that hold the axles in the spool
-Truck flange is 4mm offset from the bearing than the BRZ/FRS
-Axles step up to 35mm after the splines.
-Splines in the spool were too long





So I took it to a local machine shop and they were able to machine the 34mm inlet to 35mm. They were also able to trim back the splines so that they start a bit deeper in the diff.

However, they didn't feel they had the right tooling to cut the spring clip grooves. So I had to get a bit more creative:





I designed my own mini-lathe specifically for the job using a modified dremel. This allowed me to set the X and Y depths of the spring clip cut separately and carefully. This tool also allowed me to cut 2mm off one of the bearing shoulders so I could add it using spacers on the opposite side. Not ideal, but plenty fine for testing.

[EAGLE5]

Easy peasy!

[Berserker]

Thanks for all the details!! You went in

[ROADRACER]

I am very interested to hear your evaluation on the new handling characteristics. As I understand it a spool will create a lot of understeer and other issues.
I guess than wont be a problem if you have both wheels spinning in a drift, but will it make the transitions difficult?

[DiscoQuinn]

Originally Posted by ROADRACER

I am very interested to hear your evaluation on the new handling characteristics. As I understand it a spool will create a lot of understeer and other issues.
I guess than wont be a problem if you have both wheels spinning in a drift, but will it make the transitions difficult?

I've not had a track day yet with it, because of covid restrictions at my local track.

However, after owning 73??? other cars, and most of those being drift cars; transistions are much more predictable when you know the diff isn't going to randomly unlock on you.

The myth of understeer is real, however, this is only at low speed, tight corners. For auto-x this is a problem, for road racing, and drifting, it's not an issue. Although it does scale up the higher the grip tires you use. But if you can afford R-comps then you can afford a good 2-way.

However, I'll update this thread if I'm ever let back on the track. I live on a small island, and finding a place even to have fun and test the limits is difficult as the cops and everyone else on the island have nothing better to do.

[DiscoQuinn]

Update:

I spent time at a drift event, roasted 4 tires.

It took a year? ish? for me to collect enough resources to get a spool into my car, but today I finally got to test it.

I'm working on a project to find the most minimal changes that make the most impact on a car which has the wrong reputation from journalists: FT86 is easy to powerslide! (but hard to drift). Those two are often confused, but are quite different.

August 2020 I made a hypothesis of the issues of the car here:




It took all this time to get the spool finally into the car, but also with Covid, being allowed to test it. I live on a small island and the cops have nothing better to do so I needed track time to test.

There was two results today with testing:

#1: The diff was 80% of the problem.

You see in a powerslide, you are only oversteering towards the exit of a corner. This means that you set the maximum turn in steering angle at the apex, hold the throttle to the floor, then countersteer as the rear steps out. When powersliding you hold the throttle to the floor, and slowly dialing back the angle of the slide until the car grips up on corner exit.

The FT86 is really well setup for powersliding regardless of the slight variations between the versions. I never had any issues with managing power slides.

But drifting was a nightmare. In drifting, you're to start the slide before you enter the corner, monitor and modulate wheel speed and steering angle, then prep the cars position for the next corner. This includes transitions which change directions while maintaining the drift.

I was struggling with proper drifting in the car, without having to bash the fucking clutch the whole time and use the hand brake a lot, which is a really shitty ugly driving style, but also so so so hard on the car. Banging limiter and dragging e-brake for an hour for entries is cringy and expensive.

Trying to feather the pedal or manage traction loss in a gentle and graceful manner in the FT86 had me yelling in the car as the car would do such unpredictable things.

This is a result of an oxymoron state the car was designed in, and why, even though it's a globally sold cheap RWD, it's not the dominant drift chassis people expected. Let me explain.

Torsen, is actually an acronym from two words; torque sensing. This means that a Torsen is only a 1-way diff. It will only lock, it will only provide power to both wheels, in the state of acceleration. Basically, in order to maintain a slide, you must commit and hold the gas pedal to the floor, which is scary, and offers no precision in your slide unless it's a full throttle powerslide towards a corner exit.

Even a 5% feathering of the throttle will cause the torsen to unlock, as you've put it into a state of either coast or deceleration. This results in loss of wheel speed control, and usually the car suddenly grips up. Which is also often a surprise to the person operating it at the time. (also why the chassis has a reputation of crashing)

The Oxymoron is the Torsen+Torque Dip problem. The car comes with a torque sensing differential, BUT, it has an unpredictable torque delivery problem from the engine. These two compound into a car that is easy to powerslide, and dangerously unpredictable to drift.

Powersliding is acceleration only type oversteer, but in drifting you often use deceleration and even a middle ground between the two where you just maintain a slide or make adjustments to one.

Doing the track day today:
The spool actually allowed me to feather and modulate the throttle far more than before. Although clutch kicking was needed to maintain RPMs during some longer drifts, I had no need to clutch kick to maintain the differential locking.

I've never seen another car that has an aftermarket for upgraded clutch forks, but the FT86 has a variety of billet and forged ones. Another sign people need to clutch kick these cars too much.

Result #2:

I knew the diff was 80% of the problem, and this guess was accurate. 80% of the bad driving feel was corrected by having a predictable diff.

However, the last 20% is still a huge part of the issue, and I thought it was the torque dip and caster that was making transitions so difficult, but I was wrong.

The electric steering works only at a certain rate. In a traditional hydraulic rack, there is a rotary switching valve that can tell which direction the steering rack is moving, and diverts pressure there mechanically. This process is near instant except for cars with steering dampers.

With the electric column, there is a significant delay to when the motor starts assisting you in the new direction of the drift.

If you do slow transitions, this isn't a problem, but fast flicks, even throwing the wheel for countersteer will find the electric motor still pushing in the previous direction, which delays the countersteer and results in a spinout on track. (another reason people crash these things all the time)

Adding some caster to the front is difficult without major changes, but would assist to this problem. However, I have a spare column at home and will be deleting the assist motor altogether for testing purposes as the rack itself is manual, and many of the corollas I've drifted in the past were manual rack.

I'm not ready for added steering angle yet, as I'm just trying to improve the precision of inputs and communication between the driver and the car. Though I will be working on my own angle kits as well in the future, but from the same perspective, of modifying a little as possible to get the biggest improvements to driveability.

I'm happy the diff worked well, and will be pulling it soon to do inspection and new seals. I will say though at this point, I don't have enough money to make a batch for others.