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3,971 Posts
Discussion Starter · #1 · (Edited)
Hey Everyone,

I've recently test fit some prototype subframe brackets for Raptor Racing that will improve the safety of your modified Celica Supra. I have recommended that the design enter production and have been asked to give a quick overview of the part and installation.

In recent years, the community has made significant progress in suspension tuning of the Mk2 supra. With significant aftermarket support long gone, innovation has been driven from within the community by members like Jim King, Rabidchimp, Carlos Brown, FunkyCheeze, Suprafiend (Seamus) and George, among many others. The community itself has developed, produced and graciously shared knowledge so all of us can enjoy our cars a little bit more.

Rear subframe modifications to reduce the amount of negative camber have increased in popularity thanks to the improved availability of a reproduce-able weld-on bracket solution that can be purchased from Raptor Racing. Since this is also an ideal time to replace worn out rubber bushings, popularity of bushing installs has also increased.

With all the activity in this area, discussion has increased and members have begun to question the norms which we have assumed for years....that the rear camber can't be fixed, that Toyota can't be the only place on the planet capable of making camber bolts, that we need to purchase super expensive bushings from Australia, etc. What if better options existed? This small community has tradesmen, engineers, vendors and enthusiasts that can create progress together. We don't need to settle for mediocrity. During such discussions, Seamus questioned the rear subframe bushing design and how a subframe is actually held to the vehicle that has been modified in these ways and found some problems.

Seamus' conclusion was that Toyota's original subframe bracket, although just fine for a stock application, was insufficient and potentially unsafe when used in conjunction with urethane bushings. Rather than ignoring it as others have in the past, he created a solution and soon you're going to be able to purchase a professionally made version.

"Ok Steve, what are you trying to say?"
- If you have urethane subframe bushings, you need this.
- If you have already installed urethane bushings it takes 10 minutes to install and only two tools.
- Raptor Racing will be including this in future bushing kits.

"That's nice, why exactly do I need this?"
Toyota designed the rear sub frame, differential and suspension assembly to be fastened to the car's unibody at four points: two rear diff mounts and two two forward, larger subframe mounts. Of course, it's undesireable for premium model like the supra to transfer unwanted differential and suspension vibrations into the chassis and occupants, so Toyota fitted these mount locations with rubber bushings.

The way Toyota made these bushings is important. Each bushing is cast or bonded to both an outer shell and an inner sleeve creating a chemical bond between the rubber material and it's interfacing metal. This bushing assembly is then pressed into the mount locations. With this method, no slippage between any surface will occur and vibration can reliably be absorbed into the rubber bushing material. This can hold a significant amount of vertical load as there is a lot of bonded area. Infact, our cars are over 30 years old now and I have yet to see one that has completely failed...

Urethane bushings, however can not be easily made in this same fashion, nor be easily installed by folks like us at home. For this reason, aftermarket bushings for our subframes are always made in two parts that resemble a flanged tube. All urethane to metal surfaces are thoroughly lubricated to prevent squeaking. This is a big difference between Toyota's solution and the aftermarkets. Movement between these surfaces is actually encouraged with urethane bushings and the grease helps us with that. The drawback of this is that we no longer have a bond - the subframes movement can only be controlled through compression of the material.

Sounds scary? well, it is. The good news is that most of the loads from going around corners and general driving are in the horizontal plane - the subframe gets pushed around left, right, forward and back. The subframe mounts take most of this punishment. This bushing design falls short for loads in the vertical plane. The subframe gets loaded this way in a number of driving situations but it's most visible if you jack the car up.

"Visible you say? How the hell do you see load? That makes no sense"
Sounds crazy, but you can see the bushing deflection as it complains about being loaded this way. Don't believe me? Jack the car up and look if you have urethane bushings in your car.

you can see the deformation a bit better with the bracket removed.

This is my car when jacked via the rocker panel. You see how the bushing is making a concave shape? The subframe's own weight, combined with the spring pressure is attempting to push the subframe off the car. That bushing should not be shaped like that, it should be flat.

"Why though? That's crazy... I don't get it, It's got a bigass bolt that surely must hold things together, and how has nobody noticed this before?"
I don't know why nobody noticed. everybody was in denial? I was when I first talked about it with Seamus. Nobody took a good look until Seamus? Water under the bridge, I guess. We have a solution now.

So lets think about what's actually holding the subframe in the car while looking at the above picture. The big nut is screwed onto a big stud that goes all the way to the inside of the chassis. when you tighten that sucker down, it clamps on a silver metal sleeve that comes with your subframe kit. This prevents over-compression of the bushing and holds the two bushing halves together. Notice I said bushings halves, not subframe?

Now, look radially outward from that nut head to the subframe bore's edge.....nothing but bushing in between there. NOTHING BUT BUSHING. The grease isn't helping that bushing stick to the sleeve, which means that subframes load...which must be reacted by the little flange on that nut is pushing down on that tiny little gooey lip and puts that lower bushing under bending.

Over time, movement, and this load can cause this urethane lip to wear. If this little 5mm lip fails, your subframe will attempt to separate from the car. Not good.

Fortunately, Toyota doesn't employ idiots for the most part, and somebody considered this failure mode, even in the stock bushings and have supplied a subframe bracket (manual calls this a bushings retainer) which is bigger in diameter than the bushing hole. In the event of a bushing failure, this bracket would catch the subframe from separating from the car completely and allow you to retain control of the vehicle. It's also not just a simple washer, it has a smaller leading bolt hole which fixes the bracket to the chassis. Where a washer has the ability to spin, the bracket can not, and greatly reduces the chances of that nut backing off. Some good engineering in that little bracket. But it isn't perfectly suited for our urethane bushing application.

"Show me the bracket already"
Here's the fix. It's similar in concept to the factory bracket but has a large, flat surface to support to the subframe. Because the diameter of this bracket extends flatly out to the subframe edge, the bushing is no longer in bending, it's in compression (getting squeezed) it's now the bracket that is under bending but at least it's steel. Much, much more suitable thing to ask a bushing to do, don't you think?

no more sag

new on the top, factory on the bottom

"Ok, I'm sold. Sounds like cheap insurance. How do I install it?"

Install one at a time to avoid subframe movement.

- Chalk front and rear wheels
- Jack rear of vehicle or via differential or pinch weld
- Rest subframe on jack stands as pictured above
- Remove forward bolt
- Remove large nut
- Remove bracket
- Install new bracket
- Reinstall fasteners
- Repeat for other side

Now go out and enjoy the piece of mind....and the sweet, sweet sound of that inline 6!


59 Posts
So is it bad that I jack the rear of car up on the sub frame brackets? That's the only place in the rear that I see that is jack able. Where are you guys jacking up the rear of car at?

3,275 Posts
I recall lying down under my car, staring at these things with Seamus for a long, long time. We spent more than a couple minutes trying to figure out if we were crazy or not. Something just didn't seem right...

I'm glad to see these are going to be available to the community!

27 Posts
Hey Tire Shredder - well documented and definitely *needed* correction to the subframe bushing problem that I never knew existed...definitely in.

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