Hi,
I am designing a full tube frame to mimic my now deceased FX16 GT-S circle track stocker.
While drawing the rear suspension and mounts in 3d using Sketchup, I noticed a possible anomaly.
What keeps the rear suspension from binding when it travels?
Control arms pivot at an angle (essentially changing wheelbase, minutely.)
Trailing arms pivot at different angle.
Do the stock rubber bushings have enough "give" to prevent trailing arm from binding/stopping wheel travel?
If so, how do (harder) polyurethane bushings accommodate this?
Silly question maybe, but I just don't know
Thanks,
Brian

I'm not familiar with the AE82 rear suspension, but the same
question of rear axle binding comes up with the AE86. Rubber
bushings are used by the factory to accommodate the trailing
link movement caused by body roll. Because the upper and lower
trailing links are of unequal length, if one end of the axle drops
more than the other, binding will occur.

Solutions range from drilling holes in one of the top bushings
to removing one of the top arms, converting to equal length
links or converting to a single centrally located top link.

Binding is made worse when using poly bushes or heim joints
on the trailing links. This forces the attachment points to
deform to accommodate the change in length, and can result
in the attachment point being torn from the body of the car.

Reducing the amount of rear axle movement with very stiff
springs and short shocks alieviates the problem somewhat

Cheers... jondee86

Exactly, its the bushings that take the bulk of the angular differences in dynamic motion.


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Hi jondee86,
The FX16 GT-S has two separate control arms (parallel), a trailing arm, and the McPherson strut. Also a sway bar.
I just did some doodling in Sketchup, and it actually looks like it won't bind if there is not a lot of travel.
I drew a line depicting the axis of the control arms, then pivot the trailing arm down. The line I drew was within the centerline of the trailing arm's motion.
When I dismantled the old car, I did notice the trailing arms had a slight bend to them.
Anyone know if this is how they are from the factory?
Moto-P, would you recommmend for or against poly bushings?
Thanks Guys.

P.S. Will post a pic soon.

Assuming that this is your rear suspension...
https://partsouq.com/catalog/images/toyota/images_GR_B3/MC9690A.png

Then I can see some small potential for binding, but nothing like
the problem on an AE86 with long-travel suspension. Poly bushings
have some limited ability to compress and absorb any misalignment
caused by suspension movement, and I cannot see you having any
problems with short-travel suspension.

Just remember they are a maintenance item, and need to be lubed
on installation to reduce wear and squeaking

Cheers... jondee86

BroBri wrote:Moto-P, would you recommend for or against poly bushings?
Thanks Guys.

P.S. Will post a pic soon.

Well the use of polyurethane or rubber really depends on locations, and your preference on handling.
Polyurethane is best when very sticky tires are used, and accordingly, with very stiff suspension settings where tires will still grip enough to load the suspension.
In such case, the suspension travel will likely be minimal and much less than when using less capable tires. If the suspension must stroke a longer arc, it's best to leave places like lower arm, and upper arms, traction rods (all or some) in rubber so that articulation is smoother. You should in all cases, use ball or hard urethane for places like tie-rod ends, and toe link locators.

jondee86 wrote:Assuming that this is your rear suspension...
https://partsouq.com/catalog/images/toyota/images_GR_B3/MC9690A.png

Yes, that's the one.
I've had a hard time finding (all) the stock rubber bushings for this application.
Whiteline seems to have the poly sets available, but not sure I want to dump all that money.
Any tips on where to find stock? I think there are 2 or 3 different sizes at the rear.
Thanks Guys

Here's a taste of how it's going!

BroBri wrote:I've had a hard time finding (all) the stock rubber bushings for this application.
Whiteline seems to have the poly sets available, but not sure I want to dump all that money.
Any tips on where to find stock? I think there are 2 or 3 different sizes at the rear.

It looks very much like the rubber control arm bushings were only sold
with the complete control arm. Regardless, even if they were available
separately, they are most likely out of production now. You may get lucky
and find that some bushings crossover into other Toyota models, such
as the Ae92... but I don't have a FWD and have never researched to
see what is possible. Otherwise you are stuck with poly bushings.

Nice drawing... good luck with the project.

Cheers... jondee86

My FX has the Whiteline bushings, they weren't that expensive. I lived in the mountains and had to upgrade my suspension for the commute. As for the binding in the suspension? Never was an issue. Even when the suspension was going through the full range of motion with worn out shocks and springs.

You should check out fusion 360 for CAD.
It amazes me that anyone can get anything done in sketchup lol but F360 should walk all over it in every way.

Thank you all for the input.
Yoshi, I checked out the F360 page. Yikes! $1200/year!
Looks like I'll tolerate Sketchup a while longer

BroBri wrote:Thank you all for the input.
Yoshi, I checked out the F360 page. Yikes! $1200/year!
Looks like I'll tolerate Sketchup a while longer

That's just for the ultimate version. There is a basic version that is just missing a few things like full 3D cam but nothing that most people would miss. It's like $300/yr.
Even better is the basic version is free for personal use. There is also something about startup companies being able to use it free or something. I don't know the details on that. Whatever the case if you aren't using it commercially you should be able to apply for a personal use license or something like that.

You guys are awesome Yoshi and johnD


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