Harsh ride!

[sketchy]

Hi guys,
I have recently lowered the rear of my ae86 by installing some rear Driftworks CS2 suspension.
Since i have changed from standard rear suspension this has caused the back end of the car to hop and judder quite a lot. This feeling is very bad if accelerating whilst going over a bump!

Me and some friends think the ride may also feel too bumpy because the springs are too stiff? Though the springs are 6kg, which is a popular choice on the rear? Is the 6kg spring rate coupled with a lighter ae86 (stripped interior, lexan windows and FRP tailgate) too extreme of a combination!? Or is it not the spring rate at all…..

After some reading this hopping seems to be a fairly common side effect to lowering the rear of the car and can be resolved improved by installing some traction brackets to align the geometry nearer to a standard position. Currently looking at the T3 ones?
Would a set of adjustable four links also be necessary/advisable? If so, what is the best method for installing/setting these up?

Really appreciate some views/advise on this so i can enjoy the ride in my car again!

Cheers

James

[NoHachi]

Sounds like wheelhop, but hard to say. What bushings do you run in the rear? Have you tried adding a little extra damping to the rear shocks? Does that make it better or worse? Have you cut down the OEM bumpstops before lowering the car?

Traction brackets wouldn't be a solution to your problem usually. They run just fine without. Its not the pinion angle (4 links) either.

[sketchy]

Thanks NoHachi.

I run poly bushings in the rear, only rose joint is on the panhard rod.
In terms of damping, i've run the car on min and max and not really noticed any change in the amount of wheel hop.
I have cut down the bump stops but I could raise the car up to see if the wheel hop improves?

Damn, thought id found what the problem might be.

[totta Crolla]

Probably the best way to approach this would be either go back to stock
and then change one thing at a time or you could mix and match old and new
components to find the problem.
It might also be worth checking that the 4 link bars are moving ok and not binding in their mounts.

[NoHachi]

The easy thing to try is to set the rear ride height back to where both 4 links are pointing slightly upward again (looking in the direction to the front of the car). Watch out though, you'll notice some extra oversteer.
If this works you either have too little travel or the traction brackets might be worth a shot.

You want to confirm that you are not hitting the internal or external bumpstops. Can you take a look and see how much bump travel is left with the car in static position (how much exposed shaft). You need a good 30mm or so at a minimum. Are the rear dampers shock body adjustable? Do you see any evidence of spring bind on the springs (small nicks and scratches).

Checking for binding like totta mentions is also a very good idea. Its hard to do in practice though, since you cannot replicate the forces on the bushings easily. However you should be able to freely move one end of the axle or the other through its range of motion at a minimum.

[ep71]

i would be inclined to say that traction brackets would resolve your problems, by lowering the rear of the car the angle of your rear link bars has changed so that they are now pointing slightly up. this means that the tractive force from the axle is now acting to push the axle upwards thus compressing the spring rather than pushing the car forwards.
i have traction brackets for sale if you are interested

[zenki]

I had this too. When i raised the car the problem went away. But then the car looked shit so i lowered it again. So installing traction brackets will probably make it alot better.

[sketchy]

Really appreciate the broad range of input guys, very helpful thank you.

Nothing is fouling the travel of the suspension, i.e. bumpstops and the amount of bump travel should be above 30mm.
I have not heard any spring binding.

I have moved my car into a nice dry garage with the intention of raising the rear suspension to a stock height to see if that affects the wheel hop. I'll also check that:

The four links don't bind in their mounts.
The springs don't show any signs of binding.
Measure how much bump travel i have and set that accordingly when/if i lower it again after.

In terms of the four links and traction, i found this article from hachiroku.net very helpful. So may look into a set.

http://www.hachiroku.net/5link

[jondee86]

Hmmm.... I think I would have to call BS on that Hachiroku link. As can
be seen from the diagram, any downward force on the rear axle caused
by the trailing links, is conteracted by an upward force on the car body.
So the weight applied to the rear axle thru the springs (which is the
primary force pressing the wheels onto the road) remains about the same.

Not saying that there might not be some momentary advantage due to
inertia, before the body lifted, but I don't see that doing much when
accelerating out of a third gear corner.

I would think that the so called "weight transfer" by the rear axle trying to
drive under the vehicles centre of gravity would be more helpful to traction.
But I'm not a suspension engineer, and can't be bothered researching the
correct answer, so shoot me down...

Cheers... jondee86

PS: Check your poly bushes have not started breaking down. They can
start to break up and come loose after a bit of use. Loose bushes will
give you axle tramp.

[sketchy]

Finally checked out the suggestions!

Couldn't see any sign of binding (four links or springs) and the poly bushes have only seen about 500 miles use. Static bump travel more than 30mm.

I took the dampers off (shock body adjustable units) and wound them out to increase length nearer the installed length of my old TRD's (~1.25" increase).

It was quite dark but i could at least see the four links were at a less extreme angle. I'm pleased to say, as was my passenger,that on the test drive the wheel hop had gone and the ride was far smoother. So thanks all!

I'll see how the car sits in daylight, have a proper look at the angle of the four links and drive it a bit more, but think i may need a set of traction brackets if i do want to go lower/ need to restore the angle of the four links.

James