views on running rose joint rear links in Kp6*

[4AGEMAD]

As per title im trying to weigh up the best option for me kp,either:

buy a set of ae86 links, one end rose jointed and the other end poly bushed.

Then take them to an engineer to be cut and welded to length.

Buy t3's rose jointed links and just run that plus stitch weld the link brackets as ive herd they can crack the floors from being too stiff?

Or purchase t3's links then make up some sort of setup as kpr has done, also take in that im no fantastic welder.

Love to know your views/opinions/experiences.

Cheers

[Roman]

In my opinion / dont own a starlet / grain of salt / etc

 

Rosejointing all links on a 4 link whether triangulated or parallel is a bad idea.

 

Imagine that you had 3 out of your 4 links connected. These are triangulating the position of the diff to the body so that it moves through a particular arc, where ever it is moved to.

 

If you moved the diff through different arcs and measured the length that the 4th link would need to be, it would lengthen or shorten slightly depending on the position of the diff at the time you measured it. As since the diff is already triangulated, a 4th link causes problems. Hence some race cars going to a single upper link on one side of the diff head.

The rubber bushes allow movement as needed - so does urethane - but rose joints do not.

Since the 4 link arms can no longer lengthen or shorten at all through travel the end result is usually a combination of cracking the floor mounts, wearing out rosejoints quickly, or causing everything to flex to account for that difference instead.

 

I'm sure it would be possible to sketch up a cad model to show how much 4 links need to grow or shrink by, it might only be a few mm or less.

 

But it's bad idea in theory / in my opinion.

 

I'm not much a fan of urethane replacements either, where the factory rubber usually has a steel pin through the middle which accounts for side to side movement of the arm, urethane normally have like a big 'washer' type shape which stops movement in this direction too.

 

Which can cause binding as well, in some cases.

Out of those options I'd go for urethane one end, with the urethane trimmed down so it looks like factory rubber (no washer type shape on outside) and rosejoints at other end. Maybe with a hole or two drilled in the urethane on the upper links to allow slight growing/shrinking of length.
 

[4AGEMAD]

Appreciate your opinion thanks Roman. I have herd of people having three links both rose jointed then the 4th link having one rose joint, on poly bush with holes drilled in it.

I have asked t3 to see if they can have a bush/rose joint arm option which would be ideal.

[Roman]

Just in case my blathering above didnt make sense, here's some more nonsense to ruin the pictorial part of your brain also:

 

 

Basically... there are 6 axes of movement rotation which a joint potentially needs to do.

 

Rotation on XY, XZ, and YZ planes.

 

Then movement in the X, Y, and Z directions.

Rubber pretty much allows all of the above to occur. When the bushes get more worn out, they allow even more XYZ movement.

Generally when replacing rubber the idea is to reduce the 'slop' (X Y and Z movement, which makes it feel like the car wobbles on the diff)

 

Different 4 link ends restrict different axes in different ways, a Rosejoint restricts down to the three rotational axes and removes all XYZ movement.

On my car, the upper 4 links (non triangulated) have cutouts in the rubber bushes to allow increased movement in the X axis but keep the Y and Z axes stiff.

 

However the point of contention is whether or not the end of a 4 link arm needs to allow for X axis movement on a triangulated 4 link.

Theoretically the answer is yes, and some peoples broken floors and worn out rosejoints say yes as well.
 

[kpr]

+1 for what roman said.    I wouldn't go rose joint at both ends

 

But will get away with stiffening  it up quite a lot over factory, if suspension is fairly hard.    my setup moves freely  though the suspension travel range plus more.  this was  with the car up on stands, with just the diff case attached and moving it around by hand.

 

also make sure you check your diff for toe. if it has toe out. will  be all over the show even with a good link setup 

[Celica RA45]

what we did in the group c days was use rose joint arms along side the std arms they were only used on the top 1s from memory .peter williamson was doing this ,all he did was make the bolts longer

[spiderwebfx]

Appreciate your opinion thanks Roman. I have herd of people having three links both rose jointed then the 4th link having one rose joint, on poly bush with holes drilled in it.

I have asked t3 to see if they can have a bush/rose joint arm option which would be ideal.

 

I'm interested in hearing the response to this.  If T3 can do something, I may be keen to get one chucked in with your order if you buy off them?  I've already got the S12 4-link kit off them but didn't know that having all rose joints could 'cause an issue.

[4AGEMAD]

Thanks again for the input, solid information there.

Was on the verge of getting the poly/rose joint kit when I got this email from t3:

I'm sorry, this is not something we plan to offer. We have been making 4 links for 15 years now, and have sold thousands of sets. So far no cracked floors or torn mounts. I've run the setup on my personal KP61 for 10 years now. We do use teflon lined massive 3 piece rod ends, so they are not noisy.

Go figure, I am running adjustable suspension in the rear also so it will be a lot stiffer but with that said there will still be movement.

I feel that I may just get the T3 kit then add a polyurethane bushes to it anyway just to be on the safe side?

[Rookie]

I don't know what a KP starlets suspension pick ups/design looks like, but in a correctly designed 4 link system everything Roman is out of the realms of practicality, when you get into bind on a 4 link can be 10 or more inches of wheel travel. On my Lotus with 4 link there is no problems at all running rose joints everywhere.

 

And the reason race cars use 3 link instead of four link is to change the instant centre and aid traction, not to avoid binding in a 4 link system.

 

You may find that rose jointed links aren't your cup of tea on the road, but that is personal preference.

[4AGEMAD]

Im not worried about road noise, just want something that will give me a direct feel but not wanting components to fail.

Kp's run a triangulated 4 link.

[RUNAMUCK]

I'm pretty sure the book says that you must run rubber at one end for the street. That way it can't bind.

I wouldn't bother on a street car tbh.

the joints don't last that long on a street driven vehicle. Just not worth the hassle.

[Snoozin]

I don't get any binding throughout the travel of my diff with the t3 4 links fwiw. But have only test fitted and moved the diff through its range of motion whilst on axle stands.

If I don't like rose joints then I'll change it later but for now, rock on.

[mjrstar]

I run the standard rubber bushes in my KP and they seem to be handling the abuse pretty well..(240+ wheel kw plus semi slicks)

 

Personally I am not motivated to change to rose joints. Inless it's a reasonably hard core track weapon I don't see the benifit  

I would be all over spherical strut tops up front, and firmer bushes for the lower control arm and swaybar before considering the 4 link on a KP. / meh useless post.

[Adoom]

170kw.

I am running rose joints with parallel arms and a panhard rod. I did it because I had problems with axle tramp and wheel alignment with the factory arms/bushes.

I also tried poly bushes at both ends(I thought the rose joints were shagged, but it was diff noise), then it was pointed out that they were so stiff, the diff could only go up and down but not twist, so I went back to rose joints.

I like the direct feel. 

No problems with mounts cracking.

Noisy as in a stripped car though. I get a lot of noise transmission from the LSD. But racecar, so who cares.

[4AGEMAD]

Cheers all for your inputs, you guys are the best! 

 

I've decided i'll purchase the T3 links, i'll be running quite stiff 86 rear adjustables. Will line everything up and go through the motions of travel to check for binding etc, i'm still wary of wear/breaking etc. Might possibly add poly bushes but will see how it all feels. 

 

Thanks again 

[eke_zetec_RWD]

It won't bind AT ALL if all 4 arms are same length and parallel to each other.

BUT other than that it will. In saying that if like said above you can move it easily then roll it.

If you want to check how bad it is pull one bolt out and watch its hole alinement while you move the diff up and down. ( springs removed )

[Testament]

I dont know KP,s are they triangulated (inward pointing upper arms? or parallel with a panhard rod?

 

if they are parallel there is no bind issue ever

 

if they are triangulated I would think a stiff bushing in out end will give more bind than rose joints at both ends as the rose joints don’t resist angle changes in any direction - PROVIDED they are within their range of motion. if you run a rose joint outside its range of motion then you are going to break shit.

 

the downside is changing to rosejoints may actually allow slightly more lateral diff motion if there is no panhard rod/watts link/mumford link

 

also rose joints dont just make things stiffer, they reduce friction in the suspension system which means shocks and springs can react quicker to forces applied to the car be it cornering, braking or accelerating.

[4AGEMAD]

Kp rear has inward pointing upper arms. 

With the suspension I am using, there will be heavily reduced suspension travel compared to factory so this should minimize wear/possible bind etc. 

 

But damn T3 has a hefty price tag on those arms! will have to wait a little while so the wallet doesnt shrivel up.  

[mjrstar]

It will be interesting to see how it grips up, I went from 400lb rear springs to ~240lb springs and the increase in power down grip was astounding. keeping in mind that my car is nose heavy with the boat anchor up front.

 

If you are running mega amounts of low the triangulated 4 link will bind and actually limit max compression travel.

 

EDIT: for those unfamiliar with the rear setup in a KP they are parallel lower arm and triangualted upper arm with no other lateral mechanisim apart from the upper arms.. so going to spericals all round may requre addition of a watts link or panhard rod?

[4AGEMAD]

Not wanting 'full grip' as it were mate

Running either 6 or 8 kg springs in the rear so not too durastic.

But yeah it'll be at a sensible low, nothing crazy (famous last words).

I'll be adding a set of traction brackets to help though I am wary that itll stuff things up even worse since im repositioning 2 arms rather than the four?