Stability Under Brakes And Car Walking Around

[Roy]

Just got back from a track day and im worried i have blown a shock

The car moves around a hell of a lot under brakes. It makes it hard to stop the car as the rear end moves around a hell of a lot making it a real handful.

Its nto a brake bias problem as my my brakes are fine and its not locking brakes. I cant really jump on them like usual without the rear end wanting to overtake me.

Alignment settings are:

Front: -3.4 deg camber , 0 toe and 5.7 deg castor

Rear: -1.00 deg camber, total toe 2mm

I have big swaybars which are on the hardest setting which is another concern i have.

So to make sure i dont have enough on my mind while punting it is that at high speed the car walks all over the road. It generally takes small steering corrections to keep the thing tracking straight. Really disconcerning when you are doing 240km/h

I have replaced the front upper control arms with aftermarket ones thinking that the bushes were dead and responsible for the knocking and front end wander. The new arms have fixed the knocking but not the wander.

So, anyone ... help ! Right now i need more susp to make the most of the engine power and tyre grip i have

[CEF11E]

Hey roy Are your castor bushes in good condition?

I have found a similar situation at much lower speeds. under hard braking in a straight line going from 140 to 60 in a short distance the rear end squirms around. and am about to replace the castor arms with adjustable ones that use spherical bearings. I know a lot of people say don't use them on road cars but i have decided to give them a go.

[salad]

Why so little castor? Stock specs are 6.5 +/- 0.75deg. Increasing castor a lot could solve your front wondering around problem.

Something seems a bit weird if you've got the upper arms set short enough to get 3.4deg camber and you've still dont have much castor.

When I've gone from 1.5deg camber to 3deg, I've found I usually gain another degree of castor.

With the twitchy rear on braking, maybe try a bit more toe in?

Edited April 1, 2007 by salad

[dontfeelcold]

Swaybars don't do much under brakes unless your turning and braking.

You didn't overdo it on the ripplestrips did you?

I assume you checked the basics? (wheel nuts etc)

Edited April 1, 2007 by dontfeelcold

[Roy]

Thats all the castor i can get out of the Whiteline bushes. Im looking at getting some cusco castor arms in the next week or so.

Its also back to the drawing board...the money that was going on the new motor now needs to be diverted to suspension as it was fun but a handful at PI. ..could so be so much quicker if i could balance the car out better, especially under brakes

[Roy]

Swaybars don't do much under brakes unless your turning and braking.

You didn't overdo it on the ripplestrips did you?

I assume you checked the basics? (wheel nuts etc)

What do you mean by overdoing the ripple strips...im trying to pull the car up in a straight line...most difficult coming up to Honda where i was lifting off early through Southern Loop as the car just didnt have the control to pull it up while getting back to the left hand side for Honda. And then into MG where the car was just wagging its tail.

Also a friend following me can confirm the car is crabbing in the rear end on the high speed stuff...and it looks like its wanting to lift its inside rear tyre...so to me it sounds like the bars are too big for the rest of the suspension setup and weight of the car

[Risking]

So is the arse of the car becoming light under brakes?? or is it just moving around under brakes??

If the car is crabbing then thats going to be the first place you start to look at. Sway bars etc are obviously not going to make it crab and a crabbing vehicle is always un-easy when pulling up.

If its trying to lift the inside rear stiffen up the front bar if possible and see if it helps level the car back out.

The allignment looks okay all bar the castor, Its way to low. Has the thing had a front ender at some stage?? as someone pointed out its actually less than the factory settings.

[dontfeelcold]

What do you mean by overdoing the ripple strips...im trying to pull the car up in a straight line...most difficult coming up to Honda where i was lifting off early through Southern Loop as the car just didnt have the control to pull it up while getting back to the left hand side for Honda. And then into MG where the car was just wagging its tail.

Also a friend following me can confirm the car is crabbing in the rear end on the high speed stuff...and it looks like its wanting to lift its inside rear tyre...so to me it sounds like the bars are too big for the rest of the suspension setup and weight of the car

I mean if you drove on ripples strips to much it might have damaged something. Not sure how bad they are at PI but just a thought.

[Roy]

LOL...now i get you. Yeh, they are there to be used and i use them

The car has never had a front ender. I just checked the alignment sheet again and its actually 5.7 deg.

I dont feel there is excessive weight transfer under brakes, the car is just unsettled. Ill try and edit the vid and show what the car is doing.

I get the feeling that the 90,000km/ 6 yr old Bilsteins have had their day. They have served me well and have probably done over 3,000kms of track work

[Simon-S14]

get them on a shock dyno, that will eliminate that soon enough, and worst comes to worst you can rebuild them for around 100 each.

How are your rear subframe bushes? my cefiro under hard braking used to walk all over the place and it turned out to be all 4 subframe bushes had perished and crumbled away... making the whole rear move around a lot. ended up fitting alloy spacer/bushes and that solved that

[Roy]

With the exception of the swaybars and upper control arms, and the front springs which are all a bit newer, the shocks, bushes etc were all replaced 90,000kms/6 yrs ago.

The car gets a good once over every wheel alignment but thats not to say that the cradle bushes arent dead. Ill add that to the list of things to check

As for getting the Bilsteins rebuilt. They are a good thing when you look at the dollars and served me well, but i find with semis on the car that they dont make the car feel as nice as it does when its on streets. A few other ppls cars with different brands feel much better so im back to where i was 12 months ago with needing to get it all checked out then maybe new shocks and springs

[Beer Baron]

Why so little castor? Stock specs are 6.5 +/- 0.75deg. Increasing castor a lot could solve your front wondering around problem.

Something seems a bit weird if you've got the upper arms set short enough to get 3.4deg camber and you've still dont have much castor.

When I've gone from 1.5deg camber to 3deg, I've found I usually gain another degree of castor.

With the twitchy rear on braking, maybe try a bit more toe in?

i've actually found it the opposite on my skylines. the more castor I have the less static camber i get and vice versa. I think as the rod is pulling the assembly forward it's reducing the static neg camber. since the upper arm and the castor rod are both pulling against each other to a degree there is a limit to how much you can get out of each one.

[blind_elk]

How are the rack ends? You might have a bit of wear that is allowing dynamic changes to toe.

[Roy]

Thats what im hoping, but i think it could also be a dead shock.

The rod end boots are torn front & rear but there doesnt seem to be any play. Problem is its almost $600 from Nissan for replacements. There has to be a cheaper solution going around?

[blind_elk]

I know mine has a bit of wear in the rack, and I get a similar wander even with gentle driving around town.

A dead shock should be pretty simple to diagnose with a "bounce test".

[Roy]

Well the way the car got unweighted coming onto the striaght tells me that a shock may be dead. And the way the car moves around under brakes tells me a shock may be dead. It really bucked over the undulations. I just hope its not shocks...dont want to spend big money on shocks

[salad]

i've actually found it the opposite on my skylines. the more castor I have the less static camber i get and vice versa. I think as the rod is pulling the assembly forward it's reducing the static neg camber. since the upper arm and the castor rod are both pulling against each other to a degree there is a limit to how much you can get out of each one.

Hmm, interesting. When I wheel aligned my car Friday night, I set camber to 3.1 or so and then when I finished (after castor adjustment) it actually increased static camber to 3.25. Thinking about it a bit more pulling the LCA foward makes it a bit more parallel to the upper arm (as it's on a ~30deg angle facing backwards) and effectively makes it longer. This is just me thinking about aloud at the moment though...

Because of the angle of the upper arm, when you shorten it, it pulls the top of the upright towards the back of the car, so you increase castor by a fair bit aswell as camber.

Well this has been my experience anyway and me thinking about it a bit more makes a bit of sense to me, so good enough for me

Edited April 2, 2007 by salad

[Sydneykid]

Hi Roy, I can whip the Bilsteins on the dyno if you want, just let me know. We have the specs of brand new (out of the box) Bilsteins to compare to. I can also arrange for them to be revalved to more suite the uses that you put them to. You know the problem, you are going to have to pay 10 times as much to get anything better.

Is that rear toe out or toe in 2mm? If toe out then that is definitely a problem, if toe in then I would suggest increasing to the recommended 2mm each side.

cheers

[Roy]

Is that rear toe out or toe in 2mm? If toe out then that is definitely a problem, if toe in then I would suggest increasing to the recommended 2mm each side.

The million dollar question. Is toe in positive or negative?

I have spoken to Quadrant down here about revalving and adjustable spring seats with some higher spring rates.

Im hoping that with higher spring rates then they can help control the roll of the car and that the swaybars will be less likley to unweight the inside tyre. It was really pronounced at PI. Im hoping to get my hands on some good jap stuff....if they fall through i may just get the Bilsteins rebuilt. Dont care about streetability anymore. Just want to tie the car down so its actually quick...

[Sydneykid]

good jap stuff

That'll be interesting to see.

cheers