GeorgeNZ

I had to replace my front dampers after we found a crack in the lower bracket mid (tarmac) rally with a spare set - no dramas, but at my next track outing, I'm finding the car is unstable under straight-line threshold braking.

Basic set-up (now) is;
- 425lb fr on double adj Konis/ camber plates urethane bushes
- 29mm TB's with 185lb coils on single adj Konis - ER bushes, M030 bars
- Tyres; Bridgestone RE55s - 225/50/16 all round (DOT semi-slick)

All up weight 1400kg (3000lb)

Alignment;
front -4deg camber, 4 1/2deg caster, 1.3mm toe
rear -2deg camber, 2mm toe

I haven't spoken with the alignment guy yet, but the track alignment differs from the Targa/ Rally setting by a degree more camber and a degree or so less caster.

The set of front dampers we took out were a custom set of Koni single adjustables of unknown origin.

Could the apparent instability be due to different front damper settings?

If so - increase bump? ( I haven't had to deal with double adjustables before)

Cheers

Larry Herman

First, did you check to make sure that you didn't mess up your toe setting when you changed the struts? Any toe-out will make it darty under braking. If that is ok, I would try increasing the bump (compression) settings on the front shocks.

mikew968

George is your toe in or out?

Mike

GeorgeNZ

Larry - new alignment was done after new fronts and before the track session

Mike - in

mark kibort

thats a lot of camber up front. that could be part of the the issue, as there usually is more camber and more importantly toe under braking as the nose goes down. How is the bump look?

we had a major issue with a fellow racer, he had a broken rear suspension piece that forced the rear wheels to do all sorts of wierd things under braking. could check to make sure there is no gross issues with the suspension.

The only time ive felt this kind of issue was with a car toed out by 1/2" and the broken suspension component in the rear.

MK

GeorgeNZ

Thanks for the input - had both sets of front dampers dyno'd and it looks like I need another 6 or so clicks of bump on the new dampers to get them close to the single adjustables - the foot valve was quite aggressive.

Alignment/ suspension is being checked out before I head back out in saturday and see if the increased bump helps.

Rich Sandor

This may be a stupid question, but did the alignment guy set the toe first, or the camber first? The reason I ask is because when you dump in negative camber, the toe changes outward as well. So if you set the toe, and then set camber, you'd have to reset the toe again.

Bill L Seifert

I would think anyone that knows anything about alignment would know what Rich has brought up. But it is sure worth checking. Also, isn't 2mm of toe in the rear a lot, whether it is toe in or toe out? I run no toe at all in the rear. I would be willing to bet the problem is a toe issue. Toe out drives me nuts to drive, but then again, I ain't that good of a driver I run 1/16 of an inch of toe in in the front and zero toe in the rear. I know you NZ'ers and Canadians don't know inch stuff, but I don't know much about millimeters either. Sorry.

Bill Seifert

1987 944S Race Car

mikew968

My setup is 1mm out in the front and 1mm in in the rear.

Mike

GeorgeNZ

no worries Bill - I'm old enough to have lived with both - its about 1.6mm

Alignment checked out OK, we've dialled in another degree of castor and will see how we go increasing the bump tomorrow - weather permitting

Rassel

George
What brake balance do you have?

GeorgeNZ

brake balance is unchanged from previous so I don't think thats the cause to the change in state.

The things that have knowingly changed are the front dampers and minor changes to alignment - I haven't played around with adjusting dampers before so have no real experience with effects of changing bump/ rebound.

Until I was forced to make a change, I was working on the fact that better drivers than I had set the car up - I was comfortable with that setup in dry/ wet on circuit and road but with the new struts it wasn't as nice and had to start trying to improve things - just looking up this steep learning curve

GeorgeNZ

the offending article

http://members.rennlist.com/renn68/strut1.jpg
http://members.rennlist.com/renn68/strut2.jpg

Rich Sandor

What exactly do you mean, "unstable?"

Does it:
-Always pull to one direction (always right or always left?)
-Pull in a certain direction depending on the track surface?
-Pull in random directions?
-Or just wobble/shudder in a straight line?
Also, is it the front end that is misbehaving, or is it the rear end that is trying to step out?

If it pulls in a specific direction, perhaps one shock's bump setting is significantly stiffer than the other? If the rear end is feeling unstable but the front tracks true, perhaps the front is too soft (or the rear is too stiff) and letting the rear unload too much weight & traction... ?

Less caster and more negative camber will definately make the car "dartier" overall... the two changes together might be enough to cause the darty braking.

Rich Sandor

Are those the original OEM m030 struts? I wonder what caused the failure...

Could be:
-Poor welding
-Poor welding + damaged paint (rust damage)
-Some other braking/suspension problem... (which could break your new struts also, if not checked out..)
-Or, someone mistaking their 968 for an airplane, and getting airborne too many times...