Issues when cornering hard to the right on track

[Oldtimerfahrer]

Hi,

I have been stymied by something going on in my rear suspension for a couple of years, the root cause of which I have not been able to find and has persisted despite a number of changes to the car. I have not been on the track since last summer, but with the current situation I thought I could "pick the community brain" to get back into the garage and fix this.

 

A few facts about the current and past setups. Its a ti with turbo sway bars, OEM HD springs and yellow koni adjustables in the rear. Poly bushings all around. It has an LSD with 40% clutch pack. It has a Simons exhaust (with new hangers), which is a bit oversized. The bearings were replaced a few years ago.

 

Previously I had an OEM Eberspacher exhaust and Sachs sport shocks and I discovered that it actually lifted the right rear tire off the ground in hard right turns, as the shocks were shortened (car came on H&R springs and these Sachs shocks, which rubbed without end). I replaced the bushings and moved to the Konis, but no change. Before I put in the LSD, I had an open diff, same problem. I have not changed all these things due to this problem, but it seems odd that I have made all these changes and this annoying side effect remains.

 

What happens is that on sweeping right turns (usually on a track) when running on grippy tires, something is clunking in the rear and it has a juddering kind of action. Sounds like exhaust rattling against something but feels more substantial than a hollow exhaust. I cannot reproduce it on the street with 165 XAS tires, it is only on really hard cornering when the car is on the verge of drifting. It does not affect the controllability of the car really and it stops when you transition from off load or neutral to acceleration. I think it has something to do with load being reduced on the inner wheel (right rear). I thought that perhaps the exhaust was hitting the half-shafts, but I see no marks on the cap screws where I would have expected to see it. Virtually the only component that has not been changed are the half-shafts themselves, which have boots and I have never touched in 20 years of ownership. Is it possible that the splines are not sliding smoothly at extreme angles (extended fully?) causing this juddering sensation? Any other ideas to check?

Be well,

Andrew

 

[M3M3]

possible that inside rear wheel is light enough that it is bouncing off the ground and the springs/dampers/sway bar are not controlling it.  are your springs loose when suspension is in full droop?

 

sounds like springs/bars too soft and koni's need to be dialed up.

 

what is your definition of "grippy" tires?

 

ps...there are no "splines" to slide in the halfshafts...

[Oldtimerfahrer]

Hi,

Thanks for the input. Springs are new oem HD variants, with one dot spacers. I have not tried to compress one side, but when you put it on Jack stands at full drop, their still tight. Grippy is relative, with Yokohama a021r tires in 185/70 13 I get this effect,  with 165 xas tires I don't. Tires aren't rubbing but bouncing may be correct. I do run very light rims. The koni's could be dialled stiffer, but the shortened sachs sport shocks had the same issue and I would think they were plenty stiff, but it's worth a try. Is there nothing in the halfshaft that can contribute to this?

Regards,

Andrew

Edited April 15, 2020 by Oldtimerfahrer

[Hans]

I'd be looking at the subframe bushings 

[M3M3]

On 4/15/2020 at 2:31 PM, Hans said:

I'd be looking at the subframe bushings 

yes.  a basic assumption is that the trailing arm, subframe, diff and sway bar bushings are all good.

[visionaut]

A worn or too-loose stub-axle on one side wouldn't manifest like that, would it?  (those are splined)  Just thinking out loud...

 

Tom

[Oldtimerfahrer]

Hi,

All of the bushings are PU, so there is no slop there, they are too hard. The shocks are new but not set to hard, so the theory that it could be the light wheel tramping is plausible. . The previous shocks were also pretty hard and had the same issue, but maybe at lift the spring is stretching and the shock not controlling as it should.

A.

[Tommy]

Just for interest try without rear swaybar. Keeping inner wheel on ground instead of bouncing on and off might make many kinds of clunking disappear. You may experience some understeer but it's more a question of driving style wheter it matters or not. 

[Hans]

Did you replace subframe bushings?

[Oldtimerfahrer]

Yes, all bushings replaced...every last one last year, except for the shocks which are new and had new bushings. The stabilizer idea is a good one Tommy, thanks.

A.

[Drosselhebel]

What kind of oil are you running in the limited slip? Sounds like it could be diff chatter.

 

Edit - nevermind; missed where you mentioned that the problem predated installation of the LSD.

Edited April 17, 2020 by Drosselhebel

[M3M3]

14 hours ago, Tommy said:

Just for interest try without rear swaybar. Keeping inner wheel on ground instead of bouncing on and off might make many kinds of clunking disappear. You may experience some understeer but it's more a question of driving style wheter it matters or not. 

however, no bar results in more body roll, which means inside of car on turn goes even higher.  no rear bar usually only works if using really stiff springs and lower ride height.  oem HD springs are going to be soft.  

these cars suffer from a high CG and narrow track.  controlling body roll is a challenge.  

[jireland2002]

You are in Latvia?  I've been there several times.  Love the Rockabilly House. 

Sounds like the basic issue the too much body roll.  You should aim to keep the rear tire on the ground.  The car is falling over on it's nose.  More front roll stiffness is needed. 

[Hans]

3 hours ago, jireland2002 said:

You are in Latvia?  I've been there several times.  Love the Rockabilly House. 

Sounds like the basic issue the too much body roll.  You should aim to keep the rear tire on the ground.  The car is falling over on it's nose.  More front roll stiffness is needed. 

i'm still recovering from Balzams.

[Tommy]

12 hours ago, jireland2002 said:

 The car is falling over on it's nose.  More front roll stiffness is needed. 

Replying to Marshall, this is my filosophy too. I want the front to keep the body from rolling over and rear to hold tires on ground. This works for my racecar with 25% lsd and especially when I started with open diff. I don't have that much track experience with different cars though.