please help me diagnose an issue - felt during hard braking and LH turns

[ninekrpm]

At the track yesterday, towards the end of the day, suddenly felt that the car was squirrely (rear-end) during hard braking, after a few laps...maybe even the next session...in addition to the squirrelyness during braking, car felt unstable powering down on left handers...at that time I noticed that the infamous chassis stabilization error was showing and with reference to ABS.

My car does not have the factory diff, running a drexler and the factory diff has been coded out...

That said...upon a few searches, it points to a wheel speed senser. I am going to run the codes and see...stay tuned for that.

Any thoughts? Appreciate the feedback...

[M3SQRD]

Did you make any ride height or damper changes before heading out onto the track. I’ve run into rear end dancing issues after lowering the rear ride height and increasing R damper reb addressing other handling issue). Raising rear ride back up a bit and taking out 1-click of rebound addressed the dancing issue.

[ninekrpm]

Originally Posted by M3SQRD

Did you make any ride height or damper changes before heading out onto the track. I’ve run into rear end dancing issues after lowering the rear ride height and increasing R damper reb addressing other handling issue). Raising rear ride back up a bit and taking out 1-click of rebound addressed the dancing issue.

car was fine for the first 4 sessions...really felt it in session 5 or 6...

[jfritz27]

No reason to think you're rear toe shifted?
Stuck piston/dragging pad?

[ninekrpm]

Originally Posted by jfritz27

No reason to think you're rear toe shifted?
Stuck piston/dragging pad?

Checked toe…looks good

Piston/Pad: how to check?

To add…felt funky putting power down…

[M3SQRD]

When’s the last time the diff fluid was changed? Have you looked at the diff fluid to see if any metal shaving are in it?

Find an empty parking lot and do a series of figure eights in both directions and see if the car feels any different when under power going in one direction vs. the other.

[ninekrpm]

Originally Posted by M3SQRD

When’s the last time the diff fluid was changed? Have you looked at the diff fluid to see if any metal shaving are in it?

Find an empty parking lot and do a series of figure eights in both directions and see if the car feels any different when under power going in one direction vs. the other.

In looking at the video, I hear a screeching sound in between two slow turns…wondering if it is the diff. Would suck if it is…let’s see. Fluid was changed 6 track days ago…

Going to drain the fluid in a clear bin and see…

[M3SQRD]

Originally Posted by ninekrpm

In looking at the video, I hear a screeching sound in between two slow turns…wondering if it the diff. Would suck if it is…let’s see. Fluid was changed 6 track days ago…

Going to drain the fluid in a clear bin and see…

I hope not either. Diffs are a complex mechanism and small changes in tolerances and backlash can play havoc with a deep. I hope for the best.

[ninekrpm]

Originally Posted by M3SQRD

I hope not either. Diffs are a complex mechanism and small changes in tolerances and backlash can play havoc with a deep. I hope for the best.

Just drained the fluid...its clean and the magnetic plug had no metal shavings/residue

The mystery continues...

[ninekrpm]

did remove the wheel speed sensors...they were full of gunk. Thoughts on it being the wheel speed sensors? I would assume abs would be way off slowing down from 120 - 140...

[jfritz27]

Originally Posted by ninekrpm

Checked toe…looks good

Piston/Pad: how to check?

To add…felt funky putting power down…

Never dealt with it myself, so can't speak from experience, but probably have to remove pads, push in pistons all the way (feeling for any major difference in resistance among them), have someone apply some pressure and see if they behave equally

Might be right with the wheel speed sensor, but if there's abnormal noises then seems like it would need to be something else...

Pull any codes?

[ninekrpm]

Originally Posted by jfritz27

Never dealt with it myself, so can't speak from experience, but probably have to remove pads, push in pistons all the way (feeling for any major difference in resistance among them), have someone apply some pressure and see if they behave equally

Might be right with the wheel speed sensor, but if there's abnormal noises then seems like it would need to be something else...

Pull any codes?

found a couple of codes related to wheel speed and ICM...

considering dropping off the car to local shop (Strom Motorsports) for review...

Things I have done so far...

- Alignment is solid, no changes...
- Diff fluid looks good...
- Drive shafts look...
- Cleaned both rear wheel speed sensors (lots of gunk)
- Brake fluid reservoir looks good...

[ninekrpm]

Well...found the issue, and all I can say, it could have been worse.

The left rear bearing is missing 1 of the 4 bolts, and the other very slightly loose. WTF!!! So...so, scarry!

This explains the squirrely-ness during braking and the screeching noise.

Having Strom go over the car and replace both rear bearings with the GT4 version...

I am still scratching my head as to what caused this...

[FaRKle!]

Originally Posted by ninekrpm

Well...found the issue, and all I can say, it could have been worse.

The left rear bearing is missing 1 of the 4 bolts, and the other very slightly loose. WTF!!! So...so, scarry!

This explains the squirrely-ness during braking and the screeching noise.

Having Strom go over the car and replace both rear bearings with the GT4 version...

I am still scratching my head as to what caused this...

Yikes! Glad nothing bad happened due to that. Have your rear bearings been replaced before?

[jfritz27]

Originally Posted by ninekrpm

Well...found the issue, and all I can say, it could have been worse.

The left rear bearing is missing 1 of the 4 bolts, and the other very slightly loose. WTF!!! So...so, scarry!

This explains the squirrely-ness during braking and the screeching noise.

Having Strom go over the car and replace both rear bearings with the GT4 version...

I am still scratching my head as to what caused this...

Wow, glad you caught it.... guess that explains why the wheel speed sensor was confused

[GuyLedouche]

Originally Posted by ninekrpm

Well...found the issue, and all I can say, it could have been worse.

The left rear bearing is missing 1 of the 4 bolts, and the other very slightly loose. WTF!!! So...so, scarry!

This explains the squirrely-ness during braking and the screeching noise.

Having Strom go over the car and replace both rear bearings with the GT4 version...

I am still scratching my head as to what caused this...

That is wild. Were the bolts removed and reused?

[ninekrpm]

I replaced the wheel carrier, hubs, bearings and new bolts around 18 months ago - they have over track 15 track days on them now, obviously no street miles.

New parts/bolts were used, torqued to spec and with loctite...

Again...not sure what happened. I am speechless...

I am just so glad the bolts did not snap and I was able feel that something did not feel right early enough...

You bet, I will be marking these and checking regularly...

[M3SQRD]

Wow. Scary! Excellent find and thorough inspection skills

[ninekrpm]

Can’t take all the credit…Strom helped as well

I am glad I found it…

[GuyLedouche]

Originally Posted by ninekrpm

I replaced the wheel carrier, hubs, bearings and new bolts around 18 months ago - they have over track 15 track days on them now, obviously no street miles.

New parts/bolts were used, torqued to spec and with loctite...

Again...not sure what happened. I am speechless...

I am just so glad the bolts did not snap and I was able feel that something did not feel right early enough...

You bet, I will be marking these and checking regularly...

Are the bolts microencapsulated like the front hub bolts?

[ninekrpm]

Originally Posted by GuyLedouche

Are the bolts microencapsulated like the front hub bolts?

Yes…

[GuyLedouche]

Originally Posted by ninekrpm

Yes…

What kind of loctite did you use? I personally don't add any with microencapsulated fasteners.