13 replies to this topic

[RazerX]

Ok, not to be confused with the new rule 12 page thread...

 

So at the west coast NASA championships last year.  The car was initially good from a handling perspective.  Then first race the car goes diabolically loose.  After the race I realize the sway bar tab on the front LCA snapped off.  Replace LCA, reset camber / toe as was prior.  2nd qual race, the car is nearly as bad, loose in, at and out of turns.  I recheck toe, camber for the whole car, looks fine, hot pressures on target no lose bearings.  Put on 1 session tires for the main event.  Car is loose, like greasy hot tires loose, manageable for a few laps then gets crazy loose again.   Disappointing experience. 

 

Yes, I was checking wheel bearings and watching tire pressures.  No issues there.  

 

 

Car has been on jack-stands since (life, holidays, replacing the head).  I inspected the sub-frames looking for possible tears on the ears or elsewhere but nothing.  Bearings all good.  Camber bolt did not move.  Real head scratching begins.  I have not had a spec Miata handle that bad in 5 years.  

 

Getting to the track is more challenging that it used to be, I am trying to remedy the unknown cause in the garage.  I will put it back on scales and verify setup.  But at this point, I am now guessing shocks.  Perhaps one failed out.   From those here is that a possible culprit for the VERY loose situation?  I have ordered a new set from Mazda already (but they are on back order... so new rule change i wonder inspiring a desire for new shocks....)

 

any other ideas?

 

Thanks 

[RazerX]

Wow nearly 70 views and no comments.  I figured it was a long shot, it is like being a doctor and diagnosing an illness over the phone. 

 

I was just wondering is a shock could fail so badly that it could produce such a dramatic loose situation.  An no, no sign of oil on a shock. 

 

Some of am CA bushing esp in rear are fairly off center, not rubbing but an 1/8" from rubbing.  I suppose loaded it could create some pinching which I have experience but that is usually mid corner experience as it binds then releases.  

[Dave D.]

I would think if a shock failed that bad to be that loose, you would see a leak? Have you checked for binding anywhere? Make sure the swaybars are cleaned and lubed,and free range of motion.

[Caveman-kwebb99]

i have had similar feelings from slightly bent rear knuckle that binds in upper rear arm.  that bushing in upper rear knuckle goes bad quite often as well.  

 

The other thing is having a bad torsen can cause some handling issues as well.  

 

Cam bolts turning underload will also do this sometimes going right back to where you want them when your checking, had this issue several seasons ago once found this car was right back to on rails.  if I remember right i had a rear cam bolt that was the culprit, everytime i checked toe it was correct, got it on the lift put a wrench on it and i could turn it with about 80Lb of pressure.

 

As the post above mentions, sway bar bind can cause problems as well. but I have had a rear shock go bad in the past, no amount of tightening the car up could overcome the snap loose, changed shock was back to normal again!

 

Good luck!

[Bench Racer]

So at the west coast NASA championships last year.  The car was initially good from a handling perspective.  Then first race the car goes diabolically loose.  After the race I realize the sway bar tab on the front LCA snapped off.  Replace LCA, reset camber / toe as was prior.  2nd qual race, the car is nearly as bad, loose in, at and out of turns.  I recheck toe, camber for the whole car, looks fine, hot pressures on target no lose bearings.  Put on 1 session tires for the main event.  Car is loose, like greasy hot tires loose, manageable for a few laps then gets crazy loose again.   Disappointing experience. 

 

any other ideas?

 

Thanks 

Presume FatCat bump stops. What is your bump stop clearance? Are you compressing the bump stops beyond the first 3/4 inch compression of the bump stops? I'm here to tell anyone, if you compress the FatCat bump stops beyond 3/4 inch your going to have serious handling issues. My stop clearance were intentionally set to less than desired bump stop clearance and it was a WOW issue. Raised the car 2 turns, issue gone.

[Steve Scheifler]

All above are worth a look. Just a bad shock alone would need to be really bad, likely obvious just jouncing the car by hand (if you are a flyweight get someone big to compare sides). BUT, combine a soft rear shock with a car that was already getting pretty deep into the bump stops and suddenly you exceed the limit well described by Bench. That was a big problem with the factory hats & stops but it can still happen with a combination of ride height and/or a soft shock.

The rear spindle/upright was also mentioned. I have had similar symptoms when the upper-outer bushing had dried and shrunken from age & heat, getting quite loose in the upright. The result was dynamic toe and also inconsistent spring rate as it would rotate rather than “wind up”. Nearly killed me again and again at Road America and didn’t figure it out until the next event back home.

[Danica Davison]

If you ever have a shock question ... just have Kyle Webb sit on all of the corners of your car like he did at Sebring in November. He will tell you everything you need to know. The guy is a shock wizard apparently.

[loudes13]

I had a dead Bilstein. No external oil leaks but clearly no nitrogen in it.

[RazerX]

Thanks for the suggestions.  

No, i found no leaks on any shocks

Will check cam bolts as they are all lined up with marks.  

I don't think i am over exceeding the gap/ride height/bump stop compression as this is same ride height(w/ FatCats) i have had for 3+ years never with this issue.

I usually suspect a rear upright after changing LCA/UCA and the arms 'walk' to the ends of the bushing and rub on subframe.  While the rears are not perfectly centered they are not rubbing but changing the uprights is next on my list when I start throwing parts at it. 

 

Speaking of bushings, I found the left front LCA (that I replaced) to have walked on the bushing almost all the way to the rear where it would rub on the subframe.  I have seen that on rears (with bent arms or uprights) but not on fronts as there are two ball joints.  So is there anything besides the LCA being bent that would cause that?  Binding swaybar?????

 

Is there a way to test if a Torsen is "good" in the car?

 

Thanks.  

[Johnny D]

What the story on your 1 session tires since it all started when you put them on?

Oh and happy b-day
J~

[luvin_the_rings]

you replaced LCA? then you need to re check the cross weight with bar disconnected then re adjust bar links to perfectly no preload.  New LCA will have different shock and stab bar mounting positions. Also make sure you have symmetrical mounting configuration on the bar links. 

 

what happened during the original failure? too much curb or off track? maybe knuckle is bent? 

[RazerX]

What the story on your 1 session tires since it all started when you put them on?

Oh and happy b-day
J~

Tires are consideration, they had 6 laps on them previous to the final, but the car issues started when the LCA swaybar tab snapped.

[RazerX]

you replaced LCA? then you need to re check the cross weight with bar disconnected then re adjust bar links to perfectly no preload.  New LCA will have different shock and stab bar mounting positions. Also make sure you have symmetrical mounting configuration on the bar links. 

 

what happened during the original failure? too much curb or off track? maybe knuckle is bent? 

Yes, swapped it at the track then reset camber and toe.  Did the qual race, and checked it again, it was still within .1 degree of desired camber and toe was perfect. 

 

This weekend it will go back on the scales to determine exactly what the car is sitting at.  Barring any smoking gun for the setup validation, I will replace that front LCA and inspect the ball joint. 

 

How did LCA tab break, I would say likely it broke due to fatigue over time an not contract or a big "off" in this case.    I do however drop wheels and use some rumblestrips and curbs.  However, at that track the curbs and rumbles are very smooth as are most of the locations when i do drop tires.  

[luvin_the_rings]

let me know what you find on the cross weight.  I'm interested to know how much LCA variation translates to cross weight change.