Rear bottoming out!!!

S

SupremeGoku9

Member
Hi good people, i'm a lil new to the Z and very new here...

I'm loving the Z at the moment... I have a black 3.0i convertible on oem 17's and BC Coilovers.... It rides absolutely brilliantly out of town and around the county lanes..... But in town, pot holes and broken road can make the rear (not so much the front) feel like it's bottoming out with a nasty bang.....

What can i do to solve this or what should I be looking at as like I said, everywhere else and it is perfect and a lot of fun.
 
Check your rear springs aren’t broken. Very common fault, often not picked up ‘til MOT time.
 
Your BC Racing coilovers, like mine, have solid topmounts front and rear. That means you've lost the little rubber isolator which absorbed most of the harsh impacts that your springs couldn't cope with. It's possible that this is the source of your noise.

It's possible that you've blown a shock absorber seal, which means it's providing no compression resistance. Check for oil on the body of the shock.

It's also possible that you've set the car too low, and the shock is simply bottoming out.
 
Zedebee said:
Check your rear springs aren’t broken. Very common fault, often not picked up ‘til MOT time.
Click to expand...

Hes on aftermarket BC raciling setup so shouldn't snap, its only the original springs snap.
 
DaveP said:
Your BC Racing coilovers, like mine, have solid topmounts front and rear. That means you've lost the little rubber isolator which absorbed most of the harsh impacts that your springs couldn't cope with. It's possible that this is the source of your noise.

It's possible that you've blown a shock absorber seal, which means it's providing no compression resistance. Check for oil on the body of the shock.

It's also possible that you've set the car too low, and the shock is simply bottoming out.
Click to expand...

I heard somewhere that the BC rear shocks are compatible with stock rubber top mounts? Does anyone know if this is true?
 
Natto said:
DaveP said:
Your BC Racing coilovers, like mine, have solid topmounts front and rear. That means you've lost the little rubber isolator which absorbed most of the harsh impacts that your springs couldn't cope with. It's possible that this is the source of your noise.

It's possible that you've blown a shock absorber seal, which means it's providing no compression resistance. Check for oil on the body of the shock.

It's also possible that you've set the car too low, and the shock is simply bottoming out.
Click to expand...

I heard somewhere that the BC rear shocks are compatible with stock rubber top mounts? Does anyone know if this is true?
Click to expand...
No idea, sorry. I wanted solid top mounts, so I put up with the occasional rattle over bumps.
 
DaveP said:
Your BC Racing coilovers, like mine, have solid topmounts front and rear. That means you've lost the little rubber isolator which absorbed most of the harsh impacts that your springs couldn't cope with. It's possible that this is the source of your noise.

It's possible that you've blown a shock absorber seal, which means it's providing no compression resistance. Check for oil on the body of the shock.

It's also possible that you've set the car too low, and the shock is simply bottoming out.
Click to expand...

Yeah could be too low but I doubt it based on the "visual" ride height.... But what do I know with no prior experience with these cars... But yeah gonna get it to a good garage to check if it's not blown as you say.


Thanks everyone for your helpful replies.... It really is appreciated and reinforces why it was a good decision to join this forum. :thumbsup:
 
mac27040 said:
Zedebee said:
Check your rear springs aren’t broken. Very common fault, often not picked up ‘til MOT time.
Click to expand...

Hes on aftermarket BC raciling setup so shouldn't snap, its only the original springs snap.
Click to expand...

Any spring can snap - I had an OEM offside rear spring break at sub 30k miles and a KW Clubsport nearside rear spring fail when it had covered about 50k miles.
 
SupremeGoku9 said:
DaveP said:
Your BC Racing coilovers, like mine, have solid topmounts front and rear. That means you've lost the little rubber isolator which absorbed most of the harsh impacts that your springs couldn't cope with. It's possible that this is the source of your noise.

It's possible that you've blown a shock absorber seal, which means it's providing no compression resistance. Check for oil on the body of the shock.

It's also possible that you've set the car too low, and the shock is simply bottoming out.
Click to expand...

Yeah could be too low but I doubt it based on the "visual" ride height.... But what do I know with no prior experience with these cars... But yeah gonna get it to a good garage to check if it's not blown as you say.


Thanks everyone for your helpful replies.... It really is appreciated and reinforces why it was a good decision to join this forum. :thumbsup:
Click to expand...
If it doesn't look too low, it probably isn't. Mine is close to full height on BCs and is still lower than stock.

As someone else said, it may also be a function of how your shocks were setup for ride height. On basic coilovers (like Stance+ etc.) preload is effectively equivalent to ride height, where lower cars have higher preload. BCs allow for preload to be set independently of ride height, so it's possible to get it all wrong if you're inexperienced and end up with an undriveable car.

This doesn't typically tend to result in crashiness under compression, but it can feel like the suspension doesn't have much rebound travel (because it doesn't) over sharp compressions like potholes. Rather than bottoming out, it can feel like the shocks are 'topping out' too easily under full extension after a sharp compression.
 
mac27040 said:
why don't you stiffen the shocks to reduce springs bottoming out?
Click to expand...
That's not quite how coilovers should work.

Your spring should handle compression, rather than your shock. If the spring rate is too low (i.e. it compresses too easily), the shock will constantly bottom out because it doesn't have enough travel in the piston(s) to support the weak spring.

The shock exists to dampen the oscillation of the spring (hence calling them 'dampers'). It slows down the rate that the spring compresses under load and decompresses when unloaded, so the car doesn't handle like a pogo stick. Increasing the damping doesn't solve the issue of suspension travel, it simply passes the problem on to the shock to deal with. There's a problem here that can't be solved by adjusting the damping.

A dead shock will present as a rattling noise because it's providing no resistance to the spring's oscillation, and the forces are causing the suspension to reach its limits quicker than it would with a working shock (likely smashing against a bumpstop or the internal shock limiter under compression).
 
DaveP said:
mac27040 said:
why don't you stiffen the shocks to reduce springs bottoming out?
Click to expand...
That's not quite how coilovers should work.

Your spring should handle compression, rather than your shock. If the spring rate is too low (i.e. it compresses too easily), the shock will constantly bottom out because it doesn't have enough travel in the piston(s) to support the weak spring.

The shock exists to dampen the oscillation of the spring (hence calling them 'dampers'). It slows down the rate that the spring compresses under load and decompresses when unloaded, so the car doesn't handle like a pogo stick. Increasing the damping doesn't solve the issue of suspension travel, it simply passes the problem on to the shock to deal with. There's a problem here that can't be solved by adjusting the damping.

A dead shock will present as a rattling noise because it's providing no resistance to the spring's oscillation, and the forces are causing the suspension to reach its limits quicker than it would with a working shock (likely smashing against a bumpstop or the internal shock limiter under compression).
Click to expand...
Yup, over the years the wrong terminology has crept in. The spring is the shock absorber. The hydraulic tube bit is the damper.
 
enuff_zed said:
Yup, over the years the wrong terminology has crept in. The spring is the shock absorber. The hydraulic tube bit is the damper.
Click to expand...
They were dampers when I was growing up, but there has been a shift in the language to the use of shocks, along with sway bars, and increasingly fenders and pry bars.
 
BMWZ4MC said:
enuff_zed said:
Yup, over the years the wrong terminology has crept in. The spring is the shock absorber. The hydraulic tube bit is the damper.
Click to expand...
They were dampers when I was growing up, but there has been a shift in the language to the use of shocks, along with sway bars, and increasingly fenders and pry bars.
Click to expand...

Yes, I also call them "Dampers"... gonna get them checked and report back... :driving:

Thanks for the helpful input guys.... I can see that it was a good idea to join this forum. :)
 
You must log in or register to reply here.
Back
Top Bottom