Pennock's Fiero Forum
  Technical Discussion & Questions
  Rear coilovers and lowered cars, and spring preload

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
Rear coilovers and lowered cars, and spring preload by Bridgetown
Started on: 09-08-2014 10:57 PM
Replies: 8 (781 views)
Last post by: fieroguru on 09-09-2014 12:14 PM
Bridgetown
Member
Posts: 1210
From: Alberta
Registered: Feb 2007


Feedback score: (2)
Leave feedback

Rate this member

Report this Post09-08-2014 10:57 PM Click Here to See the Profile for BridgetownSend a Private Message to BridgetownEdit/Delete MessageReply w/QuoteDirect Link to This Post
I would like to get people's opinions/experiences with cars lowered via rear coilovers. I'm wondering specifically about spring preload. Everything I've read outside of this forum talks about the importance of properly set spring preload on coilovers. As far as I can tell all Fiero owners, myself included, with rear coilovers have no way to set spring preload when lowering their cars. I have my ride height set exactly where I would like it, but on full suspension down travel there is a gap between the top of the coilover spring and the top perch. Is this common? I have Koni adjustable dampeners and 12" springs.
IP: Logged
PFF
System Bot
KaijuSenso
Member
Posts: 911
From: Westland, MI
Registered: Jan 2007


Feedback score: (1)
Leave feedback

Rate this member

Report this Post09-08-2014 11:23 PM Click Here to See the Profile for KaijuSensoSend a Private Message to KaijuSensoEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think the big aftermarket companies use helper springs to avoid the gap and keep compression on the main spring when the suspension is at full droop.

This is what KW does on my Audi kit. They say this spring may be fully compressed when there is full weight on it.

From KW's website KW FAQ
 
quote
My helper spring is fully compressed, is this normal?
Yes, that is how it is designed. When your suspension is fully extended, the main spring is free to move around and can come dislodged from its perches without a helper spring. The helper spring is only there to retain pressure on the main spring when the shock is fully extended so that the main spring stays in place.
IP: Logged
Bridgetown
Member
Posts: 1210
From: Alberta
Registered: Feb 2007


Feedback score: (2)
Leave feedback

Rate this member

Report this Post09-08-2014 11:51 PM Click Here to See the Profile for BridgetownSend a Private Message to BridgetownEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hmmm, that is a very good solution. Is it just me, or do others have this issue on their lowered cars?
IP: Logged
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post09-09-2014 12:40 AM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
as soon as you make the springs shorter, you have a gap. cut a coil, ya get a gap. haven't tried the coil overs yet
IP: Logged
Patrick
Member
Posts: 30756
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 443
Rate this member

Report this Post09-09-2014 01:56 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

as soon as you make the springs shorter, you have a gap. cut a coil, ya get a gap.


Not necessarily.

 
quote
Originally posted by Patrick in This thread:

When shorter rear springs are installed, flipping the top plate over helps to put a pre-load on the springs which keeps them in place. When I cut the rear springs in my '84, it was a nuisance every time I jacked the back of the car up as the rear springs would come off their perches in the struts. When I flipped over the top plates, this reconfigured the strut assemblies and the rear springs were now held in place.

IP: Logged
jb1
Member
Posts: 2140
From: Tullahoma, Tennessee
Registered: May 2003


Feedback score: (3)
Leave feedback

Rate this member

Report this Post09-09-2014 04:09 AM Click Here to See the Profile for jb1Click Here to Email jb1Send a Private Message to jb1Edit/Delete MessageReply w/QuoteDirect Link to This Post
Mine has limiting straps on the rear suspension so the rear springs always in contact with the top hat and the strut..
even when jacked up off the ground the springs do not move
------------------


87GTseries 1 3800sc (7.597 @88.53 1.579 60ft)
(series II swap in progress)
85GT Northstar/ 4t80e
86GT 3800 n/a---sold
Northstar Rebuild

[This message has been edited by jb1 (edited 09-09-2014).]

IP: Logged
fieroguru
Member
Posts: 11310
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 255
Rate this member

Report this Post09-09-2014 06:38 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
The two concerns to be addressed are can the spring come out of its seat when fully extended, and does the orientation (rotation) of the spring matter.

On stock springs, if there was not any preload, the springs could move around and slide off the side of the rear spring perches (large diameter spring, small diameter strut, lots of room for misalignment). Also, the ends are not perfectly flat as the cut end of the coil is about 1/2" thick. The lower a-arms up front and the upper/lower spring perches in the rear are contoured for the spring end to be in a specific position. So if there isn't any preload, then the spring could rotate and have the ends of the springs out of these seats and make them more prone to fall off the seat.

With rear coil overs, the ends are ground flat and the perches at both ends should be flat as well, so rotation of the spring to the seat doesn't matter. Since coil overs are small diameter and have a very close fit to the bottom adjustable sleeve (less than 1/8" gap), it falling off the lower perch isn't possible. The key is how you design the upper perch to ensure the spring stays in the proper place while at full extension. This is done by adding a side support/locator sleeve to the top. I use 2" or so length of exhaust tubing and weld it to position the outside of the spring at the top. Inside works too, but clearance to the strut body at full compression is very, very tight, so I use the outside. As long as this upper sleeve is longer than the gap in the spring at full droop, the spring can't be in the wrong position.

If you have lowered your car, you can help reduce the spring gap by flipping the top strut hat as it will shift the top of the strut up about 1" and reduce suspension droop by 1" as well.

IP: Logged
Bridgetown
Member
Posts: 1210
From: Alberta
Registered: Feb 2007


Feedback score: (2)
Leave feedback

Rate this member

Report this Post09-09-2014 09:01 AM Click Here to See the Profile for BridgetownSend a Private Message to BridgetownEdit/Delete MessageReply w/QuoteDirect Link to This Post
These are my coilovers, with '88 conversion plates at the top.
What would I change on the top plate to lessen the gap when lowered?
IP: Logged
fieroguru
Member
Posts: 11310
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 255
Rate this member

Report this Post09-09-2014 12:14 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
Flip the top plates over so the bushing is on the top side.
You will need to swap them side to side to do this, cut off the studs, weld on new ones, and weld a 2" length of exhaust pipe to keep the top of the spring centered.

Flipping the top hat will lower your current gap by 1" and the 2" exhaust pipe positioner should ensure they never come out of position, even if there is still a 1" gap.
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock