Pennock's Fiero Forum
  Technical Discussion & Questions
  Rear suspension seems to bottom out over medium bumps in road and dips.. ???

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


next newest topic | next oldest topic
Rear suspension seems to bottom out over medium bumps in road and dips.. ??? by phils88GT
Started on: 10-22-2024 10:17 PM
Replies: 20 (286 views)
Last post by: fieroguru on 10-29-2024 06:05 AM
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-22-2024 10:17 PM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have an 88 GT with factory everything. Last year I changed out the worn our rear struts with KYB GR2's and the front, along with all ball joints, tie rods, etc. Weird thing is, the rear suspension, when hit just the right bump or dip in the road at just the right speed, feels like it is bottoming out. Not sure what to do about this. Anyone else have similar issues?

thanks
IP: Logged
PFF
System Bot
Patrick
Member
Posts: 37609
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 464
Rate this member

Report this Post10-22-2024 11:06 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

And this is with factory (non-cut) springs?

Even with lowering/cut springs in both my '84 and Formula, I've never had the rear suspension bottom out on either car.
IP: Logged
fieroguru
Member
Posts: 12279
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 259
Rate this member

Report this Post10-23-2024 06:57 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
The 88 rear springs are quite soft at about 145 lb/in, so the rear bump stops are pretty important. Did you replace those when you swapped struts?

IP: Logged
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-23-2024 08:03 AM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
They are uncut factor springs in the back. I will have to check on the bump stops. Been a while since I have been back there really to look at anything.

Is there anything out there in the way of stiffer springs that don’t lower the car a ton?
IP: Logged
Vintage-Nut
Member
Posts: 1015
From: California
Registered: Apr 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-23-2024 10:16 AM Click Here to See the Profile for Vintage-NutSend a Private Message to Vintage-NutEdit/Delete MessageReply w/QuoteDirect Link to This Post
KYB GR2 Vs. Excel-G Shocks: A Comprehensive User’s Guide
https://glennsaid.com/kyb-gr2-vs-excel-g-shocks/

88 rear springs recommendations by jc8367
https://www.fiero.nl/forum/Forum2/HTML/134933.html

Get your '88 spring rates here (long, but accurate) by Doug Chase
https://www.fiero.nl/forum/...050119-2-054238.html

With factory rear springs and Monroe Sensa-Trac Struts, my GT rides nicely....
------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 10-23-2024).]

IP: Logged
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 08:20 AM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Is there any way to stiffen up the rear suspension of the 88 GT without much lowering? It just seems far too soft, causing my bottoming out issues...
IP: Logged
Vintage-Nut
Member
Posts: 1015
From: California
Registered: Apr 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 09:19 AM Click Here to See the Profile for Vintage-NutSend a Private Message to Vintage-NutEdit/Delete MessageReply w/QuoteDirect Link to This Post
IMHO

With uncut factor springs, I bet your suspension issue is your KYB GR2 strut choice and not the springs.

This is called suspension dampen {Compression and Rebound} that control the energy generated by springs.

*Compression rates depend on how quickly the shock/strut compresses the spring
High compression compresses slowly / Low compression compress quickly

*Rebound rate is how fast it returns to its original, uncompressed state
High rebound allows for a softer ride / Low rebound is for stiffer.

KYB GR2 has less dampen
KYB Excel-G has more dampen

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

IP: Logged
fieroguru
Member
Posts: 12279
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 259
Rate this member

Report this Post10-27-2024 10:53 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
New bump stops would likely fix the issue. The springs rates don't change significantly, so strut wear and bump stops are the likely cause.



Some of my customers switched to coilovers to get stiffer spring rates while keeping the ride height stock, but that is much, much more expensive than just replacing the bump stops.

IP: Logged
Vintage-Nut
Member
Posts: 1015
From: California
Registered: Apr 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 03:49 PM Click Here to See the Profile for Vintage-NutSend a Private Message to Vintage-NutEdit/Delete MessageReply w/QuoteDirect Link to This Post
Listen to fieroguru - he is in the Fiero Suspension Business!

And especially if you didn't replace the bump stops when you {or the shop} installed the new struts...........
IP: Logged
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 05:35 PM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you for the advice. I installed these struts about 8 months ago. I would say they have less than 2500 miles on them. I can’t say I remember them even having bump stops on them though.

Will have to check. Next weekend probably.
IP: Logged
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 05:40 PM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

phils88GT

112 posts
Member since Oct 2023




Yup! No bump stops. And that looks like a very short travel for the strut. Something doesn’t seem right..
IP: Logged
PFF
System Bot
fieroguru
Member
Posts: 12279
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 259
Rate this member

Report this Post10-27-2024 07:13 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
The stock rear strut has 7" of travel. At stock ride height, there is about 3-4" of suspension travel.
You can gain and extra inch in compression by flipping the strut hat.
IP: Logged
Patrick
Member
Posts: 37609
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 464
Rate this member

Report this Post10-27-2024 08:58 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fieroguru:

You can gain and extra inch in compression by flipping the strut hat.


I've done that with both of my lowered Fieros, but I'm surprised that flipping the strut hat might be required on a Fiero with unmolested factory springs. I'm just wondering if something else is going on with the OP's rear suspension that's contributing to it bottoming out?

[This message has been edited by Patrick (edited 10-27-2024).]

IP: Logged
Vintage-Nut
Member
Posts: 1015
From: California
Registered: Apr 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-27-2024 09:10 PM Click Here to See the Profile for Vintage-NutSend a Private Message to Vintage-NutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Yup! No bump stops.


Also, no boot which protects the shaft and the seal from road debris.

KYB sells a 'kit' with the boot and the bumper - you need kit SB103

https://www.rockauto.com/en...+/+strut+bellow,7592

https://www.summitracing.co...position/rear?page=2

-------------------------------------------------------------------------------------------------------------------------

EDIT:
Can you check on the model of GR2 rear struts you brought?
I can only find Monroe or KYB Excel-G rear struts for a '88 and not KYB GR2 rear struts......

[This message has been edited by Vintage-Nut (edited 10-27-2024).]

IP: Logged
82-T/A [At Work]
Member
Posts: 24045
From: Florida USA
Registered: Aug 2002


Feedback score: (1)
Leave feedback





Total ratings: 200
Rate this member

Report this Post10-28-2024 05:27 AM Click Here to See the Profile for 82-T/A [At Work]Send a Private Message to 82-T/A [At Work]Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Vintage-Nut:
Also, no boot which protects the shaft and the seal from road debris.

KYB sells a 'kit' with the boot and the bumper - you need kit SB103

https://www.rockauto.com/en...+/+strut+bellow,7592

https://www.summitracing.co...position/rear?page=2



Phils88GT... I have a pair of these, unused, brand new in the box (both) with everything.

I decided against using them because the factory ones were still in great shape in my 1985 Fiero 2m4 SE, so I opted to re-use those. If you would like the ones I have, you can have them for free. I will mail them to you in the next couple of days, and then you can just PayPal me whatever the shipping cost is. PM me your mailing address and I'll send them out to you. I debated whether to sell them on eBay, but I just don't want the hassle and it's not worth it. They are brand new...


Thanks...
IP: Logged
fieroguru
Member
Posts: 12279
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 259
Rate this member

Report this Post10-28-2024 05:56 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Patrick:

I've done that with both of my lowered Fieros, but I'm surprised that flipping the strut hat might be required on a Fiero with unmolested factory springs. I'm just wondering if something else is going on with the OP's rear suspension that's contributing to it bottoming out?



Not required, but is an option if he is concerned that his car does not have adequate suspension travel.
IP: Logged
cartercarbaficionado
Member
Posts: 652
From: cusick, Washington, USA
Registered: Sep 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-28-2024 03:29 PM Click Here to See the Profile for cartercarbaficionadoSend a Private Message to cartercarbaficionadoEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Vintage-Nut:


Also, no boot which protects the shaft and the seal from road debris.

KYB sells a 'kit' with the boot and the bumper - you need kit SB103

https://www.rockauto.com/en...+/+strut+bellow,7592

https://www.summitracing.co...position/rear?page=2

they might be doing what we did on our 88 which was using 84-87 rear struts which do bolt right in. the no bump stop thing is absolutely their problem though. the kyb struts tend to not get much stiffer compression as they travel unlike Monroe or different kyb models. so they do like to bottom out quite harshly even with bumpstops installed. the solution is to use new bumpstops or steal the kit from a 90s to 2006 grand prix which comes with a progressive bump stop designed to be loaded all the time. usually its in the sport trims/HD suspension. I know it is for our 95 gtp
IP: Logged
Patrick
Member
Posts: 37609
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 464
Rate this member

Report this Post10-28-2024 03:56 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by cartercarbaficionado:

the kyb struts tend to not get much stiffer compression as they travel unlike Monroe or different kyb models. so they do like to bottom out quite harshly even with bumpstops installed.


That tends to agree with how I felt when I compared the two brands of struts. From ten years ago...

 
quote
Originally posted by Patrick Here:

I used Monroe Sensa-Trac shocks and struts in my lowered and stiffened (cut springs) '84 for daily driving and autocross for four years. Love the way that car feels.

I now daily drive and autocross an '88 Formula. When I first got the car a year ago, I put new Monroe Sensa-Trac shocks and struts in it with the stock springs. Car felt okay, but I didn't like the soft stock springs. A friend gave me a set of four '88 lowering springs along with near new KYB shocks and struts. Since I now had shocks and struts made by both companies in my hands (literally), I compared them. I wanted to use the stiffest ones, the ones with the most resistance to both compression and rebound. You might be surprised at what I found.

The KYB shocks were stiffer than the Monroe Sensa-Trac shocks. No surprise there.

However... the Monroe Sensa-Trac struts were stiffer than the KYB struts.

So I now have KYB shocks on the front of the Formula, and Monroe Sensa-Trac struts on the back.

The Formula feels pretty good, but I'm still not satisfied with the lack of stiffness in the front. I'll be removing the '88 front lowering springs and replacing them with a pair of cut '84-'87 front springs. I'll continue to use my current choice of shocks and struts (and rear lowering springs).



And I did replace the front lowering springs in the Formula with cut '84-'87 springs. The front suspension was then quite a bit stiffer, and I much preferred the feel at autocross.
IP: Logged
phils88GT
Member
Posts: 112
From: Rock Hill, South Carolina
Registered: Oct 2023


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-28-2024 09:20 PM Click Here to See the Profile for phils88GTSend a Private Message to phils88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Ok, so I went to Rock Auto and looked up the struts I bought back in March of this year. They are KYB Shocks & Struts 234005 - KYB Excel-G Gas Shocks and Struts. As it would turn out, they don't list these for the 88 Fiero GT, but they do list them for the 87 Fiero GT. I guess at the time I was so dead set on getting KYB's for all four corners that when I went to Summit Racing, because I couldn't find the KYB's on Rock Auto for the 88 GT, Summit Racing listed them (KYB # 234005). But now, I am looking and they don't have them listed for the 1988. I guess I am up a creek and will have to just suck it up and get the Monroe's from Rock Auto.

This sucks! What a waste of money! :-(

IP: Logged
Vintage-Nut
Member
Posts: 1015
From: California
Registered: Apr 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post10-28-2024 10:00 PM Click Here to See the Profile for Vintage-NutSend a Private Message to Vintage-NutEdit/Delete MessageReply w/QuoteDirect Link to This Post
When I researched the KYB and Monroe specifications:

Extended Length: 16.1" / 16.125"
Compressed Length: 9.37" / 9.375"
Stroke /Travel Length: 6.73" / 6.75"

I didn't find KYB / Monroe Compression and Rebound Rates.

KYB Valving / Dampen: "based on each vehicle’s specific manufacturer specifications"

Monroe OESpectrum Valving / Dampen: "known for their smooth ride quality and feature proprietary ASD (Acceleration Sensitive Damping) technology allowing them to adapt quickly to changing road conditions, which helps to maintain ride comfort"

So, get the boots / bumpers and try them before buying Monroe struts....

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 10-29-2024).]

IP: Logged
fieroguru
Member
Posts: 12279
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 259
Rate this member

Report this Post10-29-2024 06:05 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by phils88GT:

Ok, so I went to Rock Auto and looked up the struts I bought back in March of this year. They are KYB Shocks & Struts 234005 - KYB Excel-G Gas Shocks and Struts. As it would turn out, they don't list these for the 88 Fiero GT, but they do list them for the 87 Fiero GT. I guess at the time I was so dead set on getting KYB's for all four corners that when I went to Summit Racing, because I couldn't find the KYB's on Rock Auto for the 88 GT, Summit Racing listed them (KYB # 234005). But now, I am looking and they don't have them listed for the 1988. I guess I am up a creek and will have to just suck it up and get the Monroe's from Rock Auto.

This sucks! What a waste of money! :-(


Again, your issue is the lack of bump stops... Buy 2 of these: https://www.summitracing.com/parts/URO-008941
They are a lot cheaper than new struts, which will have the same issue if the bump stops are left off again.

There are lots of people using the KYB 234005 on the 88s w/o issue.
Monroe Sensatracs name/model has been retired and the only Monroe rear strut is the 71814 OE Spectrum. It is listed for all years of Fieros.

It has probably been 2 decades since the 88 Fiero had their own unique rear strut.
IP: Logged
PFF
System Bot

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
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock