hard rear suspension

[Flanders 47]

I took my car out for a good shakedown run (finally) and noticed that the rear suspension seems quite hard.  When I hit some cracks/bumps in the road, it's a hard THUMP from the back-end.  There's barely any dampening going on from the shocks.  I have mid-eye leaf springs (a few years old) and some KYB shocks (7 years old, minimal mileage).  Any suggestions on how to soften it up so it doesn't feel and sound like the back end of the car is going to split open on the bumps?

[rwcstang 207]

Your Shocks are most likely failing...

When I had my old mid-eye leaf springs, I had the same issue, come to find out it was my old Shocks (KYB) were failing and the leaf spring bushings were also worn out. I upgraded to Bilstein shocks and went with a de-a-lum bushing and shackle kit with greaseable fittings, the problem went away.

I would also check the leaf springs for any damage, warpage, or cracks.

[buening 66]

If those are the white KYBs, they are notorious for being stiff.   I too went with Bilsteins in the rear on mine.

[Flanders 47]

thanks for the tips.  I'll take a look at bilstens -- I was even looking at the QA1 rears, just need to see how fancy I want to get for a street car. 

[Mach1 Driver 587]

For some reason most guys today will use gas shocks, but these cars were designed for hydraulic shocks- watch this video to understand the difference. I would watch the entire thing to understand the relationship of springs and shocks and how shocks can change the spring rate, but in particular he mentions shocks at 5:30 and again at 18:00

 

[copb8 101]

On 4/30/2023 at 8:49 PM, rwcstang said:

Your Shocks are most likely failing...

When I had my old mid-eye leaf springs, I had the same issue, come to find out it was my old Shocks (KYB) were failing and the leaf spring bushings were also worn out. I upgraded to Bilstein shocks and went with a de-a-lum bushing and shackle kit with greaseable fittings, the problem went away.

I would also check the leaf springs for any damage, warpage, or cracks.

 

On 5/3/2023 at 8:28 PM, buening said:

If those are the white KYBs, they are notorious for being stiff.   I too went with Bilsteins in the rear on mine.

 

Can you guys post the specific Bilstein shocks you went with please?

[rwcstang 207]

not sure what valving you need, Street or sport, I have the sport ones, part number on my Shocks are 55-r056, seems there are modified to fit classics. only info I can find is it says RCD Classics - Bilsteins: 

http://racecardynamics.com/463-domestic#s[4][]:411&s[5][]:452&s[6][]:688&s[3][]:891&ash[3][]:891&old_selected_criterion:YTo0OntpOjQ7YToxOntpOjA7aTo0MTE7fWk6NTthOjE6e2k6MDtpOjQ1Mjt9aTo2O2E6MTp7aTowO2k6Njg4O31pOjM7YToxOntpOjA7aTo4OTE7fX0:&rg:&sid:1&h:leftColumn&k:1&ics:463&as4_base_selection:YToxOntpOjA7aTo4OTE7fQ::

https://mikemaierinc.com/products/64-73-mustang/rear-suspension/64-70-mustang-rear-bilstein-shock/

but you can buy them on certain sites: https://streetortrack.com/suspension/rear-suspension/shock-absorbers-467/bilstein-rear-shock-for-65-73-mustang-60-65-falcon-67-70-cougar-62-65-fairlane.html

 

 

[Flanders 47]

Just wrapping this up -- I put QA1 single-adjustables in the rear, and it's definitely softened it up a bit.  Still firm, but not jolting anymore over the bumps! 

[RPM 1,232]

What setting do you have then at. I've got QA1 DS 501s on all 4 corners, for around town I've got them all on the softest setting. 

[Flanders 47]

...I've got them set on "6" out of 18.  Although I might actually firm them up a bit -- I get a wierd oscillating on a few parts of the highway (where the rear end of the car actually feels like it's bouncing!) probably due to front being a lot firmer than the rear now....

[Brian Conway 269]

I get that bouncing sensation too.  Usually when the car is in first fear and the gas pedal is on the floor.  Brian

[Flanders 47]

reviving this thread....

I've been playing around with the dampening on my QA1's, and I'm pretty sure it's my leaf springs that are causing my stiff-ness.  When I push down on the rear fender, the car barely moves (and if I really give it a jolt, it bounces a bit....which explains the odd oscillating/bouncing I see on some hwy stretches). 

I have some scott drake 4.5 leaf mid-eye leafs in the back.  They are not very old, but I'm getting the sense they're not very spring-y.  I like the height of the mid-eyes, but I really want a smoother ride.   What do you guys run in the back that isn't super firm?

[rwcstang 207]

Flanders, QQ, when you installed the leafs did you tighten the bolts/shackles when the car was on jacks stands (wheels off the ground) or when the car was on its full weight (on ground)? maybe the leafs are binding when on full weight causing the stiffness. 

[Flanders 47]

yeah good thought -- I'll re-check.  I put them in a few years ago, thought they were tightened while car on the ground.  

[TexasEd 200]

Loosen them back up and see if it relieves a bind

[Vicfreg 787]

I finally went with Eaton Spring (the old Detroit Spring) and used 5 leaf springs on my '68.  They have the original spring patterns from Ford, and reproduce them with high quality steel.

I used the part number for the GT suspension.  The car is stiff, with a firm ride, but no bouncing.  I have Bilsteins.

Did the same on my '70 convertible.

One other possibility is that your driveshaft is binding.   I had this happen years ago, because I measured my driveshaft length when the car was up in the air.  Big mistake.  I installed the driveshaft when the car was in the air, and it seemed to fit fine.  But the car did ride and handle funny.

I found this out later when my rear universal joint failed.....

 

[Flanders 47]

reviving this thread again.

I've loosened off the shackles completely, and the car is still super-stiff when I try and bounce the rear end.  I have QA1 adjustable shocks on softest setting.  Shackle is at the 5 o'clock position (maybe 4:30) which seems to be ok.  I don't think it's binding.

I think the scott drake mid-eye 4.5 leaf springs are just stiff.  And having the rear end so much stiffer than the front really makes the car oscillate funny on the highway.

I may try Eaton's stock-spring-rate leaf springs that lower the car by an inch.  ML1567-1.   Any other opinions?

[rwcstang 207]

Hey @Flanders sorry to hear you didn't get it resolved.

do you have your original shocks on hand or possibly purchase some KYB gas or bilsteins (soft setting)? maybe swapping them to eliminate the shock or leaf?

Another option is to call Qa1 to see what they can do for you, maybe the shocks can be serviced or checked for inspection if under warranty.

 

 

[Flanders 47]

the qa1's are definitely working -- on the softest setting i can push/pull the shaft (when they are out of the car) relatively easily.  On firmest setting, it's a lot harder.