hard rear suspension

[Flanders 45]

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 196]

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 63]

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

[Flanders 45]

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 529]

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 97]

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 196]

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 45]

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 1,159]

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 45]

...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 257]

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