Car rides too rough - Chevelle Tech
Brakes, Suspension & Steering Conversion questions & more.

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post #1 of 70 (permalink) Old Jan 30th, 20, 12:40 AM Thread Starter
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Tony
 
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Car rides too rough

Hey everyone,

I'm just wrapping up a rebuild of a '68. Everything is new. Here's a quick breakdown:
'
  • Strange Dana S60
  • 496 BBC
  • Bilstein shocks (Front PN 24-131506, Rear PN 24-009294)
  • Moog springs (Front PN 5400, Rear PN CC507)
  • UMI rear control arms (PN 401417-B)... heim joints in front end, rubber bushings on rear end of uppers, poly on lowers.

When I first got the car on the road, the ride was brutal to the point of being unsafe. It was basically like having no suspension at all. I read about the mistake of using poly bushings on the upper control arms in the rear, so I switched back to fresh rubber bushings. That helped some, but not enough.

The way the car rides is hard to describe. It's bouncy, but it really almost feels like the suspension is near fully extended, especially in the rear. I don't get the sensation of bumping up so much as a sensation of falling and slamming down hard. Before I put the rubber bushings on the uppers, I know for sure the back tires came off the ground regularly when I was driving around at 45mph or so. I'm not sure that isn't still happening some.

The car also sits pretty high (see attached pics). I don't mind that so much, but I figure it's an indication of the problem. What I'm hoping you guys can help me with is to figure out what I've done wrong here. Is it simply that the springs are too stiff? They're supposed to be OEM replacements, and Moog is a great brand. Is it the Bilsteins? I had them on my last car ('02 Trans Am) and loved them. I don't mind a firm ride, but this is unsafe. Maybe the rear suspension is in a bind (despite switching away from poly bushings)?

Thoughts on my next move?
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1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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post #2 of 70 (permalink) Old Jan 30th, 20, 1:07 AM
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Eric
 
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Re: Car rides too rough

Those are pretty heavy springs.

You're just jealous because you can't hear the voices!

1967 Olds Cutlass 468 BBC/T400
1963 Plymouth Fury 440/Torqueflite
2007 Ford Mustang GT (momma's car)
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post #3 of 70 (permalink) Old Jan 30th, 20, 3:21 AM
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Re: Car rides too rough

Hi
Solid nylon ,heim joints and poly bushes all contribute towards harsh suspension . Not flexible enough .
Remember the replacement parts re shocks are valved universally as a stock replacement . What u are experiencing is part mismatch I suspect .

Aftermarket Springs are quite often wound differently to an OEM spring . Fewer but thicker coils . I strongly doubt the aftermarket springs are exact copy of the OEM specs .

Fit poly bushings to areas that have high wearing bushings only . Then be aware of the DURO [measurement of softness ] for poly bushings . Often the 2 softest ratings are fine to use .


Maybe change springs and or custom shocks eg Kings etc etc
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post #4 of 70 (permalink) Old Jan 30th, 20, 8:14 AM
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Jeff
 
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Re: Car rides too rough

I would buy the springs Mark Sevetske is selling. They are 1" lower then true stock springs. Today what spring companies call stock is way to high. Your suspension is at the top of its arc being up that high. So for starters I would change to SC&C 1" lower springs.
https://scandc.com/product/spc-perfo...-72-gm-a-body/

Then I would remove all poly from the suspension control arms. It does NOT work. I would use Delrin spherical bushings.
I have those on my 69 el Camino and there amazing. It rides very smooth.. I have the SC&C Stage III front control arm package, a Lee 14:1 box with Spohn Delsphere rear control arms. I did use rubber on the uppers at the rear end..
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post #5 of 70 (permalink) Old Jan 30th, 20, 10:54 AM Thread Starter
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Tony
 
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Re: Car rides too rough

Thanks for the replies, guys.

I don't want this to come across as argumentative (I'm the one asking for help, here!), but I do want to clarify the poly bushing part. I don't want to prove you wrong, but I want you to prove me wrong. I don't agree that we have to replace all poly bushings because in some places they should work. For example, a poly bushing on the front, lower control arms does not provide any opportunity for binding because there's no situation in which it should be allowed to twist. Also, the rear LCAs should only bind if there is a tilting motion of the rear axle (e.g. one tire drops into a pot hole while the other is on even pavement). That binding can be alleviated by the heim joint on the front allowing the LCA to turn/twist. If both the front and rear joints were poly in that case, you'd have a problem. The bushings on the top of the pumpkin that the rear, upper control arms attach to clearly have the propensity to bind and should only be rubber (which I've fixed).

As for the springs, it appears that the SC&C springs have a higher spring rate in the front (535 vs 358) and about the same in the rear (135-150 vs 158) compared to what I already have. My guess is Jeff is right that my suspension is "at the top of the arc" which is part of my problem. Perhaps the SC&C springs are stiffer but shorter and would allow more travel. I think the ride of the car supports this theory, because I don't feel a jarring bump when going over a bump in the road so much as I feel a bang when going over a drop in the road. If I hit line of uneven pavement when the back of the car drops down (e.g. going from concrete to asphalt where the asphalt is slightly lower), it feels like the suspension completely unloads (especially in the back), the tires come off the ground, and then I'm jarred when the tires hit the ground again.

I'm eager to hear any additional input (suggestions of spring/shock combos, troubleshooting ideas, theories on poly bushings, etc, etc). I'm an analytical guy, so get technical.

1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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post #6 of 70 (permalink) Old Jan 30th, 20, 10:59 AM
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Eric
 
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Re: Car rides too rough

If your hearing and feeling a bang when a wheel drops, its probably due to the shock hyperextending to its end stop due to the height of the car.
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You're just jealous because you can't hear the voices!

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post #7 of 70 (permalink) Old Jan 30th, 20, 11:04 AM Thread Starter
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Tony
 
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Re: Car rides too rough

Quote:
Originally Posted by oldcutlass View Post
If your hearing and feeling a bang when a wheel drops, its probably due to the shock hyperextending to its end stop due to the height of the car.
I totally agree. That's exactly how it seems.

1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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post #8 of 70 (permalink) Old Jan 30th, 20, 11:36 AM
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Bruce
 
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Re: Car rides too rough

There's nothing wrong with using Poly PROVIDED you lubricate the heck out of them. Inside and out - use way more lube than seems "normal (after assembly you'll wipe off the excess)."

Loosen up all your suspension bolts, then drive the car a very, very short distance. Then with the car on the ground tighten the suspension bolts.

With the increase in suspension height you'll need extensions for your shocks.

Are your front springs installed properly? The top needs to clear the "crown" at the top mounting point. The bottom needs to align with and in the slot on the front A arms.

If you still have your old rear springs you could swap them back in and see if there's a significant impact on the ride quality.
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post #9 of 70 (permalink) Old Jan 30th, 20, 11:36 AM
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Re: Car rides too rough

I’m a firm believer that the weight rating of a spring is pretty useless if you don’t know the weight of the car.
A spring rated at “x” lbs/in could be very different in “similar” cars.
Big block, small block, aluminum heads, headers vs manifolds, battery in the trunk, on and on and on.
You should weigh your car and get front and rear weights in addition to the total.
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post #10 of 70 (permalink) Old Jan 30th, 20, 12:03 PM
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Re: Car rides too rough

Quote:
Originally Posted by 67_LS1 View Post
You should weigh your car and get front and rear weights in addition to the total.
Where do you go to get your car weighted?

I pulled into a "not busy" (no trucks at weight station) highway weight station once to ask if I could get my car weighted and the operator looked at me like I was drunk. After a bit of discussion he allowed me to drive on his scales. I only wanted an overall FYI weight as my car was loaded down with vacation luggage at the time.


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post #11 of 70 (permalink) Old Jan 30th, 20, 12:05 PM Thread Starter
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Tony
 
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Re: Car rides too rough

Quote:
Originally Posted by NickeyChevelle View Post
Loosen up all your suspension bolts, then drive the car a very, very short distance. Then with the car on the ground tighten the suspension bolts.
What does this accomplish?

Quote:
Originally Posted by NickeyChevelle View Post
With the increase in suspension height you'll need extensions for your shocks.
I think this is potentially a great idea. Even if it's not a solution, it's a great troubleshooting step. I didn't even know these existed. Looks like they're cheap, and they ought to be easy to install!

Quote:
Originally Posted by NickeyChevelle View Post
Are your front springs installed properly? The top needs to clear the "crown" at the top mounting point. The bottom needs to align with and in the slot on the front A arms.
I believe they're installed properly. I can take pics if need be.

Quote:
Originally Posted by NickeyChevelle View Post
If you still have your old rear springs you could swap them back in and see if there's a significant impact on the ride quality.
They went to the scrap yard.

1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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post #12 of 70 (permalink) Old Jan 30th, 20, 12:07 PM Thread Starter
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Tony
 
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Re: Car rides too rough

Quote:
Originally Posted by RAIDER SS View Post
Where do you go to get your car weighted?
I assume a local speed shop would have a set of scales. I've seen shops around here have a "free scale" day to get some visibility. Maybe that's a typical thing for them to offer (for a price, usually).

1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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post #13 of 70 (permalink) Old Jan 30th, 20, 12:24 PM
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Re: Car rides too rough

I also have Moog 5400 in my hardtop, 360 lb/in spring rate (from memory) and those should not be the problem although they sit a little high, but factory photos of 68's show them sitting a touch high in front. I think the "correct' cargo coil for 68 Chevelle is CC501, but I really don't think those CC507's are actually the source of the trouble, but the shocks fully extended as the other guys are saying. I ended-up switching both my 68 Chevelles to Moog 5385 rear springs. For my hardtop (and adjustability at the strip) I have air bags in the rear springs.

Even when I had solid rear aluminum lower control arm bushings and ladder bars on my 68 hardtop, it did not ride like you are describing.

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post #14 of 70 (permalink) Old Jan 30th, 20, 12:25 PM
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Re: Car rides too rough

[QUOTE=RAIDER SS;11222688]Where do you go to get your car weighted?

I use Cat Scales. They are nationwide. They charged me $12 and you get a total and individual axle weights.

catscale.com for locations.

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post #15 of 70 (permalink) Old Jan 30th, 20, 12:32 PM Thread Starter
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Tony
 
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Re: Car rides too rough

Quote:
Originally Posted by 67_LS1 View Post
I use Cat Scales. They are nationwide. They charged me $12 and you get a total and individual axle weights.

catscales.com for locations.
Sweet. There's one 30 minutes away from me. Oh, and the URL is https://www.catscale.com... not plural.

1968 Chevelle 2-door coupe restomod... 496ci BBC, Holley 950, T-56 Magnum, Dana S60, and an idle that shakes the ground.
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