Rear bounces excessively over bumps at 20-30mph

[68 Sport Satellite]

Got the '68 Satellite with mostly all upgraded suspension in the last few years. I think I may have paired some pieces up incorrectly and this may be causing my issue. The car feels great going in a straight line. It feels great on the freeway at 60 - 80 mph with occasional dips and bumpies. However, for in-city driving between 20-30 mph, when the car rolls over some successive bumps (not even big ones), the rear of the car bounces all over the place maybe 2-3 times. With a few successive bump runs in a half mile stretch it's getting to be annoying with the up and down pogo action. Maybe I can secure a couple of heavy lead bricks in the back?? :icon_confused:

It wasn't until I had the pleasure of driving Dennis H's '68 Coronet with HD leafs, 26.6" tall rear tires, and Bilstein sport tuned shocks that I loved it and decided I was tired of putting up with my car's behavior.

I've researched a lot about characteristics of a soft spring / stiff shock vs stiff spring / soft shock setup, as well as OEM setups with just adding large swaybars and it seems everyone has their opinion. In general, I think I now favor a compliant soft spring setup with larger sway bars, BUT I have already spent the money and installed some items on my car, so I'm hoping you the FBBO community can help me minimize my future spending and time and frustration and recommend what single item you would try first to solve my problem.
CURRENT CAR SPECS:
275/60/15 Rear tires on 8" wheels, 215/70/15 front tires on 7" wheels
Hotchkis rear leafs (160 lb/in) with Hotchkis shackles
Edelbrock IAS shocks all around
Global West tubular sub-frame connectors - welded at both ends
torque boxes welded at all four corners
Hotchkis upper control arms and steering rods
Stock lower control arms with welded box plates
stock strut rods with new rubber
new stock pitman and idler arm
new .092" torsion bars (this is a small block car, but going to 451 big block)
2" drop spindles from Magnum Force
I have the nose of the car just a bit dropped from flat (maybe 1")

I know the Hotchkis leafs have a rep for being stiffer than stock. I'm thinking these leafs may need a softer rear shock, but I'm not sure.

I need to decide if I go to a shorter rear tire (would the 1" shorter 255/60/15's make a difference?), different rear shocks (sport tuned Bilsteins from Hotchkis are top on the list if they will solve the problem), or change out my Hotchkis leaf springs and shackles for Mopar HD leafs.

 

[RustyRatRod]

I'd go for the simple stuff first. Check the condition of the shocks.

 

[Hemi Rebel]

Can you push down on the rear of the car and make it bounce?

 

[Someotherguy]

sounds like worn out/defective shocks to me..

 

[68 Sport Satellite]

These shocks were installed by my go-to alignment shop less than 1500 miles ago. I doubt that they're bad or defective. They feel great most of the time. They pass the "stand beside the car and push the car down rebound test".
Many shocks that are not suited to the rest of the combo can pass this test, but then when driven on the street and subjected to a bump they will do the bouncies.

I've been a passenger in an old Huyandai excel one time with shot front shocks. We were going through a tunnel and there was a dip in the road and man oh man - that front end didn't settle down until a full 15 seconds later, bouncing all over the place. The rear of my car is not that bad. If it hits one bump it's fine. If it rolls over 2 or 3 successive dips or bumps close together, the front stays put, but the rear does 3 bounces and then if it hits another one it does it again. Somehow I think it's a component mismatch issue. When I rode with the guy driving the coronet over the same stretch of road that gave my car the bouncies, his car performed fine. His wife was in the car with us and seemed to think it may be my rear tires to tall for my stiff springs because a friend of theirs had talked about a similar problem. Lots of people run 275/60/15 in the back though, but not sure if they have this problem with stiffer than stock springs. I'm willing to do the logical thing to fix this, but I don't want to just pick the shocks because they're the cheapest. Actually tires are not much more expensive to try some 255/60's, but if I'm wrong, then I'll end up changing out all 3 items....

Anyone else have this problem before?

 

[Hemi Rebel]

What angle are the rear shackles at? The ideal position is to have the shackle at a 45 degree angle with the spring eyelet further toward the rear of the car than upper shackle to frame mount. No more than that. If it isnt the shocks, then look for a spring issue. Maybe with the car on the ground the springs are against the frame at the rear mounting eyelet

 

[RustyRatRod]

ok.

 

[HT413]

I dunno, but i dont think a softer shock will do it. I would think a shock with greater dampening characteristics would be needed to quiet the car down while softer shocks would just get overwhelmed even more. If it were me, i think i'd buy some tunable shocks and do some experimenting with compression and rebound rates while going over those very same bumps that annoy you.

 

[5.7 hemi]

One word.....Bilstein!!!

 

[jessipup]

From an old dirt bike racer. Bounce is controlled by shocks. Compression is how fast or slow your suspension compresses and rebound is how fast or slow it goes the other way or so to speak bounces back up.
And this is all accomplished by the shim stack or internal valving and the oil moving from the upper chamber to the lower chamber and back again.
So on a top of the line system you can seperately control how fast the oil can move from top to bottom= compression damping.
And how fast oil moves from the lower chamber to the upper chamber=rebound dampining.
So knowing this, if you have bounce? Now you know your shocks are not doing what they are supposed to do.
It could be wear, but you have pretty much ruled that out,
So Is it misapplication=the wrong shock for the job.
Overpressurization? supposing that you can add air. Adding air is a BIG no-no.
Shocks are for dampining. Springs are for support don't try to mix the two.
Or is it simply bad shock desgn/low quality manufacturing and internal components.
Dude IT'S your shocks.

 

[Ron 73]

The standard bounce the car test can be deceptive sometimes, going down the road and different speeds road conditions its not just sitting still, id have to say wrong application of shocks or ones that are malfunctioning, I gave up a long time ago with "its brand new" brand new ive bought things more then once that had to be taken back, things arent made with the same school of thought of the welfare of the customer and quality were looking for anymore, sad but true.

 

[68 Sport Satellite]

What angle are the rear shackles at? The ideal position is to have the shackle at a 45 degree angle with the spring eyelet further toward the rear of the car than upper shackle to frame mount. No more than that. If it isnt the shocks, then look for a spring issue. Maybe with the car on the ground the springs are against the frame at the rear mounting eyelet

Good point. The rear shackles are pointing in the correct direction with the spring eyelet further toward the rear than the upper shackle to frame mount. The angle is not quite 45 degrees, but more like 60 degrees, which is the only way it mounts up with these aftermarket "geometry corrected" hotchkis leaf springs.

 

[68 Sport Satellite]

One word.....Bilstein!!!

that's what I keep thinking! However, I haven't heard anyone tell me yet that the Bilstein's will behave any differently than the Edelbrock IAS shocks. One thread I read on another forum website said they did this change and found negligible difference. They had Mopar HD leafs though.

I wonder if the tuned Bilstein's are stiffer than the IAS's? I agree I don't want a softer shock - I don't think...

 

[68 Sport Satellite]

Seems the consensus is shocks! Since I have Hotchkis leafs and would like to keep those and they are the most expensive item to swap....

...and since I'm considering the Hotchkis tuned Bilsteins, I'll give Hotchkis a call tuesday morning and see if they agree. They should be able to tune them for my setup with their springs.

They only sell them as a set I believe. I would love to just get 2 for the rear to try out since the front is behaving just fine.

Thanks all. I'll let you know how it turns out.

 

[jessipup]

I don't know if the Bilsteen has adjustable dampining. But I would say try to find some even if it's only rebound. Then you can just trun a clicker and feel the difference. I went with adjustable ones on my wideglide and all around they were much better than stock but I also found that when I carried a heavy load ( like a fat girl) I had to turn up the clickers....
Nope scratch that I googled some and they make bilstiens look K-mart cheep
$$$$$$$$$$$$$ 250-500$ Have you lightened this car up a bunch or went with a much different rate spring, and yes mounting angle. Go oner these topics with the Hochkiss tech guys msybe one of these items will cause him to think in a different direction

 

[Jim Bob The Dancing Bear]

I have the same springs with stock replacement KYB shocks and 225/70/14 tires. I do not have the problem you have. I would buy the Hotchkis Bilstein shocks. I will have them once these wear out.

 

[68 Sport Satellite]

I have the same springs with stock replacement KYB shocks and 225/70/14 tires. I do not have the problem you have. I would buy the Hotchkis Bilstein shocks. I will have them once these wear out.

You've got the hotchkis leafs? However, if you're running 225/70/14 tires in back, that's only 26.4" tall, while my rear 275/60/15 are 28" tall. That's why I was thinking if I dropped down to 255/60/15 (27" tall) my problem may go away instead of changing shocks. If I assume everything is good, that would be the answer. Then I have to decide would I rather keep that rear tire size or keep the shocks I have. I'm undecided on the tire. I don't care what shocks as long as they work.

 

[5.7 hemi]

I have some kyb's on my rear with 275-60-15's and it rides really nice and the rear springs are from mcveigh's on ebay...car is a 64 polara 500.

 

[Propwash]

I'd have to agree with the other guys...I'd look at the shocks. Gotta say though, in my '68, the only real excessive bouncing my car has in the rear is when it's parked....LOL

 

[RustyRatRod]

I'd have to agree with the other guys...I'd look at the shocks. Gotta say though, in my '68, the only real excessive bouncing my car has in the rear is when it's parked....LOL

You been bouncin yerself again?