spastic rear suspension

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hobbsza

hobbsza

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Today I took the "ruster" out for a short drive to check my alignment and tire clearance. and while I was carving the corners I hit a man hole mid curve which didn't stick up very high at all but it slung my rear end all over the place. My car is a 1974 Plymouth duster with 1.16 firm feel torsion bars, bilstein shocks, all new poly bushings, 1 1/8 front sway bar, and hotchkis rear springs. is the issue my lack of a rear sway bar? any help would be greatly appreciated
 
"Slung rear end all over the place", as in slid the rear tires out? Or are you saying that the rear started wallowing around?
Sounds like you just lost some traction due to one tire being on a steel manhole.
 
ChrisPerry said:
Sounds like you just lost some traction due to one tire being on a steel manhole.
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Which can be accentuated greatly by alignment issue's caused by maladjustment or bushing and steering component wear.

(As in tires fighting each other and having one give affects the whole car)

Or even bad shocks.
 
This is also what low profile tires can do for you. Since there is much less sidewall, there is much less flex that the tire can absorb, so all that energy gets transferred into the wheel and suspension. Tires act like shock absorbers themselves. The shorter the sidewall, the less efficient they are at absorbing shock, so they transfer it instead.
 
RustyRatRod said:
This is also what low profile tires can do for you. Since there is much less sidewall, there is much less flex that the tire can absorb, so all that energy gets transferred into the wheel and suspension. Tires act like shock absorbers themselves. The shorter the sidewall, the less efficient they are at absorbing shock, so they transfer it instead.
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Except your tires aren't really supposed to absorb shock. That's why there's suspension to begin with. Yes, taller sidewalls do absorb more shock, but they also allow the rims to wallow around within the confines of the tires because of the soft sidewalls, giving the car a loose, sloppy feel.

Seems to me the OP has upgraded his suspension accordingly for the low profile tires (better shocks, higher spring rates), so it's not likely a low profile tire issue. Unless you figure that none of this could have ever happened with a set of BFG T/A's, because he wouldn't have had enough traction to do what he was doing to begin with.

TrailBeast said:
Which can be accentuated greatly by alignment issue's caused by maladjustment or bushing and steering component wear.

(As in tires fighting each other and having one give affects the whole car)

Or even bad shocks.
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Except he's rebuilt the suspension and is running Bilsteins.

ChrisPerry said:
"Slung rear end all over the place", as in slid the rear tires out? Or are you saying that the rear started wallowing around?
Sounds like you just lost some traction due to one tire being on a steel manhole.
Click to expand...

Exactly. Hard to tell from the description. One wheel hitting a steel manhole cover while everything else stayed planted could definitely upset the balance of the suspension. Would make a difference if you have a limited slip diff too.

hobbsza said:
Today I took the "ruster" out for a short drive to check my alignment and tire clearance. and while I was carving the corners I hit a man hole mid curve which didn't stick up very high at all but it slung my rear end all over the place. My car is a 1974 Plymouth duster with 1.16 firm feel torsion bars, bilstein shocks, all new poly bushings, 1 1/8 front sway bar, and hotchkis rear springs. is the issue my lack of a rear sway bar? any help would be greatly appreciated
Click to expand...

Sounds to me like you got bounced by the manhole cover. Even well tuned suspension will be upset and thrown out of whack in that situation. Also, the stiffer you make your suspension and the more you lower your car, the more you reduce the amount of suspension travel you have. Making the suspension stiffer can greatly improve handling, but you can definitely go too far. What works well on the race track doesn't work well with pot holes and man hole covers. If the suspension is so stiff it doesn't absorb any force, just transfers it, your tires can lose contact with the ground and you can get skipped all over the place.

Now, if the car felt sloppy during the recovery, it could be in part because you don't have a rear sway bar. Keep in mind the Hotchkis leaf springs were intended to be used with a Hotchkis rear sway bar. Suspension has to work as a system. I'm not saying you have to do everything out of the same box, but you DO have to keep things balanced. 1.16" torsion bars are big, even by big torsion bar standards. I run 1.12" bars on my Duster, and I run the rear with 121 lb/in springs and a 7/8" Hellwig sway bar. I've been pretty happy with how my car is balanced so far. Your front bars are even stiffer than mine, so I would suspect that your rear suspension is set up too soft for what you're running up front. The mismatch could cause problems when you try to recover from a situation like the one you described, even if it's not that noticeable under "normal" conditions.
 
72bluNblu said:
Except your tires aren't really supposed to absorb shock. That's why there's suspension to begin with. Yes, taller sidewalls do absorb more shock, but they also allow the rims to wallow around within the confines of the tires because of the soft sidewalls, giving the car a loose, sloppy feel.
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Says who? You? LOL

Every single tire made absorbs shock. Just like every wheel and every single piece of the car including the driver.
 
RustyRatRod said:
Says who? You? LOL

Every single tire made absorbs shock. Just like every wheel and every single piece of the car including the driver.
Click to expand...

Yes Rob, all tires absorb some amount of force. Even "low profile" tires. Higher profile tires obviously can absorb more force.

The difference is that your shock absorbers were designed to absorb force. Your tires are designed to improve traction. In fact, they are designed to transfer force, although their design also means they absorb some too.

So, sure, you can put big balloon tires with super soft sidewalls on your car to have it ride like a Lazy-Boy. But if you do that your car will handle like a Lazy-Boy too. Or, you could match your springs and shock absorbers to the amount of force being transferred by your tires, resulting in a better handling car.

Since the OP has upgraded all of his suspension accordingly, just slapping a set of crappy higher profile tires on his car won't solve his problem.
 
I was comparing low profile tires to stock height tires........not "big balloon tires", whatever those are.
 
all seems plausible especially if the tire that hit the man-hole cover as the one with the "load" associated with the way the car was turning at the time. Example is if you were turning to the left and you hit the manhole with the right rear tire. Naturally the right rear tire will have more load on it when you are turning to the left. and the right tire will have very little load on it in the same situation. I would not add a rear sway bar unless the car has a tendency to understeer. I have had the same thing happen in my dart with a small water puddle. It kinda reminds you as to how grippy your tire actually are. yes on pavement they are fine but on a surface with a smooth finish, its a whole different story.
 
RustyRatRod said:
I was comparing low profile tires to stock height tires........not "big balloon tires", whatever those are.
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So was I, because stock height tires with 14" rims have more than enough sidewall to feel sloppy when you try to do anything other than drive in straight line. And they sure as heck won't help the OP.

Now, my comment about the "big balloon tires" and having your car handle like a lazy-boy was obviously an exaggeration about having your tires absorb a lot of shock to better illustrate my point. Yes, you can have your tires absorb a lot of force, or you could use them for what they're supposed to be used for (traction) and leave the shock absorption to the shock absorbers. Weird, right?

And like I've said a couple of times now, it's pretty obvious the OP has matched his tires to the rest of his suspension, so that isn't the problem anyway because the Bilstein shocks he's running are designed to deal with the additional suspension forces that come with better traction, lower profile tires and increased spring rates.
 
What your car did is why every car and SUV on the road uses IRS today,it's called
tramp,and it's what solid hotchkiss rear axles do when one wheel hits something sharp.
RRR's right,the OE guys knew it, and the bushings and tires were selected to try &
minimize it.Making the suspension stiffer and less compliant, along w/low profile rollers
(which I love),exposes the ugly side of the OE system.Unless you experienced a less
than effective enough shock damping "shudder",you had better get used to it.
 
Killer6 said:
What your car did is why every car and SUV on the road uses IRS today,it's called tramp,and it's what solid hotchkiss rear axles do when one wheel hits something sharp.
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Most likely, the sideways shock of the manhole cover slowed the axle down instantaneously, the body kept moving and twisted the leaf springs sideways and they loaded up a lot of twist energy. Then the tire released from the cover, and the springs put their stored twist energy into the axle, the axle accelerated rapidly sideways, and the result was a wild sideways oscillation of the axle and rear end of the car. The shocks are not in any position to damp or control this.

Standard multi-leaf springs are very prone to twisting sideways so are not a good way to locate an axle sideways. The best way I know to manage this is in an A-body is a panhard rod. (Or watts linkage.) Monoleafs also can help but not as good as something more solid like a panhard rod. (And a 4 link with the 2 upper links to the tunnel and not parallel would be better.) Sway bar connections may indeed help some, but they are not really designed to control sideways movement of the rear axle.

Not all leaf sprung live rear axle suspensions are created equally, and some will behave better. In the old rallying days (this situation happens ALL the time in rallying), Pintos rear leafs and live axles were fairly bad for this on rough corners; Mistibishi designed rear leafs and live axles (Colts and Arrows) were a lot better. But the Datsun IRS was much better, and Opels with a panhard rod standard to sideways locate the live rear axle were very good in this situation too.

The old A and B body rear leaf springs are just not good at all with sideways impacts on the rear axle; just grab the rear quarter of one and start to shake it back and forth and you will see how you can get it to oscillate back and forth very easily. For this reason, if I ever get to building up an A-body for rallying, I'll change the rear suspension to coilovers and pan hard rod, with parallel 4 links.
 
The rear end got all loose feeling and drifted? I have the same thing happen to both my Mopars when I hit the gas too hard below 30 mph.
 

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72bluNblu said:
So was I, because stock height tires with 14" rims have more than enough sidewall to feel sloppy when you try to do anything other than drive in straight line. And they sure as heck won't help the OP.

Now, my comment about the "big balloon tires" and having your car handle like a lazy-boy was obviously an exaggeration about having your tires absorb a lot of shock to better illustrate my point. Yes, you can have your tires absorb a lot of force, or you could use them for what they're supposed to be used for (traction) and leave the shock absorption to the shock absorbers. Weird, right?

And like I've said a couple of times now, it's pretty obvious the OP has matched his tires to the rest of his suspension, so that isn't the problem anyway because the Bilstein shocks he's running are designed to deal with the additional suspension forces that come with better traction, lower profile tires and increased spring rates.
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Your argument has me totally lost. I don't know what the heck you're talkin about or why you are even still responding. I didn't say larger tires would help. That was not my point.

My point was that as the sidewall height decreases, the ability of the tire to help absorb shock also decreases. Period. That was all. In other words, there will be some of this he might just "have to live with".

Even an Indy car that hits an irregular object on the track can be thrown into the wall.
 
nm9stheham said:
Most likely, the sideways shock of the manhole cover slowed the axle down instantaneously, the body kept moving and twisted the leaf springs sideways and they loaded up a lot of twist energy. Then the tire released from the cover, and the springs put their stored twist energy into the axle, the axle accelerated rapidly sideways, and the result was a wild sideways oscillation of the axle and rear end of the car. The shocks are not in any position to damp or control this.
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What? Sideways shock??? The dude rolled over a freakin manhole cover by his own
account "not sticking up very high",and one wheel went up,and the other went crooked
cause it's a solid axle and it has no choice. An ineffective shock will allow the wheel that
hit the bump to repeat the offense,dribbling like a basseball, in a turn that means going
sideways.
Oh, and I'm not sure which Datsun IRS you speak of,but the semi-trailing a-arm
set-up was prone to jacking like a corvair. Not that impressive.I watched vintage foot-
age of GM trying to roll the swing axle corvair,w/the accompanying posts like "All I saw
was the corvair NOT rolling over repeatedly",missing the difference when it did.When
the corvair was in rebound after going over a small "whoop" and the driver cut the
wheel, over she went and quick,every time. Like 'em or hate 'em, Nader was rite.
 
72blunblu I actually picked the torsion bars from reading your build on your duster ha just went a little stiffer, I don't lose traction I don't have the power for that yet lol it just hopped to the side, it wasn't anything crazy I was just curious if anyone had ran into it and if so what they did to fix it. and thanks for the pointers for the sway bar. idk if any of you are from southern California but I took the car up Palomar mountain when I first got it (bone stock) and tomorrow I'm going back ill post some pictures I'm pretty excited to see what itll do now.
 
RustyRatRod said:
I didn't say larger tires would help.
Click to expand...

Thats OK RRR, I will. Taller more compliant tires would've sucked up that
sharp irregularity and not upset the solid axle anywhere near as much. Fact. Wanna
see what a freakin' tire will go thru' suckin' it up? Watch the above mentioned GM
footage on youtube when they've got the camera on the rear wheel,then get back
to me.
 
Oh, lol welcome to FABO hobbza, and yes we have all experienced the "hop to
the side". You have to pretty much get used to it, looks looks a cool ride,maybe
some photos of it in action soon?
 
Killer6 said:
What? Sideways shock??? The dude rolled over a freakin manhole cover by his own
account "not sticking up very high",and one wheel went up,and the other went crooked
cause it's a solid axle and it has no choice. An ineffective shock will allow the wheel that
hit the bump to repeat the offense,dribbling like a basseball, in a turn that means going
sideways.
Oh, and I'm not sure which Datsun IRS you speak of,but the semi-trailing a-arm
set-up was prone to jacking like a corvair.
Click to expand...
OP's post reads like he was going sideways when he went over the cover; he was 'carving corners'. Just offering some ideas of what might have happened and some reasons why. Since he has Biltsteins, it is going to be have a LOT better response than 'spastic' or 'dribbling' for a simple forward hit on a cover.

The Datsun 510 rear suspension is indeed a semi-trailing swing arm but did not have any real jacking tendency. My Mistsubishi Starion rally car has a similar design and was nothing but stable.

I'll make one harsh statement: Please don't bring in early Corvairs in an attempt to disprove actual racing experience that you don't possess, in racing that you never have been involved in. There is a lot of great info and knowledge here, but people on this site don't show any real knowledge of rough road suspensions. The idea that a live rear axle can never behave well is simply not true; the most advanced designs were in rally cars in the late 70's and early 80's like Toyota, Opel, and Ford.

The panhard rod is a solution to a lateral location problem of live axles that is often used. It IS the solution of choice for NASCAR live axles, and is used with a jacking screw mount to give 'wedge' adjustment, which is adjustment of the rear roll center. It would not be easy though in a leaf sprung car as the spring mounts would have to be such to not bind with the panhard action.

And in the OP's case, if he had a very solid lateral locating device, and indeed hit something like a raised manhole cover sideways, it might knock a low profile tire off of the rim instead.......Oooops! A taller stock tire will have some give for that, as I think RRR has been saying.
 
nm9stheham said:
Since he has Biltsteins,

The Datsun 510 rear suspension is indeed a semi-trailing swing arm but did not have any real jacking tendency. My Mistsubishi Starion rally car has a similar design and was nothing but stable.

I'll make one harsh statement: Please don't bring in early Corvairs in people on this site don't show any real knowledge of rough road suspensions. The idea that a live rear axle can never behave well is simply not true; the most advanced designs were in rally cars in the late 70's and early 80's like Toyota, Opel, and Ford.

And in the OP's case, if he had a very solid lateral locating device, and indeed hit something like a raised manhole cover sideways, it might knock a low profile tire off of the rim instead.......Oooops! A taller stock tire will have some give for that, as I think RRR has been saying.
Click to expand...

If the Bilsteins weren't dialed in yet, they would not have proper control
and allow for more effect than if they were,that was all I offered.......
I guess witnessing my friends Datsun jacking and him bouncing the same
side of the car off both guardrails doesn't count as experience.......in the '80's
I simply said "like a corvair",because it is the basic phenomenon,a Datsun
is NOT anywhere near as bad,but can still do the same at the wrong moment.I also
directed fellow members to watch the vid because it is interesting & instructive about
that period in time in the automotive world.
I read the OP's carving .. He didn't say drifting,...and of course the susp.
is side loaded,he's in a corner. And hitting a sharp obstruction momentarily causes the
impact side to lose 100% of it's grip,and compromises the available traction on the
opposite tire,..momentarily you've lost over 50% of your grip...and the back steps out.
We are talking paved roads w/ real world condition issues,and a susp. that
is set-up for hard-paved tracks, NOT a rally, so I'm not sure why that is relevant.
 
WOW! What a lot of information. One area that has not been mentioned is; How many wheels were actually adding traction to the equation? If the only rear wheel that was on the ground (or had weight on it) was the same one that hit the manhole cover, what did we think might happen? somehow all the fancy parts and engineered combinations in the world won't change the laws of physics. Racers have been trying for years. Any given tire has only so much contact patch, and like money it can only be spent once. Going forward or going sideways. The percentage you use going one way will leave what's left for the other.
 
Killer6 said:
Thats OK RRR, I will. Taller more compliant tires would've sucked up that
sharp irregularity and not upset the solid axle anywhere near as much. Fact. Wanna
see what a freakin' tire will go thru' suckin' it up? Watch the above mentioned GM
footage on youtube when they've got the camera on the rear wheel,then get back
to me.
Click to expand...

Thanks. It's nice to see someone else got my point. That tires ARE a part of the suspension system, no matter how much you might not want them to be. LOL
 
This situation is exactly why I have 295/50-15s on10s, on the back. And they are at 24psi, most of the time. I drive/prowl the streets, and I never know what I will encounter.
295s have almost enough sideways rubber in my combo and at the relatively slow speeds I might be whipping about, that just one tire usually has enough grip to keep me on track. I hit lots of bumps, oily/sandy patches, potholes and what not that sometimes/often flip the rear over. That's what makes it exciting. Recovery management.
The 24 psi is required for long tread-life on 10s.Plus it does give a nice ride. I have become accustomed to the slight roll-over as the tire takes a set. I have pretty stiff shocks, and pretty flat springs, so the back is pretty controlled. Plus with the 24 psi, she will hammer over speed bumps and scare/hopefully embarrass, those pesky fart-canned tunerboys who crab-crawl over them as I hammer on by.

Having bragged on my car a bit I must add this one thing.
I once also purchased a 74 Duster.One day,I took it out for a maiden voyage.Just a mind-my-own-business, check-it-out tour. My mind was somewhat disengaged from driving(try to imagine that), when I happened upon two pairs of diagonally set train tracks. Well traffic was moving along at 45 or 50 mph, and as I was daydreaming, I suddenly found myself headed for a shallow ditch, which I was not going to avoid. Crazy man!,what just happened? Well after coming to a stop, I Looked things over and found no obvious reason for the wild ride, so I gently got back on the road and continued my way home.
So out came the jack, and stands, and the creeper. Nothing could I find amiss. Well SOMETHING had to be wrong. I pulled the wheels off and searched and searched, but found nothing. So back on they went,out came the stands, and down went the floorjack. Plop.
And then I saw something odd.
The car didn't "land" right. You know when the floor jack goes down fast the car "lands", right? Well this one kinda crashed like jello. What's up with that I thought,never having seen that before.
Well Now I had a search. What I found was that the inner apron was more or less flapping in the breeze. That portion that is normally welded to the firewall, kinda wasn't.And the portion that is normally welded to the framerail, mostly wasn't.And the portion that is normally welded to the shock-tower, sorta wasn't either. Both sides.Rust had taken most of it.
So I don't know what actually was holding that thing together, or how I got as far as I did; but one thing I knew;Since I was no bodyman, and since the car had been free,This car was never gonna see the road again. Out came the powertrain, and the brakes, and then I called for the scrapper.

Long story short,check your aprons. AJ strikes again!
 
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