How to get rid of understeer in a 1970 340

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2 Darts said:
Recommendations:

  1. Stiffer front T-bars ~1.0" or greater.
  2. Stiffer front anti-roll bar. A 1 1/8" bar is available.
  3. Rear anti-roll bar. Even those that mount on the axle are better than nothing.
  4. Same size wheel and tire F/R. Larger rear tires promote understeer.
  5. Fresh F/R suspension bushings. Polygraphite preferred but even new rubber bushings better than old ragged worn out stuff.
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All the bushings were changed last year ,used polygraphite all around . Will look into the Hellwing . I beat the new crap boxes yes , but when I push it I get understeer , not when braking into turns but when accelerating into long sweepers or accelerating out of the turn . Feels like the front wheels are lifting and the car is not responding to the steering .
KYB had those on my ramcharger in the 70's , those ride hard real hard. What about Koni , they still around , worked well back in the day , will also look into bilstein . Have a feeling the KYB will rattle my teeth , a least that's what I remember in the ramcharger , up here with the potholes and rough roads they might break the car .
 
jerry6 said:
All the bushings were changed last year ,used polygraphite all around . Will look into the Hellwing . I beat the new crap boxes yes , but when I push it I get understeer , not when braking into turns but when accelerating into long sweepers or accelerating out of the turn . Feels like the front wheels are lifting and the car is not responding to the steering .
KYB had those on my ramcharger in the 70's , those ride hard real hard. What about Koni , they still around , worked well back in the day , will also look into bilstein . Have a feeling the KYB will rattle my teeth , a least that's what I remember in the ramcharger , up here with the potholes and rough roads they might break the car .
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On long fast sweepers you don't exactly want the rear end fishtailing though. I can show you a video example of why.

hmmmmm..

Wonder if this is more of a floaty-loose kind of feeling as opposed to the front tires skidding outward.

What are your alignment specs?

How tight is your steering box?
 
Steering box is tight , firm feel stage II , alignment specs , that I don't remember , pretty sure I gave the shop specs off the board here for the new radial tires instead of factory settings . Good point on the floaty feeling as opposed to tires skidding outwards , will have to run a few more test
 
Given everything else you've listed so far, I might start to suspect the tires. Tall sidewalls can give the car a "vague" feeling in response to your inputs, can come across as steering or alignment issues. Your 225/60/14's are pretty short, so there really isn't any more sidewall than on a 15" tire, but it could still be adding to the issue. Not to mention the generally lousy tire compounds that are available in those sizes.

Based on everything you've done already, after you confirm the alignment I'd go back to recommending 1"+ torsion bars, front and rear sway bars, and a better set of shocks. The Bilstein RCD's make for awesome shocks, and they're not as expensive as some of the adjustables out there. After that, you're pretty much just left with tires.
 
Do you have a posi-trac diff? If so, and if the diff is tight, it will very much tend to push the front end straight ahead under power (and somewhat even under coasting) when the rear tires have good traction. (I have to be careful with diff tightness for RWD rallying on gravel; too tight, and if the rears hook up at a spot, it is straight ahead towards the trees...yikes!)

Have you ID'd your tire brand/model? That would help to know. Soft sidewalls will make the ride good but add to pushing with a heavy front sway bar. Are there any scuff marks up the sidewall, even a little bit, after the front end 'floats'?

The KYB suggestion was for low cost with something at least decent; I won't gainsay any others' experiences with them; they are not top performers. As said, you can do a lot better with Bilsteins. Yes, Koni's are still there, but for general use on regular road surfaces that go up and down and have some surface roughness, I have found Bilsteins to be much better. Koni valving has always seemed to be focused towards road racing surfaces and parking lot auto-x'ing, and seemed to me harsh on regular road surfaces even when adjusted towards the soft end. Anything that is going to have some good performance valving is going to be a bit harsh feeling, IMO.

ANd, BTW, my thoughts on rear anti-sway bar size are just off the cuff based on car wieght and somewhat heavier rear springs, not calculated or anything like that. So take it for what is.
 
A posi trac diff.....
Uhhh, how about a "Sure Grip" ??
I've seen no specifics regarding your alignment. In the one picture of the car in a building, the LF wheel looks to have slight positive camber. Not good. To get any decent steering response, you'll need some NEGative camber, at least 1/2 a degree. An alignment that starts with POSitive camber often has near ZERO caster as well. POSitive caster helps the tire stay flat against the pavement in the turns when the body leans. You may not think it, but even a stiffly sprung, big sway bar car does lean some when centrifugal forces set in during a turn.
My settings preferences are as follows: 1/2 to 3/4 degree NEG camber. 3-5 degrees POS caster and 1/8" toe IN. To get there you might need adjustable UPPER control arms. I was able to get these numbers in my 70 Charger (Similar suspension) by using Moog PN 7103 offset upper control arm bushings in my stock control arms!
Don't be afraid of KYB shocks. They are okay for a low priced shock. Bilstiens, Fox, Afco.... all reputable shocks but they are much more expensive. Shocks alone will not eliminate understeer. You can chip away at it with a proper alignment, larger front sway bar, a medium rear bar and increased tire pressure. I set my car to 36 front 32 rear.
 
Don't turn the steering wheel too far.
 
I'll look for shocks , sway bar and alignment , see if it helps
 
72BBSwinger said:
Lose the rake, that kills caster as well as overall balance and CG.
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Close to zero rake , the avatar photo is on a steep driveway , recent photo
100_0650_zpsf872df7b.jpg
 
I never put rear sway bars on these cars, unless everything else is perfect and you want to dial in a little more roll rate. My experience is they induce oversteer.
 
GMachineDartGT said:
I never put rear sway bars on these cars, unless everything else is perfect and you want to dial in a little more roll rate. My experience is they induce oversteer.
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Been waiting for you to post something , the Stage II steering box I bought off you is working really well , thanks .
1 VOTE NO SWAY BAR , noted
 
Ways to move the car towards oversteer/away from understeer:
- Stiffer rear anti-sway bar
- Higher rear roll center
- Stiffer rear springs
- Stiiffer rear shocks will increase the car's transient oversteer tendencies (when you turn in), but this may mask the actual over/understeer of the rest of the chassis unless you check it in long corners after the shocks have setted into a stready state attitude
- Anitsway bar end links type/design can also modify the roll stiffness in each end for different degrees of turn tightness

But it is all relative to where you are starting with the front end for the same factors too. So what is good/bad is relative to each car's combination, and what moves 1 car too far towards oversteer may be just right for another cars' front/rear combo.
 
I'm going for new Bilstien shocks and going to have the torsion bars and springs looked at , they are over 7 years old , might be time for a change . Wil see how that helps , then rear sway bar .
Thanks
 
jerry6 said:
I'm going for new Bilstien shocks and going to have the torsion bars and springs looked at , they are over 7 years old , might be time for a change . Wil see how that helps , then rear sway bar .
Thanks
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Existing springs will be fine. You don't drive it daily or anything. If they are not sagging the only real way to check them is to remove them and put them in a Spring Rating device/tool.
 
good god yall... he is running POS tires, this isn't some big freaking mystery...
 
RustyRatRod said:
I'm rubbin off on you.
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And that might not be a good thing , making ASSumptions about the tires I'm using at the time . Hahaha , Using BFG gforce r-1 , not for the street , just some fun on track , nothing serious .
 
I have a ton of mods to make the car handle better, but when I take the 255x45x17 Nittos tires off and put the 215 and 245 14 inch BFG T/A's back on, the handling goes out the window. The tires do make a tremendous difference.
 
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