How to get rid of understeer in a 1970 340

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jerry6

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Stock 340 torsion bars , sway bar front , gas shocks not sure the brand ,Firm feel stage II steering power box 8 3/4 rear with HD leaf springs , no sway bar . When I'm on the gas in a big sweeping turn I get understeer , feels like the front wheels are lifting off the ground . Other than that the car stays level , does not lean over . 225-60-14 tires up front , 235 60 -14 or 15 out back depending wheels I use that day .
Any ideas ?

Thanks
 
Ideally you want a neutral balance but most setup for a slight understeer
You could try a rear sway bar should take some understeer away
 
Where to buy the right sway bar . There does not seem to be any mounting brackets in the back . And what size bar would be est with standard bar up front ?
 
Ive said it before, these cars were massively undersprung from the factory in the front. They also understeered like crazy. You'd think that the solution to your understeer issues would be a rear sway bar, but that's usually not the case with these cars. You already have HD springs in the rear, which means the rear spring rate is pretty close to correct for a well-handling car.

Judging from the ride height of the front end in your picture, you've probably got a couple things going on. One is that the car is low enough in the front that even with 340 bars you're probably bottoming the suspension out on your bump stops when you're loading it up. Not as much lean, but your suspension isn't working either. The other is that with the rear of the car up in the air like that your rear roll center is pretty high.

Bigger torsion bars in the front, 1"+, should allow you to run that low without bottoming anything. Front and rear sway bars. If your car didn't have a rear sway bar, then you don't have any brackets. Same in the front. Hellwig makes some great bars for these cars, and they won't set you back your first born like the Hotchkis bars will (although they are REALLY nice). If you're really serious about handling better, you'll need to consider lowering the rear of the car as well to get that roll center under control.
 
I would start by lowering the rear to get the roll center lower. This will actually increase understeer, but I agree with 72bluenblu that this needs to be lower; with the rear in the air, there will be a lot of transitional oversteer as you dive into a corner, and it will be hard to make a good transition to the desired steady state over/understeer. And he makes a good observation on the low front end...do you ever bottom out the front suspension on bumps or strongly undulating raads?

The added rear sway bar should help your understeer. I cannot tell how much the HD rear leafs are helping, but would not assume they are stiff enough to get the right rear roll stiffness. (I just don't know the spring rates).

Give us better info on what shocks you have front and rear; there are a huge variety of gas shocks. These are important in transitional steering attitudes; thewring match F to R will cause the car to do odd things when diving into a corner.
 
everything else above is spot on, i'll go for the unmentioned, your trying to handle on 14" tires... the tires available for a 14, even most 15's are not handling tires.
 
Over 40 year old technology.
If a canyon carver is what you want, get out the checkbook.
Otherwise, save your money and keep it straight.
 
Back does not sit high , the pic is on a steep driveway that slopes down towards the street at the rear bumper , front end never bottoms , ever no matter how many frost heaves and dips I hit , car does not bounce hits the bumps with no bobing around . Better pic of how it sits
100_0650_zpsf872df7b.jpg
 
Johnny Dart said:
Over 40 year old technology.
If a canyon carver is what you want, get out the checkbook.
Otherwise, save your money and keep it straight.
Click to expand...
Tell that to the some of the new crap boxes that try to keep up on the back roads , 40 year old tech ain't that bad .
 
OK, then start with the rear sway bar.....shocks? Looks like the Hellwig is 3/4" only. That or 11/16" is probably as small as one would go on this weight range of car to be close....
 
nm9stheham said:
Give us better info on what shocks you have front and rear; there are a huge variety of gas shocks. These are important in transitional steering attitudes; thewring match F to R will cause the car to do odd things when diving into a corner.
Click to expand...

No idea the brand shocks , they are a matching set front and back gas shocks , seem to do the job well ,at least they test as good , but obviously should be changed for something better . Car does not bottom out , does not bob and weave on frost heaves and the like , hits the bump up and down no bounce . People are really impressed on the ride / handling , but the understeer bothers me .
Any good reasonably priced shocks on the market these days ?












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KYB Gas-Adjusts are fairly decent for the price; I used to rally on them. But they don't compare to set of Bilsteins. Define 'reasonable'....LOL
 
nm9stheham said:
KYB Gas-Adjusts are fairly decent for the price; I used to rally on them. But they don't compare to set of Bilsteins. Define 'reasonable'....LOL
Click to expand...
Reasonable , under 1000.00 , preferably 3 or 4 hundred ?
 
Sub-frame connectors on car?
 
nm9stheham said:
OK, then start with the rear sway bar.....shocks? Looks like the Hellwig is 3/4" only. That or 11/16" is probably as small as one would go on this weight range of car to be close....
Click to expand...
I worry about the size , to big or to small and you end up with no gains ,could make it worse . Solid or hollow ? Was there ever a stock option in 70 ?
And the way they mount , there are different methods , or am I dreaming that ?
 
Louie70Dart said:
Sub-frame connectors on car?
Click to expand...
I have them , have not installed , yet , debating if it will devalue the car , not that I'm selling it , just really not into doing something I might regret . Had a set on an old Dart , made a BIG difference .
 
Reason I ask is I wonder if the body couldn't be flexing under torque when cornering. Are they easy to R&R? That I don't know. I have heard of people who bolted them in, and others who burned/welded them in. Some even went so far as to contour them to fit the under belly, then had a good clean weld the whole length.
 
jerry6 said:
Reasonable , under 1000.00 , preferably 3 or 4 hundred ?
Click to expand...

Well, the KYB Gas-a-Justs will cost you under $130 for all four. If you're willing to spend $400, you could get something better. I don't mind KYB's, but I'm not going for high performance handling.
 
Louie70Dart said:
Reason I ask is I wonder if the body couldn't be flexing under torque when cornering. Are they easy to R&R? That I don't know. I have heard of people who bolted them in, and others who burned/welded them in. Some even went so far as to contour them to fit the under belly, then had a good clean weld the whole length.
Click to expand...
I don't think so , no cracks in the paint in those places that crack when there is flex , also if i jack up one side of the car I can open and close the doors and they line up and sound right . It's a pretty olid car , but the connectors would help , just a big decision .
 
Many people think lowering the car makes it handle better. I like the lowered look, but the new angles the control arms are sitting at causes the front roll center to drop, which makes the car roll over easier, which really sux as far as handling goes. Many people like Bilstein shocks, and tons of people have nothing but bad things to say about the KYB Gas-a-Just. I like QA1 Stocker Stars. About $150 each for single adjustables. Wow! What a difference they made on my Charger. I had purchased them for one of my Darts, but the Charger needed them more. There was a rear sway bar available in '76 only. It mounted on the frame, and the ends connected to the shock mounts on the springs. I'd get that type, not the ones that bolt to the differential. I'd check bump steer. The tires could be turning as they move up and down on acceleration, and could feel like understeer. Our racecar had 1/4" of toe change per inch of suspension travel, and played havoc with the controllability upon braking into turns. A quick and dirty check is to put the car on stands, with stands under the rear axle, a jack under one of the lower control arms compressing it until the front of the car just lifts off the stands, and then lower it and see if you can see the tire turn left or right at all. Ours was easily visible, although I made a fixture with a dial indicator so I could dial it in to less than .020" toe change per inch of suspension travel, which is what you want.
 
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.
 
jerry6 said:
Reasonable , under 1000.00 , preferably 3 or 4 hundred ?
Click to expand...

Go add an adjustable rear sway bar from Hellwig. It will change that understeer real fast.

Do you have a stock front sway bar? Adding a 1 1/8 front will help the front grip by not rolling over so much.
 
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