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Discussion Starter · #1 ·
I can keep it going straight but it becomes a challenge. It has a tendency to want to twitch around on me once I get over 105 and I'm running 108 in the quarter now. I have good air pressure so its not the tires. Alignment is good, suspension is all new. I have braces n crap. I had thought at one time that it was getting air up under the hood so I lowered the front end a couple of inches and that seemed to help.

Recently I lowered the back of the car down about 3 inches with shorter tires and some rear suspension work. The twitch is back now. On these old mustangs the hood lip is straight and I guess it tends to grab air and become an air foil at speed. I don't want to run it without the hood. It could also be that the front underneath around the engine is catching air and trying to lift it up.

Would spoilers help stablize it without slowing me down? I've heard that the R model front valance helps but I don't like the way they look. I also don't care for the chin spoilers at all.

I would prefer to put a small air dam under the front valance. It would be maybe a 2 inch deal that doesn't show up too much but gives it just a little push to keep air from getting up under the car. Unfortunately, I haven't found that anybody makes one so I would have to make my own. I'm not sure that is the problem though. Maybe it needs a rear deck spoiler too?

Maybe the tail off a Cessna? LOL.
 

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Go grab one off your local riced out celica! Yeah, Downforce is good stuff for stability, most the weight is in the rear of the car while accelerating, so a front valence would be good for some downforce on the front tires
 

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A front spoiler would help, however, have you checked out your steering box? Most of these cars, still running the stock setup, have a lot of play. You can check Maer Racing and Tony Branda for front spoilers. A front spoiler will also help with cooling as it creates a negative pressure area behind it which helps pull air through the radiator at speed.
 

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You might want to check the bump-steer of the front end also. When the front end rises, the wheel alignment count have too much toe in or out.
 

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Had the same problem with my 65 coupe until I added a cheap fiberglass front spoiler...problem solved!
 

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Hottarod do you have power steering?If you have a worn control valve it can cause a wandering feeling even though everything else is tight.I saw a neat article once where they were taking pictures of cars at the top end of the track.You wouldn't believe some of the distorted hoods and bumpers that they saw.While I doubt this is a problem for you as your car is steel it might not hurt to have someone take a pic at the line.Also if you have adjustable shocks on the front are they letting the car settle back down after weight transfer?I would try a little spoiler under the chin somewhere,better to have that than a crashed car and maybe your life on the line.Be careful until you get sorted out


<font size=-1>[ This Message was edited by: frdnut on 5/14/02 1:11am ]</font>
 

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Have never had this problem with my 65 FB, and its running over 130 MPH. I did have the car checked front to back with a laser to make sure it was running straight and had it weighed at the corners to make sure the weight distribution was OK. Some minor adjustments were made in alignment, but have never had that "lifting" feeling. All valances are stock, no rear deck spoilers.

Ron
 

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Mine is solid as a rock, and it goes around 130mph. I would be looking into the front end.

Are the shocks relatively new? Dead shocks will make one feel that way.

I'd also check the steering box, and tighten it up a little if it's loose. If there is more than an inch of free play in the steering wheel, you've got too much. Have someone move the wheel back and forth with the front tires on the ground, and see where any 'slop' is coming from.

I'd have the front end alignment double checked. The camber and caster MUST be adjusted by unbolting the upper control arms and adding/subtracting shims between the arm and the shock tower. (back up behind the front springs) Most shops are hesitant to do this because it's pretty much a 'trial and error' affair. It's a real pain in the ass to do it right, so many shops totally skip this process and only set the toe-in. (all you need to do there is twist the tie-rod sleeves)

The car needs to have maximum caster. This also makes the car harder to steer. Extra caster also makes the front wheels 'center' themselves when you let go of the wheel. No enough caster will make the car 'wander around' at speed.

You'll also want to check the toe-in. If the front end doesn't have enough toe-in, the car will want to wander pretty bad. If it actually has toe OUT, it will be VERY hard to control at speed. You can do a quick check of this with a tape measure. Measure between the tread bars on the front and back side of the two front wheels. You should get a larger 'back' measurement, meaning the wheels are actually toed inward.

You also need to check and see that the upper control arm bolts (where they mount to the shock tower) are tight. If they are loose, the shims will fall out and the suspension will be free to move all over the place.

Check to make sure the strut rods are in good shape and tight.

Check all the front end parts to make sure the ball joints, tie rods, drag link, and idler arm are all in good shape.

You don't need to do anything fancy to make the car feel solid. As long as everything feels good, and you are running plenty of air in the slicks, all should be good. I would recommend around 12-16 pounds in a 26" tall 9" slick.

I'd get the alignment re-checked by someone that will allow you to be RIGHT THERE as they do it, and have them add as much caster as they can. The front control arm bolt will run out of theads as maximum caster is reached.

One more thing... Extra soft rear springs that sit the back of the car down too far will also let too much air get under the front end... which will cause it to lift at speed. If your car has the stock 35 year old springs on it, get some new 'GT' springs, and get the car leveled out.

Good Luck!

_________________
Mike Burch, 66 mustang real street
302 4-speed 289 heads, 10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367

<font size=-1>[ This Message was edited by: n2omike on 5/14/02 2:21am ]</font>
 

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I have to throw my 2 cents in as well. My 71 doesnt get twitchy till 140, and I know its in my linkage, all of its a lil loose, just real spendy to replace. I plan on running the mach 1 airdamn to help this problem. I wanna break 175 in this car! The one thing that stopped me from goin any faster was my windows both popped outta the seals. Scary as hell, big loud "WHUMPA" thought I blew a tire!
 

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My 65 fastback goes over 110 in the 1/4 and I have no noticable twitchy action going on. No spoiler front or rear, and no hood either.
It has been lowered in the front 2" plus, and 2" in the back approx. I have the original P/S that has not been rebuilt.

Maybe the rear end is set over to one side to far, or not quite square with the car? Just some thoughts, could happen.
 

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Discussion Starter · #12 ·
Manual steering, new shocks. I'm going to have my alignment checked. It was ok until I skidded it on the track. Maybe I can get them to dial in some more caster this time.
 

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My coupe has been 170 with the previous owner & 150 with me, no problems but it's as low as the rules allow. Do not run with no hood, the air space will syphon away any signal the carb has & you won't cure this problem anyway. You really need to check the steering box. Make sure the front shocks are in good shape & go to an alignment shop you know does fast race cars. They'll check everything to make sure it's tight, not just within tolerance. Also you'll get a different caster, camber & toe in adjustment. After that, it'll rock. Had to do the same thing with my Spoiler when it got to 110.
 

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GTR, just wanted to let you know that I used the fact that I was running w/o the hood to share an example of a real poor aero package and still not haveing any issues at speed, I was pretty sure it is not the best way to go and was not intended as advice, but my hood dont fit any more
. I did not know about the carb signal being messed up running like that, so I guess I can expect better performance when I do get a hood on it.
 

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Discussion Starter · #16 ·
Theres a shop in Marshall next to OReillys that I used the last time and he did a good job. I will probably take it back over there. The owner has raced for years and personally supervises the work on my setup.
 
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