Mysterious front end shake at speed

[Blas]

Interesting; unless both of you are looking in the wrong area for the rack adjustment (that's doubtful) the factory may have used a different steering rack. You say that cars #2608 & #2613 do not have the adjuster, but car #2932 does... Could we get a few other cars in and around this chassis series to check theirs and report back...Say between #2500 and up...If you both send me an email address I'll send a photo of the adjuster on mine. I'd like a photo of your setup for reference too if one of you could send one...Yours probably adjusts too, but differently, perhaps the bolt or a shim below it. It's easily seen from above looking from the passenger side of the engine compartment.
My email is below...
EDIT 1:
Reading your post closer...Maybe a clarification of the directions is needed: The 17mm nut is a locking nut for the 7mm hex-ended stud it's connected to. Loosen the 17mm and adjust the 7mm hex stud, then retighten the 17mm nut while HOLDING the 7mm in position so as not to tighten it anymore when locking the 17mm nut.
EDIT 2:
More directions from my notes:
Adjustment: Jack the front end, Then loosen the large locking nut slightly, then snug down the bolt that actually pulls the steering rack's gears together. Turn the latter bolt with a box wrench or socket until the steering wheel just starts to have some drag when turned from side to side. The slightest turn of the small bolt makes a bit difference in loose and drag on the steering wheel. When it is just barely "loose", snug down the locking larger nut. The front wheels should be off the ground to do this properly, to feel for any "drag" at the steering wheel. Tightening the adjustment forces a nylon ball against the racks spiral shaft and removes the lash. While you're in there, check the pinch bolt on the clamp where the steering shaft attaches to the pinion shaft. They sometimes loosen and this can cause play in the steering shaft, as well. Also, check the pinch bolts at the U-joint on the shaft, too. Even if they're loose, they won't allow the steering shaft to come off the rack and pinion as the pinch bolts fit through a notch in the steering shaft

[madmaxx]

Remeber to inflate tires between 18-22psig, not the standard 32 psig. This is detailed in the SPF owners manual.

[Got the Bug]

Blas,

I pointed my iPhone and a flashlight at the steering rack and snapped this pic.

I was thinking that there might be a center screw to adjust if the nut was loosened, but there's no groove.

[Blas]

Your are good to go. They have replaced the hex head stud with a slotted head stud, probably a better way to go as it would be difficlut to over-tighten it with a screwdriver vs using a wrench...Keep us posted.

[WardL]

Here is the pinion gearbox for 2608:

[jhv48]

Blas, I think he's saying that there is no way to adjust the center screw after loosening the 17 mm nut. There appears to be no slot for a screw driver nor is there a center hole for the 7mm hex key.

[WardL]

JHV48, Thanks for saying exactly what I was trying to say! 2613 seems to have maybe a slot to turn the enter bolt. There is nothing on 2608. Wonder if they actually made a change between 2608 and 2613? 2613 has a nice coat of paint. 2608 has a bare nut and bolt. 2608 has traded hands and I don't know what the previous owner may have done. Thanks JHV48 for clarifying what I was trying to say!

[Blas]

Odd...I wonder if your bolt is in backwards? Slot towards the inside by mistake? Lack of paint is noted too.

[JST4FUN]

#2660 looks just like #2613. Mine has a little shake, seems to vary with road surface conditions for the same speed range. Tire pressures are set to 20 but haven't had them force balanced yet. The car sat for most of it's life before I bought it with 1100 miles on it and guess I have only driven it another 1400 in a year. The person who put it together and maintained it for the previous owner said he couldn't resolve it and thought it was the tires. I haven't really tackled it yet, now I'm getting interested!

Thanks to Blas and the rest for sharing their insight!

[Nantucket427]

Cobra Valley's R/T Super High Performance Ball Joints
They make all the difference in the world. I got new tires, balanced them three time but the ball joints were the problem

[WardL]

I spin balanced the front tires and they were both out of balance. Still shakes, but like Joe said, various speeds and road conditions change the shake dramatically. So if the front tires were out, seems to make sense to balance the rear tires next. I suspect the ball joints Natucket suggest would be great, but wonder how you can blow out ball joints in 4,000 miles.

[Silverback51]

It's not that they are blown out after 4000 miles, it's that they are not designed for the application they are used on.

[WardL]

balanced the rear tires today. They were out a little. The Cobra seemed to ride smoother after the rear balance, but the shake was still too much. Now I'm thinking about getting additional small weights to test on the road. Put a weight on front tire and see if it is better. Has anyone ever done that? Your basic trial and error!

[Gaz64]

Although you should fix your ball joint issues, have you considered your wheels could be non concentric with the hub, or the front brake discs are the balance issue?

[jhv48]

Before you start replacing ball joints, have the fronts balanced while on the car. Might take a while to find a shop that can do it and it will take about 2-3 hours to complete both wheels.

But once done, if the shake still persists, it is not the wheels. Then look at the ball joints.

The shake you are experiencing seems to be characteristic of SPF for some reason. It took me about a year to finally rid my car of the 60-70 MPH willies. Now, it just shakes a bit if the tires are cold and have been sitting too long.

Balancing the entire front rotating assembly is the best solution right now.

[Da Man]

I know you think it's a front end shake, but have you considered the drive shaft?

While they are really small on these cars, a friend of mine with a 2011 Mustang recently went through a long and frustrating process trying to find a vibration that was at a very specific speed (60-75 mph). He had the wheels and tires balanced off the car, on the car, had the tires and wheels checked for out-of-round, even replaced the front rotors. The dealership, while acknowledging the problem, threw in the towel and was unable to explain it. They had even gone as far as to replace the outer tie rods and, finally, the steering rack.

Finally, he was told by some sage older fellow at a car show to change out his drive shaft for a 1 piece aluminum unit. Presto! Vibration gone. The cheap Ford boat anchor that was installed at the factory was found to be hopelessly out of balance and causing the vibration at one specific speed range.

[Jerry Clayton]

Shaking at a specific (repeatable) speed range can be air buffetting---stalling around the bulges of the body---

It can maybe be found where the body is in trouble by putting several strips of brightly contrasting to paint color strips of yarn on the body and photographing at different speeds from a drive by point or another vehicle(must be far enough away to not cause a draft)

You also can try driving in close formation with another vehicle(van, suv, semi,bus) and see if it changes---

[WardL]

Thanks for the suggestions. I'll work on the front wheels on-the-vehicle spin balance. I think I can really tell the rear wheels are smoother riding since they were balanced. This is a shimmy and not a shake. The shimmy seems to come from the front of the Cobra causing the steering wheel to move back and forth very quickly. Wonder if the rears will fit up front if I don't turn sharply? The tires are 335/35 ZR 17 and 275/40 ZR 17. I would do this to check if the rear tires are any smoother than the rear. When I bought the Cobra (used) the front was too low and the tires would scrape on the body. If the fronts have balance issues, the scraping could be a cause.

[Jerry Clayton]

I am assuming that you are balancing those tires/wheels with weights both inside AND outside edge of wheel?

And are there any engine balancing shops around you where you could balance rotor/hub and then with tire/wheel mounted on the hub???

[ekrupa2]

Originally Posted by Blas

Your are good to go. They have replaced the hex head stud with a slotted head stud, probably a better way to go as it would be difficlut to over-tighten it with a screwdriver vs using a wrench...Keep us posted.

Blas - attached a pic of 2632. Looks like I have the hex center bolt as you had described. Do the arrows describe what Olthoff's have outlined? Loosen the larger nut and adjust the center with an allen key or socket?