High speed instability

[Chubbs]

Last night I reworked the alignment again, up to about 9.9 degrees caster on both sides, and about -1.25 camber both sides. It's been raining like crazy here for the past few days, so I can't drive it yet. I'm hoping it might calm it down though. Not only does increased caster increase stability anyway, but doing so also rotates the tie rod bracket downward, which helps with the geometry of the Tie rods we've been talking about.

If it's still unstable, I think drilling new holes in the hub mounts is the last remedy (though I'm not looking forward to taking the whole front end apart) Relocating the steering rack doesn't work due to the heat exchanger location (unless that is also relocated). Longer shocks to increase ride height would work, but is an expensive solution.

To be specific, the car cruises pretty well at 70 mph on the highway. I can cruise 1 handed with no issues, and it drives mostly like a "normal" car. My issue is bumps, and especially bumps when under acceleration. I would say i've had the scariest situations at around 40 mph, under heavy throttle, on bumpy pavement. For my Boxster and Charger, the same stretch of pavement is no issue, it's a one handed affair with the skinny pedal on the floor. But in the goblin, just crossing a bridge (there's one just down the street) is a terrifying experience.

The rear toe link mount is installed correctly. And, for what it's worth, I don't feel the issue in the rear. It seems like a steering issue to me.

 

[Gtstorey]

I don't know that the Goblin will ever approach the driving characteristics of the Charger or Boxster, we are talking about a 1600 lb kit car for better and worse. The over boosted electric steering doesn't help any. I have the Saturn Vue EPS to install with assist adjustable to install this winter.

You can drill the hub without pulling the front end apart although it make take right angle drill or attachment. I just adjusted mine to where it needed to be, held it in place with C clamps, and used the hole in the arm to guide the drill bit.

 

[Ross]

Finally found a bump steer kit for our Goblin kits. Not cheap, $155, but it should work.

Checking for bump steer on the front of my goblin:
So Dale E and I put a lazer pointer on my front brake disk, and moved the front spindle from the bottom to the top if the suspension travel. We moved the billet arm up and down, and discovered the lower we put the tie rod end, the less the bump steer. Dale also taught me how to correct bump steer by using a bump steer kit like this one

The Cobalt rack has M14.x1.5 threads on the end of the steering rack.
Which will replace the Goblin's tie rod end:

I haven't checked the rear for bump steer, but theoretically the bump steer kit could be used on the rear too.

 

[Gtstorey]

You may want to confirm the threads on the bump steer kit, if it isn’t to late. The one listing I just looked at shows 9/16-18 threads on the rack side. It’s listed for the Fox Body Mustang.

 

[Ross]

You may want to confirm the threads on the bump steer kit, if it isn’t to late. The one listing I just looked at shows 9/16-18 threads on the rack side. It’s listed for the Fox Body Mustang.

Where did you find that info? I only saw the M14x1.5 in the question and answer section.

Question:Will this fit my 98 ford expedition
Answer:Th threads are M14x1.5
By Christ is Risen on May 11, 2021

Question:Will this fit 67 c10
Answer:It’s threads are M14x1.5.
By Christ is Risen on April 9, 2021

 

[Gtstorey]

I first found the dimensions on speedway motors site.

QA1 BAX102 Bump Steer Kit, Mustang, Kit

Changing suspension components sometimes leads to bump steer or unwanted toe change during suspension travel. Correct this problem with QA1's easy to install Bump Steer Kit. This kit features QA1's premium chromoly steel, heat treated, self-sealing and self-lubricating X series rod ends and an...

www.speedwaymotors.com

I checked the qa1 website under the instructions listed for the bax102 instructions and it gave the year mustangs it fits and the diameter.
https://www.qa1.net/assets/uploads/documents/intallation_guides/9919-178_rev_bump_steer_kits.pdf
It looks like bax104 for the 94-04 mustang has the 14mmx1.5 thread, if all the cross referencing I’ve done is right.

https://www.moog-suspension-parts.com/universal_outer_tie_rod_ends.asp

I didn’t check the ball joint taper on any of this and the odds of it matching are pretty remote. You would likely still need a custom arm made for it to mount to.

 

[Justinreed7]

Your 1/8th toe in recommendation...is that based on you sitting in the car, or with the car empty?

As others have mentioned, mine changes quite a bit depending on the loading in the car. With my wife and kid sitting in it (roughly the same weight as I am, combined), the front wheels toe out a bit, even though they are 1/8 in when the car is unloaded. So, I set toe-in with them sitting in it, and now when the car is empty, it's about 3/16 to 1/4 toe in at the front (rear stays constant at 1/8, roughly).

The car is flighty, mostly under power. I think taking weight off the front end, such as accelerating, and especially while accelerating AND hitting bumps, the thing is a white-knuckle terror machine. It will completely swap lanes before I can get a handle on it. Cruising on the highway is perfectly fine.

I originally set the alignment with no weight in the car, and it was even worse. Toeing the front in a bit seemed to help, but more work is still needed.

what you are describing is your rear toe moving under load. replace the rubber control arm bushing with poly inserts or solid bushings. your control arms are moving causing the lane walk

 

[Gtstorey]

DF needs to make a bump steer kit, seeing how simple it really is and at $150+ it should be easy to make a profit.

 

[Gtstorey]

It’s raining here today so I’ve done some searching on the bump steer kit.
It does look like the taper is different on the mustang than the cobalt/goblin. There is a chance that the taper could be re-cut but haven’t tried to research.

I’ve come up with another couple of options for using rod ends. You can get 14mmx1.5 coupling nuts and male rod ends but the problem there is they are 14mm id so the hole in the arm is bigger so you would have to drill and sleeve or get a custom made arm. DF could probably make this change pretty easily since it’s drill a 14mm hole instead of a taper.
The other option is to use a 5/8 rod end and make a custom 5/8-18 to 14mmx1.5 coupler and drill the arm out to 5/8. You can use a piece of 1” tubing and a 5/8-18 threaded tube end on one end. On the other end a 7/16-20 tube end drilled and tapped to M14x1.5. Summit has a listing for these pieces, although be careful and make sure tubing id all matches. And they have 5/8 rod ends. This just leaves 5/8 bolts, nuts and spacers. Plus the M14x1.5 tap and drill bit, and welder.

 

[Waterdriver]

From Brad's (aka George) post on creating a bump steer solution.

Shadow Lou Racing, street,track,autocross Goblin

Changed the Ackerman to almost 0. Car feels better in the turn. No correcton in input needed. Need to play with different toe setting to smooth out the feel when turning from driving straight. No other side effects. May have to raise rear tire pressure. waiting for my test driver to check it...

dfkitcar.com

 

[Gtstorey]

From Brad's (aka George) post on creating a bump steer solution.

Shadow Lou Racing, street,track,autocross Goblin

Changed the Ackerman to almost 0. Car feels better in the turn. No correcton in input needed. Need to play with different toe setting to smooth out the feel when turning from driving straight. No other side effects. May have to raise rear tire pressure. waiting for my test driver to check it...

dfkitcar.com

Making a new arm really wouldn't be to hard with fairly basic tools, but making it look good isn't quite as easy. I was trying to come up with something to use the existing arm.

 

[Chubbs]

what you are describing is your rear toe moving under load. replace the rubber control arm bushing with poly inserts or solid bushings. your control arms are moving causing the lane walk

That makes sense, but the control arms are brand new. Sure, the bushings are still rubber, but new rubber is better than old. If that were the problem, wouldn't everyone have the same issue? Or, maybe everyone does have the issue, and they just ignore it as the nature of the best.

I did a bunch of modding to the front tie rod brackets this weekend, but the result didn't really help much. I'll post up pics later. Bump steer in the front must be less, but it still didn't fix my lane-wandering issues.

 

[Rttoys]

What tire pressure are you running? I know if I go over about 25psi, everything is bouncy. I run at or near 20 for the street.

 

[Chubbs]

What tire pressure are you running? I know if I go over about 25psi, everything is bouncy. I run at or near 20 for the street.

I'm higher than 20, though I can't remember exactly what they were. I think I was around 25 front and 30 rear.

I'll try reducing them to see what happens.

 

[Gtstorey]

You may want to recheck your alignment settings. Mine did some of what you are talking about on my initial alignment. I did a string alignment the second time and it got a lot better.

 

[DCMoney]

I'm higher than 20, though I can't remember exactly what they were. I think I was around 25 front and 30 rear.

I'll try reducing them to see what happens.

That's way too high, I'm 17f 19r with Bridgestone RE-71R's and street driving.

That makes sense, but the control arms are brand new. Sure, the bushings are still rubber, but new rubber is better than old. If that were the problem, wouldn't everyone have the same issue? Or, maybe everyone does have the issue, and they just ignore it as the nature of the best.

I did a bunch of modding to the front tie rod brackets this weekend, but the result didn't really help much. I'll post up pics later. Bump steer in the front must be less, but it still didn't fix my lane-wandering issues.

I had a loose camber bolt that under hard acceleration it would cause the entire car to shift, also caused my steering wheel center to change, easy to tell with the center mark on the steering wheel. Was scary as hell.

The camber bolt wasn't even that loose, I didn't find the issue until I had the car on skates and was moving it in the garage, pulled on the rear wheel to move the car over and felt it shift slightly. Adjusted the camber and tightened the hell out of the bolts and haven't had that issue since.

 

[Waterdriver]

Making a new arm really wouldn't be to hard with fairly basic tools, but making it look good isn't quite as easy. I was trying to come up with something to use the existing arm.

I was more referring to the bump steer tie rod ends than the spindle arm he built. You can use your same spindle arm. I believe the spindle arm in the pic was used for testing and he had dialed out ackerman.

 

[Gtstorey]

Really the only difference in what he did and what I was suggesting was the the 14mm to 5/8 adaptor (although he used 1/2 and maybe used a reducer in the arm). I was trying to come up with something that didn't need a lathe, although you could probably drill and tap the adopter without a lathe with the proper technique.

 

[Rttoys]

I'm higher than 20, though I can't remember exactly what they were. I think I was around 25 front and 30 rear.

I'll try reducing them to see what happens.

I bet bringing it down a good bit will help a lot. Stock cobalt is 32 psi ft and rear, but they weigh 3000+#. We are at 1500ish# so you can somewhat guess at half that psi. I would bet, somewhere between 15 and 20# you’ll find a happy medium between too soft (causing a high speed vibration) and too hard (causing drivability problems ).

 

[Bajakid1450]

I would like to say that I will have the new rear suspension production ready for sure by next spring, but time just send to fly by.

We are getting close to finishing the the instructional video cars. This will free up a lot of time.

I have finished redesigning the rear suspension and as soon as the material arrives I will fabricate two prototypes for testing. This should happen in the next few weeks and will give us a better idea of a production time frame.

View attachment 28162

Lonny, as soon as one of these become available let me know ASAP. I drive my goblin almost every day maybe 10-60 miles a day. This would help out a lot on the highways. You were saying this should be available in the spring, I’m working with Hahn racecraft and they are building me a “Built for Boost” 2.4L right now and should be ready in the spring too.