V1 Ross's extended city, easy entry Goblin- 06 SS/SC, NW Arkansas

[TheNuker]

I guess the first question is has anyone else had wheel hop under hard braking? I never experienced this on my first goblin even after 100s of hard stops, building up my muscle memory of where the cut off line is between lockup and controlled braking.


Nuker-

 

[Rttoys]

How many people are running progressive springs up front? Have you tried a linear spring on the front suspension?

I changed mine to progressive springs on the front, a few months ago. The street driving is much more smooth and on the track (autocross) it seems to still do very well. I want to say it’s the same or better on the track as with the regular stock springs, but hard to tell. I know it didn’t hurt, that’s for sure.

 

[Kyle]

has anyone else had wheel hop under hard braking?

I have but only in the front and on a crappy chip sealed road.

 

[Waterdriver]

Did your control arms bolt in nice & flush? I noticed that on mockup, my upper arm has about a 1/2”-3/4” gap from the pivot point at the heim joint that will take some torque to squeeze into place.

This can cause the A-arm to want to deflect, one direction or the other when a load is applied at the spindle end due to it being under constant tension from being spread apart.
I had shimmed the trailing end, chassis mount side of the A-arm to remove any pre-loaded tension to it.
Might be something else to look at.

 

[AZmoto]

Did your control arms bolt in nice & flush? I noticed that on mockup, my upper arm has about a 1/2”-3/4” gap from the pivot point at the heim joint that will take some torque to squeeze into place.

I have the same situation. By the time I get it all bolted flush to the frame the inner heim is cocked to the point where it contacts the washer. I added a single washer between the heim and the frame so that it doesn't have to stretch the control arm as far when tightening it down. It no longer rubs the washer but still looks less than ideal.

 

[AZmoto]

This can cause the A-arm to want to deflect, one direction or the other when a load is applied at the spindle end due to it being under constant tension from being spread apart.
I had shimmed the trailing end, chassis mount side of the A-arm to remove any pre-loaded tension to it.
Might be something else to look at.

Do you have a pic of your shim setup?

 

[Waterdriver]

It sounds like you might have done the same thing.
Rear arm: Double stacked washers between rod end and chassis.

Front arm: No washer between rod end and chassis.

 

[Ross]

This can cause the A-arm to want to deflect, one direction or the other when a load is applied at the spindle end due to it being under constant tension from being spread apart.
I had shimmed the trailing end, chassis mount side of the A-arm to remove any pre-loaded tension to it.
Might be something else to look at.

Good point! Maybe my A arms are already sprung, and that makes them easier to twist. A few washers, then I can take it for a test drive and see if it fixes the issue.

 

[Waterdriver]

Since they have been twisting and causing that hopping, you might want to do a visual check on the welds at the spindle end of the A-arm for any cracks.
Just to be sure.

 

[ctuinstra]

The thing about oscillations or reverberations is that once it starts, it can cause so many things to react over and over making it very difficult to pin point the start. You maybe noticing the effects and not the cause. The arms maybe flexing because of the strain them then reacting to it. The arms may be the effect and not the cause. But you have covered about everything there is with the suspension and still haven't solved it yet. Maybe it's time to back up out of the tunnel and step back and look at it from a different light. Your car is the only one that we know of that is doing this, so it shouldn't be anything with the DF design or materials, or even much to do with the adjustments because you have tried them all and not every car is set up with the exact same adjustments.

I'm with Brad. You could have something with the brakes, especially the rotors or pads. Since this only happens under braking, that could be the start of the oscillation and everything is reacting to it. Maybe if you were to join the meet up at the Lake of the Ozarks, we could swap out parts to see if that makes any improvement. We've shared components before.

Every time I brake hard, I first think that I hope no one rear-ends me, then I think of your wobble.

 

[Ross]

Unfortunately my car is "special", so I agree, it is not a design issue. Anybody willing to put a camera on their front suspension, and do a hard brake? I would like to see a baseline of a Goblin's front suspension, and if your uprights appear to twist.

I see the uprights twisting before the tire starts hopping... I think. I mean it is suppose to twist when the suspension moves up and down, (Edit: True for some cars with brake anti-dive, but not our Goblin.) but I think I see it twisting from the brakes being applied. What do you guys see?

Today I shimmed the front A arms to remove tension in them, and checked the arms for any bends. The passenger side is not quite flat on the upper A arm, and I'm not sure if it is bent, or within normal tolerances, with a small twist before welding. The drivers side was flat, so I decided to video it instead.

Then I mounted 2 GoPros and went for a dusk test drive to capture video.

 

[Rttoys]

I can video mine, but it’ll have to wait till Monday. Too much going on from now till them to do it, unless I try to do it during autocross. We will see.

 

[Desert Sasqwatch]

Unfortunately my car is "special", so I agree, it is not a design issue. Anybody willing to put a camera on their front suspension, and do a hard brake? I would like to see a baseline of a Goblin's front suspension, and if your uprights appear to twist.

I see the uprights twisting before the tire starts hopping... I think. I mean it is suppose to twist when the suspension moves up and down, but I think I see it twisting from the brakes being applied. What do you guys see?

Today I shimmed the front A arms to remove tension in them, and checked the arms for any bends. The passenger side is not quite flat on the upper A arm, and I'm not sure if it is bent, or within normal tolerances, with a small twist before welding. The drivers side was flat, so I decided to video it instead.

Then I mounted 2 GoPros and went for a dusk test drive to capture video.
View attachment 22590

Ross, I hate to ask, but is the front part of your frame tweaked from the off-road a while back? It might be difficult to make straightness and diagonal measurements on a fully assembled chassis, but it might be worth the piece of mind to to do these checks if possible, IMO. Having a tweaked frame that doesn't provide for a squared up and symmetric mounting points for the suspension could be a contributor to an oscillation. Weird things can happen from asymmetry within dynamic structures and you potentially have a prime example.

 

[Ross]

Ask away! I'm putting this out there because I want your opinions and ideas. So thanks for reading this, and sharing, I am learning.
I will look down my frame tubes and visually check. Can also grab my 6' level, and take a picture. With all the side pipe welding on a frame, there naturally would be some weld shrinkage, which the big blue DF weld jig will minimize, but I'm not sure it could completely eliminate it. Curious how straight a goblin's frame should be.

My first autocross had the wheels hopping. My goblin had never been off roading at that point, and the car was still green, I was learning it. It did hop with the Cobalt tires, but it was a smaller issue, as I never tried to stop that quickly until I got to an autocross event. So I was surprised at how much the wheels would hop. At that point there was many possible reasons, but slowly I have been reducing them, one at a time.

 

[Brian74]

I bought my sandrail with a tweaked front end, as I could never get the alignment to come in. Previous owner had landed it wrong at least once. I was able to determine the issue by utilizing a laser pointer plumb bob hung from the frame in various spots, working outward to inward on the frame, marking the points on the floor, and then measuring squareness of the various points. Took one steel 3/8” spacer bushing on the lower right beam to get it straight again.

 

[Rauq]

Not to change the topic, but did anything else ever come of your snapped steering arm? Was it concluded that your A/T impersonation caused that issue? I feel like I read about a consideration that all the new kits get the A/T solid design as opposed to the scalloped/lightweight original version at some point.

 

[Vwsaabvt]

I've seen it mentioned about rotors but without response yet (or maybe i missed it), have you checked your rotor runout yet?

 

[Waterdriver]

Unfortunately my car is "special", so I agree, it is not a design issue. Anybody willing to put a camera on their front suspension, and do a hard brake? I would like to see a baseline of a Goblin's front suspension, and if your uprights appear to twist.

I see the uprights twisting before the tire starts hopping... I think. I mean it is suppose to twist when the suspension moves up and down, but I think I see it twisting from the brakes being applied. What do you guys see?

Today I shimmed the front A arms to remove tension in them, and checked the arms for any bends. The passenger side is not quite flat on the upper A arm, and I'm not sure if it is bent, or within normal tolerances, with a small twist before welding. The drivers side was flat, so I decided to video it instead.

Then I mounted 2 GoPros and went for a dusk test drive to capture video.
View attachment 22590

In watching your video it looks like it's the upper A-arm doing the moving. Like its winding up a spring and then releasing.
From you pic, has the rod ends always been threaded out that far?

How many threads are still in the A-arm? Maybe flexing there?

As for the brakes, does it pull to one side or the other? Or does it basically still go straight under braking and just shudder like it does?

 

[Ross]

Brian74 & Desert Sasq - I looked down my 4 main frame rails, and there is some curvature at the weld points, like I expected, from weld shrinkage. I'm curious if your frame has this too. Mostly on the bottom 2 rails.

Rauq - The snapped steering arm was replaced. I replaced both sides, as DF comp'd me the parts, as they were out of the AT solid design, so I am back with scalloped parts. Both sides probably had metal fatigue.

Andrew - not yet. I am more concerned about the movement in the billet uprights before the hopping occurs. Whether the rotors are out of true or not, the uprights shouldn't have flex. I think if I fix the flexing, then the hopping will stop. If I'm wrong and still have hopping, I will start checking things like brake rotors.

Waterdriver - I agree, the last video made me think the upper A arm was flexing. I also was concerned about the amount of threads showing on that heim. The bottom heims are tucked in already, and the top still needs extra length. I could transfer some of those threads over to the wheel end of the A arm, but it too is threaded out quite a ways. I figured it was pretty evenly balanced between the 2 sides, but I need to check for movement there. The car brakes nice and straight, and only shudders if I press too hard. I noticed today that as I slow down speed, I can brake more without hopping.

I will see if today's video sheds any light on the issue. I concentrated on the upper A arm today.
I did some red neck engineering, and used 3 sticks of wood to make a tripod that holds a camera directly over the upper A arm.
Also have a GoPro on the upper frame rail. I will do some video editing, and see if I get some new clues.

 

[Ross]

Todays new camera angles on my hopping issue. I'm still seeing movement, but not sure where it is coming from.
Video here.