High speed instability

[Chubbs]

I think, or at least I hope, that I finally had a breakthrough on this today. The car has actually been getting worse, despite my best efforts to align it. It's difficult for me to get the same measurement twice, which had me suspecting I was doing it wrong.

Today on the highway, about 70 mph, the thing was basically undriveable. I was White knuckle all the way home just trying to keep it on the road. Letting off the accelerator resulted in darting to the right, somewhat violently. Accelerating had it pulling to the left. It was finally bad enough that I was convinced something was wrong, beyond what an alignment would do.

Turns out, when I jack the car up, both rear wheels wiggle probably 1/4 inch. The culprit appears to be the lower ball joint, which was new when I built the car. Closer inspection showed oil or grease on the bottom of one of them. They don't have zerk fittings to regrease them. I'm guessing they were inferior Chinese parts. They've been on the car less than 500 miles since the build.

New Moog parts are on the way. Both rear bushings, and ball joints. The rear bushings I don't think are necessary at all, but I'm determined to eliminate any wiggle in this suspension at all. Hopefully next week I'll have positive news that this issue is solved.

 

[Whidbey Goblin]

I think, or at least I hope, that I finally had a breakthrough on this today. The car has actually been getting worse, despite my best efforts to align it. It's difficult for me to get the same measurement twice, which had me suspecting I was doing it wrong.

Today on the highway, about 70 mph, the thing was basically undriveable. I was White knuckle all the way home just trying to keep it on the road. Letting off the accelerator resulted in darting to the right, somewhat violently. Accelerating had it pulling to the left. It was finally bad enough that I was convinced something was wrong, beyond what an alignment would do.

Turns out, when I jack the car up, both rear wheels wiggle probably 1/4 inch. The culprit appears to be the lower ball joint, which was new when I built the car. Closer inspection showed oil or grease on the bottom of one of them. They don't have zerk fittings to regrease them. I'm guessing they were inferior Chinese parts. They've been on the car less than 500 miles since the build.

New Moog parts are on the way. Both rear bushings, and ball joints. The rear bushings I don't think are necessary at all, but I'm determined to eliminate any wiggle in this suspension at all. Hopefully next week I'll have positive news that this issue is solved.

I’m glad you discovered it before something bad happened. I just discovered one of my front HEIM joints has play in it. Passenger side upper that attaches to the spindle. I have 10 days till my track day anyone else experienced this?

 

[Rttoys]

Since some others are reporting looseness, I have been checking all suspension parts after each autocross. So far all is tight.

 

[Chubbs]

I just discovered one of my front HEIM joints has play in it. Passenger side upper that attaches to the spindle. I have 10 days till my track day anyone else experienced this?

Since you mentioned it, mine has some slight play up front as well. It's very small, but if I start yanking on front suspension parts, I can get it to jiggle a little bit, with an accompanying rattle.

Both left and right front does this on mine. All the locking nuts are tight. It's definitely one, or perhaps all of the heim joints. If they all have a couple thousanths inch of play, they can add up to a bit of movement.

Again, it's very slight, and I just chalked it up to there's no such thing as a perfect fit. It doesn't result in any wheel movement, or at least none that I can tell.

 

[Waterdriver]

I’m glad you discovered it before something bad happened. I just discovered one of my front HEIM joints has play in it. Passenger side upper that attaches to the spindle. I have 10 days till my track day anyone else experienced this?

Which event are you planning to go to?

 

[baustin]

I’m glad you discovered it before something bad happened. I just discovered one of my front HEIM joints has play in it. Passenger side upper that attaches to the spindle. I have 10 days till my track day anyone else experienced this?

Yes, I just realized I had this happening on both upper control arm outer rod ends. I just swapped out the original ones and installed these: https://www.summitracing.com/parts/fkb-kmx12-10

So far after a couple drives, no issues. In my garage I could previously push on the upper area of the front tires and feel the movement and hear the clunk from the inner ball moving within the rod end. I don't feel this movement or hear the clunk now. Only replaced the uppers, didn't change the lower outer rod ends.

I went with the FK version based on this discussion, they had worked successfully for other Goblins already:

Front End Heim Joints

This post got me thinking. The heim joints used for the spindle pivots are able to be greased. Or at least the ones I received with the kit are. On the threaded end, the very bottom, is a small grease hole. Using a grease gun with a rubber tip attachment, press against this hole and apply...

dfkitcar.com

I'm sure after some wear, they will go back to behaving similar, it wasn't enough to be a large issue but I think it was measurable and raised questions during autocross tech inspection about if it was a bad bearing hub (which it wasn't in my case).

 

[Whidbey Goblin]

Which event are you planning to go to?

Oregon Raceway Park with HOD May 7. Come down if you can make it!

 

[Dsteinhorst]

I’m glad you discovered it before something bad happened. I just discovered one of my front HEIM joints has play in it. Passenger side upper that attaches to the spindle. I have 10 days till my track day anyone else experienced this?

I also had to change out four of my heim joints because of looseness. I just chalk it up to part quality. Mine weren't causing any symptoms except an awful groaning noise.

 

[Df274]

so i got a question? has anyone come up with a different set up for the rear spindle. i notice my tires on the rear move in to the frame under deceleration and bumps. high speed its okay. i had the goblin upto 140 mph so far. i had to add a front spoiler and am about $1000 in alignment alone.

 

[Ross]

Are you still running the stock rubber bushing in the control arms? Replace them with Moog or OTTP bearings will reduce suspension movement.
Otherwise, there are some different rear suspension designs in the prototype stage.
DF is working with Justin Reed on a design.

ccannx has also done a prototype.

 

[Rauq]

Are you still running the stock rubber bushing in the control arms? Replace them with Moog or OTTP bearings will reduce suspension movement.

This cannot be overstressed. I have not ever seen a Cobalt SS with good original rearward lower control arm bushings.

 

[Desert Sasqwatch]

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
View attachment 28240
The Cobalt rack has M14.x1.5 threads on the end of the steering rack.
Which will replace the Goblin's tie rod end:

View attachment 28239

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

Ross, did you get the bumpsteer kit installed? Any feedback on how well it works? Photos of the installation? Thanx!

 

[Ross]

That QA1 BAX102 won't fit our goblins.
The rod end side of sleeve has a 5/8"-18 LH thread, while our goblin has M14 x 1.5 threads.

Maybe this one will fit our goblins. It fits a Corvette, which has the M14 x 1.5 threads. There are a few kits for the 'vette.

 

[Chubbs]

After replacing the ball joints and bushings, I'm gearing up for another test drive and setting alignment again.

I did my best to place the car on a level surface (concrete garage floor), and I zeroed my angle gauge level with the ground. Then I put it on the center tunnel of the car. Turns out, my car leans forward about 1.5 degrees (rear higher than front). All the control arms are level, or at least visually level.

So, when setting caster...is the 8.5 degrees of caster set relative to the center tunnel of the car? Or relative to the "level" ground? Apparently, they are different measurements, at least on my car. The tutorial said relative to the center tunnel, but now I'm questioning everything.

 

[G Atsma]

Caster is always relative to the ground

 

[Ross]

That QA1 BAX102 won't fit our goblins.
The rod end side of sleeve has a 5/8"-18 LH thread, while our goblin has M14 x 1.5 threads.

Maybe this one will fit our goblins. It fits a Corvette, which has the M14 x 1.5 threads. There are a few kits for the 'vette.

I stopped buy the auto parts store, to see if a Corvette steering bump stop kit would work on our Goblins.
The 14mmx1.5 threads are correct, but the tapered shaft on the Corvette is a steeper angle...
If I were to modify the DF steering arm to have the steeper angle, then the Corvette bump steer kit would work, but the 'vette tie rod ends are not quite the right fit.

I still haven't found a bump steer kit for our Cobalts.

The 'vette part is sooo close, I wonder if the DF billet aluminum steering arm would slowly conform to shape.
The top of the tapered shaft is the same diameter on the two parts. 15mm down the taper, the Cobalt is 14.6mm in diameter, while the 'vette is 15.6mm. So 1mm bigger in diameter over 15mm of length. The vette tie rod end fits into the DF billet part, with only 3 threads exposed at the top.
tightening it would pull the part in, and start stretching the base of the billet aluminum tapered hole.

Kind of like an aluminum wheel using tapered wheel nuts that weren't made for it... after a few drives, and repeated tightening, the aluminum wheel eventually gets a matching taper to the nuts. Sounds like a bad idea, but maybe...

 

[Scott #321]

I would strongly recommend getting the steering arms machined if you go that route. I'm all for taking some chances but not on steering and brakes.

 

[Gtstorey]

The last time this was discussed I looked through a list if tie rod ends and didn’t see any tie rod ends that that matched ours that was likely to have a bump stop kit.
I don’t know that a tapered reamer would be out of budget if one could be found to match the corvette taper, especially if the cost is shared by a rental fee among all on here that might want to use it.

i am fairly satisfied with how mine works with the way that I drilled the hub after moving the arm for no bumpsteer but if I ever made much change to castor or ride height I would be screwed.

 

[Gtstorey]

The best I can tell there are 2 common ball joint/tie rod tapers and reamers are somewhere around $100. It is more than likely 1.5" per foot taper but could be 2" per foot, but I couldn't find any thing online to confirm for the Corvettes.

 

[Desert Sasqwatch]

Just a thought: if someone has the 'old' DF steering arms laying around, trying the standard 1.5 inch per foot reamer to see if it matches the Corvette bumpsteer tie rod ends? This would be a little bit expensive ($150 tie rods & $100 reamer) to try, but hey it's only money.