Mystery chassis issue

I was competing down at Walesboro near Columbus In yesterday. There was a large 90 degree turn which I was taking in second gear, near the redline. After the big turn was a three cone slalom. As I came off the throttle and braked for the first slalom cone it felt like I ran over a shoe with the right front...thump... then the car snap spun and I went off course into the corn field on the left. It happened so fast I cannot tell you which direction I spun, let alone do any countersteering. Not knowing why I spun off I took the corner at slightly reduced speed next run and again felt the sensation of running over a shoe and an instant of instability but did not spin this time.

So I thought perhaps I was running the air pressure a bit too low and the tire somehow folded and lost grip so I added a pound and half air to the right side of the car. Apparently this helped because I did not have the trouble again.

Thoughts?

Recently when I had the car on jackstands I noticed a rattle on the right rear with the engine turning the wheels over while up in the air. It was on the right side only. There is no looseness in the wheel and it rattles under no other circumstances. So I suspect the CV or wheel bearing. I guess I'll just replace both.

Although I cannot see how it relates to the spin a rattle seems to need attention. Last time I ignored a rattle on my 85 Reynard (may it rest in peace) the wheel came off as the cv was actually in six pieces. The car ran and handled fine right up til the rotor center broke from the disc and the wheel came off.

I am thinking of Pegasus for the part. Other options?

Right front suspension binding?

I'm thinking some part of the suspension is locking solid momentarily, then freeing under the weight transfer from braking. Hence the feeling like you ran over something, as the suspension suddenly goes from locked to free moving.

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Originally Posted by tlracer

Right front suspension binding?

I'm thinking some part of the suspension is locking solid momentarily, then freeing under the weight transfer from braking. Hence the feeling like you ran over something, as the suspension suddenly goes from locked to free moving.

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Sounds plausible...how can I check that please?

I also thought perhaps it was wheel hop on the braking.....low on gas in shock?

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Originally Posted by t walgamuth

Sounds plausible...how can I check that please?

I also thought perhaps it was wheel hop on the braking.....low on gas in shock?

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I'd start by getting it up in the air, removing the shocks, and moving the suspension through its entire range of motion, front and rear.

Then maybe have the shocks dyno'd if you don't find anything.

Rattle at the rear? I often hear the gearbox innards rattling around, especially in neutral. Once up in the air a wheel bearing problem is pretty easily diagnosed.

What make, year of car?
Loose, failing suspension piece causing outside rear toe out?
How is the alignment ?

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Originally Posted by Rick Kirchner

I'd start by getting it up in the air, removing the shocks, and moving the suspension through its entire range of motion, front and rear.

Then maybe have the shocks dyno'd if you don't find anything.

Rattle at the rear? I often hear the gearbox innards rattling around, especially in neutral. Once up in the air a wheel bearing problem is pretty easily diagnosed.

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Thanks Rick!
Since the wheel does not feel loose while in air, I have been thinking it may be the CV rattling while the wheel bearings are holding the wheel steady.

John at Pegasus suggested I check the brake rotors as well.

Also a question: It has the 2" shorter wheelbase kit on the rear which increases the angle on the driveshaft a few degrees. Is this known to shorten the life of the CV joints? If I want it looks as if I can simply take the bolts out and move it to the other holes for a stock wheelbase.

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Originally Posted by jrh3

What make, year of car?
Loose, failing suspension piece causing outside rear toe out?
How is the alignment ?

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Sorry just saw this post. It is a 98 Van Dieman with a honda conversion.

I believe the alignment to be perfect. The heat distribution across the tire is even.

I would suggest checking the swaybars carefully - a few years ago Phil and his codriver had cracked one at a national tour unbeknownst to him and the car behaved extremely erratically as a result. It took a couple events to track this down, once replaced, was perfect and "back to normal". Given you autocross the car primarily, I'd strongly suggest leaving the wheelbase shortening kit in, those CVs have been in the car since it was converted to a Honda - even if you had to replace them, that'd be a 5 year item at minimum. The shorter wheelbase will be helpful and is worth keeping.

-Mark

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Originally Posted by lowside67

I would suggest checking the swaybars carefully - a few years ago Phil and his codriver had cracked one at a national tour unbeknownst to him and the car behaved extremely erratically as a result. It took a couple events to track this down, once replaced, was perfect and "back to normal". Given you autocross the car primarily, I'd strongly suggest leaving the wheelbase shortening kit in, those CVs have been in the car since it was converted to a Honda - even if you had to replace them, that'd be a 5 year item at minimum. The shorter wheelbase will be helpful and is worth keeping.

-Mark

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Can I just look and see the crack?

Tom, if you haven't changed the setup, the most likely culprit was bottoming out. The front end setup is "zero droop" so if you bottom out the car hard the tire(s) will lift off the surface. The increase in tire pressure helping reduce the problem would also indicate this.


Phil

Oh, yes, thanks for reminding me of the no droop. I would not have put that together at all. I am also going to do something with the shock pressure....if I can find out what to do.;)

Thanks again for a great car Phil!

I hope your new car is coming along.

zero droop is the other direction - rebound not bump

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Originally Posted by Rick Kirchner

zero droop is the other direction - rebound not bump

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Absolutely, but in this case I believe the issue was with bottoming out on a surface irregularity while loaded and turning, probably not long AFTER getting off the brakes. The resulting "thump" would be just like Tom is describing (I've had this myself in this car) I'm just pointing out that this MIGHT be situation where the zero droop configuration causes a sudden loss of traction. All a guess on my part, but I do know the car pretty well. All the other suggestions make no sense to me as there would be some indication of those possibilities in the course of a normal autocross run, not a "mystery" one time / one place situation.

Phil

So I put the car up and removed the wheels. I now believe the rattle is simply the floating calipers. I also checked pressure in the penske shocks and found they varied from 51# to 65#. So I'll add air or nitrogen to the shocks, and raise the tire pressure a bit and perhaps raise the car a quarter of an inch.

Thanks very much guys!

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Originally Posted by t walgamuth

So I put the car up and removed the wheels. I now believe the rattle is simply the floating calipers. I also checked pressure in the penske shocks and found they varied from 51# to 65#. So I'll add air or nitrogen to the shocks, and raise the tire pressure a bit and perhaps raise the car a quarter of an inch.

Thanks very much guys!

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Nitrogen only. Air only in an emergency ie at the track with a flat shock and no nitrogen handy
Previous owner knows the car and could have a different view, but my shock guy's dyno experience (at least with Penskes) is that the shock doesn't do much if pressures are <150 psi

cheers,
bt

Thanks BT!

Lazenby (hawke) liked dual parallel links for his rear lower control arms.

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Originally Posted by fvracerone1

Lazenby (hawke) liked dual parallel links for his rear lower control arms.

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Do you have a picture of that?

I am searching for a place to add nitrogen to my shocks. No luck so far in Lafayette.

I found a place in Indy to put in the gas for me. They want me to bring the shocks in.

To remove the shocks does the gas work to pre load that works against you like a gas street shock? Should I just let the gas out that is in them before trying to remove them?

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Originally Posted by t walgamuth

I am searching for a place to add nitrogen to my shocks. No luck so far in Lafayette.

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You can add air that came through a dryer, as many shops have these days. On a car that is softly sprung, and only doing short runs, 50-60psi is really all that is required, so I would not expect that is your problem. 80 psi is probably the theoretical minimum, although I use 100 so that I have some margin.

Thanks Greg.
In searching around a bit it sounds like I may be able to get the suspension to a height which will make the shock/spring be possible to install without fighting the gas pressure? I am hoping this is the case.

There is no need to bleed off the canister pressure to remove the shocks. Once you have the car in the air you can unbolt the shock/spring as a unit. You may need to slightly lift the wheel end to unload the bolts enough to remove them. Be sure to support the wheel end so it's not putting undue stress on the suspension rod ends once the shocks are off.

the gas doesn't really work against you because the suspension has more travel than the shock, so it's no big deal.

You should be able to get nitrogen at any tire shop these days. If you don't have a shock filler I'd crank up the pressure maybe 20 psi higher than you want to go as some will escape as you pull the chuck off. You have to be fast. You'll know what I'm talking about when you do it.

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Originally Posted by Rick Kirchner

the gas doesn't really work against you because the suspension has more travel than the shock, so it's no big deal.

You should be able to get nitrogen at any tire shop these days. If you don't have a shock filler I'd crank up the pressure maybe 20 psi higher than you want to go as some will escape as you pull the chuck off. You have to be fast. You'll know what I'm talking about when you do it.

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If you intend on keeping and racing the car for a while (years!), you could go to your local welding supply store and buy or lease a small tank. It will last a long time, but it will always be in the shop when you need it. I would heed my own advice, however, may nearby pal Steve (RF 93) doesn't seem to notice when i sneak into his garage and borrow the tank :)

cheers,
BT

I found a shop in Indy which will do it. I got two shocks off already, no problem. Biggest thing was figuring out which wrenches. Most fasteners seemed to fall in between metric and US so no matter what I used it was loose.

Thanks for the guidance guys!

Just got back from a South Bend region event at the Tire Rack. They ran three heats with each person getting four runs. The car ran perfectly but slid a lot. I am wondering if the shocks are now too hard or if the tires are losing their grip...or both?

I will say I drove better than the other day. No spin outs. I was putting the car where I wanted it pretty much all the time. Some of the turns were very close together and I was in them almost before seeing them. Sitting so low in the car is not an advantage for seeing the course.

After the second run I noticed coolant running out from the engine cover. I pulled it and found I had not gotten the radiator cap on good.....second time I did that. With it right next to the air filter it is tough to get enough fingers on it to get it good and tight.

Two day event at Grissom next weekend.

Was there a balance change as well as the sliding? If not, then it may just be surface, as I've noticed that usually as a set of Hoosiers goes off, there is a balance change that goes along with that.

HTH,
Jason

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Originally Posted by Unbalanced Engineering

Was there a balance change as well as the sliding? If not, then it may just be surface, as I've noticed that usually as a set of Hoosiers goes off, there is a balance change that goes along with that.

HTH,
Jason

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It wanted to push a bit but I was able to balance with a bit of air pressure change.