Rear bar problems, and wheel hop.
 

A few weeks ago I swapped out the OE 28 mm front bar for a 30 mm bar, and installed it with poly end links and bushings. After driving around on it for a few weeks, I was really pleased. So I decided to install the matching 19 mm rear bar using poly end links and bushings too.

Couple of days ago I was in a hurry to get to an appointment. Knowing that the exit off the highway was a nice, wide, long S turn, and it was a dry sunny day, I took it fast (about 55mph), like I have done dozens of times before. Neary poopy my pants as the rear came around and the car had extreme over steer! Damn, I really thought I was going to lose control for a minute. Just let off the gas a little, and steered trough it, and all ended well. For a moment there I was making steering corrections faster than a rally driver in a Subaru.

So, the 19 mm bar had to come out. I can't take a chance of that happening again, or having someone else drive the car and suddenly get megga over steer.

I really didn't think that going from 15 to 19 mm would make such a big difference in the steering. I know the increase of 2 mm is about 3 x the stiffness of the original bar, and I expected it to ride rougher due to being 4 mm thicker. The over steer to the extent I experienced it was not expected or a good thing.

Today the 15 mm bar went back in, and I used the poly end links to give it a little more response. Also noticed that the factory bushings had rubbed off the paint on the bar, and the bar was rusting there. This on a car with less than 40K miles and garage kept! So I sanded the bar down and painted with black rustolium. Also cleaned the bushings, and greased well before installing.

While the car was up on the jack stands, I put in a pair of KYB GR2 rear shocks. Nothing very exotic, just a quality dual tube gas replacement for the OE Decarbon shocks. I was surprised to see the OE Decarbon shocks were worn. They provided very little resistance, even when pushed/pulled with my hands, although they still held their gas charge and expanded to full length when removed. BTW, the OE shock top bushing was in perfect condition, and I re-used it because its much larger diameter than what came with the KYB, and actually fits through the hole in the body. The KYB did not. The OE is about 2" in diameter, the KYB replacement is about 1-1/4" tops.

The Decarbon shocks were the cause of the floaty rear. The KYB GR2 shocks are a little firmer than stock, according to their writeup, and they performed very well when I took the car for a test drive down a bumpy windy country road. The rear stayed planted on the rough stuff, and a funny "clunk" noise I used to hear on bumps was gone.

I couldn't find my 14 mm combo wrench, and figured I was mis-placed when I worked on the car last. Surprise! There it was on the top nut of the end link! The box end still firmly gripping the nut! This after a few days of driving! Made sure I didn't make that mistake again.

Just a little dissapointed that the new shocks did not fix a bad case of wheel hop on burn-outs. They did help, but the wheel hop is still there.

Yea, the 19mm rear bar is too big to jive with the 30mm front. A 32/19 combo with stiffer springs all around and you would be in good shape, but otherwise it's definitely a better choice to leave the stock rear bar in place.

Sway bars are one of the trickiest parts of the suspension to upgrade properly, and can cause quite a commotion (as you noticed) when they aren't selected properly.

- Justin

To help with the rear wheel hop, go to eBay and look up a set of tubular LCA with grease fittings. They are much stronger that the "U" shaped stamped OE on the car now. They are quite easy to install and should provide some better handing all around also.

Just based on thickness:

(19/15)^4 = % stiffness increased. In this case, 2.57x the original bar. That's a lot compared to the 1.31x you upgraded in the front. Glad you are OK!

While you are upgrading your suspension, replace the rear LCA's. They are just stamped steel parts that can be deflected by hand.

I thought about using new LCA's but the problems I read about using poly bushings on the LCA's is severe binding, which usually results in breakage of the LCA mount on the axle.

I read where the sock lca bushing is hollow, to allow for greater flex and prevent binding on turns, etc, and that switching to the Moog solid rubber bushing fixes the wheel hop issue. I like the durability of poly bushings, but the reports of suspension bind and mount failure is so common that can't afford to use them on a daily driver.

Next change is to install a poly bushing in the torque arm mount. The OE looks to be spread, so it needs to be changed.

Then I'll decide about the LCA's after seeing if the T/A bushing helps.

There is so much info out there on Fbody cars, and some if it conflicting, it takes time to decide which is right for my application. Thats why I post about what I'm doing, so others can tell me about their experience.

Thanks!

A cheap upgrade to the stockers is to box them. If you've got a welder it's a no brainer.

The cheapest way to upgrade the rear LCAs is the box the stock ones with a flat piece of relatively thin steel to eliminate a lot of the flex, and then replace the stock bushings with hard rubber solid bushings to cut down on the flex (but not eliminate it).

This is for DD type vehicles. Specialized uses require specialized solutions, but that doesn't apply in this case.

- Justin

not doing 20-30mph over the posted speed limit tends to reduce oversteer as well

I get the SEVERE binding you are worried about would involve a LOT of torque and really HARD driving (something I don't see in your DD) and the fact that they do have GREASE fittings built into them should be no problem. I have had them in my car for over 12 years now and they have worked fine.

This sounds like a good solution. I don't have a welder, but most shops around here can weld.

What is actually happening to the LCA's under launch? There is no lateral force on them, its all front/rear compressive forces. Does the U shape spread open?

Is there another bushing manufacturer besides Moog that makes a solid hard rubber bushing?

Thanks!

Under launch there is no lateral force, but the U shape allows them to flex in the manner you described. Boxing the stock one in controls a lot of that flex.

Here's a pic of a stock 4th gen LCA that has been boxed in. This was taken on my car a few years ago:

http://www.fquick.com/images/vehicles/full/4227950.jpg

- Justin

I didn't read your whole post but yes a 4mm increase in rear bar is huge hahah. I never had any problems with the 30/19 combo but if you're used to a tiny rear bar I guess it can be a pretty unexpected jump.

You are also on stiffer front springs than his stock v6 has, which weighs heavily on rear bar sizing, not to mention the LS1 is a bit more nose heavy (IIRC), mostly due to the engine hanging over the front axle line, whereas the v6 sits behind it..

- Justin

yep a 30/19 combo wont really work, Thats the great thing about doing mods one at a time you now know exactly why you have over steer. It sounds like you like a good handling car. I would just go ahead and get a 32 or 35 front bar and keep the 19 rear. The 32 or 35 / 19 will transform the way the car feels. Good luck with it

very interesting. didn't realize the weight distribution was that much different. I guess when that's off a 35# difference in spring rate is a lot more noticeable.

when I had the 35/19 combo the rear reacted really slow, but if the 19 seems way too big now it'll probably end up being nice and balanced then

What I don't get is why this V6 Firebird with a basically stock motor and 3.73 gears w/posi gets such bad wheel hop.

Especially when compared to:

- the car with 3.08 and open rear, never a wheel hop issue. Lots of useless tire spin, but no wheel hop.

- my 96 Camaro w/5 speed and posi (3.23 gears IIRC). Drove that car to 160+K and never wheel hop, and it had the two piece drive shaft to boot.

So why is the same rear that is in V8 cars hopping badly when just a V6 is driving it?

I've been looking for problems with the stock parts, IE bad bushings, broken pieces, etc. Its not like I just added 100 hp from NO2 and got wheel hop. Its just a posi and gears that are causing:

- More hp/torque to the rear at launch due to the gear change.
- More resistance to wheel spin due to the Eaton Truetrac, which in turn puts more stress on the drive-line components (like LCA bushings and T/A bushing).
- Mild hp increase due to tune and exhaust.

So I am more inclined to look for bad or broken/worn parts. Keep in mind the car has less than 40K miles, so I would think the bushings and all should be in good shape. Unless age (12 years) is a major player. Think the LCA bushings are failing just due to the added stress and possible dry rot? I looked, but you just can't inspect a LCA bushing that is installed... LOL!

Excuse the long post, just thinking in writing (kind of like thinking out loud!)

spherical rod ends?

maybe your pinion angle is off causing the wheel hop?

I don't know about the pinion angle. What ever stock setup is had, it still has. Spherical rod ends are a bit overkill, but would work if I wanted to spend that kind of money.

Geez, its just a stock V6 with stock 16" wheels and tires! I don't get why it has this wheel hop problem.

its an fbody? incorrect pinion angle could lead to wheel hop though and i know you've done rear end and drive shaft work. might be worth checking intsead of spending money unnecessarily!

Traction issues as in tires might be adding to issue as well. The vette guys have hop issues when they don't use drag radials, right?

Yeah, the 98 F'bird. The wheel hop started after the 3.73 and Truetrac were installed. Had wheel hop before installing the LS1 drive shaft, and after. Without an adjustable T/A, I would not know how to change the pinion angle.

It has the BF Goodrich Traction TA radials, 235 x16. Nothing super sticky.

I'm wondering if I've trashed the LCA bushings from the extra load now that the posi is in there?

Sent an email to Moog asking them about their rubber bushings. Want to know if they are equal or better than the GM 1LE spec bushings.

ah true. have you given relocation brackets a thought?

Today I put in the poly torque arm bushhing by Energy Suspension. Although it is poly, the bushing is a softer compound than their sway bar or end link bushings.

And the bushing can be changed by just removing one nut, and grinding off one of the two rivets that hold the OE bushing in place. Once one rivet is ground off, the bushing can be rocked until the other side breaks free of the rivet on the other side.

The OE bushing is two pieces, and the piece left in the half of the bracket that comes off can have the rivets drilled or ground off in a vice.

Then the new bushing is slid onto the torque arm, and its bolted back together. Tight fit, but it can be done with just a 15 mm socket and open end wrench.

I was surprised that the one piece bushing makes the ride a little tighter. It looks like the two piece had spread apart and was allowing some movement, but not much.

So the moment of truth. Came to a dead stop, and hit the gas, and..... wheel hop. Not as bad as before, but its still there. If I apply the break, and bring the rpm up to about 1500, then release, there is no wheel hop. So preloading the suspension prevents wheel hop. Bet the problem is the LCA bushings.

So, next change is LCA bushings.

Oh well, I'll get this nailed down soon. At least the parts I installed were not real expensive.

I have a pair of boxed stock LCAs sitting in my garage... $20 if ya want em.

Yeah, but right now I don't want to get into welding on new brackets. For one, I don't trust the local shops to get it on square, and the shops I do trust, will charge a bit because of the labor involved. Good is not cheap.

I hope it doesn't come to that.