Improving "sketchiness" at high speed.

[BR3W CITY]

*As my usual, this will be a long post.

So my truck has started to reach the point where "good enough" just isn't safe, and certain areas need to be shaped up. Recently I re-did a bunch of stuff including my whole heads/topend, and my truck should be in the high-11's with the driver mod (provided my mystery-meat converter doesn't eat itself).

At 70-120+, things just get a little sketchy in the front. It likes to wander a bit up , things feel a little sloppy and some vibrations don't help.

(LS powered '66, 72 front suspension stuff/PS, hydroost)
I added single adjustable Qa1's end of last year and they helped control things a bit, and I did a new outer tierod end, pitman arm and alignment a while back as well. Under most conditions, these changes have made it pretty well mannered and easy to drive, but the wander never really changed.

I do have a front swaybar, and its bushings all look decent.

The steering gear seems to have aged poorly, so I'm guessing at least some fault lies there. I don't have any form of steering stabilizer, nor any kind of pressure modifying valve on the hydroboost.

I'm also wondering if its possible that the weightloss of the inner fenders changed the load on the front springs enough to change my front alignment. I didn't think ~35lbs would do that but I could be wrong.

Other thought? Lazy balancing, mistorqued lugs, wind?

[Super73]

How much caster did you put in it when aligned? I don't use factory specs and put as much a posible. Makes a difference!

[Marv D]

My pile was a handful on the top end, and shutdown. In fact scary as hell. I would rather take the Nova at wheels 6' in the air launches 9.teens and trapping @ 145 rather than that truck through the traps at 107 and mid 12's.

So I put the sway bar back on (yes,, you read right SWAY bar) and put some weight on the rear (15 gallon fuel cell and raced with 15 gallons) It settled it right down on the top end and surely didn't jurt the launch. In fact just before I retired it last year it was running 10.6's @ 122 and was BOREING. Maybe if I had gone back to something making me crap my pants every pass I would have tolerate the STUPID problems it kept throwing at me.

Now that's just my pile and you may already have a sway bar. But don't be so quick to condemn them. It's a simple bolt on that is worth a 'try' ,, right?

[BR3W CITY]

Super73 - I've never done my own alignments besides the "out the door" guestimate alignments with a string and such. I have my local I trust (not a racing shop) do most of my wheel/tire/alignment stuff. I don't know how many *s its currently running.

I'm using a front swaybar kit already, I've never bothered to unhook it for launch yet. I see so much street time that it just drive better with it attached.

I also already have a 16-18gallon cell as far and low as possible.

[BigDan3131]

Has the steering gear been tightened at the nut? You know what I'm talking about right to take play out of the wheel? You said you have a newer front end but did you replace all the bushings including the ones in the rear? Hopefully not with rubber ones. Since its a truck was it 4 wheel aligned?

[PGSigns]

I would do the caster mod and have it re-aligned and get them to put 5 or 6 degrees in it with about an 1/8" of tow. http://67-72chevytrucks.com/vboard/s...d.php?t=501241
Jimmy

[Super73]

Originally Posted by PGSigns

I would do the caster mod and have it re-aligned and get them to put 5 or 6 degrees in it with about an 1/8" of tow. http://67-72chevytrucks.com/vboard/s...d.php?t=501241
Jimmy

Exactly my thoughts. If it is factory caster settings, they don't seem to like 80mph +

[Ont67shortbox]

is the power steering still hooked up.Mine used to float like crazy on the top end,came back,took the power steering belt off 100% improvement

[BR3W CITY]

Originally Posted by BigDan3131

Has the steering gear been tightened at the nut? You know what I'm talking about right to take play out of the wheel? You said you have a newer front end but did you replace all the bushings including the ones in the rear? Hopefully not with rubber ones. Since its a truck was it 4 wheel aligned?

The little "adjuster nut" on the gear itself? I haven't tightened that. Anytime I've asked about that in the other sections, everyone just says it ends up ruining the steering gear. I know its there to take up some of the lash in the gear. Would you say its worth trying?

The 71-72 front stuff was installed by the PO before I got the truck, though I've done my best to troubleshoot his install. Everything jives pretty well for the most part. I have not replaced ALL the bushings, only a few as-needed very very early in owning the truck 5+ years and before it had an LS motor.

I'm ASSuming it was a 4 wheel alignment, but I can't promise with certainty that it was.

Originally Posted by PGSigns

I would do the caster mod and have it re-aligned and get them to put 5 or 6 degrees in it with about an 1/8" of toe. http://67-72chevytrucks.com/vboard/s...d.php?t=501241
Jimmy

Originally Posted by Super73

Exactly my thoughts. If it is factory caster settings, they don't seem to like 80mph +

I will do this...he may VERY well likely have used a stock #, as I didn't provide him a specific goal/tolerance to hit. I suppose unless he knew I wanted the extra tow, he wouldn't have done and done that on his own.

Originally Posted by Ont67shortbox

is the power steering still hooked up.Mine used to float like crazy on the top end,came back,took the power steering belt off 100% improvement

Its hydroboosted so I can't disconnect my power steering unless I don't want brakes

[Kyle@FTP]

Originally Posted by PGSigns

I would do the caster mod and have it re-aligned and get them to put 5 or 6 degrees in it with about an 1/8" of tow. http://67-72chevytrucks.com/vboard/s...d.php?t=501241
Jimmy

Originally Posted by Super73

Exactly my thoughts. If it is factory caster settings, they don't seem to like 80mph +

Some smart fellers in here. I would start here as well. The truck wasnt designed to do 80mph. In the long drawn out front suspension we are doing, we designed in a bunch of static caster so in shut down when the nose drops its still stable as could be.

[BR3W CITY]

Great segway for me to ask; when should I expect my prototype? Heheheh

[Kyle@FTP]

As much as I would say its being shipped that would be far from the truth. I have consumed by the day to day of the shop and getting customer trucks out the door. We tried to have the first version in metal for the open house next week and didnt even come close!

But it is coming.

[BR3W CITY]

Good thing...my truck isn't getting any slower

[vin63]

Originally Posted by BR3W CITY

I'm also wondering if its possible that the weightloss of the inner fenders changed the load on the front springs enough to change my front alignment. I didn't think ~35lbs would do that but I could be wrong.

Other thought? Lazy balancing, mistorqued lugs, wind?

More than likely, not the weight, but the aero effect of no longer having the inner fenders to maintain a low pressure area under the hood. As you go faster without the inner fenders, the air pressure increases under the hood, creating lift.

As an example, I first ran my 1963 Chevy II without inner fenders when I competed in local bracket classes (high 12 second passes). When I stepped up to run Super Gas in the mid 1980s, at 120+ mph, I had to install inner fenders to keep the pressurized air from sucking the air/fuel out of the carburetor (not sealed to the cowl scoop). The other benefit I found was the car was a lot more stable at speed.

[BMERDOC]

I agree with the guys here. Make sure that box is tight and then more positive caster and more negative camber. The factory specs are atrocious. 1/16th toe per side (1/8" total).

[OutlawDrifter]

i think a custom alignment will definitely help out, total agreement with the guys above.

also consider, at 100mph, i bet that thing is also trying to lift off. the body was never designed for down force. some kind of splitter or air dam on the bottom of the bumper would help out.

[74CustomK20]

Vents in the fender well coming to outside the body to get rid of the pressure?

[ptc]

Originally Posted by OutlawDrifter

i think a custom alignment will definitely help out, total agreement with the guys above.

also consider, at 100mph, i bet that thing is also trying to lift off. the body was never designed for down force. some kind of splitter or air dam on the bottom of the bumper would help out.

Originally Posted by 74CustomK20

Vents in the fender well coming to outside the body to get rid of the pressure?

Front end geometry is #1, then steering is next. I hope you are not using a stock steering box????? As for the hydroboost, yes you can still use it with the pump, just try bypassing the steering and plug those lines. Use manual steering at the drags. Your NOT turning!!!!

Areodynamics plays a critical roll at high speeds.... imagine what this truck would look like in a wind tunnel???? I think a rolling 'brick wall' would be a good description. If you cant reduce drag or release pressure then keep it from coming into the body in the first place.... pan the bottom at least past the front wheels. Close the leading edge of the wheel openings with lexan.

Have you ever looked under an F1, indy or even a GTP car? everything is enclosed!

[Super73]

I am sure I could stand some aero adjustments.. but 145 mph things "feel" good. Might go faster though..

[BR3W CITY]

Originally Posted by ptc

I hope you are not using a stock steering box????? As for the hydroboost, yes you can still use it with the pump, just try bypassing the steering and plug those lines.

I'm using the ps gear from the '70's donor truck that the front end is from. I think the gear was replaced in the 90's with a parts store rebuilt. I'm using that until she gets the RnP. The weird part is that if you isolate each part of the steering system, its all individually nice n tight.

Disconnecting the ps every time I tracked it would be prohibitively annoying, and messy. I'm still convinced some sort of orifice reducer or one of those adjustable flow regs is at least partially needed for that end of things. (and the over boost is a different sensation from the general high speed sketchiness).

The aero definitely needs work. The truck is on this borderline between quick street truck, and very quick street truck but a whole chunk of things need to happen to really take it there safely, and it looks like some work on the aero is gonna be in that group.

[ptc]

Originally Posted by BR3W CITY

I'm using the ps gear from the '70's donor truck that the front end is from. I think the gear was replaced in the 90's with a parts store rebuilt. I'm using that until she gets the RnP. The weird part is that if you isolate each part of the steering system, its all individually nice n tight.

This should be OK, I was thinking the stock 60's truck box!!!! thats a NO NO.... lol

Disconnecting the ps every time I tracked it would be prohibitively annoying, and messy. I'm still convinced some sort of orifice reducer or one of those adjustable flow regs is at least partially needed for that end of things. (and the over boost is a different sensation from the general high speed sketchiness).

If you made your lines so they have quick connect couplers in them, then they could be easily swapped out in minutes.... see pic!

The aero definitely needs work. The truck is on this borderline between quick street truck, and very quick street truck but a whole chunk of things need to happen to really take it there safely, and it looks like some work on the aero is gonna be in that group.

Aero stuff really works wonders, and its cheap as long as you stay away from carbon fiber!!!!

[Super73]

Hey I have a stock manual truck steering box

[ptc]

Originally Posted by Super73

Hey I have a stock manual truck steering box

DUDE!!! ---- you have to evolve!~!!

[Hollow65]

No power steering here, just my noodle arms. Truck is fine at 130. No front sway bar either. I did have steering slop but tightened at the box. I think I heard it called a worm gear?

[Super73]

Originally Posted by ptc

DUDE!!! ---- you have to evolve!~!!

I will, its called rack and pinion when I go round tube front.