Rocket lift bar shock/spring question

[17m fan]

If the chassis was set exactly per the Rocket set up book, how would a car react without any preload at all on the lift bar spring? New to me car and what little I have ran it, I am chasing a chassis that is not getting up on left rear. Don't matter if track is heavy or super slick. Had everything apart and nothing is in a bind. Put a jack in front of the left rear and the tire goes forward like it should..just not on the track. The only thing I found wrong (not ran since) is there wasn't any preload on the spring. Any thoughts?

[andy16]

no preload wouldn cause the problem your having i dont think. iv had friends cars back off before during a race or either they forgot to preload it also. need to check your u joints and yokes to see if your pinion angle got to high under acelleration and got in a bind or cracked. i think w no preload the arm gets a head start on the spring and hits the spring w more force causing a all of a sudden stiffening and prob causing a delayed tire spin maybe around 1 second after wot? although iv never experimented w it thats my theory.

as far as your chassis hike run a softer tire/ more bite/ more j bar angle/ with car at ride height make sure your bottom left 4 link bar is running up hill/ use a 6-0 shock in front/ stiffer lr spring softer rf spring/ lower your rf ride height 4 turns but keep same bite/ make sure left axle isn broke/ make sure driveshaft isn bottoming out in tranny

* if your desperate for l/r hike under acelleration angle your shock and spring on the torque arm back towards rear of the car at the top 10 degrees angle. just slide the top mount back. it didn handle well for me but will help get the rear moving

[17m fan]

What I am experiencing now is a car that is easy to drive just no forward bite at all once feature time rolls around. It has fair bite early in the night. Just once as it slicks off, it will blow the tires off at anything more than about 2" of throttle...and being just as easy as I can giving it fuel.
So, I can assume by your theory of the bar getting a head start on the spring, that may be my issue. I have already checked the things you mentioned like u joints, yoke bottoming out, angle of the lower bar etc.
I have tried the long upper left bar and the short bar with extension as well and it didnt do anything for bite. I will dig into it again and give it another shot this weekend. Thanks for the reply

[dualdj1]

stiffer lr spring

stiffer lr spring reduces hike, to increase hike you go softer LR. The spring compresses more at ride height, and thus it will expand more as the car rolls/corners, helping hike.


So, my suggestion would be go with a softer LR (should notice a difference at 25lbs lower), pierce recommends preloading the 5th coil for slick, not sure about other chassis makers, so that may be worth a try. and as always more angle in the j-bar, clear down on the pinion if it's not already, or up on the chassis, or both.

[andy16]

well that to me is argueable. depends on your theories i guess. to my own knowledge as the left rear indexes the birdcage pushes the spring into the chassis .by stiffening it it can cause chassis hike earlier and more lr traction earlier until it gets on the bars and the spring becomes irrelevant. i understand the stored energy theory on soft lr springs but i havent seen it demonstrated sucsessfully at my home track under conditions i see on a daily basis. the way my program works if you soften rf you gotta stiffen the lr. if you soften the lr and the rf that usually frees the car up . more than one way to skin a cat tho not knockn it but i just hadn had any luck myself w a condition of spinning the tire and no hike by going softer. i even tried the stacked spring and a stacked preloaded spring went right back to the 200-225 and went to work on the shock in front w more sucsess in my humble opinion.

[ncracer1st]

where is your lead mounted?

[17m fan]

None..Running steel block & heads v/s super lates

[andy16]

well you said earlier your setup was exactly from the manual, what setup are u running the d-55 setup, low wedge, they all are a little different. i run a steel block n heads and to get my percentages to a recommended level i had to add 50 lbs to the rr area . you might need some more rear %. i wouldn be afraid to get up to 2400lbs to get my percentages right. just tryn to help but im just guessing if we dont know your percentages bite and spring shocks etc. good luck only a few more left this year:)

[17m fan]

They are right with the setup as far as bar location, length, percentages, wedge (have varied this some as I have ran it), ride height, j bar height, springs etc. My usual track runs limiteds at 2400 lb on 1300's or harder all around. They have closed for the season and trying to get some more seat time at another track that only runs supers.
When I did run lead (two 30 lb weights) on it, I moved them all over the center of the car...nothing made much of any difference to me except once I put one of the weights up on the horizontal bar and the other really high on the the usual vertical bar. I have found that the more left rear I put in it...keeping ride heights the same, the better it drives.

[7uptruckracer]

If your making the changes for the slick like adding bite and dropping to lower bars to reduce the rear steer in the slick sometimes lowering the RRLB can let that tire dig in. I'd for one being it sounds like a drive issue look at adjusting a bar on the BC or your 5th arm derives most of your drive on throttle.....CHeck your 5th arm shock to make sure its working correctly and valved right.....

[17m fan]

If your making the changes for the slick like adding bite and dropping to lower bars to reduce the rear steer in the slick sometimes lowering the RRLB can let that tire dig in. I'd for one being it sounds like a drive issue look at adjusting a bar on the BC or your 5th arm derives most of your drive on throttle.....CHeck your 5th arm shock to make sure its working correctly and valved right.....

That,s when I found the 5th coil had no preload on it. The shock works smooth as silk.

[dualdj1]

Yeah Andy, understand what you're saying too. That was kinda my thought on it originally, however we've had good luck with the soft spring getting us more hike, so I know it works. The caveat, is that you have to have traction to get indexing and hike. Softening the spring isn't going to help traction, only hike, so you have to do other things to help it apply force to the lr wheel, such as raise LUL, change j-bar, etc. All else being equal, with having decent traction, you should get more hike from softer spring, or at least get up to your limiter quicker.