Rocket Blue violent bouncing back and forth

[PushinTheLimit]

I ran my first ever late model race this past weekend and my car did ok, but I was having issues on corner entry and middle corner. Here is my setup...

Left %: 54.2
Rear %: 54.98
Springs: 500 LF, 375 RF, 250 LR, 225 RR
Rod Locations (from bottom/total) : LR Top 2/4, LR Bottom 4/6, RR Top 2/3, RR Bottom 2/3

The track was a really small, stop and go type of track. It was tacky most of the night. The problem I was having was when I went into corner entry and tried to get back to the throttle, the car would violently rock back and forth so hard that the only way I could get it to settle down was to completely back off and slow down. It didn't do it that bad all the time, but it would still bounce some even when the car rotated good in the corner. The car was setup to run a slightly bigger, slicker track than the one I ran on, so I knew it wouldn't be a perfect setup underneath it for this track in particular.

The shocks I'm using are double-adj. Afco's and they were set up for more of a slicker track. I didn't adjust the shocks as I just wanted to get some seat time in the car and learn what I needed and not get in over my head in adjustments. I haven't dynoed the shocks but was told by the one that set it up they should be fine.

This week, I'm going to a track to where my car was originally setup for. But what would cause the car to bounce so bad that I would lose my forward drive off the corner? Should I have increased the LR compression and lowered the RR compression on the shocks? Would shocks really cause the car to act that badly if not properly set? I was also told that running an Afco 6-0 shock in front of the LR would help keep the car bouncing as much.

I'm still very new to all this so thank you for any advice.

[powerslide]

Bouncing like locked up on the LR bars bouncing or felt like it was the RR bouncing?

I had raised my rear r/h up earlier in the year and it only left about 1.25in before the RR ran out of rebound travel. On a heavy track the RR tries to climb the bars, more so on stop and go tracks than on momentum tracks. When it was heavy/rough i could feel it beating the RR underslung out, i was just along for the ride that night, it was pretty erratic.

[PushinTheLimit]

Bouncing as in the entire chassis was rocking side to side that it would've thrown me out of my seat if I wasn't strapped in tight. It only did it that bad about 3 times all night, but about 75% of the other times mid corner it was bouncing the rear that you could hear the car trying to drive off, but kept loosing traction.

It was driving off the corners fine (it was still a little tight on corner exit, but decent) but the chassis rocking back and forth would've knocked fillings out of anyone's teeth.

[Matt49]

It sounds like you're getting violent hike up causing the whole rear end to get unstable. First of all, put a limiter chain on it to control how much it hikes up. Secondly, slow down the hike by raising your lower left bar on the frame. This rod adjustment will also help with the corner exit tightness issue you described.
The 6-0 shock in front might also help you as long as it isn't a high gas pressure deal. The 0 isn't really a 0 and it will slow down the hike up. And the 6 will help keep the car more stable on entry but it can also free entry some because it will hold rear steer in the car.

[7uptruckracer]

If your on slick track shocks you could have it bouncing because of the shocks especially if you have a soft RF and a full Open on Compression and no rebound LRF it will definitely bounce. Also check J Bar rake that can make you POGO

[grt74]

Sounds like a chain limiter problem to me,shorten your chain

[PenskeShocks]

I would recommend having your shocks dyno'd so you atleast have data on them. Shocks can have a huge effect on weight transfer and cause a lot of the issues your describing. I have seen plenty of guys chase their tails and tune around a bad shock set-up. At the very least, have them dyno'd so you can show someone what you really have in them.

[let-r-eat]

Very typical when someone has a slick track setup on a tacky track. Matt49 gave some good info. Limit the hike by controlling it someway by shock/chain. I see scuds using setups for the slickest tracks on tacky ones. Don't work. You have adjustments. Use them.

[PushinTheLimit]

It sounds like you're getting violent hike up causing the whole rear end to get unstable. First of all, put a limiter chain on it to control how much it hikes up. Secondly, slow down the hike by raising your lower left bar on the frame. This rod adjustment will also help with the corner exit tightness issue you described.
The 6-0 shock in front might also help you as long as it isn't a high gas pressure deal. The 0 isn't really a 0 and it will slow down the hike up. And the 6 will help keep the car more stable on entry but it can also free entry some because it will hold rear steer in the car.

Is it ok to put the 6-0 shock in front AND use a limiter chain both together? We currently don't have a chain on the left rear so I'll look into that.


If your on slick track shocks you could have it bouncing because of the shocks especially if you have a soft RF and a full Open on Compression and no rebound LRF it will definitely bounce. Also check J Bar rake that can make you POGO.

I'll be checking the shock settings tomorrow to see where they were all set, but I'm sure it was set to a more slick track setup. I haven't checked the J bar so I'll look into that.


Sounds like a chain limiter problem to me,shorten your chain


Thanks... I need to look into putting one on it since we currently don't have one.


I would recommend having your shocks dyno'd so you atleast have data on them. Shocks can have a huge effect on weight transfer and cause a lot of the issues your describing. I have seen plenty of guys chase their tails and tune around a bad shock set-up. At the very least, have them dyno'd so you can show someone what you really have in them.


I was hopeing we could get by with these Afco shocks until I decided to go for some Ohlin's or Integra's. I'll check into this as well.


Very typical when someone has a slick track setup on a tacky track. Matt49 gave some good info. Limit the hike by controlling it someway by shock/chain. I see scuds using setups for the slickest tracks on tacky ones. Don't work. You have adjustments. Use them.


Thanks, I guess I just didn't think the shocks and bar settings would cause the car to act as bad as it did on a tight tacky track. This weekend we are going to a track that my car is presently more setup for. I'm going to leave it for the most part alone till we run hotlaps and see how it goes. Then we'll adjust from there.

[7uptruckracer]

Look up the Afco M2 Tuning Guide and Settings Guide even it you don't change anything you can familiarize yourself withe their base settings see how the shocks function and how to tune them with clicks. I'd call Rocket as well get their baseline book they will normally mail it for free, Just to see where your car is they also in their new books have all the shock brands you would probably use and the settings they would like

[jedclampit]

All good stuff above.
My take is this a result of the lr tire loading and unloading often and hard,increasingly oscillating, it's really hard on the drive line. I'd bet you have a large gap between the spring and the coil over nut on the lr with a 250 there. You probably have multiple issues going on, but are really lacking in shock rebound on the lr.

Get on a baseline Rocket deal.

[Matt49]

It's absolutely okay to run a chain AND a shock in front. The chain should be tied off at the axle tube, not the birdcage.
People will disagree with me on this but I think running a chain is an absolute must on the LR for two reasons:
1) If you rely on a shock to limit travel you will cause damage to your shock. Not sure about anybody else but I think what we pay for shocks is insane and I'm certainly not going to put one through that kind of abuse.
2) If you use anything mounted to the birdcage (like a shock) to limit travel, you will get inconsistent results as you make bar angle or length adjustments. This is why you want your chain hooked to the axle tube. There are several nice kits out there. We use the one from PPM but there are equal if not better ones available.

Not to get ahead of ourselves but adjusting travel limit on the LR can be a very valuable tuning tool also.

[PushinTheLimit]

Thanks Matt. I actually live just 30 mins from PPM and seen their chain limiter kit. I'll give them a call and see what they can get me for this weekend.

[JJ128]

Can any of you Rocket guys give the man a measurement from the bottom of the frame rail to the top of the axle tube so that when he does get a chain he knows where to set it?

[7uptruckracer]

Depends on what car Black rocket is 13-14 depending on if your running LRU Shortner. Underslung is one drop and Orange and Blue are another I can when I get home!!

[PushinTheLimit]

I have a Rocket Blue. PPM had two different chain kits, one that went around the bearing, and the other around the axle. I ordered the one that just went around the axle for now. Any measurements would be very helpful... thanks everyone!

By the way, pardon my ignorance, but what is underslug? That's a new term to me.

[fastford]

I have a Rocket Blue. PPM had two different chain kits, one that went around the bearing, and the other around the axle. I ordered the one that just went around the axle for now. Any measurement would be very helpful... thanks everyone!

By the way, pardon my ignorance, but what is underslug? That's a new term to me.

underslung means you have a frame rail/ tube running front to back under your axle tube, ive never run a limiter chain on an under slung chassis, i make sure that with the lf rear at full drop and the right side jacked up, the left shock is not bottoming out, essentially your using the frame as a limiter. a chassis that is not underslung has nothing below the axle and you really need a chain or you could destroy a shock . also on my underslung chassis i wrap a piece of roll bar padding around the lower rail to help cushion the impact. also i saw where some one is making a thing like a spring rubber to put there, been meaning to check on one, good luck

[PushinTheLimit]

Ok, now I understand. This car isn't an underslung chassis. I also called Rocket Chassis and have them send me their setup book. Hopefully we can get my car ready for this Saturday and I will update this thread with the changes I made and how it worked.

[Len72P]

If your shocks are built for slick tracks and adjusted slick , you probably have very little rebound on the left front and left rear. Even if you go to the larger track , hot laps might produce same effect , maybe less violent. I would get ready to add rebound. Also your corner entrance can effect chassis badly. If you are letting it drop off the bars , then turning , them nailing the fuel , wuppy , hang on. Ensure you are entering on the fuel and brakes before getting off fuel. You must be on the fuel or the brakes and turning at same time or you will drop off the bars. Also tighten up compression on left rear behind to help keeping it on the bars.

[grt74]

there sounds like there could be a couple of things going on,ill bet that if you put the car on jack stands and put a jack under the rr and raise it like the car is in the corner the lr birdcage is over indexing(just 1 thing that came to mind)also like some of the other guys have said it will kill your lr shocks over time,so that being said i would never run the car without a chain limiter and it is a very useful tool,now once you put a chain on it,if the car looses forward drive youll have to find it somewhere else,i would work there 1st if the car is good at your home track

[PushinTheLimit]

If your shocks are built for slick tracks and adjusted slick , you probably have very little rebound on the left front and left rear. Even if you go to the larger track , hot laps might produce same effect , maybe less violent. I would get ready to add rebound. Also your corner entrance can effect chassis badly. If you are letting it drop off the bars , then turning , them nailing the fuel , wuppy , hang on. Ensure you are entering on the fuel and brakes before getting off fuel. You must be on the fuel or the brakes and turning at same time or you will drop off the bars. Also tighten up compression on left rear behind to help keeping it on the bars.

I think you just nailed it. After watching the video again, I was letting off the throttle before the turn, turning in, then I would brake before I got back to the throttle again. So that probably got it off the bars then I shocked the suspension so bad that I over extended the LR shock. Makes sense to me.

The track I'm going to this weekend is most likely going to start off a little tacky and then dry up and blow off to be somewhat dry. So I figured I would set the shocks about in the middle between a tacky and dry setup and then adjust from there for the heat and feature races.

[PushinTheLimit]

Something else I noticed when I was looking under my car last night, the lift bar (I think that's what it's called) is hitting one of my lower chassis bars. The very tip of it looks like it has been digging in and has slightly bent that chassis bar. I don't know if that was done in the past before I bought it, or if I did it racing the other night. When it's on jackstands, the end of the lift bar is right against that chassis bar... when I jack up the rear, it pulls away from that chassis bar, but not by much.

Is that normal for a Rocket? Looks to me that the front of the lift bar should move slightly left even an inch and that would solve the problem... or would it?

[7uptruckracer]

The lift bar comes off your rear end and is the long bar with a series of holes that your 5th and 6th arm mounts to and on the rocket it has a heimed tube that is about 11 1/4 inches long that connects to the right side of the lift arm and to a chassis mount the sets your side to side measurement on your lift bar. I'm not sure what bar it could contact it either will hit your driveshaft on the left side and I hope not your inner rail on the right side if that what your referring to if it is let us know and we will get you the measurement I think its 11 1/4 it could have broken something in the part and made it hit it maybe wrap the spot in tape to check for a rub this week. Let us know we will get you measurements

[PushinTheLimit]

http://i99.photobucket.com/albums/l297/goldeneagle_10/1381419892_zps591b79ab.jpg (http://s99.photobucket.com/user/goldeneagle_10/media/1381419892_zps591b79ab.jpg.html)

http://i99.photobucket.com/albums/l297/goldeneagle_10/1381419853_zps038b7897.jpg (http://s99.photobucket.com/user/goldeneagle_10/media/1381419853_zps038b7897.jpg.html)

[PushinTheLimit]

The first picture is with the rear sitting on jackstands and the second one is with a jack under the rear. It pulls away from that chassis bar a little, but it is nowhere near the driveshaft as you can see it in the background.

[powerslide]

At ride height is the lift arm straight w/ the bar above it that the 5th coil and 6th coil mount to?

[PushinTheLimit]

I'll check tonight when I get home... I'll also set the car down and take a picture of where the lift bar is and post it on here.

[7uptruckracer]

The helms that mount it could be screwed to far out or magnets not level check your pinion angle too! Your lift bar should be 36-44 inches and your stabilizer from that lift bar to chassis is 14 1/4. And your chassis drop on a non under slung is 12 7/8 to 13 1/8 from top of axle tube to bottom of rail with car elevated on the blue fronts

[let-r-eat]

What are the top and bottom bar lengths? Someone has messed with something.

[TALON75]

Check your jbar measurement also, the rearend may be too far to the left pointing the liftarm too far to the right. might just need to lengthen the stabilizer bar that is connected to the midpoint of the liftarm, either way it should not hit that tube at all.

[PushinTheLimit]

The helms that mount it could be screwed to far out or magnets not level check your pinion angle too! Your lift bar should be 36-44 inches and your stabilizer from that lift bar to chassis is 14 1/4. And your chassis drop on a non under slung is 12 7/8 to 13 1/8 from top of axle tube to bottom of rail with car elevated on the blue fronts

For that 14 1/4", is that tip to tip, or is that center hole to center hole? If it's tip to tip, it's right on 14 1/4"... if it's center to center, it's 13 3/4". Also, my J-bar is sitting in the bottom hole on the right side of the rear end.

I didn't get to measure anything else last night as we were working on some starter issues. Thanks for all the help so far everyone... it's been very informative for me.

[7uptruckracer]

The stabilizer measurement is center to center any heim or tube measurements will be center to center so 14 1/4 could be your problem there if you lengthen it it will push it farther away . And by j bar measurement he means lateral location of the rear end which you measure from your upright 90/10 bracket to your RR inside frame rail your 90-10 bracket bolts to the top of your rear end it's the pair of somewhat triangular ears on the top measure from the outside of the right bracket to inside of RR frame rail but I suspect you might have found it with the stabilizer arm on the lift bar

[PushinTheLimit]

Thanks so much... then yeah, but lift bar is 1/2" to 3/4" too far to the right. I'll adjust it to 14 1/4" and that should adjust the rear end back to the right instead of so far left. I had a couple of guys comment on my last race that the rear was tucked in really far left in the car.

[Lizardracing]

It's a good idea to wrap the chain with tape to keep the links from getting tangle up. I like the chain used on swing sets that's has the plasitized rubber coating. It's cheap enough and easy to work on too because it doesn't leach glue that duct tape can after repeated heat cycles and car washes.

[7uptruckracer]

You tucking the LR is a product of your bar angles and with the fact you were on slick track shock settings you were probably hiking really far with no limiting chain. So don't worry about that get your Lateral Location Checked. Get your Lift Arm Stabilizer arm the right setting. Even back out your shock settings to suit your track conditions and set your chain and you should notice a big difference in drivability. Really Really make it a point to call Rocket tell them you'd like a Setup Book for your Chassis and they will mail it to you! We don't mind giving you this info but its all in there!

[PushinTheLimit]

Thanks Lizardracing, I've had a couple of guys mention that about the chain. I'll make sure and take care of that too.

[PushinTheLimit]

You tucking the LR is a product of your bar angles and with the fact you were on slick track shock settings you were probably hiking really far with no limiting chain. So don't worry about that get your Lateral Location Checked. Get your Lift Arm Stabilizer arm the right setting. Even back out your shock settings to suit your track conditions and set your chain and you should notice a big difference in drivability. Really Really make it a point to call Rocket tell them you'd like a Setup Book for your Chassis and they will mail it to you! We don't mind giving you this info but its all in there!

Yes, thank you for all your suggestions. I called Rocket a couple days ago and they are sending me a book, so it should arrive any day. Probably not in time for my race this weekend, but I got on off weekend after this one... so I should have some time to sit down and read through it and get familiar with the setup. The track I'm going to this weekend will be starting tacky, but slick off most likely by feature time and is much larger than I race on last weekend.

I'll update this thread on Sunday how the car performed and see how all the changes did for it. Thanks again everyone... you've been a huge help.

[big88fan]

I'd say to much j bar angle and/or right lower bar to low on the frame

[let-r-eat]

big88fan,He said the Jbar was in the bottom hole on the pinion. I'm certain depending on the bracket he's using that is gonna make things harsh.

[big88fan]

The bottom hole is ok if it's hard tires

[PushinTheLimit]

Quick update: We went to race at North Georgia Speedway last night. The track was a 1/3 mile very slick track. The car drove very smooth and didn't pogo at all. It was predictable and I was able to control it with the throttle off the corner. I had it too free in the heat race and went to the LCQ and finished 3-4 spots from making the feature. It was mostly due to my inexperience and not the car this time. But with some seat time in the car, I think we'll be in good shape next year.

The only trouble I had was with my transmission... had a terrible time trying to get it into low gear from neutral. But the shifting linkage has some swivel bolts in them and I think that was causing the problem. We're going to fix that and go run a practice day at Cleveland Speedway in 3 weeks.

[7uptruckracer]

Did you get your lift bar straight? Check your drop as it slick go to your max LR drop number. At full drop check your LRU bar angle and we index the LR upper bar down on the slot on the birdcage you also add some LRF shock compression if it gets slick the blue does have issues with what your describing though it's common to run 475 LF 325 RF 200s across rears and work with your bars shocks and 5th coil settings you want 4" of travel on your fifth coil or so sounds like it was better for ya!

[PushinTheLimit]

Yes, we lengthed the lift bar brace and looks like it didn't hit the lower chassis bar this time so that was an improvement. Where the J-bar mounts to the rear looked to have worked itself loose and was probably flopping up and down and could've caused alot of the erratic behavior. We tightened it up and moved it up 3 notches.

I adjusted my shocks to be inbetween a slick and tacky track setup, that seemed to work pretty good but I could've set them to a completely slick setup as the track was very slick all night even in hotlaps.

We are going to go back and run the first track again where I had all my problems and make a couple bar changes and shock changes and see how that goes for us. I expect the car to be much better this time around and much more driveable. Seat time and more seat time is what I need!