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kellfree
06-15-2010, 04:03 PM
We have an old GRT chassis that is a 2 link/3link (trailing arm on each side and a pull bar in the center).

The car gets in the corner real nice, through the center beautifully, but when the driver starts to get back in the gas the wheels start to spin and he's being as easy as he can on the throttle to not spin the tires but trying not to get run over at the same time.

The 4-bar cars ofcourse pick the throttle up in the middle of the corner and are checking out. Without going to a 4-bar or adding 200 lbs to the back of the car... anyone have any ideas?

J bar.
Spring in front on both sides.
Shock in rear on both sides.
Brake floaters on both sides.
Pull Bar with 700 lb spring.
90/10 shock.

usafracer
06-15-2010, 05:16 PM
Get rid of the spring in the pull bar. Go with a biscut setup. The spring tends to bottom out and cause you to loose traction.

Next time you go out take a zip tie and put it around the slider and that will tell you how much the pull bar is moving.

kellfree
06-15-2010, 06:12 PM
We have a movement indicator on it and on a normal night it's usually around 1/2" away from bottoming out and the spring still has a way to go before we run into coil bind. I made sure the 3/4" bolt and the opposite spring plate in the mechanism bottom out against each other before the spring got close to coil bind. It normally moves about 1 3/4" total of the 2 1/4" of room it has.

I'm not against trying the bisquits and they may just be what we do next. The only reason I havn't is that we have went to a lighter spring a couple times to get to this one. Each time we went lighter it helped... A LOT.

I know if we go to the next lighter spring again, it will bottom out. But the bisquit is going to limit movement a great deal compared to what's going on now... right? Or am I misinformed? If I go this route, which one on the following page would offer the better results? Where would you recommend starting on hardness? Soft, Medium, Hard?

http://www.daymotorsports.com/shop/Suspension/Torque-Absorbers-%26-Eliminators/Torque-Absorbers

usafracer
06-15-2010, 06:34 PM
I run the soft bushing. You might be rotating too far as well. With the biscut pull bar I get about 3" of movement I am not exactly sure I have never measured but I will do that this weekend.

Dirtrunner35
06-15-2010, 07:38 PM
The less movement the pull bar has, the more shock the tires will have, making the tires lose grip. 1 3/4 movement of the pull bar is ok. (from a side view of the pull bar where it is attached above the rear end, third link). Is it in front of the axle or behind from a 12:00 position ? J-bar or panhard bar , what length and angles? Also what angles are your lower trailing arms? What springs and tires ?

kellfree
06-15-2010, 07:59 PM
The pull bar bolts up dead on at the 12:00 position above the centerline of the axles with the car sitting at rideheight. It is the only hole that we can put a 3/4" bolt in. It is all of the way at the top. The frame mounted end is in the lowest available hole. It is 28" total length. I have never measured the angle... just played with placement in the frame end til the driver was most comfortable with it. It is maybe at 15-20 degrees running downhill from the top of the rearend towards the front of the car to the frame mount.

We are running a 21" center to center solid J-bar. Again... I have never measured the angle... but will. The pinion end mounts dead even with the center of the pinion. The other end is 4" above that. It does run down hill from the frame mount to the pinion mount... but not a whole lot. If I had to guess... about -10 to -15 degrees. (I will get an accurate angle tomorrow.)

The trailing arms are 17" on the left and 17 1/4" on the right.
The left trailing arm is at 34 degrees. The right is at 23 degrees.
Springs are 200 on LR and 175 RR.
Tires are Hoosier IMCA G60s (not allowed to run AR's).

When it spins the tires... it does not try to turn the car to the wall nor to the infield. It seems pretty nuetral across the car as far as keeping it straight. Like a dragster doing a burnout.

Kojak_9x
06-15-2010, 08:46 PM
Try this... Lose the 90/10 if you are running one and go to the biscuit bar with red bushings little to no pre load.. Thats the way I run mine and I like it.

bmodracer
06-16-2010, 07:25 AM
Sorry if I missed it somewhere, But, How much rear % and Cross % are you running?

kellfree
06-16-2010, 09:49 AM
58% Rear
49% Cross
Total weight w/ driver is normally 2500 to start the race. (2450lb rule)

Also... he's not 3 wheeling the car coming off or doing anything wild... not even on the nights when the track just happen to be real tacky. The car looks real calm all the way around the track. The driver is getting in the corner just as fast and sometimes faster than the leaders... he'll pass them. But as soon as it's time to gas & go.. he has to baby it and get his doors blown off. Very frustrating for him.

We're normally 1 or 2 gears higher (numerically lower) than most of the others too just trying to save the motor from the real high RPMs and make it last. Even went to a highend cam trying to reduce the lowend tourque that seems to be hurting us.

We've been running a 4/10 mile high banked... in a couple weeks we're going to some smaller (1/3 & 1/4 mile) and flatter tracks.

washeduptoo
06-16-2010, 10:33 AM
I think if you went to numerically higher gear, you would have less wheel spin and the rpms would decrease or be close to what your turning now. That has been our experience.

c12_racing
06-16-2010, 01:16 PM
I would put the spring behind on LR or increase LR spring to 225 or 250 and leave it in front. Also, I'd think about getting a progressive spring for the pull bar if you keep it.

Dirtrunner35
06-16-2010, 08:47 PM
I had a stock car with a 3-link and the springs were on the lower trailing arms in front of the axles. I put the springs on the axle and liked it better. If you figure the motion ratio with a 15" lower and the spring in front of the axle 5 inches, a 150 spring is actually a 95lb spring. I would raise the cross a little and put your RR lower arm level, to lessen the over steer.

Kojak_9x
06-17-2010, 12:24 PM
I would also consider going to a 225 lr, keep it in front and put your RR on top or behind the housing. I like mine on top.

What air pressures are you running?

Your cross seems just a bit low. I would run around 52% but dont go over 53.

Your rear looks right on if your on alky but if on gas I would knock it down to. about 56 or more depending on what the car/driver likes.

What are you running for front springs?

c12_racing
06-17-2010, 12:57 PM
One other thing that will hookup the car on a slick track is to move the pullbar to the left.

Fox_hunter42
06-23-2010, 09:49 PM
This is gonna sound stupid, but here goes. Make sure your 3rd link isn't fully extended and stopping rear axle wrap. Also verify your axle dampening shock isn't fully extended. I got in a wreck and bent everything on rearend, when putting it back together the replacement shock wasn't the same lentgh. My car would spin violently coming off corner, I would spin out everytime, just like someone picked the back tires and and threw the car sideways. I finally got tired of not finding what was wrong and just started removing things. Took the shock off while sitting on all four tires and the rear end jumped. Raced it without and almost won my heat and was really moving forward in feature. BUT!!! be careful this will make it very loose on entry.

I ran LR (225#) in front, shock behind. RR (200#) behind, shock in front. Trailing arms level. J-bar mounted to right side of pinion-center hole, and 7 degrees up to left side frame. 3rd link with progressive spring, light preload, mounted 7 inches above rear housing, and 13-15 degrees downhill to frame mount. Centered on rear, but it was adjustable side to side. I also found that while cornering, the left side axle tube was hitting my underslung frame rail. This was basically lifting left rear off track. I cut about 1 foot of frame rail out and re-attached a chunk of tubing below main tube. This allowed me another 3 inches of travel, keeping more weight on LR coming off corner. Hope I helped

dluna11w
06-24-2010, 08:29 AM
Your trailing arm angles are too steep. The car has to be gaining a TON of rear steer when he goes to pick up the gas, causing a loose condition. Or if it looks calm something is binding somewhere or the lr shock is really limiting travel. How much shaft is showing on the lr shock at ride height? Also, spring in front on rr will be more loose on the gas compaired to spring behind. I'd move that on top or to the rear.

charcoal01
06-24-2010, 12:40 PM
Your trailing arm angles are too steep. The car has to be gaining a TON of rear steer when he goes to pick up the gas, causing a loose condition. Or if it looks calm something is binding somewhere or the lr shock is really limiting travel. How much shaft is showing on the lr shock at ride height? Also, spring in front on rr will be more loose on the gas compaired to spring behind. I'd move that on top or to the rear.

agree with this. put that RR on top of the housing and lower your angles on the trailing arms. i raised my LR trailing on to around 35 degrees static and the thing came of the corner ok but then started to push towards the wall and would snap loose about the flag stand. simply moved the bar back down one hole to around 22 degrees static and the snap loose went away. i also run a longer RS bar and only about 5* uphill, to reduce the amount of rear steer the car is getting in the middle of the corner and coming off.

with both trailing arms up that high you're making the RR tire walk way back as you start to enter the apex and load the RS of the car. then with that much uphill angle on your left side, once you start to apply the gas you're getting even more steer out of the left side and also instant traction because of the steep angle and you're simply over driving what the rear suspension can handle.

get your angles back down to around 15-22* up on the left side and 0-10* up on the right side trailing arms. set the rear end either neutral or trail the rr just a bit, maybe 1/8th to a 1/4 inch. (this is mostly going to help on entry, if the car is a little tight). i dont think three links generate enough side bite or have enough adjustment to control the amount of rear steer the 4 bar cars can make. i think you'll find the car has a lot more drive after you lower the bars.

mod54n
06-24-2010, 03:02 PM
With the numerically higher gear you will be able to control the wheel spin a lot better.

FastRedRaceCar
06-28-2010, 11:17 AM
You didn't say what type of panhard bar you're using. To make that 2 link hook up off the corner you need to try running a short straight bar to the left side of the pinion. Makes the car react very quick and you will feel a difference off the corner.

Dirtrunner35
06-28-2010, 08:23 PM
So, if you have "backed it into the corner" and are driving through the turn with the throttle, then the loading on each rear tire will have a large effect on how the race car handles. Increasing the load on the right rear tire will tend to make this tire push forward harder and the back end will come on around as you apply the throttle. Increasing the load on the left rear tire will make that tire push forward harder and tighten up the rear end of the race car.
The tire pressures look good. On my old 3 link I had my RR lower arm 2 inches lower than the LR to keep rear steer down. I would also agree with putting the j-bar/straight bar on the left side of the pinion.

Dirtrunner35
06-28-2010, 08:24 PM
So, if you have "backed it into the corner" and are driving through the turn with the throttle, then the loading on each rear tire will have a large effect on how the race car handles. Increasing the load on the right rear tire will tend to make this tire push forward harder and the back end will come on around as you apply the throttle. Increasing the load on the left rear tire will make that tire push forward harder and tighten up the rear end of the race car.
The tire pressures look good. On my old 3 link I had my RR lower arm 2 inches lower than the LR to keep rear steer down. I would also agree with putting a straight bar on the left side of the pinion.

Vardarfrals
07-01-2010, 03:16 PM
Thank you maurice, would the reset also kick my music off the hd?

wardy49s
07-04-2010, 10:50 PM
Having the same problem but my pull bar is not in the center of the rear end, it is more towards the right side of the rear end. Any way around that ? In order to get the pull bar to the center have to do alot of cutting and bending. open to ideas.