Old build 23 T-bucket I bought a year ago has problems with the rear end stepping out sideways when it hits a bump. Really gets your attention on the highway at speed! Front and rear have been aligned, shocks are new (Pro Shocks SM-600s). Suspension is wishbones, coil springs, panhard bar. Panhard bar is parallel with the axle and is as long as can be fitted. Springs are from coil overs, 240 pounds per inch, 12 inches high - which is about the minimum due to clearance issues. Spring buckets are 4 inch inside diameter, so the choice of springs is limited unless I order custom springs. Car has a BBC (396) and turbo 400, Chevy 12 bolt rear and weighs 2360 pounds with me in it. Front axle weight 1140, rear 1220 - again with me in it. Here is an old photo: Front end now has hydraulic shocks and I have no issues there. I'm guessing that maybe the rear has too much travel? You can easily get the car to bounce by pushing down at the rear. Any suggestions? I'm trying to avoid going to coil-overs. If no good ideas, can anyone recommend a good chassis shop in San Diego? I'm in the South Bay and with this thing as twitchy as it is, I'd really not like to drive it too far... Thanks!
Is your panhard level [in line w/the axle] & how long is it ?? Get under it & show some pics, if possible . dave
Are you sure about the coil over spring weight? I tried 175 Pounders and I could barely push down on mine. 240 seems like it would ride like a brick.
Really sounds like a panhard bar problem. If it is too short, then it will cause excessive lateral (sideways) movement with up and down travel. You may have to remove it and change the setup to lengthen it.
Here's a photo of the panhard bar. It measures 39.5 inches. [/URL][/IMG] Springs are labeled as 240 pounds per inch. I bought them from Speedway. I don't have a way to check the actual weight per inch.
"Spring buckets are 4 inch inside diameter, so the choice of springs is limited unless I order custom springs." I just checked Speedway, they have lots of 4" springs. Also, they recommend a WAAAY softer spring in their charts for your rear weight. About 130 lbs. Look at an AFCO 22125cr for example. Maybe the things so stiff it just launches itself off the bumps? Tire pressures on a light car should be set lower than you're used to as well. "Stepping out sideways" must be exciting on the highway!! Ralph
Maybe I'm not seeing it right, but it looks like the right end of the panhard bar should be connected to the frame. The way that's setup, it's not doing anything. Maybe it's the angle, but that doesn't look right at all. Edit: I just expanded the pic and the bar goes from one end of the axle to a bracket on the right side of the axle.
"Maybe I'm not seeing it right, but it looks like the right end of the panhard bar should be connected to the frame. The way that's setup, it's not doing anything. Maybe it's the angle, but that doesn't look right at all. " The right end is on the axle. Could the bar be hitting the body? Is it square to the frame/rearend?
???? Get 2 strippers over there. Make sure they weigh about 120lbs each and are really hot looking. Have them sit on the back of the car while you measure. Try them together on one corner and you should measure close to 1" movement. Try them on either rear corner and you should measure about 1/2" movement. If you got the cash or a really good game you could get 4 strippers @ 120 lbs each over there. That way you would be able to measure better
Spring calcs are not what would seem 'proportional' with supposed laden weight. The charts are quite accurate, (I argued with recommended values myself until I learned the formulae) JW Performance in Campbell installed some coil-overs in a 'glass '29 roadster. They were so stiff they cracked the brackets at the frame in St. Louis, Mo. on the way to the NATS. Minnesota Street Rod Ass'n members trailered the roadster to the NATS (Peoria, Il.) and made repairs in their giant tent booth! They also replaced the too-stiff coilovers with some 120 lb.? (can't recall now) but owner Norm said the ride back was heavenly!
I started off with 170 pound per inch springs, but that was when the panhard bar looked like this: I should maybe try putting them back in now that the panhard bar is level. Here's a better photo of the panhard bar showing it is hooked to the rear end housing, passenger side. [/URL][/IMG]
This may have zip to do with this, and you said you had the front front aligned. What is your toe in and caster settings in the front? If I may ask...
Hi ... The pan hard bar set up is wrong ..its set up as if the suspension travel is at its lowest point..the bar should be set up with 10-15 degrees down at the mounting point on the axle so the bar can travel through an arc to being nearly level as the suspension travels up...The way it is now...its dragging the axle further to the left as the suspension moves up and will cause something similar to bump steer.....
Frame is square tube. The panhard bar is not hitting anything and it is square to the chassis and the rear end. If someone found 4" OD, 12 inch springs on Speedway, could you share the part number? Need to find some strippers to do the load test.... Left end of the panhard bar is connected to the frame. Front end castor is 5.5 degrees. Toe in about 1/16".
Maybe the attachment point to the axle is too far to the right? By the way, it's done this ever since I bought it, but it had so many other problems that I'm now down to solving the twitchiness. Front end was horrible. New king pins, and a stiffer tie rod as well as grinding rivets off the hubs that were deforming the wheel solved that. Hydraulic shocks (most recent front end mod) have made it fine. Had a bad cam. I could go on....
tfeverfred's illustration has me thinking that maybe the mounting point on the right side of the axle should be the same distance to the right of the axle center as the left side mounting point to the center of the axle?
From my perspective, somethings loose, have you looked at the wishbones for cracks and or bearing bushing failure? I'd look there.
That is what I would do. Ok, I have stared at your pictures and nothing really jumps out at me except the length of the panhard bar. I know everyone says they need to be as long as possible and level, but I have never been able to get one that way yet and have had no handling issues whatsoever.; On my Sons bucket we had to angle the panhard to clear things, just the way it had to be. The car runs right down the road with no ill handling issues. On my other Son's rpu we had to also angle it slightly, and it is very short because of the way things worked out. Again, the car drives straight and has no problems on potholes or bumps. My point is that maybe your panhard is so long it is flexing. It looks a little thin to me for that length. The other possibility is that the coil springs are rocking in their pockets. Can you shove the car sideways and see any deflection? Finally, do you have a SoCal stabilizer on the front end ? Don
Didn't change the spring cup position, Fred. Everything is tight, no cracks. I've stared at all of the brackets and welds. A too thin panhard bar MIGHT be an issue.it's .825" OD. The only deflection when pushing the car sideways is in the tire sidewall. No SoCal stabilizer on the front end. Front end is very docile now. I'll see if I can get someone to follow close enough to spot any issues. I was thinking of finding someone with one of thos "GpPro" cameras to mount back there. Here's a photo of the wishbone: [/URL][/IMG]
========================== It steps sideways while driving ~ straight ahead, or just when in a corner? On a one wheel bump? On a two wheel bump, like an expansion joint? If when driving straight, always in the same direction, left or right?
Steps sideways when going straight. Seems to be a two wheel bump - like a bad expansion joint. It happens so fast that I'm not sure if it's left to right or right to left. My gut says right to left and back.
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