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Technical Model T Roadster front end shake (spring reverb?)

Discussion in 'Traditional Hot Rods' started by Johnny Wishbone, Sep 18, 2013.

  1. Johny I had a 24 roadster with similar set up that did the same thing. It's not death wobble but tire hop that just happens and is scarier than shit at 60mph. I could never get rid of the bounce so I got rid of the car. Not what you want to hear. I all ways suspected the NEW bias tires I had. I just don't think they work on the light front ends and they don't make them like they used to. Good luck. I will check back on this thread to see if you solved the issue.

    -Don


    Posted using the Full Custom H.A.M.B. App!
     
  2. Hi John, I doubt its the tires as you have had so many wheel/tire combos with the same issue. Have you checked the camber side to side and maybe get the toe in checked on a machine just to know it is right also you could try removing the panhard rod and see if the character of the problem changes and you may see it happening more clearly. Good luck mate. JW
     
  3. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,791

    tfeverfred
    Member Emeritus

    It works on a car with a solid front axle. Been done this way for years on T Buckets. Just learned something new.
     
  4. boutlaw
    Joined: Apr 30, 2010
    Posts: 1,239

    boutlaw
    Member

    Johnny, you never responded to John Evans suggestion about tire pressure. You indicated you had changed tires 7 times but no mention of the pressures you ran. I had some bounce in my coupe and dropping the pressure to 22 virtually eliminated it. Easy to check. I'm sure a lot of us are interested in your findings, so keep us posted.

    BOutlaw
     
  5. Post #4 says he runs 24 lbs. up front. JW
     
  6. iagsxr
    Joined: Aug 26, 2008
    Posts: 239

    iagsxr
    Member

    What happens if you unhook the panhard bar?
     
  7. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    I have run the tires as low as 20 psi and it still does it but not as bad. At 20 the tires are pretty mushy, 24 is about as low as I can go and still have them feel like normal tires. I have run these as high as 32 and it gets worse with more pressure. Basically what I did was to drive the same stretch of road, fill front tires to 32, then stop and drop 2 pounds, drive, drop 2 more pounds etc. 24 seems to be my happy medium. I don't have the funds at the moment but when I do I am going to get a model A axle with a 2" drop to move the bones in a little so I can hook my shocks to the bones and narrow the front end a little. I'm thinking maybe my really wide spring is allowing the front axle to flop around and all the other Roadsters I've seen have a much shorter spring. I don't know what else to try, I posted on here thinking I must have missed something simple but I have tried all the suggested fixes everyone has suggested and the stupid thing still does it. I am also going to borrow or build a jig to shave my tires and eliminate what little runout they have just for good measure.
     
  8. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    I have not tried to remove the panhard bar but I don't see how it would change anything as it did this before I installed it, but if I get a good weather day I will try it and let you know. I am willing to try pretty much anything at this point.
     
  9. iagsxr
    Joined: Aug 26, 2008
    Posts: 239

    iagsxr
    Member

    Ok, I missed where it had been added. My take is the spring should locate the axle laterally. The panhard bar and spring move in dissimilar arcs, at some point in the suspension travel it has to cause a bind. That's not the problem, but I'd still unhook it as an experiment.

    I don't like the way you're setting toe. Bomb can a stripe around the tire, rotate the tire against a scribe to make a line, measure toe with the weight of the car on the tires. See if it measures the same.
     
  10. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    I don't think that's it but I can check it to be sure. I was just talking to a dirt car friend of mine and he suggested the same thing.
     
  11. iagsxr
    Joined: Aug 26, 2008
    Posts: 239

    iagsxr
    Member

    While you're at it check the toe on the rear wheels.

    Before I had a real tire scribe, a 1x4 with a nail in it worked just as good.

    Looks to me like the front spring's too wide. Can the shackle mounts be turned 180* ?

    Does the front end move if you step on the frame rail?
     
  12. I think the shackle angle looks right at around 45*, I have seen many that they are 60* or more. Can you lube the spring to see if that changes the character of the issue. Here's mine to compare . JW
    [​IMG]
     
  13. iagsxr
    Joined: Aug 26, 2008
    Posts: 239

    iagsxr
    Member

    Gotcha, I was looking at it wrong. The shackles pivot towards the tires in bump, not up. So are there marks on the top of the axle where they're hitting?

    OP, your dirt track buddy have a Go-Pro? A lot of the dirt guys around here mount them to their cages. I'd aim it for starters at the shackles.
     
  14. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,791

    tfeverfred
    Member Emeritus

    Take EVERYTHING apart and redo it with ALL the info you have now. At this point, trying to pin point the problem has yielded nothing. What have you got to lose?
     
  15. It's only an observation, but I notice there are no rebound clips on the spring. I would be interested to see if that might make some difference .
     
  16. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,791

    tfeverfred
    Member Emeritus

    Without re reading, has replacing your present shocks with tube shocks been considered. That along with a total redo might solve the issue. So far, in one post or another, you'd have redone the entire thing. May as well.
     
  17. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,215

    2OLD2FAST
    Member
    from illinois

    Here's my $.02 , T's are built on ladder frames [NO torsional ridgidity] , when the wheels start bouncing you're actually twisting the frame [slightly] but it's enough that the shocks are mounted to a frame that's moving rendering them useless, in my case of wheel HOP [not wobble] it took multiple tries to get 4 round tires & believe me , the rear tires can be every bit as responsible for the bounce as the front !!
    dave
     
  18. fab32
    Joined: May 14, 2002
    Posts: 13,985

    fab32
    Member Emeritus

    Once again the old "death wobble" issue. If your really disgusted with this problem and would like to put it to rest call SoCal and order a steering dampener. All of the advice you've been given so far is good............and after you've tried it all (maybe twice) don't you think it's time you started enjoying your car? EVERY VW that ever left the factory had a dampener and the one SoCal sells is a copy.
    Make sure your front end settings are within specs install the dampner as per instructions. Take a drive. If the problem still happens take the dampener off, put it back in the box you got it in and send me a PM. I'll send you the purchase price and pay the postage to my place. I've put them on every car I've built for he last 40 years and NEVER have a wobble issue (SoCal puts them on every car they build just to ensure this doesn't rear it's ugly head).

    Frank
     
  19. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    I will look into that for sure! I have a lot of stuff to try, you guys have to give me a minute.... I have checked the runout and the toe on the rear axle and it checks out, everything is lubed up and the shackles do not hit the spring. The frame does move when you step on it, the front spring is kind of soft and I have been trying to find the leaf I took out of it to try it with it back in since I have changed a bunch of other stuff since it was in before. The dirt cars around here run Chevelle style suspension, we were just talking about measuring toe, he runs 1/4-1/2" toe out on the dirt cars so they are waaaay different and would most likely drive like total ass on the street. I have no rebound clips on the spring and I tried taping the whole spring to see if that changed anything but no luck. I was thinking about putting some on though. I have not gone back to the tube shocks, but I got a pair of shock mounts from a buddy so I could try it. I am also thinking the front spring is too wide and I am looking into changing that. Back to the stabilizer, it sort of ranks up there with putting really small skinny radials on my car in my mind. Maybe I'm thinking wrong, but I know plenty of people who are not running a stabilizer and their car doesn't do what mine does so it seems I should be able to achieve the same result. I have had a set of short skinny radials on the car and it's much improved, so it seems to me that I could go the 70's look with some spindle mounts and motorcycle tires and get it to quit, but that isn't really fixing the problem. I'm admittedly hard headed and I can't let this thing beat me so I have to make it not shake with tall tires too.:D
     
  20. If the spring was too wide the spring hangers/shackles would be on the wrong angle, yours are not. I'm betting it's the scrub point, that's why it changes very slightly with the different tyre heights and widths. Hope you find it soon and it's an easy and cheap fix. Cheers, JW :)
     
  21. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    I mean the spring is wider than the springs on some of the other Roadsters I have been looking at. Your RPU has a dropped Super Bell Model A axle I'm guessing? Your setup is similar to mine with the spring over axle, but my wishbone center is 41" and a Model A is 36.5" as is a 32 and 33-36. Some of the cars I have looked at have a 36.5" wishbone center and have the spring mounted to the bones making it even shorter. I was just thinking a shorter spring would be less likely to rock back and forth due to much less leverage.
     
  22. 54sled
    Joined: Feb 11, 2012
    Posts: 251

    54sled
    Member

    Every bucket/roadster I've been in does a little shaking,just whoa her down a little.lol
     
  23. I understand what you are saying there but how can the axle move side to side in relation with the frame with that panhard rod ? My axle is 47 1/2'' and 36'' centres. I have only had the RPU up to 50 mph while being towed but all felt good at that, just hope it still alright well above that. JW
     
  24. the-rodster
    Joined: Jul 2, 2003
    Posts: 6,945

    the-rodster
    Member

    This isn't the "death wobble".

    That is a shimmy, left to right, of the steering.

    This is a BOUNCE, left to right, of the wheels/tires.

    Rich
     
  25. Johnny Wishbone
    Joined: Aug 10, 2009
    Posts: 314

    Johnny Wishbone
    Member

    It's more of an up and down kind of thing. The steering wheel doesn't really move, it just vibrates some. JW, the axle isn't moving but it seems like the spring is pivoting on the spring perch. Imagine instead of the spring being bolted to a flat perch it was hooked to a hinge or pivot of some sort with nothing to hold it flat. Not sure if that makes sense.
     
  26. Ha Ha kind of get it, was just out studying my front end trying to imagine what and how and came away with a slight brain ache :confused: I will keep thinking. JW :)
     
  27. An early response hit on the issue. It's force variation (R1H - rotational 1st harmonic) within the tire, and when it rototes at a certain RPM (vehicle speed) you hit upon a matching harmoic frequency in your chassis. Very common, even in modern cars, somewhere near 65MPH. A proper tire shop can measure the force of the tire tread as it rotates on their balancer, and rotate the tire relative to the wheel to minimize it. No reasonable amount of balance weights can eliminate it in all cases; its not a balance issue... Its a FORCE issue.

    Modern OEM's can offset machine the bolt pattern slightly, and mount tires pre-measured for the high-force point (ever seen those green dots on the sidewall.... thats it). They will line the high force point up with the low point on the rim (rim closest to the bolt pattern - often set at the valve stem hole).

    I've done this in current production vehicles at a OEM.

    Steve
     
  28. junk yard kid
    Joined: Nov 11, 2007
    Posts: 2,718

    junk yard kid
    Member

    has anyone suggested trying the balancing beads? Apparently they can dampen this kinda stuff. I use them with good results.
     
  29. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    Some wheels are off a bit slightly but nobody's going to purposely build a off center wheel.
     
  30. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    Maybe there's multiple issues on this car. Any chance the 60+ vibration is from an out of balance rear tire, drum or bent axle, out of phase drive shaft or unequal U joint angles? I've also only seen the tire "dribble" (with both front tires coming off the ground and no right to left movement of either tire) on one car. Was also a T, but with a rigid tube axle, hairpins and no front shocks and bias plys.

    The original front spring had a crack in one leaf and was replaced by a new one from Speedway. Always drove perfect but now was scary when you hit a bump at speed. Owner seemed to think a leaf needed to come out as was done when the car was built and voila! never bounced again. Have no idea why and when the car got a 6-71 later on we put it back in and did fine with the added weight.
     

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