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Technical Launch issues

Discussion in 'The Hokey Ass Message Board' started by 1great40, Jun 27, 2015.

  1. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    It's been my lot in life to only experience the most oddball of the oddball problems when it comes to building hot rods. I have a '40 Ford pickup on an '86 Ranger chassis and thankfully I have it almost completely sorted. One problem that had been dogging me from the start was lack of OD in the 700R4. I held off on tackling that till I got the engine running correctly so that the truck was completely driveable. Last week I took it to a local trans shop well known to the hot rodders in the area and he had it fixed in short order. Turns out there was a stuck valve in the valve body that had been fouled since the transmission was rebuilt. While it was at the trans shop, I asked about a couple other observations I had namely; the shift points were lower than I liked and the truck always seems to lurch when you're taking off. The lurch was so bad that I actually changed the pedal ratio on the accelerator cable so that it is possible to feather the gas with a little more finesse in order to get it off the line smoothly.

    The trans guy said that he didn't the shift points were that awfully low and I had to agree with him to some extent since I was forever nursing the truck off the line to avoid the lurching, therefore letting the truck shift early.
    I asked if he thought the lurching was a torque converter problem but he told me that the transmission and torque converter were working correctly. Indeed, the truck now shifts and goes into OD and the converter locks up correctly. He felt that the lurching was some sort of mount or other driveline component torquing up when it was accelerated any harder than a minimal takeoff.

    In order to arrive at the correct wheelbase with the Ranger frame, I turned the leaf springs around 180 degrees and installed them with the longer portion of the spring toward the front of the truck. Although I can't see under the truck and drive it at the same time I'm wondering if I'm winding the springs up when I hit the gas? Has anyone experienced a situation like this? FWIW I'm using after market engine and transmission mounts for the Chevy 4.3. The rear trans mount is adapted to the Ford crossmember with a stout but home made plate. The Ford crossmember is attached to the vehicle frame through large rubber bushings and that crossmember was originally intended for a Ranger with a manual box. I'm wondering if I have created a can of worms here. I checked out another Ranger with an automatic and the crossmember is hard bolted to the frame. I'm wondering if I have too much rubber between the tranny and the frame? I'd love to straighten this out since the rest of the truck has really come out nicely.
     
  2. BamaMav
    Joined: Jun 19, 2011
    Posts: 5,178

    BamaMav
    Member
    from Berry, AL

    With the springs reversed, you might be wrapping them up a certain degree. You might need a stiffer leaf in the front section to counteract the flex, or something like a old type slapper bar that would stiffen the front of the spring under acceleration. I doubt the cross member rubber is the problem, I wouldn't think that the trans would move enough to make it lurch unless the mounts were broke.
     
  3. gas & guns
    Joined: Feb 6, 2014
    Posts: 370

    gas & guns
    Member

    I'm guessing the springs are good place to start. Mopar super stock springs were designed long in back, short in front to prevent axle wrap. (Just an example, not familiar with ranger springs) But what you have going would be opposite of design.
     
  4. chessterd5
    Joined: May 26, 2013
    Posts: 649

    chessterd5
    Member
    from u.s.a.

    An old sleeper trick on street cars was to clamp some half inch rebar to the top of the leaf spring. This acted like traction bars controlling spring wrap with out seeing slapper bars under the springs. You could try it & see if that helps. If it does, then play with the length & position of the rebar till its fine tuned. If not, then you can eliminate the springs & concentrate some where else.
     
    loudbang likes this.

  5. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Thanks, I'll look at that!
     
  6. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,608

    Rusty O'Toole
    Member

    Most leaf springs are short in front for stiffness, to control axle wrap, and long in back for flexibility and soft ride. You have reversed this. So, I bet you don't have spring windup in reverse lol.

    If you stiffen the front (long) part of the spring you will louse up the ride. Instead I suggest you add a reaction point such as a traction master type bar between the axle and frame.
     
  7. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    I certainly am going to try immobilizing the crossmember and then doing some type of spring wrap mitigation on the rear axle. I'm just thankful that you guys seem to think that the lurching is related to a driveline issue as well. I suppose I should have just relocated the spring hanger brackets and used a shorter overall spring when I built the truck. I like the idea of the traction master bar. The truck rides like a truck already, not really bad but it's no Lincoln. If I could fix this without adversely effecting the ride, that would just be icing on the cake.
     
  8. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Tonight I cut a 4 foot length of Uni-Strut in half and clamped a 2 foot section to the top surface of the main leaf on the front half of the springs. I used 1 clamp on each side, grabbing it mid span. I cranked up the clamps until the front half of the spring was flattened out and hard up against the Uni Strut. The test drive showed much improvement, The truck doesn't lurch nearly as bad as it did before. It's making me think that traction bars may help the situation after all. Can someone explain to me why bars like Traction Masters don't cause a bind in the rear suspension as the spring articulates? From the pictures I have seen online, it looks like as the spring moves up and down, basically pivoted from the front spring eye, the bar which is pivoted from a different point would want to bind the suspension after a small amount of travel.
    The even better news is that my newly-arrived Harbor freight flyer with the 20% coupon didn't blow out of the bed of the truck on my test drive!
     
    Last edited: Jul 1, 2015
  9. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Today I removed the Uni-strut because I was headed for a moderately long drive to a show. The first thing I noticed was when I pulled into a gas station and stopped, I put the truck in park, released the brake pedal and the truck lurched forward about 2 inches. I'm reading that as spring wind up because the truck was still on high idle when I stopped. So I really think the traction bars are required. Can someone please school me as to why I would want the traction master style instead of typical Lakewood style slapper bars.
     
  10. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Hi all.Today I finally got a chance to crawl under the truck while a buddy ran the shifter from park to reverse to drive and back again. There was no motion at the trans mount or crossmember mounts (just like you guys said) but the rear end, well that was another story! That thing is jumping all over the place. I would say the total swing from reverse to drive is about an inch vertical. And the engine was only at a fast idle, I didn't want to see what would happen if you gunned it to take off.

    So with that observation I'm going to order a set of traction bars from James Duff suspension. I'll have to lengthen them to work with my reversed springs but from what I have seen, I can't afford to have the springs winding up like that every time I take off. I will report back on the results when I get them installed.
     
  11. saltflats
    Joined: Aug 14, 2007
    Posts: 11,037

    saltflats
    Member
    from Missouri

    If you would have to lengthen them why not just make some that fit / Maybe even like cal track
     
  12. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    I looked into making a pair myself but by the time I make the brackets and buy Heim rod ends and other hardware, the Duff units are a steal at 99 bucks. The Cal Tracks look great too but they are over 3 times the cost. Probably well worth it if you're trying to hook up better and shave a couple tenths off your time but they're overkill for my application.
     
  13. Why not have a proper set of leaf springs made for it instead of a band aid that may not totally cure you're problems?
     
  14. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    Not quite true [but nearly there]
    For the spring to twist down at the front the rear must twist up [ they both share the torque reaction proportionally and transfer the vertical loads to the hangers/shackles ]
    Reversing the spring doesn't change the vertical loads , the short end is now on the shackles.

    The problem is Torque as well as torque reaction. Torque reaction is at the pinion and torque is at the axle
    Torque will always be greater due to gear reduction.

    The rear axle is trying to push forward [accelerate] against the front hanger [resistance] causing the longer part of the spring to try and curl [literally trying to shorten the wheelbase]. The rear part of the spring can't stop this because it is floating back/forth on the shackles.
    You need arms going forward from the centreline of the axle to the centreline of the front spring eye [similar to 3rd gen Camaro rear arms ]
     
    Last edited: Aug 5, 2015
  15. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,608

    Rusty O'Toole
    Member

    AKA a reaction point. Your idea will work if the end of the arm is fixed rigid to the rear axle. Otherwise it will do nothing. An arm not on the centerline of the spring will control axle hop even if it pivots on both ends. One is enough. The idea is to keep the axle from twisting.

    If every action causes an equal and opposite reaction, then the force applied by the tires to the road, will try to turn the axle in the opposite direction. In other words a torque reaction.
     
    loudbang likes this.
  16. JOECOOL
    Joined: Jan 13, 2004
    Posts: 2,760

    JOECOOL
    Member

    My opinion is just have the correct spring built. A GOOD spring shop should be able to fix you up.
     
  17. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    The reaction to torque at the tyre footprint is thrust at the axle centreline [this is what propels the car]
    The reaction to torque at the pinion trying to rotate the pinion is lift at the pinion [ this needs to be controlled ]
    The torque [or thrust] at the axle is always greater than lift at the pinion due to gear reduction.

    I will actually correct some of my comments previously written [I've been doing some thinking]

    When the axle rotates [backwards] it creates lift at the front spring eye, and downforce at the rear spring eye. Because the front half is shorter it is stiffer than the rear half so there is more lift than downforce. At the same time it can also control the greater force trying to propel the car forward.

    By reversing the springs and having the short end at the rear you will have more downforce than lift, which in the real world doesn't happen so it tries to lift the rear end off the ground [think of having short rearward mounted ladder bars]
    Add to this the forward thrust against the softer half of the spring , and the leafs will try to "S" shape themselves creating a bad hop.

    The OP needs to rotate the springs around [ short in front ] and remount the hangers and shackles to get the desired wheelbase.
    He doesn't need custom springs
     
  18. indyjps
    Joined: Feb 21, 2007
    Posts: 4,515

    indyjps
    Member

    Exactly correct. If the longer rear of the spring moves the mount off the end of the frame, new springs are needed that are overall shorter length bit with the same front to rear length ratio.

    Shouldn't need to have springs made, check other small trucks (S10, dakota, etc) to find a set that will fit on the frame and mount on the axle using the factory centering pins.

    Leaves can be removed or added to dial in the ride once the springs are mounted correctly. Clamping should be the last step and is really a dragstrip launch tuning exercise not needed for everyday driving.
     
  19. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    Thanks for the really great technical explanations! The limitation in the case of my truck is if I moved the springs rearward to maintain the stock orientation of the spring, the rear shackles would be about 4 inches past the end of the frame. I like the suggestion of looking into springs from other small trucks to see if there's something that might fit. I guess you can see why I was looking into the traction bar solution. It seemed like the simplest, least expensive way to counter the rotation of the rear end. One of the posts did mention that I would need only one bar installed to counter the rotation and I can see that working. At that point it would be economically feasible to fabricate one myself, since my materials costs would be pretty small at at that point. The illustration provided by Ricks Garage was very helpful in that it answers one of the questions I had posted early on in this thread: What keeps the traction bar from causing a bind in the spring articulation? The illustration shows that the front anchor point of the bar pivots when the spring moves. Since the ride height is perfect and the handling seems good too, I'm still leaning toward building something and giving it a try.

    I really appreciate all the input! And like so many threads on the HAMB, I'm sure it has helped many more guys than just me.
     
  20. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,852

    Gearhead Graphics
    Member
    from Denver Co

    Maybe I'm way off.. maybe not.
    What about taking the spring pack apart, and then leaving the long leaf backwards and putting the rest of the springs on forwards like they were meant to be. can still mount the axle where you had it and then the springs are more like they should be.
     
  21. indyjps
    Joined: Feb 21, 2007
    Posts: 4,515

    indyjps
    Member

    Agree with gear head graphics, it's worth a try.

    Still think you'll have issues if the front of the spring is longer than the rear. My reasoning is - every leaf spring vehicle I've seen has the rear axle centered on the spring arc, or biased towards the front of the spring arc. There's got to be a reason the OEMS set it up this way.

    Even if you could get an equal spacing front / rear using a different set of springs I think it will help.

    Instead of 1 traction bar, look under a third gen camaro, there's a link from the axle to trans mount that controls axle wrap, you could probably grab one of those used for a few bucks and mod it to work. Less costly than buying a tube, heims, etc to make a traction bar.

    Trouble with off the shelf traction bars, they will be too short for your "long front" spring, hitting the spring instead of the spring eye. This will aggrivate spring wrap, then unload.
     
  22. 1great40
    Joined: Jan 1, 2008
    Posts: 471

    1great40
    Member
    from Walpole MA

    If I do that, I end up with the shorter section of the 2nd and 3rd leafs forward like you say. That puts the ends of those leafs further away from the spring eye than they are now. Assembled like you suggest the wrapping motion will result in putting more force closer to the mid point of the main leaf, probably making the wrapping worse, not unlike the too short slapper bars that Indy mentioned.

    In any event, there's no denying that the OEMS engineer the springs the way they do to both suspend the axle and maintain it's position front to rear and rotaionally. I installed this axle like this about 15 years ago when I first started building the truck and tried to find information on the pros and cons of the setup. There was a little information regarding oversteer/understeer issues but thankfully, I'm not experiencing any of that, the truck pretty much goes where you point it. From my observations, there's no doubt that the spring wrapping is a problem. I think the answer is either the bar or find a set of shorter springs
     
    Last edited: Aug 5, 2015
  23. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member



    The long front part of the spring isn't the only issue, it is the short rear part.
    Traction bars going forward will stop the torque forces from bending the spring, but they will not stop the rear end tying to lift off the ground [or the rear squatting down]

    If the OP took his car for a blast up the road and slammed on the brakes, their would be a lot of dive [actually lift in the rear] it would actually have good rear bite under braking conditions

    The whole 3rd gen Camaro set up is what he needs. By using coils you are disconnecting the tendency for the springs to squat .
     
  24. 34toddster
    Joined: Mar 28, 2006
    Posts: 1,482

    34toddster
    Member
    from Missouri

    Why not do it right have a spring company build a set of correct springs that work, problem over on to something else!
     
  25. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,608

    Rusty O'Toole
    Member

    The idea is to control the forward/backward movement and twisting, while allowing the freedom to move up and down.

    http://tractionmaster.com/
     
  26. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    Understand it only controls movement not forces.
    If in the below drawings the rear of the spring was SHORTER , the axle would try to lift in relation to the rear spring eye.
    Add the lower traction device, [with a fixed length] and the rear half of the spring with the forward driving torque will try to "Pyramid" themselves [ probably aggravating the situation ]
    Having the stiffest end of the spring mounted on shackles doesn't help.

    [​IMG]

    In a normal situation with the shorter front spring ,the torque reaction tries to push the rear axle down and lift the front spring eye up [ similar to anti squat ]
    These traction devices work well on a normal leaf spring situation.
     
    Last edited: Aug 5, 2015
  27. rockfish
    Joined: Apr 11, 2001
    Posts: 445

    rockfish
    Member

    Like others before him have also said. This is the right way to go. No band-aid fix and no searching for other used spring packs that may or may not work.
     
  28. indyjps
    Joined: Feb 21, 2007
    Posts: 4,515

    indyjps
    Member

    The spring mounts need to be moved. Making a new spring with long front and short rear will not solve it
    Relocated spring mounts and springs with at least equal length front and rear sections will be an improvement-these can be new or from a donor vehicle.
     

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