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Technical School is in, Chev parallel front end setup

Discussion in 'The Hokey Ass Message Board' started by Reidy, Jun 6, 2020.

  1. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    I am after some direction on parallel leaf spring front ends. I have read as much as I can find on HAMB, but there is a lifetimes worth of reading I may have missed something. A lot of the posts appear to veer off to the ford Transverse spring setup or suggest the original poster go and read up on the subject.

    Also thanks to all that helped me out on my last question. It helped me to come to the conclusion to go with the original design but do whatever I can to make it as good as it can be.

    I am happy to read up, but I have not seen any reference material suggested and most I can find locally seems to cover the ford setup.

    Essentially the short version of my question is, what would you do to make a 40’s/50’s parallel leaf front end in a chev pickup as good as it can be for a daily driver. Please don’t state the obvious such as ensure all parts are in good condition like new. Please don't mention IFS or transverse setups. They can have their own discussion. Let’s assume we have a bare chassis and a bare I beam and we want to lower the thing by about 4 inches from stock.

    I will list all of the questions that come to mind that hopefully will get covered.

    1. Are wider or longer leaf springs an advantage?

    2. Is there a ratio that the fixed end (back) should be higher or lower than the shackle end?

    3. Are longer shackles mounted higher an advantage?

    4. Is it better to try and lower more by flatter springs and changed mounting points or dropping an axle?

    5. Is there a point where too much drop of an axle, excluding scrub line becomes a negative due to spring wind up on braking?

    6. Are sway bars a plus for this setup?

    7. Is there an ideal angle for shocks?

    8. Chev is side steer as I understand, do I stick with side steer or go cross steer?

    9. Have camber and caster angles changed with the changes in tires over the years?

    10. All of the other things that I have not even thought about?

    I have decided to go parallel I beam front and since I am building from the ground up I may as well get this as good as I can.

    Please educate me or point me in a direction that I can get educated.

    Thanks all

    Steve from down under.
     
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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    This is the most important thing, I'm glad you understand it.

    This might depend on what parts or services are available, or what you can do at home. They all work, and a combination might be the way to go, so no one change is too drastic.

    Side steer works, although you will have to watch out for bump steer when you lower. Make sure you understand what causes it with the steering method you choose.
     
  3. That's a lot of questions. Can you tell us more about the project?
    What axle and springs are you using? What is the weight of the truck?
    There are lots of variables, hard to make a blanket statement that covers everything.
     
    trollst likes this.
  4. I would suggest a pair of Posies super slider springs and the Bilstein shocks they offer as well.
     

  5. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    I don't drive my '37 Chevrolet pickup everyday, but could be with no problems. I have new springs that were custom made for the weight of the truck so it rides nice, a '41 Chevy steering box with all NOS internal parts so it steers nice and tight, disk brakes on the straight axle, and new tires. It drives as easy as my '03 Toyota and rides about as good. I have a sway bar installed on the front to control body lean. The steering ratio's of the older cars and trucks is pretty quick, so higher speed driving requires a steady hand and no sudden moves. Variable ratio gear boxes took care of this in later years.
    I used tube shock mounted straight up and down, then found they were stiff, by angling them forward 20 degrees, the ride was softer and more predictable.
    Caster angle will need to be checked after the car or truck is road worthy, mine needed 4 degrees with the way it's setting in the photo you see.
    My new spring set just slightly curved up, you could almost call them flat. It will bottom out when hitting speed bumps to fast, that will always be a problem when the springs mount under the frame rails.
     
    Elcohaulic likes this.
  6. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    To answer the question of what I am building the starting point is the truck in my picture. For additional information please go to https://www.jalopyjournal.com/forum...ruck-42-chev-long-read.1195381/#post-13606588

    But in saying that I want to learn how to make a parallel front end work really well.

    For this to make sense I should outline what I would like to achieve. I am after a truck that will fit in a standard garage that is reliable and functional. Its main use will be swap meets and hardware/parts pickup. Likely maximum distance away from home will be 120 miles with this truck not expected to exceed 65 miles an hour due to our heavy road policing. I am keeping it low thrills bench seat, basic paint and such. Something to be proud of but if it gets a knock I will be disappointed but not devastated. I will aim for a max load carring of around ¾ ton.

    To achieve this I have sourced a 1942 ¾ ton Chev chassis. I will put the tinware on this chassis. The truck will have a timber flatbead tray made out of Australian narrow leaf Ironbark. The running gear will consist of a full pressure Chev 261 (already purchased and hopefully a good block. Manual gearbox, most likely T5 and rear end will be parallel springs with diff to suit. At this point it will be Mazda BT50 as they are the right width and have a Chev 6 bolt stud pattern.

    The front I beam is yet to be finalised. My truck has wide fenders, about 76” across. The original I beam has large stub axles and is very heavy duty. I am looking at either a Chev, Dodge or International beam that will be easiest to adapt. I have a few in mind. All of these are available at around 54” king pin center to center.

    Tires will be a 265-70/16 SUV style to fill up the fender openings. To get this back to a ride height of about 8’” under the running boards I need about a four inch drop.

    Steve from down under
     
  7. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    Joe, you have a very nice truck. It looks like I could learn a lot from what you have acheived.

    Steve from down under
     
  8. Dropped axles are great for lowering, but also can increase spring wrap under braking.
    Personally, I would consider running smaller tires and changing the wheel openings if you want it low.

    My F-1 pu runs the stock front axle, not dropped, with the front springs de-arched and a couple leafs removed. It rides pretty good for what it is....

    DSCN0088.JPG
     
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  9. goldmountain
    Joined: Jun 12, 2016
    Posts: 4,442

    goldmountain

    I would be concerned with getting good spring shackles and bushings since a lot of those old trucks missed some intervals with the grease gun.

    Sent from my SM-T350 using The H.A.M.B. mobile app
     
  10. ...here's how I did the cross-steer in my 37 Chevy,...Saginaw 525 manual steering,(65 Malibu) 37 @ byron high.jpg homemade frame mount, all Speedway steering rod, tie rod and steering arms, new kingpins, blocks between axle/springs for the gasser-like stance I wanted, worked great, could steer with 2 fingers, no bump-steer, rode pretty decent with all orig spring pack...
    37 coupe build 217.jpg 37 coupe build 218.jpg
     
  11. Gary Addcox
    Joined: Aug 28, 2009
    Posts: 2,528

    Gary Addcox
    ALLIANCE MEMBER

    Personally, I would convert to cross-steering and be done with it. Your truck, in my humble opinion, should use the next step up from the Vega (maybe GM 525) or even one step up just to overkill it a bit. Overkill isn't a bad thing. With cross-steering, the box in mounted well ahead of motor mounts and headers and connected with DD stock and perhaps one or two Borgeson u-joints. This is one place you NEVER want to save a few bucks. Side-steering often introduces bump-steer if not carefully designed with same length drag link to rear attachment perch and parallel lines, etc. Cross-steering is so much better. Henry Ford began using cross-steering in his Model Ts through 1927, then returned to it in 1935, so go figure. Good luck with your build.
     
  12. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    Thanks so far. This is what I am after. I would like to achieve two tings from this thread. The first is to gain knowledge and the second is if someone does a search they can learn about parallel leaf front ends.

    Is bump steer completely eliminated or just improved with cross steer? Are longer leaves an advantage when going this way?

    Rusty1, I would be interested in a photo of your front spring mounts. Also is there a reason for the shackles to be at the back? My truck had the shackles at the front.

    Steve from down under
     
  13. Just for reference purposes of some readers, the GM 525 box is commonly known as the Holden HQ - HX box in Australia.
     
  14. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    Thanks X38, that makes it a lot easier to find, maybe. I am not sure what is going on but I live near Ipswich, and in the last few years most of the wreckers have shut up shop. I assume all the cars went to scrap.

    Steve
     
  15. They are available.
    On ebay
    [​IMG]

    Gumtree
    [​IMG]
     
  16. Phil1934
    Joined: Jun 24, 2001
    Posts: 2,716

    Phil1934
    Member

    If back is fixed then axle must move forward when you hit a bump, a little harsher. With shackle in back axle will move back as it hits a bump.
     
  17. indyjps
    Joined: Feb 21, 2007
    Posts: 5,377

    indyjps
    Member

    Im asking questions instead of providing answers. I've wondered about leaf spring suspensions - Chassis / spring layout is defined by other vehicle systems - if it werent - are there optimal methods.

    Any benefit to having the spring eyes in the same plane, would having the front or rear higher offer any benefit? EX: rear spring eye mounted higher, does this change the ride?

    Does front axle placement on the spring make a difference. Should it be centered or is there a benefit to having more leaf length in front or behind the axle? EX: axle biased toward the front of the spring, does this improve ride?
     
  18. ...37 Chev passenger cars in the US had the shackles at the rear,and the axle is pretty much centered on those springs front to rear.......here's a shot showing that the steering & tierod were pretty parallel...and some front spring pics, (factory cast.)
    37 coupe build 190.jpg 37 coupe build 187.jpg 37 coupe build 140.jpg
     
  19. Phil1934
    Joined: Jun 24, 2001
    Posts: 2,716

    Phil1934
    Member

    You can see the front spring end is higher which helps anti dive when braking.
     
  20. Longer springs will ride better than shorter, all else being the same. I agree that rear shackle is a little better for ride, since as the spring compresses and gets flatter, the axle will move a bit rearward to make it absorb some of the bump, vs pushing the axle into the bump as happens with front shackle.
    Removing some of the short leafs can soften the ride, at the expense of ultimate load carrying and reduced spring rate. Cross steer does not eliminate bump steer, but it makes it much less and easier to build since it allows more freedom for steering box placement (really pitman arm end where it connects to the drag link). A newer style box like suggested will steer better than the original box, with less effort. Convert to cross steer and a newer box and gain both benefits. Shock angle effects the shock ability to function. Straight up is 100% effect, and as the angle increases the shock effectiveness changes per the cosine (cos) of the angle. At 30 degrees off vertical the shock is about 87% effective vs straight vertical.
    Sway bars (really anti-roll bars) help with all suspension designs including parallel leafs, for controlling body roll in turns. I try to put sway bars on both front and rear if I can on my builds.
     
  21. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    With cross steer, it is best to have a panhard bar that is the same length and parallel to the drag link.
    This forces the axle to move in the same arc as the drag link.

    By parallel, I mean it can be further forward or behind, higher or lower , or to the left or right. Just try and get the Angle and length identical to the drag link.

    Being in Aussie [the land of 4x4's] if you want to keep it side steer, then use an early 80's Toyota Hilux 4x4 power steering box.
    There is 2 types of Hilux boxes. One for independent front suspension. And one for a Diff/ Live Axle front suspension.
    It is the Diff Live Axle type box you need. [they are side steer]

    here is a Toyota box [as an example]
    Capture2.PNG

    Edit: With a side steer, You can never 100% eliminate mechanical bump steer because the pitman arm arcs on a vertical plane and the steering arm arcs on a horizontal plane [so they compromise by eliminating bump steer in the straight ahead position]
     
    Last edited: Jun 8, 2020
  22. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    To make sure I am on the right track this is how I read it so far.
    1. Don't drop the axle to far as it will cause spring wind up on braking.
    2. Go for a cross steer setup.
    3. Go for a longer spring if possible.
    4. Sway bars are good.
    5. Keep shocks reasonably upright.
    5. Put the shackles at the back.
    On thing I have not got my head around yet and I would like more info if possible is front/rear spring eye height and dive. If I have read this correctly the front should be lower than the back and the back should be higher than the stub axle. I am guessing this is harder to achieve with flatter springs.

    My other question is that my truck setup at present does not have the springs truly parallel. The front is narrower then the back. Is a panhard bar as essential compared to true parallel springs?

    Thanks

    Steve from down under
     
  23. ...with parallel springs, under normal driving, I don't think you'd need a panhard bar...just my 2 cents..
     
    kevinrevin likes this.
  24. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    A general statement that could be potentially misleading.

    With side steer and parallel springs.........NO! [you are correct]
    With cross steer and parallel springs.........YES!

    With cross steer the purpose of a panhard bar is not to prevent side movement BUT to force the axle to move in a similar arc to the drag link [cancelling any mechanical bump steer]

    Normal driving would benefit from a panhard bar more than driving on off road surfaces [where the surface constantly requires steering input]
     
  25. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    A lot of info, a lot of miss info and some good suggestions.
    The 37 3/4 ton should have six lug brakes but they are Huck brakes that may not stop the best.

    You can find a lot of info on the 37 trucks here including the specs on the springs.
    https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1942-Chevrolet-Truck.pdf
    If that doesn't work click on this https://www.gmheritagecenter.com/ Click on Archives, click on vehicle information kits and when the next page opens click on 1937 Chevrolet truck.
    Page 33 shows a side shot of a 3/4 ton. No running board height though.

    I'll PM you a link to a page on another board that details how a guy in South Africa put Toyota front brakes on his mid 50's Chevy truck designing and fabbing the caliper brackets. The Moderators may consider it off topic for this board though.
    For what you are doing for engine I don't see a reason to change springs to wider springs. 1/2 ton springs in place of the 3/4 ton springs might lower it a bit and soften the ride a bit. Spring rates are in the GM herritage pfd. I wouldn't pull a bunch of leaves out though as the springs just keep on sagging then and my truck is a prime example of that. What was supposed to be a quick and nasty lowering job to go to two events and then tear the truck down ended up being used for 15 years and over 100K miles.
     
  26. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    This depends on the set-up and is generally only true with trailers that have straight frame rails and deep arch springs.

    Most modern[ish] cars have a "Z" or kick up in the front rails , so if doing a gasser type straight axle it is more correct geometry to have the shackles at the front.
    A spring will lengthen along the "Datum line" [shown in this drawing with sliders instead of shackles]
    By having the axle mounted closer towards the fixed pivot will minimalize the wheelbase change.

    By mounting the spring at an angle [upwards at the shackle end] causes the arc of the axle movement to cancel out the spring lengthening [this lengthening happens after the axle due to shape]
    upload_2020-6-10_18-40-9.png
    Here is a leaf spring set up in a normal kick up frame.
    upload_2020-6-10_19-28-30.png
    The shackles can be at the front on a front axle and on the rear with a rear axle.
    With Vehicles without a kick up in the frame, it is common to use relatively low arch springs long hangers and shackles.
    If this is the case, The OP could have the shackles at either end [if he is careful with spring eye heights]

    One last thing, wheelbase shortening/lengthening due to suspension compression is more detrimental to the rear axle because the wheels are always perpendicular to the axle [roll steer]
    On a front end, the axle/Tie-rod/ Spindles simply parallelogram themselves and dont cause roll steer [as long as bump steer is sorted out]

    Here is a 1950 Chevy pickup power steering conversion [being advertised on the net] It is a recipe for disaster [with the spring and the drag link arcing opposite each other]
    upload_2020-6-10_19-42-6.png

    upload_2020-6-10_19-48-58.png
    If The OP's pickup requires an outboard mounted steering box [as above] I would suggest a Mitsubishi L200 /Pajero/RWD Sigma power steering box for a RHD vehicle.
    The sector shaft is on the RH side of the frame rail, and the steering shaft is on top of the frame rail
    The Pajero also has a telescopic steering shaft with universals at each end [it will bolt onto the L200/ Sigma box]

    here is a RHD Sigma power steering box
    upload_2020-6-10_20-0-27.png
     
    Last edited: Jun 10, 2020
  27. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    Mimilan

    Thanks for the detailed post. It has certainly got the grey matter working and I now now why the springs are setup on my Falcon ute the way they are. You not only know your stuff but can explain it.

    I can visulise how the flattening of the spring during compression causes the axle to move away from the fixed pivot. I can also see if a line was drawn horizontal from the fixed pivot and the axle was on or above this line any increase in axle height would cause the the axle to move closer to the pivot due to the arc of the line. For me this is a big light bulb moment. If we can get the decrease due to the arc to equal the increase due to the spring flattening our axle would move in a purely vertical motion.

    The 42 Chev chassis that I will be using is in the flat class of things. If I were to go cross steer would I be correct if I had a dropped fixed spring mount at the front that placed the spring somewhere around spindle height and mount the shackles up higher at the rear. To achieve this I would run the leaves outboard of the chassis rails. The 42 chassis is very narrow with a spring center of 26 3/4". If I use a later chev axle it has a spring center of 31 7/8" which means the springs would be outboard. It also has the total width that I need. By mounting the shackle pivots high at the back and using flatter springs I would achieve the total drop I need without utilising a dropped axle. This also helps with the spring windup problem of dropped axles.

    This appears to solve almost everything, except brake dive, I think, I am happy to be wrong on this one.

    Once I get the rest sorted I will be then looking at where the steering box will go, but the options look good.

    Steve from down under, or as some Kiwi's I work with refer to it as the West island.
     
  28. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    With Anti dive, you want the wheelbase to slightly lengthen during suspension compression.
    This is the opposite to the forces applied during braking [axle resistance vs chassis momentum]

    By mounting the hanger at the rear , the spring tries to act like a "pole vault" with the correct geometry.
    A rear shackle defeats this.
    Another factor is brake torque on the axle tries to turn the spring into a "reverse ladder bar" but the front 1/2 of the spring has the opposite effect.
    That is why you need the centre-pin of the spring offset closer to the rear. [with a rear hanger]

    Don't overthink too much about the axle drop. With a deep drop the compression loads from axle resistance vs chassis momentum tries to induce positive caster [twisting backwards to shorten the wheelbase]
    But the brake torque is also applied over a greater distance due to a greater drop, it will try to induce negative caster [twisting forward]
    These 2 forces try to cancel each other but brake torque is greater than compression/tension forces.
    It only increases the loads on the spring pad

    Use rear mounted hangers if possible, and cross steer.
    Mount the drag link so the steering box ball-joint [centre] is 25mm higher than the opposite end ball-joint. Being level is a myth.

    The reason is ,the drag link will always move in an arc. The first 25mm it arcs outwards, the next 25mm it arcs inwards and reverses itself back to zero .Then if there is another 25mm of travel it arc inwards a bit more than the original position.
    a 1200 mm long [48"] drag-link will only arc inwards 0.26 mm with 25 mm [1"] of travel.

    Another thing I haven't mentioned is increasing the springs further apart
    This increases roll stiffness without increasing suspension stiffness [a good thing] The only compromise would be limiting the steering lock.

    With those steering boxes I suggested, the Pajero box is taller than the Sigma box.

    edit: once you understand these principles.
    You'll see why single axle caravans and car trailers are the curse of our highways with sway [roll steer]
    And why trailers with tandem rocker equalizer suspension should have the brakes on the rear axle [if only 2 wheel braking]
     
    Last edited: Jun 10, 2020
  29. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    Here is a drawing from the 1937 engineering manual used to show the improvements for 1937 Chevrolets over the previous years. Explains why you could get bump steer or other problems.
     

    Attached Files:

    Mimilan and RMR&C like this.
  30. Reidy
    Joined: May 13, 2016
    Posts: 221

    Reidy
    Member

    Thanks for the diagram Joe. It is interesting that moving the box forward improved the situation.

    I have been processing all of the information, particularly the stuff from Mimilan.
    Is there an advantage to a panhard rod over a watts linkage in a cross steer setup?

    Steve from down under.
     

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