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Dan Woods opposed coil front suspension

Discussion in 'The Hokey Ass Message Board' started by hemisteve, Jun 17, 2009.

  1. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    It was I who mentioned hydraulics. What you say will work: we have the entire outside diameter of the current springs available for a hydraulic cylinder. Despite the tiny travel it has enough piston area to displace a decent amount of fluid, so damping valves can work simply plumbed between the primary and secondary cylinders. The secondary cylinders act directly on coil springs of whatever configuration one wants, mounted wherever one wants, without the need for separate dampers.

    The only concern I have here is with the durability of the hydraulic seals. My first idea was merely to use a large hydraulic cylinder connected to damping valves and a reservoir in lieu of dampers. That way the weight of the front end is not supported on hydraulic pressure. As the seals wear the damping action will deteriorate as it does with conventional dampers, but the front end won't begin to sag or anything.

    Your way one can run bigger hydraulic cylinders and get greater fluid displacements, so within the limitations of seal life it can work very well indeed.
  2. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    Hey, the theoretical speculation is the interesting stuff :D
  3. DrJ
    Joined: Mar 3, 2001
    Posts: 9,422


    I heard, back when these were first on the road from a guy who owned/drove one, that if the bungs that go into the springs aren't long enough or the spring isn't fastened to them at both ends that the springs could fall out if you pop a wheelie and the bellcranks pull out the bungs, or just get air on a dip.
    So design accordingly...
  4. Yeah but from the outside looking in (with my "zero" knowledge of the fundamentals involved) this is going wayyyyyyy over my head.

    There's so much in my brain vault that stuff is starting to fall out.

    As is relates to this subject, I just want the straight up answers....can't handle the why's and what if's. :)
  5. firehazard55
    Joined: Sep 17, 2009
    Posts: 6


    At the risk of being attacked for being the new guy to the thread I'd like to offer an idea. Seems like you could make a hydraulic cylinder of a sort with a valve stem on each side of the piston on the body and charge both sides of the "shock" with nitrogen. Then you could dial it in depending on how much you charge either side of it. Just a thought, I'm not an engineer but it's just a thought....
  6. CoolHand
    Joined: Aug 31, 2007
    Posts: 1,918

    Alliance Vendor

    That'd be fine as a spring. That's pretty much how gas springs are made, they just have different seals so they don't seep over time, like a gas filled hydraulic cylinder would.

    But that wouldn't really do much for damping, because air or nitrogen aren't real viscous.

    You'd have to have another parallel system to damp the movement of the suspension.

    Other than that, the idea is certainly serviceable.
  7. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    I've only recently found this thread so this may be a little out of date.

    I built this chassis for Gerry and it's somewhere in the region of the 8th or 9th
    T bucket opposed coil chassis i've built, albeit a lot cleaner than Dan's original design.
    It also has an opposed coil independent rearend.

    I pioneered 'correct' model T & model A hot rod chassis', bodies and related components in England during the mid '60s into the '70s. Prior to this there was very little if anything at all being built here which was even close to contemporary American
    hot rods, nobody here seemed to have the right idea about them back then.
    Over the years I've manufactured various early Ford chassis, T bodies
    (8 types), A bodies (3 types), Tube axles, radiators, suspension components, wheels pick up beds, gas tanks etc. All before anybody else here got on the bandwagon.
    I've known Dan Woods as a friend since just after he came back from Vietnam (1969 ?), to date, over 40 years. Through Dan, back in the early 70s, I got to know many of his contemporaries as friends including Lil' John Buttera, Art Chrisman, Steve Davis, many of the original team from Roth studio's and even Ed Roth himself and many others. Some of these guys were and are genius' and to say much of their thinking rubbed off on me would be an understatement.
    For Boyd Coddington in 1982, I came up with the original '34 roadster concept which was eventually developed into the Boydster style. I designed almost the entire new wheel range for Boyd when he started up the wheel business again in 1998. Also, designed the Led Zephyr, and the whole (build almost the entire car from aluminum), concept for the Aluma Truck, and the Aluma Tub, which was the natural progression of the same concept. Plus many other suspension components including the 'banana' front uprights, aluminum dropped axles and related components, which Boyd used on his later chassis
    In the past decade I developed, produced and marketed the 'New' Stromberg 97 carburetors (which are far superior to the originals), with my partner in the company. Nobody in the US could believe we did that in England !
    I guess that's a pretty good CV and should go some way to show I know what I'm about with hot rod design and construction, particularly T Buckets.
    First and foremost I'm an artist, fabricator and engineer. I'll at least do sketches or renderings to get a feel for a project, with pen and ink drawings where necessary for overall layout and machining detail, or else i'll use CAD/Solidworks. Very little is guesswork although at times I can be left scratching my head over some problem or other.

    This thread started as a question about who still builds opposed coil frontends and ended with discussions about springs, needle rollers, friction shocks, and Dan Woods' original Milk Truck front suspension.
    Here's my two cent's worth in no particular order....

    Dan built the Milk Truck around the age of 16 to 18 in his home garage as a show car, not a street driver. I doubt he was a chassis genius back then so suspension design and geometry probably didn't come into it. The single coil spring at the front just looked cool and that was enough. It led to Dan getting a job at Roth studio's until he was drafted so, I guess, it did the trick. The single vertical coil has no roll stiffness at all. It would work ok in a straight line but, as somebody said here, would act like a three wheeler in corners - so no good for the street.
    Also, Dan's never worked in south Florida. Since the early eighties he's been in Salinas, Cal. working in and around Carmel/Big Sur building multi million dollar houses.

    Do horizontal coils work ?
    Of course, will work at any angle. However, in a system like this using unequal length bell cranks, the spring rate would need to be calculated on the basis of wheel loading x motion ratio x bell crank ratio - which, on this front end is 2 to 1 (6" x 3" bellcrank arms), for example : If the front wheel loading was say, 272 lb, this would be multiplied by the motion ratio - lets say a loading of 439 lb at the bell crank axle locator, this would then be multiplied by 2 (bell crank ratio), to give a figure of 878 lb/inch for the spring rate. The springs can be wound either stiffer/shorter or softer/longer to retain correct frame height & depending on the ride required but they must remain under compression throughout the suspension travel - same as any other suspension type. Frame ride height adjustment is by adjustable clevises on the spring cones - approx' 1" at the cone, 2" at the end of the bellcrank long arm.
    Actual spring calculation is a little more complicated so this is the simple version.
    As it happens, because the rear end was a little more complicated to figure I had the spring rates for this car calculated at McLaren's F1 racing in Woking, Surrey, who also build the Mclaren F1 road car. So I'll add - nobody there saw anything wrong with this suspension at all, even the friction shocks, despite the sophisticated systems they deal with on a daily basis.

    There's also some questions here about whether friction shocks work:
    Almost all the T bucket chassis i've built have been fitted with friction shocks whatever spring medium is used, transverse leaf, torsion bar or opposed coil, because they can be hidden or combined with another component - Torsion bar arms. Dan Woods designed his opposed coil setup with friction shocks simply because they work & are invisible - they're part of the bell crank, I do the same for the same reason. I have no idea what friction material Dan used but I use Nylatron, a tough, graphite impregnated Nylon used in engineering and it works fine.
    I recently spoke with Jim Capon, the owner of another opposed coil suspended T
    I built around 34 years ago (he's driven that car 140 mph), he said the front suspension works great, with the occasional tweak of the friction shock compression cone.
    Any and all other ideas for alternative shocks are a no go really because, shocks can't fit inside the front springs without having larger dia. springs and gas shocks,pipes and parephernalia. There's no way of running a torsion shaft through the bell crank pivot back to behind the radiator with yet more bell cranks, it's an engineering nightmare with little space through the frame rail or between the engine and radiator. The thought of using small 1" dia. shocks immediately rings alarm bells with me because they will simply not be able to deal with the energy absorbed as heat. They're too small.
    The one and only disadvantage with friction shocks is they work on a 50%/ 50% ratio which means they damp the same amount in bump as in rebound, whereas tube shocks usually have less damping in bump than rebound. But it's no big deal, friction shocks work, otherwise I wouldn't fit them.
    At the end of the day it's all down to what somebody wants, a really clean, sharp setup with a bit of maintenance here and there, or a maintenance free, clunky looking setup. It's all about compromise.

    The use of roller bearings in the bell cranks:
    All of the opposed coil assemblies i've built prior to this used bronze bushes and they work great. However, for this one I felt I'd use something a little more sophisticated as it should cut down some mechanical friction and perhaps give a better ride.
    So I decided to use the same type bearing as used in Jag' rear end lower control arms, and similar to those in driveshaft UJs. Not the type used for high speed shafts which are needle rollers but the type used for reciprocating motion - back and forth. Same type of movement, same type of bearings - Seems quite logical thinking to me ! There are no greasers fitted, but they could be. However, I figured these bearings would run for many thousands of miles simply packed with grease, which would be replaced/repacked, I hope, during routine maintenance.

    Using the bell crank arm as a Panhard rod:
    That's exactly what I did here. Not entirely sure which way it was done but I think the LH arm fits into the circular hole in the axle locator, the RH has a slot to allow shortening through the arc. The whole point throughout was to keep the front end as minimal visually as possible, so this was the compromise. The downside to this layout is, it will produce some lateral frame movement on uneven sufaces because of shortening through the bellcrack arc - similar to that experienced with shackles on a transverse leaf spring (or Woods' original opposed coil setup which used rod ends as shackles), & without the use of a panhard rod. On smooth tarmac it shouldn't pose too much of a problem.
    Far from this setup being not thought through, as somebody previously mentioned here, a great deal of thought (involving chassis dynamics theory, geometry, engineering & aesthetics), went into every part of this chassis and while certain aspects of the geometry may not be 100% in the opinion of some, at the end of the day it's a T bucket hot rod which needs to look great & be safe first and foremost, and secondly, drive in reasonable comfort on the occasions it'll be taken out when it isn't raining here. It isn't a family car where expectations are somewhat different.
    I'll say again: This chassis, as with every other vehicle chassis on the road today of whatever type is a compromise between, aesthetics, engineering & safety, comfort, ease of use, and even time & financial budget - both of which are never enough to do things as we would all wish to do.
    I found Dan's original rear mounting position of the lower centre link (under the front crossmember), left something to be desired as - on cars with front brakes: The braking torque wanted to turn the whole front end over itself with the lower axle mounting lowering it's position and attempting to overcome forward weight transfer, lift the front crossmember upwards, thereby unloading the springs. I found it best to mount the lower link as close as possible to the bottom of the front axle tube and extend the link as far back as possible behind the radiator. This would cut down on caster change and bump steer during suspension movement and provide less lever action of the lower link to lift the front crossmember during braking.
    I think this lower link could be even longer and would probably work best as an apex (Y), locator with the rear mounts located somewhere under the motor mounts. This would also provide lateral location of the front axle while doing away with the bellcrank lateral location system.

    After all this discussion about the above which really are no more than picky details which obviously have already been thought through prior to or during the chassis build. I can't fail to notice some things in later pics of Gerry's car - alterations to the rear chassis which have been made, which I would say are far more serious than the previous discussions.
    I'll attempt to explain here:

    The only instructions I had when I could be finally persuaded to agree to build this T was, A tall top T bucket like Leg Show with an opposed Coil front end and no rear radius arms - and it would be Candy Red.
    The whole design of the car was down to me and I had kicked the idea of an opposed coil independent rearend around for quite some time beforehand.
    I wanted to do the chassis with as few fastenings showing as possible, in particular the front end would be as minimal as I could make it- even less so than on my own T chassis.
    The rear end without radius arms posed quite a few problems because it meant the lower control arms would have to be solid units of the type used on Jag's to keep the wheels in the correct place and control torque reaction. I opted for the tapered paddle design I used simply because it was the strongest (an internally braced tapered box), and the cleanest, when assembled with the tapered rear uprights - which are a continuation of the same taper as the paddles but angled upwards to the hub carrier. Everything tapered and with as few obvious fastenings showing as possible.
    When the rearend is mounted without radius arms like this, all power and braking loads are transfered though the differential and rear crossmember into the kickup and into the main frame rails. So the whole assembly needs to be extremely strong to resist vertical, horizontal and axial torque loadings, plus bending and twisting loads in the rear crossmember and kickup. Normally with a Jag' rearend in a hot rod this is handled by radius arms which transfer power and braking loads through the vehicle thrust line directly into the chassis. Torque loads are normally handled by small dia. strut rods, which I almost always attach to the main rails rather than the kickup.
    With this chassis, as I intended to mount the diff' behind the rear crossmember requiring a cantilevered & sculptured mounting, I felt it needed a system which integrated the whole assembly of main rails, kickup, rear crossmember and differential into one unit.
    I already intended, and made, a small bellypan to cover the bottom of the body just to keep things clean under there, and in order to transmit rear end loadings directly into the main rails I extended the control arm lower diff' mounting forward on the thrust line with two tubes which picked up the chassis inner crossmembers by way of tabs just outside the bellypan - all that could be seen were these two tubes and the driveshaft passing through the 'pan.
    The whole point of this was to transmit loads directly in a straight line between the differential housing and frame rails which in turn located the whole rear assembly horizontally, vertically and axially without relying on the cantilevered crossmember to do a job it's not designed to do.

    However, i've noticed this whole lower diff' locator has now been removed and in it's place are the normal bolted-in small strut rods angled upwards and outwards to maybe 2/3rds the height of the kickup.
    This has now seriously compromised the integrity of the whole rear frame/rearend assembly to the point where I wouldn't be surprised if fatigue doesn't begin to take it's toll at either, the cantilevered part of the rear crossmember mount where it's welded to the sculptured tube or, more likely, at the base of the kickup where it's welded to the main rails - two rectangular section butt welds !
    It doesn't take much to imagine the tortuous route the power and braking loads now have to take through a series of 90 and 45 degree bends to be fed into the chassis, whereas the original design fed these loads directly into the main rails in a straight line with very little torque loadings being fed into the crossmember at all. The small strut rods now fitted only feed loads into the kickup, not the main rails and, being bolted in with no triangulation serve little purpose whatsoever to keep that rearend aligned.
    Last edited: Jul 13, 2012
  8. nrgwizard
    Joined: Aug 18, 2006
    Posts: 1,184

    from Minn. uSA

    Hey, EE-1;

    Thanks for the thoughts 'n' info. :) .

    As I rather like this suspension.

  9. One Finger John
    Joined: Mar 18, 2009
    Posts: 459

    One Finger John

    EE-1, have you contacted Gerry and conveyed your thoughts and feelings to him? Or is he already aware of the situation and has his own reasons for the departure from the original design?

  10. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    Well John, as it happens, no I haven't contacted Gerry about this. I built this chassis about 16 years ago now and as far as I'm aware Gerry has only been working to get it finished in the past few years and has some ways to go yet - so no real hurry. I guess he wanted to put his stamp on it by changing it around, who knows ? People do stuff - never mind the physics and dynamics ! I only realised a while ago the changes had been made.
    As soon as I figure how to add images I'll do so.
    Ed Wimble.
  11. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    Read my earlier post here Gerry regarding roller bearings and restricted movement...same as Jag rearend lower control arm bearings, roller bearings with restricted movement - worked on far heavier Jaguars for years, and still do ! I've never come across one of these bearings in a Jag' rearend which is actually worn out, and I have worked on a few.
    Also, plastic bushes will be far worse than brass or bronze for the bellcranks, which Woods & I have used a number of times before. Dan always felt these could be improved, I found they actually worked ok as long as they held grease, same as a kingpin bush in fact.
  12. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    Ed, it sounds like you feel the way I do when I have to explain to a building contractor that it was not from boredom that I spent sixteen hours working out that detail section, that a lot of head-scratching about a lot of issues went into it, and that he isn't going to reinvent it in twenty minutes on the back of a fag packet and expect the rest of the building to work out as intended!

    Good to know about the Jag bearings. The '31's design is bell cranks all over the place, and I can't help dreaming some into the Morris too. They'll probably be brass/bronze-bushed with provision for greasing.
  13. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    Yep, happens all the time. People come to me initially as I know these things inside out, have a fertile imagination, and they don't. Once they've had time to check it out and think about things, they become the experts and I'm the idiot cos' I should've done things this way or that.
    It beats me as to why , 1. people have to fix things that aren't broke, even before they use it and, 2. like to say how they improved what I did....when I take a look, they've cut out some perfect hand shaped TIG welded pieces which I spent hours making, usually for free, and replaced them with a bit of old box section and some scabby MIG welds, ha ha.
    Like I say, it happens all the time - what I call OPE's - other people's ego's.
  14. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    I did contact Gerry a couple months ago regarding his mods to the original rearend design and explained my concerns. He replied saying he was putting a lower locator back but not to the original design.
    However, my question now is: If he intended putting a lower locator back in there, why has he already fitted the small bolt-in torque control strut rods as the lower diff' locator renders them completely obsolete.
    I suspect, as most rods running an independent rearend use these strut rods, Gerry maybe thought they would be enough to hold the rearend in place without giving any thought to the structural design of the rearend, crossmember & kickup as a complete unit.
    I'm curious to know where he's now going to fit the forward mount of this 'intended' lower locator as the original tube crossmember location is now missing & not been replaced.
  15. FunnyCar65
    Joined: Mar 11, 2007
    Posts: 2,069

    from Colorado

    Bringing this one back up,is anyone making components for this style setup?
  16. A Boner
    Joined: Dec 25, 2004
    Posts: 5,659

    A Boner

    After reading all of this, I couldn't help but think about torsion bars. Unless the coil springs are part of he desired look, I would think that a torsion bar set up would be smaller, and more easily hidden and thus have a more simple look.

    Dan Woods stuff was always slick, and very interesting. Wish he would get back into hot rodding!
  17. japar
    Joined: Jun 30, 2007
    Posts: 266

    from Seekonk Ma

    There is a nice write up on the Milk Truck in Hot Rod Delux nov 09

    Attached Files:

  18. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    Problem is, while it takes care of springing you'd still need damping, which takes you back to square one as regards the quest for visual simplicity.
  19. Maybe the solution for "traditional" rods is a cheaper, simpler version of the Sachs rotary vane damper used on F1 cars. It's already designed to work on the link end of a torsion bar. (SORRY for the big photo).


    Seems like, with a little development, a simple Gerotor oil pump could be adapted to serve as a rotary shock that could be "concealed" as an old style friction shock.

    Somebody run with it and solve this problem once and forever!
  20. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    Hmmm. A typical 4-5-tooth gerotor has 225° of input rotation between minimum and maximum chamber volume. A set-up that has torsion bars with short arms to a solid axle might rotate the arms 75° over the entire suspension travel - which is an extreme amount compared to torsion-bar ifs. So, even when rock-crawling one would never use more than a third of the available pumping cycle. In everyday use one would be using perhaps an eighth. This might not be an issue, as the displacement is quite linear.

    I suspect that one would need quite a large-capacity pump, though, to generate enough displacement in the 30°-odd rotation one would be using most of the time for the valving to be able to do its job.

    Something like a long-lead roller screw springs to mind, to convert the radial motion to axial. I don't find anything with enough lead ready off the shelf, though.
    Last edited: Dec 26, 2012
  21. How about putting the outer pump housing inside a concentric planetary shell, kind of like a steering quickener with the pump mounted concentric to the shafts? Then you'd have (in effect) a 2:1 overdrive on the angle generated by the bar arm.
  22. chaz75
    Joined: Dec 3, 2008
    Posts: 14

    from Mesa, AZ

    ok this is still an unanswered question, is anyone currently building a frontend like this for sale or perhaps parts or a kit to do this, I really like this look and I am really curious to have this answered. Chaz
  23. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    Well, there's always the "Houdaille" rotary vane shock (stock Ford equipment for many years from the 30s), or the Armstrong lever arm shock used for almost as long - both very simple and efficient designs. Trouble is, it's more parts & clutter to be fitted, negating the whole point of the visually simple opposed coil T bucket front end.....All this discussion about shock absorbers and some other design elements discussed in this thread have been gone over and over again many times since the mid 60s, It's all been absolutely wrung to death. - Perhaps many on here haven't been into hot rods long enough to know that. - Friction shocks work, so do Jag' type roller bearings in applications where restricted movement occurs and are more than adequate for a lightweight T bucket. On the other hand, Bronze bushes are able to withstand much higher loadings than engineering plastic in applications such as: king pin bushes, bell crank fulcrums etc. - particularly in situations where the plastics are machined with thin wall sections. The plastic is more likely to be squeezed out of the bore than deal adequately with the high loadings. No more than common sense and a bit of research is necessary here to figure any of this out. Need I say, "not exactly rocket science ! "
    Last edited: Jan 24, 2015
  24. EE-1
    Joined: Oct 3, 2009
    Posts: 34

    from London

    I've built a number of T buckets with torsion bars also, both longitudinal and transverse types - my own T uses transverse bars - visually much simpler than the opposed coil. However, people who want to use the opposed coil setup do so because they like the look of the horizontal springs. In all situations on a T bucket where levers are used as part of the suspension system, particularly the front end, I'll incorporate friction material between the lever fulcrum and the frame/clamp plates simply because it works very well and cannot be seen.
  25. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,255

    Rusty O'Toole

    How about Rotoflo shocks? Compact and simple, no fluid or valves, they work by squishing soft rubber around. Could be the answer.
  26. Martin Harris
    Joined: Aug 3, 2014
    Posts: 318

    Martin Harris

    Thanks for your detailed write-ups on this subject Eddie. Always been a fan of your Ts as well as Dans, but was unaware of the connection until I caught up with this thread.
    Good to have input on the opposed coil subject from an expert.
  27. Citroen 2CV suspension arms use a neat big diameter bearing;

  28. GAB-KC
    Joined: May 1, 2008
    Posts: 46


    Just a little idea for some homebrew hydraulic shocks for the Dan Woods type front end. Pretty basic and easy to make. DOM tube for a smooth interior and a drill rod shaft with aluminum piston. Number and size of holes in piston would be the experimental elements.
  29. rfraze
    Joined: May 23, 2012
    Posts: 2,003


    Thanks for one of the most interesting and informative threads.
  30. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,040

    Ned Ludd

    How do you deal with the rod volume displacement?

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