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How to build an early hotrod frame

Discussion in 'The Hokey Ass Message Board' started by brianangus, Dec 23, 2006.

  1. hey i have a question im going to to be starting to build my model a frame tomorrow and i am going to use stock dimensions with a 4 inch kick in the rear i plan on channelling the car will this be an issue?
  2. It shouldn't be, long as you are going fenderless. If you get hung up, call me---I'm just down the road from you, in Barrie.---Brian
  3. goetzcr
    Joined: Jul 21, 2010
    Posts: 123


    Would it be possible for you to move to Virginia. We welcome Canadiens with open arms.
    brEad likes this.
  4. Ask me again about the end of January, when there's three foot of snow here and colder than a witches tit!!! I might be pretty easy to convince then.---Brian
  5. It's even nicer down here in Georgia, Brian- hardly ANY snow (just an occasional tornado)... :)
    Joined: Aug 9, 2011
    Posts: 136

    from Nanaimo BC

    Fellow Canuck here Brian. I've read thru twice. Awesome info.
    JMHO but stay in Canada. Move to the west coast. No snow!! A bit of Rain instead.
    You can drive your iron every day of the year. No bugs, no salt on the roads.
    We've got room for ya'.
  7. Today I had a question out of Redlands, California :Hi.
    Mike McCurdy from Redlands, CA. You seem very knowledgeable on early Ford suspensions and I have a question. I have a Vintage Chassis Works forged dropped axle that needs to have the perch bosses and king pin bosses finish machined. I can get the dimensions of the perch and king pin but need to know how close to fit the finished inside diameter on the axle for the perch and king pin.----------------
    I would machine both the perch boss and the kingpin boss for a "precision sliding fit" which is basically what you would achieve with an "on size" reamer. The kingpin bosses should be 0.8125" diameter, +.0005 to .001", and I can't remember the perch diameter, but for it too the reamed hole should be .0005 to .001" oversize from the actual part diameter. These are not a press fit, but as the name implies, a sliding fit with no discernable "wobble". The kingpin is a straight thru bore. Some of the early perch bolts had a tapered shank, in which case the hole diameter is not as important as having the correct taper on the hole.---Brian--Nov-2011
  8. Boxcar's 1928
    Joined: Aug 30, 2011
    Posts: 474

    Boxcar's 1928

    another just in time thread for me! thanks
  9. h2omonkey
    Joined: Dec 8, 2008
    Posts: 165

    from vegas

    Thanks for the great thread, I've read thru it a few times over the past year to decide on what route to take with my build.I've always been more of a bolt on guy with cars,mainly playing with bikes but want to give building my on hot rod from a shot.I don't have a ton of money but I do have time, so I can always do something more than once if needed. So after doing my studying here,I have a questions on chassis/suspension setup for a newbie I haven't really seen addressed, what part of the set up should you tackle first, motor/tranny placement, front suspension, rear suspension?
    What I'll be working on is a 1950 jeep cj, I have 472 caddy motor, no tranny yet but will be something with a clutch, want to keep the body, front fenders and radiator support in factory position, nine inch out back, haven't decided on front yet but probably a suicide setup off the front of the frame. I know it's silly but hot wheels made a 42 cj car a few years back a lot like what I want to do if anyone has seen it.
    I was thinking getting the motor and tranny in position first was most important, then front suspension, then rear end and frame dialed in. Oh, and I plan on using the stock jeep frame, because it's in great shape and it's free so it will be something good to learn on. Thanks for reading my ramble and any info you might give.
    Last edited: Dec 14, 2011
  10. Emery asks the following:I read your post with great admiratiion and will be using this information building my t. As you said the front axle caster of about 6 degrees I have read else where that it should be 7 to 9 degrees not to question your knowledge. I have it at 7 degrees at this time and held in place with clamps so changing it is a simple matter. My next question is that when using the original radius arms where should the mounts be in relation to the frame? My frame is z'd in the front by 3 inches. Should my mount be 1.5 inches below the frame as you said in an earlier post or can it be were it falls on the frame? Mine ends up at about the middle of the frame from top to bottom. Your help is much appreciated.
    I always use 6 degrees, but that figure is somewhat "nominal" one degree either way isn't going to hurt things. As far as the location point for the rear of your front radius rods is concerned--
    That point (height-wise) is more or less "fixed" by the angle your front axle sets at and the built in angle beteween the radius rod and the axle boss it attaches to. In general, if you don't heat and cut/bend the radius rods near the axle, that imaginary point is going to be too close to the ground, making a rather stupidly long plate hanging below the frame of your car. It looks like hell, and is dangerous as well because it can hit speed bumps and other ostructions on the road. The way most people solve this issue is to set their front axle to the correct 6 degree caster, let the weight of the car down onto the front and rear wheels, and if the rear end of the radius rod is hanging too low, then use a sawzall to cut about 3/4 of the way through the radius rod from the underside right close to the axle, heat above the cut area to cherry red, and bend the tailing end up untill it sets about 1 1/2" below the frame of the car, let it cool, then weld up the cut. This way the axle caster is correct and you don't have a big goofy looking radius rod bracket hanging 9" below your frame. If yours falls about at the middle of the frame top to bottom, then you're fine. Drill an oversized hole thru the frame at that point, weld in a solid steel "bung" and tap it for the radius rod bolt.-----Brian
  11. mufasavnvmc
    Joined: May 14, 2011
    Posts: 11

    from Iowa

    Merry Chrismas and thanks for your explination of why. Not just an answer. I think that is why so many have read your post and found thier answer, as I have here. thanks to you again.
  12. Gremlinguy
    Joined: Oct 29, 2009
    Posts: 495


    Awesome thread Brian!!
  13. Ken--My tires are Coker Classics, purchased 7 or 8 years ago. They are Radials. They cost $1019.00 shipped to my door. (Cokers Canadian dealer is in Montreal._ Fronts are 165R15 and rears are P235/75 R15. They are absolutely great tires. Ride well, wear well, and look fantastic.
  14. Shockley---For a comfortable riding car, 4" clearance for rear axle travel is essential, and sometimes you are still going to bottom out. I wish now that I had C notched my rear frame 1" in addition to the 4" step. Of course, my suspension is fairly soft, but my car was built to be a daily driver, and I take great objection to having my guts shook about by a stiff suspension. Front axles should have at least 3 1/2", preferably 4" clearance where they exit under the frame rails.-----Brian
  15. Brian just wanted to say thanks for all the info. I am putting it to use as I am building a frame for a Model A coupe. I'll post some pictures when done.
  16. [​IMG]

    Uploaded with

    So then, what I'm getting from all this is that I should change the front mounts on the ladder bars on my old wasanaltered to be near the driveshaft. Going up on the saw- horses soon to be made into as good a street chassis as I can get without re-inventing the whole wheel. I've learned a lot here about "K" and "X" members.
    Hope I'm not hi-jacking here, thought the "show and tell" might stir some conversation. Thanks, Mike
  17. Mike---What you have there will work okay. Its not "ideal" but there will be enough chassis flex to make it somewhat forgiving, and with the Panhard bar you shouldn't be scrubbing tires. Depending on what you use for a body and how rigidly the body is mounted to the frame all come into play. Personally, I would add either a K or an X member to cut down on some of the frame flex.------Brian.
  18. ^^^^I plan to add at least a "K". I will probably re-install a driveshaft loop that I foolishly cut out in the beginning of this project. That will also double as a mount for seat belts.
    There will be a roll bar added, mostly for looks, but also to help stiffen the kickup. It will have two braces that will go back to the top crossmember that mounts the coil-overs.
    Thanks, now back to class!
  19. killerbunny
    Joined: May 21, 2012
    Posts: 51

    from serbia

    I agree...<object width="1" height="1" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase=",0,40,0"><param name="undefined" value="" /><param name="allowScriptAccess" value="always" /><param name="src" value="" /><param name="allowscriptaccess" value="always" /><embed width="1" height="1" type="application/x-shockwave-flash" src="" undefined="" allowScriptAccess="always" allowscriptaccess="always" /></object>:)
  20. I was re-reading this thread for reference, and just had an epiphany!
    Welding suspension brackets requires a weld that is a full bead connecting both parts, but not done all at once, because of the high heat involved. Therefore, a series of short beads that eventually connect with each other is superior to a bead run all at once. Wow! The light just came on!
    I'm really not the sharpest knife in the drawer...
    brEad likes this.
  21. Zandoz
    Joined: Jan 23, 2012
    Posts: 307


    Brian, I'm in the process of planning the frame for a T Bucket/Modified. I understand the logic behind mounting the rear radius rods as close to center as possible, but in my case what is possible is not very close. There is no room to run them inboard of the frame, and outboard I need to get them out far enough to clear the body. I'll be using coil-overs on the rear.

    My question is, do you have any pointers for optimizing the design of the suspension with outboard radius rods? is there any advantage to using high misalignment heims or spherical rod ends for the forward radius rod mounts?


  22. snot275
    Joined: May 11, 2012
    Posts: 131


    wow... this thread has FLOORED me. EXCELLENT write ups Brian. I've learned more in this thread than I have from any other source. THANK YOU!
  23. Don't confuse what is "perfect" with "what will work". I have built rods exactly as you are describing, and they worked okay. I didn't use Heim ends, rather I used Pete and Jakes neoprene bushed rod ends with a plate on each side, both at the front and rear of the rods and there seemed to be enough "forgiveness" in them to account for any strange torsional moments that the radius rods encountered. It is however, imperative to run a Panhard rod with this type of set-up, because there is nothing else to keep the rearend centered in the chassis.----Brian
  24. Zandoz
    Joined: Jan 23, 2012
    Posts: 307


    Sounds good. I'll start looking for those neoprene bushed rod ends.

    Another radius rod question comes to mind. I am planning on using the style of radius rod where one bar is straight, and the other curves into the straight bar, just before the forward mounting point...and has a girdle/web between the bars near the axle end.. I have always seen this style of bar mounted with the straight bar on top. Is there any reason they can not be mounted with the straight bar on the bottom? The frame I am planning is going to be very low...about 6" ground clearance. I'd like to avoid anything below the frame rail, and mounting the straight bar on the bottom would do that...and with using a low mount bracket on the rear axle, it would keep the lower bar near level with the ground.
  25. No, thats not a good idea. When you accelerate, the tires try to turn foreward. This makes the axle tube want to rotate in the opposite direction. You need to have the lower radius rod mounted at least 3" below the center of the axle tube and the top bar above the axle centerline at least 3". If you don't maintain these offsets, the lower radius rod gets so much compression transmitted to it over a short lever arm that it will buckle.
  26. Zandoz
    Joined: Jan 23, 2012
    Posts: 307


    Below is a sample of the axle brackets sold for the rods I'm looking at. Based on a 3" diameter axle, it appears that the upper rod would be less than an inch and a half above the axle center line. The two rod attach points are 6" center to center. From what you are saying it sounds like these are not a good way to go...true?

    No matter if I use these brackets or ones that keep the bars at 3" above and below the axle centerline, the question is does it matter if the straight bar is on the bottom, instead of the top?

    I do not know if it matters or not, this car is not going to have a high power motor...just a little V6.

    Attached Files:

  27. Without getting into a lot of geometry and physics, ---The reason the brackets you have shown are shaped that way is so that the top of the bracket won't interfere with the floor of the car during suspension travel. When you accelerate, the axle tries to counter rotate, which throws the lower radius rod into compression and the top rod into tension. The top rod is kept in a straight line between its attachment point at both ends, because if it had a bend in its design the tension imposed on it would tend to pull it straight and destoy the intended geometry. There is a lot of mechanical physics along with practical necessity involved in the design of rear radius rods. They are shaped the way you see them on most hotrods because that style has been proven over and over again to work effectively. If you feel the need to do it a "new" or "different" way, then by all means go ahead. If you get away with it, your golden. If you end up getting on the go pedal a bit heavy and your rear axle decides to counter rotate and bend the radius rods, then you will understand that there is a reason most rods are built the way they are.
  28. Zandoz
    Joined: Jan 23, 2012
    Posts: 307


    My intent was not to do something novel...I was hoping to keep the front end of the lower bar from being below the bottom of the frame. I guess I'll just have to locate the mounting point as high on the frame rail as possible, and hope for the best.


  29. Go back to post 286 and look at mine. I think they would solve your problem.
    They come to a point at the front with a piece of tube in the center, and a hiem on the end. Up out of the way, and strong enough to withstand God knows how many wheelstanding launches with 33x13.50x15's and a 400" small block on alcohol.
    Notice the panhard bar, you will defiantly need it. Mike
  30. Zandoz
    Joined: Jan 23, 2012
    Posts: 307


    Mike, yes, something like that would work. Are they "off the shelf" or custom fabrication pieces? I've seen ladder bars built like that, but they have been very pricey.

    I am definitely planning on a panhard bar. I would have preferred a watts link, but there's no room.

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