I have a 32 Ford rod with a triangulated 4 bar rear suspension that is breaking/bending the front lower brackets. Has anyone else had a problem like that. I didn't build the Chassis but I didn't have any problem until I swapped to a more powerful Engine. I always thought the mounting points were a little on the thin side but they worked fine for years until now. What I don't understand is why the force that is causing the problem is from the lower Bars wanting to move Forward (direction of thrust) as I would think the Pinion Gear trying to climb the Ring Gear would want to Pull the lower bars in a Rearward direction? I can Email some Pics but they are to big to post here. Anyone have any Ideas. Thanks.
Axle wrapping up like others with spring. Wonder if they might be some sloop in the bushings of aal the bars?
Wouldn't the rear end housing try to rotate in the opposite direction as the tire rotation? That would put the bottom bars in compression, or pushing on the front mounts. Bob
No wheel Hop as the car is so light I get wheelspin before that happends. The Frame is not Boxed in that area and I plan to remove and replace the bad parts with a design that will spread the load and be stronger in all directions. Mostly wondered if anyone else had experienced this problem.Thanks for the replys. Any more Experiences and/or Ideas are welcome.
Darrell,sent me the photos,,the problem is what I have seen in the past and feared was the problem,,the frame is not boxed in the area where the lower 4 bar is attached,,it just ripped the mount & a portion of the bottom of the frame loose. Poor construction,,plain and simple. you can repair it or take the car to a component hot rod shop.HRP
needs some gussets of some sort....my coupe has broke the rearend brackets (design issue) and started pushing the front rear brackets forward , once I start racing it....and its a low hp ride. I added some outer plates to make it double shear and that helped a ton and added some bracing to the rearend brackets and welded up the brake lines on the brackets (places were the brackets are bent).....yours is a fairly easy fix...but the paint will probably be a little goofed up.. make a outer piece to go along with what you have...that has a long teardrop of sorts to transfer the load farther up the rail
I have also fixed lower brackets like that. It just needs to reinforced in the correct areas to accommodate the power
Yeah, badly done. All the forces are fed into a single piece of unsupported strap. There is no way that wasnt going to fail. I dont like triangulated 4 bars anyway, they put a lot of extra force into the components that a 4 bar with a Watts or a Panhard do not.
WHOOOOAAAAAH........ I was thinking of a triangulated on my next build, you suggest I should stick with the usual parallel four bar (which I have on my current coupe)............?
Had a similar problem with a TCI "pro street " frame. (quite a few years ago) Didn't tear, but bent the shit out of it. I had to pull it on a frame bench. The owner built a brace forward and it's been fine since. It is a high HP car, but none the less, I was disappointed with TCI
Yeah. Much better, IMO. The parallel 4 bars wont fight each other if they are set up right, and you can adjust the rollcenter independently from the 4 bars if you use a Watts or Panhard.. And usually the top bars go in from the frame on a triangulated 4 bar, which puts the rollcenter a lot higher than I like to have it. The advantages of a triangulated 4 bar are less cost ( less bars, heims, or bushings ), and it also takes up a bit less space. But I like the adjustabillity and ( IMO) better design.
In that picture the bracket is twisting off during bodyroll, or more realistically the body twisting under acceleration The torque at the axxle which causes forward compression forces and the body to torque over to one side There is not enough compliance in the bushing compared to the narrow piece of frame that the bracket is welded to. The lower arm always stays inline with the axle tubes unless there is balljoints at the rear [ or the front ] Triangulated 4 bar is a good simple system but there needs some compliance for bodyroll. If the triangulation is on the upper tubes the instant centre is at the point where these bars intersect. The rear end rotates around this pivot point , the will be some slight sideways arcing [swinging] from the lower brackets around this pivot point [ as well as torsional twisting ] The greater the distance between the uppers and lowers make the rotational problem worse, but lessens the compression / tension forces. use some balljoints
The bottom line is,,the frame needed to be boxed there was nothing to prevent this from happening. HRP
Bob is right lower bars are under compression. You might get by by moveing the bars higher closer to the frame
On A lot of the pretty 304 stainless 4 bar setups the actual bars themselves are about only good for up to 300 HP motor with auto trans .....450 500HP.especially with Manual trans will wrap them up like a horseshoe... some even came with single shear bracketry.....
Straight up insufficient materials strength at the attachment point. This is not an issue with the design of the 4-link, just really poor execution.
Uuuhh that bracket is not broken The metal it was attached to ripped The weld is good , the bracket is good ! What ever it was welded to failed ( frame )
The area where the frame has sheared was simply the first, weakest point in the arrangement. The force applied lever that is the bracket for the link (along with the strap it is welded to, was sufficiently strong and rigid for the application), was simply transferred to that spot. The weld should have a strength maximum of 70,000psi., less, of course, because it is combined with the parent metal. Mild steel has a strength of 40,000-45,000psi., or so. The constant cycling of the suspension, and the attendant push and pull of the link on that bracket simply flexed that weak point until it cracked, and broke. This is why it is a bad idea to weld a suspension bracket to a poorly supported single-plane. Boxes, and triangles, are your friends.
to be quite honest I find the 1/8" material most early Ford aftermarket frame rails are made of insufficient thickness to build bracket off of to support any real horsepower....Also its alloy is very soft in relation to an orig frame. Henry's Frames were hi carbon steel with added strength due to their torsional ability,inherent to the actual steel material he used. any suspension attachmment should probably be attached to at least a 1/4"thick backing plate larger than the actual contact area of the bracketry.....
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